All the patterns described above were examined using examples of polymerization one monomer (homopolymerization). But, as is known, it is widely used copolymerization– co-polymerization two or three monomers. It is carried out to obtain polymers with a wider range of properties, to obtain materials with predetermined properties, as well as in fundamental research to determine the reactivity of monomers. The copolymerization products are copolymers.
Basically the mechanism of radical copolymerization is quite similar to the mechanism of radical homopolymerization. However, there are several problems here.
1) Opportunity copolymerization - will units of both (or three) polymers be included in the polymer chain, or will each monomer be polymerized separately and a mixture of homopolymers will be formed?
2) The relationship between the compositioncopolymer and composition taken for the processmixtures of monomers. What is meant here is differential copolymer composition, i.e. its composition At the moment(if we take the integral composition, i.e. the composition of the entire mass of the copolymer, then it is clear that at a large depth of the process it will approximately coincide with the composition of the mixture of monomers, however, at different depths of the process macromolecules with different ratios of monomer units can be formed).
If the differential composition of the copolymer matches with the composition of the monomer mixture taken for polymerization, then copolymerization is called azeotropic. Unfortunately, cases of azeotropic copolymerization are quite rare; in most cases the differential composition of the copolymer is different on the composition of the monomer mixture. This means that during the polymerization process, monomers are not consumed in the same proportion as they were taken; one of them is consumed faster than the other, and must be added as the reaction progresses to maintain a constant composition of the monomer mixture. From here it is clear how important it is not only quality, but also quantitative solution to this problem.
3) The nature of the structure of the resulting copolymer, i.e. whether a random, alternating or block copolymer is formed (see pages 7-8).
The solution to all these problems follows from the analysis kinetics formation of a copolymer macromolecule, i.e. stages chain growth during copolymerization (since the copolymer macromolecule is formed precisely at this stage).
Let us consider the simplest case of copolymerization two monomers, conventionally designated by the symbols A and B. The chain growth stage in this case, in contrast to homopolymerization, includes elementary reactions of not one, but four types: indeed, during growth, “living” chains of two types are formed - with the terminal radical unit of monomer A [~A, for example, ~CH 2 –CH(X) ] and with the terminal radical unit of monomer B [~B, for example, ~CH 2 –CH(Y) ] and each of them can attach to “its own” and “foreign” monomer:
The differential composition of the copolymer depends on the ratio of the rates of these four reactions, the rate constants of which are designated as k 11 ...k 21.
Monomer A is included in the copolymer according to reactions 1) and 4); therefore, the rate of consumption of this monomer is equal to the sum of the rates of these reactions:
M 
monomer B is included in the copolymer according to reactions 2) and 3), and for it:
The differential composition of the copolymer is equal to the ratio of the rates of entry of both monomers into the copolymer:
IN 
This equation includes difficult to determine concentrations of radicals. They can be eliminated from the equation by introducing quasi-stationary condition: concentrations both types radicals (~A and ~B) constant; as in homopolymerization, the quasi-stationary condition is satisfied only at shallow process depths. From this condition it follows that the rates of mutual transformation of both types of radicals are the same. Since such transformations occur via reactions 2 and 4, then:
Substituting the resulting expression for into the equation for the differential composition of the polymer, we reduce it and, after a series of transformations, we obtain:
E 
then the equation is called Mayo-Lewis equations(sometimes called Mayo's equation). This equation reflects the dependence of the differential composition of the copolymer on the composition of the monomer mixture and on the values of r 1 and r 2. The parameters r 1 and r 2 are called copolymerization constants. The physical meaning of these constants follows from their definition: each of them expresses comparative activity of each radical in relation to “its own” and “foreign” monomer(constant r 1 – for radical ~A, constant r 2 – for radical ~B). If a radical attaches more easily to “its” monomer than to a “foreign” one, r i > 1, if it is easier to attach to a “foreign” one, r i< 1. Иначе говоря, константы сополимеризации
характеризуют comparative reactivity of monomers.
The left side of the Mayo-Lewis equation is the differential composition of the copolymer. On the right side, two factors can be distinguished: 1) composition of the monomer mixture [A]/[B]; 2) a factor including the copolymerization constants r 1 [A] + [B]/r 2 [B] + [A] = D (we denote it by D). It is easy to see that for D=1 d[A]/d[B] = [A]/[B], i.e. copolymerization is azeotropic. As mentioned above, cases of azeotropic copolymerization are quite rare, i.e. in most cases, D ≠ 1. Thus, the factor D is the factor that determines the difference between the differential composition of the copolymer and the composition of the mixture of monomers. If D > 1, then the copolymer is enriched in monomer A compared to the original mixture (i.e., monomer A is consumed in a greater proportion than monomer B). At D< 1, напротив, быстрее расходуется мономер В.
The value of the factor D is completely determined by the values of the copolymerization constants; therefore it is copolymerization constants determine the ratio of the differential composition of the copolymer and the composition of the mixture of monomers taken for the reaction.
Knowing the values of copolymerization constants also allows one to judge the structure of the resulting copolymer, as well as the possibility or impossibility of copolymerization itself.
Let us consider the main options for copolymerization, determined by the values of copolymerization constants. It is convenient to present them graphically in the form of curves of the dependence of the differential composition of the copolymer on the composition of the mixture of monomers taken for the reaction (Fig. 3).
R 
is. 3. Dependence of the differential composition of the copolymer on the composition of the monomer mixture.
1. r 1 = r 2 = 1. In this case d[A]/d[B] = [A]/[B], i.e. at any composition of a mixture of monomers occurs azeotropic copolymerization. This is a rare option. Graphically it is expressed by the dotted line 1 – azeotrope line. An example of such a system is the copolymerization of tetrafluoroethylene with chlorotrifluoroethylene at 60 0 C.
2. r 1 < 1, r 2 < 1 . Both constants are less than one. This means that each radical preferentially reacts with strangers monomer, i.e. we can talk about an increased tendency of monomers to copolymerize.
A) Copolymer composition. Differential copolymer composition enriched with the monomer that is low in the mixture of monomers(curve 2 in Fig. 3). This is easy to deduce from the analysis of the factor D in the Mayo-Lewis equation: for [A]<< [B]
D
< 1, следовательно, d[A]/d[B]
< ,
а при [B]
<< [A]
D
>1 and d[A]/d[B] > . Curve 2 intersects the azeotrope line, i.e. at some one In the ratio of monomers, polymerization is azeotropic. This ratio is easy to calculate, because in this case D = 1; from here:
B) Copolymer structure. Since each radical preferentially attaches to to someone else's monomer, in the copolymer there is a tendency towards alternation. If the copolymerization constants are not much less than unity, this tendency is not very pronounced, and the copolymer is closer to random than to alternating [the microheterogeneity coefficient K M (p. 7) is closer to 1 than to 2]. But the smaller the constants, the more the polymer structure approaches alternating. The limiting case is an infinitesimal value of both constants (r 1 → 0, r 2 → 0); this means that each radical reacts only with a “foreign” monomer, in other words, each of the monomers separately does not polymerize, but together they form a copolymer. Naturally, such a copolymer has a strictly alternating structure. An example of such a system is the pair: 1,2-diphenylethylene - maleic anhydride. There are also cases when one of the constants is infinitesimal, and the other has a finite value; in such cases, only one of the monomers does not itself polymerize, but can form a copolymer with a second partner. An example of such a system is styrene-maleic anhydride.
3. r 1 > 1, r 2 < 1 или r 1 < 1, r 2 > 1 . One of the constants is greater than one, the other is less than one, i.e. one of the monomers reacts more easily with its “own” monomer, and the second with a “foreign” one. It means that one monomer is more active than the other during copolymerization, because reacts more easily than others both radicals. Therefore, when any composition of the monomer mixture, the differential composition of the copolymer is enriched with units of the more active monomer (in Fig. 3 – curves 3’ for r 1 > 1, r 2< 1 и 3’’ для r 1 < 1, r 2 >1). Azeotropic polymerization is not possible here.
The structure of copolymer macromolecules in this variant is closest to statistical. A special (and not so rare) case: r 1 r 2 = 1, i.e. r 1 = 1/r 2 , while the values of the constants are not much more or less than one. This means that the comparative activity of monomers towards both radicals is the same(for example, at r 1 = 2, r 2 = 0.5, monomer A is 2 times more active than monomer B in reactions with both the radical ~A▪ and the radical ~B▪). In this case, the ability of each monomer to enter the polymer chain does not depend on the nature of the radical, which he encounters and is determined simply probability clashes with each of the radicals. Therefore, the structure of the copolymer will be purely statistical (K M ~ 1). This case is called perfect copolymerization- not at all because in this case a copolymer with ideal properties is formed (rather the opposite), but by analogy with the concept of an ideal gas, where, as is known, the distribution of particles is completely statistical. The most famous examples of such copolymerization include the copolymerization of butadiene with styrene at 60 o C (r 1 = 1.39, r 2 = 0.78). In the general case, the option “one constant is greater than one, the other is less” is perhaps the most common.
4. r 1 > 1, r 2 > 1. Both constants are greater than one; each of the radicals preferentially reacts with its “own” monomer; the system has a reduced tendency to copolymerize. Concerning composition copolymer, then it must be depleted the monomer that few in a monomer mixture. This picture is exactly the opposite of that observed for option r 1< 1, r 2 < 1, а на рис. 3 была бы представлена кривой, зеркально подобной кривой 2. Но этот вариант copolymerization rare; we can only mention the copolymerization of butadiene with isoprene at 50 o C (r 1 = 1.38, r 2 = 2.05), where the constants are only slightly greater than unity. But, unfortunately, there are cases when both constants are infinitely large (r 1 →, r 2 ); in this case, copolymerization simply does not occur, each of the monomers is polymerized separately and a mixture of two homopolymers is formed (example - a pair: butadiene - acrylic acid). A very useful option would be where the constants would have a large, but final size; in this case would be formed block copolymers; Unfortunately, no such cases have yet been found.
The term “copolymerization constants” should not be taken too literally: their values for a given monomer can change noticeably with changes in reaction conditions, in particular, with changes in temperature. For example, when copolymerizing acrylonitrile with methyl acrylate at 50 o C, r 1 = 1.50, r 2 = 0.84, and at 80 o C, r 1 = 0.50, r 2 = 0.71. Therefore, when giving the values of constants, it is necessary to indicate the conditions.
As a manuscript
Sapaev Hussein Khamzatovich
Radical copolymerization
acrylate and methacrylate guanidines with vinyl monomers
02.00.06 - High molecular weight compounds
dissertations for an academic degree
candidate of chemical sciences.
Nalchik-2009
The work was carried out at the Department of Macromolecular Compounds of the State Educational Institution of Higher Professional Education “Kabardino-Balkarian State University”
them. HM. Berbekova"
Scientific supervisor: Doctor of Chemical Sciences, Professor
Malkanduev Yusuf Akhmatovich.
Official opponents: Doctor of Chemical Sciences, Professor
Rusanov Alexander Lvovich
Doctor of Chemical Sciences, Professor
Beriketov Anuar Sultanovich.
Lead organization: Institute of Petrochemical
synthesis named after A. V. Topchiev RAS
The dissertation defense will take place on _______ June 2009. at_____hours at a meeting of the dissertation council D 212.076.09 at the Kabardino-Balkarian State University named after. HM. Berbekova at the address: 360004, KBR, Nalchik, Chernyshevsky, 173, building 11, conference room.
The dissertation can be found at the Scientific Information Center of KBSU named after. HM. Berbekova.
Scientific Secretary
dissertation council T.A. Borukaev
GENERAL DESCRIPTION OF WORK
Relevance of the topic. The development of science and technology at the present stage raises the problem of obtaining new polymer materials with a given set of properties. That is why in recent decades, in the field of chemistry of high-molecular compounds, the creation and research of synthetic polyelectrolytes has received intensive development. They are widely used in various fields of industry, technology, agriculture, medicine, and in the future their role and importance will undoubtedly increase.
It is known that compounds containing a guanidine group have a wide spectrum of bactericidal action and are often used as therapeutic agents, bactericides and fungicides. In this regard, the synthesis of new copolymers of various compositions based on guanidine acrylate (AG) and guanidine methacrylate (MAG) is of particular interest, since the introduction of a guanidine group into polymer products should impart significant biocidal activity to them. This is especially true for aqueous solutions of flocculants, in particular polyacrylamide (PAA), which is easily subject to microbiological destruction in the presence of bacteria and mold.
During radical polymerization and copolymerization of water-soluble monomers, the nature of the reaction medium significantly affects the kinetic parameters of the synthesis and the characteristics of the resulting products. This is due to a change in the reactivity of the reacting particles due to their ionization, solvation, complex formation and intermolecular interactions in the reaction medium. Therefore, the complicated nature of the copolymerization of ionic monomers also determines the relevance of studying the features of the formation of guanidine-containing copolymers based on vinyl monomers.
Taking into account the above, we believe that the synthesis and study of the properties of new guanidine-containing copolymers opens up new opportunities for the synthesis of polymers with the required set of properties.
Purpose of the work and main objectives of the study. The purpose of the work was to study the possibility of obtaining new high-molecular copolymers based on AG and MAG with acrylamide (AA) and guanidine monomaleinate (MMG) in aqueous solutions and, taking these results into account, the targeted synthesis of new polymers of cationic nature with biocidal properties, studying the mechanism and kinetics features of these reactions. To achieve this goal, it was necessary to solve the following tasks:
1. Study of the possibility of obtaining new copolymers based on AG and MAG with AA and MMG and the synthesis of new cationic polyelectrolytes on their basis.
2. Establishment of the basic kinetic laws of the radical copolymerization of AG and MAG with AA and MMG in aqueous solutions, determination of copolymerization constants and intrinsic viscosity.
3. Study of the influence of the structure and properties of polymerizing particles on the kinetics and mechanism of radical copolymerization.
4. Study of physicochemical, bactericidal, toxicological and flocculating properties of synthesized monomer and polymer products.
Scientific novelty. The fundamental possibility of the participation of AG and MAG in radical copolymerization reactions with AA and MMG has been shown; The kinetic patterns were studied and the copolymerization constants of these processes were calculated.
The basic physicochemical properties of the synthesized polymer products were studied using spectroscopic (IR, 1H NMR), thermophysical (DSC, TGA) methods, as well as elemental analysis. Methods have been developed that make it possible to obtain these copolymers with specified parameters (composition, structure, molecular weight).
For the first time, based on AG and MAG, new guanidine-containing water-soluble copolymers with AA and MMG of various compositions and structures have been obtained by radical copolymerization.
The biocidal and toxicological properties of the resulting polymer products were assessed. It has been shown that a number of guanidine-containing AA copolymers have low toxicity. The greatest biocide is exhibited by copolymers with AA containing 30-70 mol. % acrylate component. It was revealed that copolymers of MAG with MMG exhibit pronounced fungicidal properties.
The flocculating properties of new guanidine-containing copolymers of AA with AG and MAG were studied and the possibility of their use in water purification processes was shown.
Practical value of the work. As a result of joint research with the Bacteriological Laboratory of the State Sanitary and Epidemiological Surveillance of the KBR and with the pharmaceutical association "Elfarmi" (KBR, Nalchik), it was established that the synthesized copolymers have significant biocidal activity against gram-positive and gram-negative microorganisms, and copolymers with MMG have a pronounced fungicidal activity. Along with biocidal properties, copolymers have low toxicity, and with an increase in the units of the acrylate component in the copolymer, the toxicity decreases. It was revealed that copolymers of AA with MA and AG have effective flocculating properties; optimal conditions for their use in water purification processes have been found. The most pronounced flocculation properties are possessed by the copolymer AA with MAG composition 70:30. Moreover, the presence of guanidine units in the macromolecules of AA copolymers gives the flocculant resistance to biodegradation under the influence of bacteria and mold.
Approbation of work. The main results of the work were reported and discussed at the III All-Russian Scientific and Practical Conference “New Polymer Composite Materials” (Nalchik, 2007), the I All-Russian Scientific and Technical Conference “Nanostructures in Polymers and Nanocomposites” (Nalchik, 2007), the All-Russian Scientific and Technical Conference practical conference of young scientists, graduate students and students. (Grozny, 2008), All-Russian scientific and practical conference “Ecological situation in the North Caucasus: problems and ways to solve them.” (Grozny, 2008).
Publication of results 8 articles have been published on the topic of the dissertation, including 1 article in a journal recommended by the Higher Attestation Commission of the Russian Federation.
Structure and scope of the dissertation. The dissertation consists of an introduction, literature review, experimental part, discussion of results, conclusions and a list of cited literature. The work is presented on 129 pages of typewritten text, including 24 tables, 32 figures. The bibliography includes 210 titles.
MAIN CONTENT OF THE WORK
Chapter I. The main kinetic patterns and features of the reaction of radical polymerization of acrylic monomers in aqueous solutions with changes in various parameters (pH, temperature, change in monomer concentration) and in the presence of various neutralizing agents were considered. Analysis of the presented literature data allows us to conclude that the detected kinetic features are mainly a consequence of specific interactions of charged macroradicals and low molecular weight counterions present in the reaction solution. It also seemed undoubtedly important to evaluate the influence of the nature of the reaction medium on the polymerization process of the monomers under consideration, in particular, to conduct a comparative analysis of kinetic data during the polymerization of acrylic acids in organic solvents and in aqueous solutions.
ChapterII. The experimental part is presented. Objects, research methods, methods of synthesis and kinetic studies are considered.
Starting materials. AG and MAG are synthesized from guanidine and acrylic (methacrylic) acid. MMG is a qualified product of the “analytical grade” brand. Acros company. The initiator was ammonium persulfate (APS) (NH4)2S2O8, ethanol was absolutized according to the standard procedure, diethyl ether was dried over alkali and distilled twice over sodium metal. Acetone - dried over CaCl2, and then boiled and distilled twice over P2 O5.
Research methods. The kinetic features of the radical copolymerization of AG and MAG with AA were studied by the dilatometric method. The characteristic viscosity of polymer solutions was determined in an Ubellode viscometer. 1 N NaCl solutions were used as a solvent to measure the intrinsic viscosity. The work used physical and chemical research methods - elemental analysis, IR and PMR spectroscopy, viscometry, DTA, DSC.
Chapter III.The discussion of the results
3.1.Radical copolymerizationguanidine acrylateAnd guanidine methacrylateWithacrylamide
Water-soluble copolymers of AA with salts of acrylic and methacrylic acid, depending on the molecular characteristics, are used as flocculants and stabilizers of disperse systems, thickeners and structuring agents. Taking into account the high biocidal activity of guanidine-containing compounds, which have long been successfully used in medicine and in various fields of industry, it seemed necessary to study the possibility of synthesizing new copolymers based on guanidine-containing monomers of the acrylic series and AA. Since it would be natural to expect that newly created copolymers may exhibit new important properties and characteristics that are not inherent in the original homopolymers. Along with the expected practical significance of these polymers, the study of the kinetic features of the radical copolymerization reaction is undoubtedly relevant in the scientific aspect, primarily from the position of assessing the reactivity of the synthesized monomers under the conditions under consideration.
Before carrying out systematic kinetic studies in the copolymerization systems we were considering, the optimal conditions for carrying out these reactions were determined - an aqueous environment; total concentration of copolymers [M] = 2 mol l-1; [PSA]=510-3 mol l-1; 600C.
The composition of the AA:AG copolymers was determined from elemental analysis data since the chemical shifts of protons –CH2-CH= in the 1H NMR spectra of the comonomers are close and overlap. The data is shown in Table 1.
Table 1
Data on the elemental composition of AA:AG copolymers
| Ref. composition AG:AA | WITH | N | H | R = N/C in copolymer |
| Mass., % | ||||
| 80:20 | 38.85 | 29.33 | 6.90 | 0.755 |
| 50:50 | 41.99 | 26.62 | 6.96 | 0.634 |
| 40:60 | 41.85 | 26.74 | 6.80 | 0.639 |
| 20:80 | 44.15 | 24.77 | 7.30 | 0.561 |
| 10:90 | 47.37 | 22.31 | 7.00 | 0.471 |
To calculate the comonomer content, we used the ratio of nitrogen and carbon content in the copolymer R = N/C (%), based on the consideration that
NSP = NAGX + NAA(1 – X) (1)
CSP = CAGX + CAA(1 – X), (2)
where NAG and CAG are the content in AG, NAA and CAA are the content in AA, X is the proportion of AG in the copolymer and (1 – x) is the proportion of AA in the copolymer.
From here we have the equation:
NAGX + NAA(1 – x)
CAGX + CAA(1 – x)
Solving this equation and substituting values for the nitrogen and carbon content in the corresponding comonomers, we obtain expressions for calculating X, i.e. proportion of AG in the copolymer. The composition of AA copolymers with MAG was calculated using 1H NMR spectroscopy data, using the integrated signal intensity of the methyl group of the MAG comonomer, which appears in the strongest field and is not overlapped by any other signals. A third of its integral intensity will be equal to the value of the conventional proton for the MAG unit - “1H (M2)”. Protons related to the signals of the CH2 groups of the copolymer chain appear for both comonomers together in the region of chemical shifts 1.5 – 1.8, therefore, to determine the conditional proton of the AA unit “1H (M1)”, the contribution of two protons was subtracted from the total integrated intensity of these protons (I) MAG unit and the remaining value were divided by 2 (equation 4):
“1H (M1)” = (I - 2 “1H (M2)”) : 2 (4)
From the results obtained, the molar content of comonomers in the copolymer, expressed in mol.%, was determined (equations 5 and 6):
MPAA = [“1H (M1)” : (“1H (M1)” + “1H (M2)”)]100% (5)
MPMAG = [“1H (M2)” : (“1H (M1)” + “1H (M2)”)]100% (6)
As can be seen from the curves in Fig. 1, at all initial molar ratios of comonomers, the copolymer is enriched with acrylate comonomer units, and the MAG–AA system is characterized by a greater enrichment in the MAG comonomer, in contrast to the AG–AA system. This indicates the greater reactivity of MAG in the radical copolymerization reaction and corresponds to the data on the reactivity parameters of acrylic (AA) and methacrylic (MAA) acids available in the literature. The greater reactivity of the MAG monomer compared to AG is probably due to greater delocalization of the charge of the carboxyl group in the monomer molecule, as indicated by the shift of the signals of the vinyl protons of MAG to a higher field compared to AG in the 1H NMR spectra. The lower reactivity of acrylamide compared to AG and MAG may be due to the specific structure of ionogenic
Rice. 1. Dependence of the composition of the resulting copolymers in systems:
AG-AA (curve 1) and MAG-AA (curve 2)
on the composition of the initial reaction solution
monomers, in which there is electrostatic attraction between the positively charged ammonium nitrogen atom and the carbonyl oxygen atom of the methacrylic acid residue, the electron density of which is increased (Scheme 1).
where, R= H, CH3
Scheme 1. Zwitterionic delocalized structure of AG and MAG
This attraction causes delocalization of the negative charge along the carboxylate anion bonds of AA and MAA. Due to this delocalization, the relative stability of the corresponding radicals is higher compared to acrylamide. In the case of MAG, a higher delocalization of electrons along the C-O- bond in the methacrylate anion is observed compared to AG, which is confirmed by the greater enrichment of the copolymers with the MAG comonomer compared to AG.
Because We studied copolymerization at low degrees of conversion, then to calculate the copolymerization constants we used the analytical method; the values of the constants calculated by this method are presented in Table. 2.
table 2
AG(MAG) (M1) –AA (M2)
Given in table. 2 r1 values< 1 и r2 < 1 свидетельствует о предпочтительном взаимодействии макрорадикалов с «чужим», чем со «своим» мономером в обеих сополимеризационных системах. Значения произведения r1r2 < 1 говорит о выраженной тенденции к чередованию в обеих сополимеризационных системах. Кроме того, r1>r2, which confirms that the probability of addition of comonomer radicals to the monomer molecule of MAG and AG is slightly higher than to the AA molecule. The closeness of relative activities to unity during MAG-AA copolymerization indicates that the rate of chain growth in this system is controlled by the rate of diffusion of monomer molecules into macromolecular coils, and the diffusion rates of comonomers differ little from each other.
Thus, the radical copolymerization of AA with AG and MAG makes it possible to obtain copolymers with a high content of ionic groups.
However, despite the fact that the relative activity values we obtained indicate a lower reactivity of the AA monomer compared to MAG and AG, the study of the copolymerization of these comonomers in aqueous solutions showed that as the concentration of ionic comonomers AG and MAG increases in the initial reaction mixture the intrinsic viscosity values decrease.
To understand the mechanism of copolymerization of AG and MAG with AA, the rate of this process in an aqueous solution was studied using the dilatometric method. PSA was used for initiation.
The study of kinetics under these conditions showed that the copolymerization reaction of AG and MAG with AA occurs only in the presence of radical initiators and is completely suppressed when an effective radical inhibitor 2,2,6,6 - tetramethyl-4-oxylpyridyl-1-oxyl is introduced into the reaction solution. A spontaneous reaction—polymerization in the absence of a radical initiator—is also not observed.
The reaction solutions were homogeneous over the entire range of compositions, and the resulting copolymers were well soluble in water.
It was shown that in the reaction being studied, the dependence of the degree of conversion on the duration of the reaction under selected conditions (aqueous medium; total concentration of copolymers [M] = 2 mol l-1; [PSA] = 510-3 mol l-1; 600C) is characterized by a linear section of the kinetic curve to conversion of 5-8%.
The study of the kinetics of copolymerization showed that with an increase in the content of ionic monomer in the initial monomer mixture, the values of the initial polymerization rate 0 and intrinsic viscosity simultaneously decrease during the copolymerization of AA with AG and MAG (Fig. 2).
Fig.2. Dependence of the initial copolymerization rate (1.4) and intrinsic viscosity (2.3) of the copolymer MAG with AA (1.2) and AG with AA (3.4) on the content of the ionic monomer in the initial reaction mixture
Moreover, for the first system (during polymerization with AG), the course of this dependence is more pronounced. The results obtained are in good agreement with the known literature data obtained by studying the kinetics of copolymerization of N,N-diallyl-N,N-dimethylammonium chloride (DADMAC) with AA and MAA in aqueous solutions. In these systems, it was also found that the rate of copolymerization decreases with increasing DADMAC content in the initial reaction solution, and for AA this increase is more pronounced than for MAA.
From Fig. 2 also follows that the highest molecular weight samples of copolymers (judged by the values of ) are obtained in monomer mixtures with a high content of AA.
Apparently, the most likely reason for the observed decrease in the chain growth rate constant with increasing concentration of the ionic comonomer is that the concentration of highly hydrated acrylate and methacrylate anions in relatively hydrophobic uncharged coils of macroradicals turns out to be lower than their average concentration in solution, which is indirectly confirmed by a decrease in the reduced viscosity of the copolymer solution with an increase in the content of AG and MAG units.
It is more logical to associate the decrease with the structuring effect of AG and MAG ions on water molecules, which leads to a decrease in volumetric effects, i.e. the quality of water as a solvent for PAA deteriorates.
It is obvious that the phenomena observed during radical copolymerization with the participation of ionizing monomers AG and MAG cannot be explained only on the basis of classical concepts, and the parameters r1 and r2 can only serve as conditional values reflecting the influence of certain factors on the behavior of a given monomer during copolymerization.
Thus, in all likelihood, the observed features and differences in the series of monomers under consideration are explained by the complex nature of the contributions of various physicochemical processes that determine the course of the copolymerization reaction of AA with guanidine-containing monomers of the acrylic series. At the same time, the main contribution to the change in the effective reactivity of polymerizing particles is made, as we believe, by associative interactions between guanidine and carboxyl groups (both intra- and intermolecular) and the structural organization of the corresponding monomers and polymers during the copolymerization process.
To establish the equation for the overall rate of copolymerization of AA with AG and MAG, experiments were carried out for variable concentrations of AA, AG, MAG and components of the initiating system while maintaining constant concentrations of the remaining components of the reaction system and reaction conditions.
3.2. Radical copolymerization of guanidine acrylate and guanidine methacrylatewith guanidine monomaleinate
Radical homopolymerization and copolymerization of guanidine-containing compounds is the object of study by many authors, mainly in connection with the possibility of obtaining polymer materials with a set of specific properties, including biocidal ones. However, there is little information in the literature regarding the study of radical copolymerization processes of ionic monomers containing the same functional groups.
In this regard, the study of copolymerization processes of guanidine-containing ionic monomers seemed to us very relevant.
It is known that maleates, due to the symmetry of their structure, spatial factors and the high positive polarity of the vinyl group, do not form homopolymers in the presence of radical initiators. The experimental results obtained in this work also showed that homopolymerization of MMG under the studied conditions is difficult. For example, the degree of conversion of MMG monomer into polymer under conditions ([MMG] = 2 mol l-1; 600C; [PSA] = 510-3 mol l-1; H2O; polymerization time 72 hours) is about 3% ( = 0.03 dl g-1). All these facts indicate a significant contribution of the above factors to the process of homopolymerization of the system we studied.
At the same time, it is important to note that when studying the reaction of radical copolymerization of MMG with MAG, a number of copolymers of various compositions with fairly high values of intrinsic viscosity were obtained.
Radical copolymerization was studied in aqueous solutions, PSA was used as an initiator ([I] = 10-2 – 10-3 mol l-1) in the temperature range (40 - 600C). It was previously established that in the absence of an initiator, polymerization does not occur.
Copolymerization was carried out to various degrees of conversion, and the following patterns were revealed. In all cases, the formation of copolymers enriched in MAG units compared to the initial mixture of comonomers is observed (Table 3), which indicates the greater reactivity of MAG in chain growth reactions. Copolymerization occurs only when there is an excess of guanidine methacrylate. If there is an excess of guanidine MMG, then neither copolymerization nor homopolymerization of MAG is observed.
Table 3
Dependence of the copolymer composition on the initial composition of the reaction solution during copolymerization of AG (MAG) (M1) and MMG (M2)
2.00 mol/l, [PSA]= 5·10-3 mol·l-1, Н2О, 600С.
| No. p / p | Starting comonomers | Copolymers M1:M2, | |||
| M1:M2, mol.% | AG-MMG mol.% | , dl/g | MAG-MMG mol.% | , dl/g | |
| 1 | 40:60 | 90:10 | 0.35 | 75:25 | 0.15 |
| 2 | 50:50 | 95:5 | 0.55 | 68:32 | 0.20 |
| 3 | 70:30 | 75:25 | 0.88 | 90:10 | 0.27 |
| 4 | 80:20 | 97:3 | 0.93 | 96:4 | 0.41 |
| 5 | 90:10 | 98:2 | 0.98 | 98:2 | 0.53 |
Note. was determined at 300C in a 1N aqueous solution of NaCl.
The composition of the synthesized polymer products was confirmed by H NMR and IR spectroscopy.
The predominant contribution of the steric factor to the reactivity of MMG in the copolymerization reaction with AG and MAG is confirmed by the values of the copolymerization constants, which are presented in Table 4.
Table 4
The value of effective copolymerization constants in systems
AG(MAG) (M1) –MMG (M2)
([M]sum = 2 mol l-1; [PSA] = 510-3 mol l-1; 600C; H2O)
3.3.Physicochemical and biocidal properties of the synthesized copolymers
NMR research1 H and IR spectroscopy The polymer compounds synthesized in the presented work confirmed the expected structure of the research objects. The study of the 1H NMR spectra of the synthesized copolymers made it possible to determine the comonomer composition by analyzing the integral intensities of various signals.
A study of the synthesized copolymers using differential thermal analysis (DTA) and differential scanning calorimetry (DSC) methods revealed their high thermal stability, and the copolymers turned out to be more resistant to high temperatures than the original homopolymers (research was carried out up to a temperature of 10000C). Thus, for PAA, a 30% weight loss is observed already at a temperature of 170 0C; for the AA-MAG copolymer (90:10), a 30% weight loss is observed at 300 0C, and for a 30:70 copolymer at 280 0C.
Bactericidal activity studies showed a priori expected significant bactericidal and fungicidal activity for a number of copolymer compositions. It was revealed that the AA-MAG copolymers (70:30), (50:50), (10:90) have the greatest biocidal activity against Staphylococcus aureus. Biocidal activity depends on the amount of AG and MAG in the macromolecular chain. In relation to Candida albicans, the most active samples were AA-MAG (10:90) and AA-AG (20:80).
Copolymers of AG and MAG with MMG are not active against the studied microorganisms, but have high fungicidal activity against the pathogenic fungal microflora Candida albicans. It is noteworthy that the corresponding homopolymers exhibit bactericidal activity, but do not have fungicidal activity. Thus, the greatest antifungal effect was obtained for samples of MAG copolymers with MMG with the initial comonomer composition of 50:50 and 70:30.
Toxicity Study a number of copolymers of AA with MAG and AG using the bioindicator Daphnia magma Strauss revealed that the toxicity of the samples depends on the composition of the copolymers; with an increase in the content of guanidine acrylate and methacrylate, the toxicity of polyacrylamide flocculants decreases.
Study of the flocculating properties of new acrylamide copolymers
To evaluate the flocculating activity of polyelectrolytes, an aqueous suspension of kaolin was used as a model system.
Since the flocculating ability is influenced by the charge of the macromolecule, copolymers with varying degrees of acrylate monomer units in the macromolecular chain were chosen for the study. PAA was used as an object of comparison.
In Fig.3. shows the influence of the concentration of flocculants of different compositions on the flocculating effect (F), which was calculated using formula (1)
F = (n0 - n) / n, (1)
where n0 and n are, respectively, the optical density of water (determined by the turbidimetric method) in the absence and presence of a flocculant (and coagulant).
Fig. 3. Dependence of the flocculating effect F on the concentration and composition of 1-PAA copolymers; 2- AG-AA (20:80); 3- AG-AA (40:60); 4- MAG-AA (20:80); 5- MAG-AA (40:60); 6- MAG-AA (30:70)
Experiments conducted on one batch of natural water (turbidity 4.2 mg l–1, color 48.5 degrees) showed an increase in the flocculating effect with increasing copolymer concentration for all flocculants. This is a consequence of an increase in the concentration of macromolecular bridges formed during the adsorption of macromolecules on the surface of dispersed phase particles, which formed large aggregates of dispersed phase particles and macromolecules and reduced the stability of the system.
It was revealed that samples of MAG-AA copolymers are characterized by larger F values compared to AG-AA. Comparison of data at a constant concentration of flocculants indicates an increase in F values when moving to copolymers with a higher content of MAG and AG units. Meeting the standard F = 0.7 (determined at n = 0.172 and = 364 nm, corresponding to the turbidity of purified water) is achieved at lower concentrations of the AA:MAG copolymer compared to PAA.
The maximum flocculating effect is observed with a copolymer with a composition of 70:30. Obviously, in this case, an optimal relationship is realized between the charge density and the flexibility of macromolecules, which ensures that polymer bridges cover a larger number of particles of the dispersed phase, increasing the size of the flocs and the flocculating effect.
Determination of the residual copolymer in purified water using the Burkett method showed the absence of polymer in purified water, which indicates that under the conditions studied, the copolymers almost completely interact with colloidal particles.
CONCLUSIONS
1. For the first time, the composition, structure and some properties of new copolymers based on AG and MAG with AA and MMG were synthesized and established using a complex of physicochemical methods.
2. The kinetic features of the radical copolymerization of AG and MAG with AA and MMG in aqueous solutions were studied, the copolymerization constants and intrinsic viscosities were determined.
3. It was revealed that a decrease in the copolymerization rate with an increase in the concentration of the ionic monomer is associated with a specific feature of the structure and properties of the polymerizing particles, which results in an increase in the cutoff constant.
4. It has been established that during the radical copolymerization of guanidine-containing monomers in aqueous media with an excess of MMG, low molecular weight polymers are formed, which is caused by the significant influence of spatial factors and the high positive polarity of the vinyl group of MMG due to which this monomer does not form homopolymers.
5. Bactericidal and toxicological tests of the synthesized copolymers based on AG and MAG were carried out on a number of cell cultures. It has been shown that with significant biocidal activity, they are characterized by low toxicity. High antifungal activity was found for copolymers of AG and MAG with MMG.
6. The flocculating properties of AA copolymers with AG and MAG were determined and the optimal conditions for their effective use in water purification and disinfection processes were found.
- Sapaev, Kh. Kh. New multifunctional nanocomposites based on clay minerals and biocidal polymers for water purification [Text] / Kh. Kh. Sapaev., S. Yu. Khashirova., A. V. Labazanova., Yu. A. Malkanduev / / 1st All-Russian Scientific and Technical Conference “Nanostructures in Polymers and Polymer Nanocomposites”. - Nalchik: KBSU, 2007. - P. 245 - 249.
- Sapaev, Kh. Kh. Features of radical polymerization reactions of acrylate and methacrylate guanidines [Text] / Kh. Kh. Sapaev., S. Yu. Khashirova., N. A. Sivov., Yu. A. Malkanduev // III All-Russian scientific and practical conference “New polymer composite materials”. - Nalchik: KBSU, 2007. - P. 160 - 164.
- Sapaev, Kh. Kh. Conformational behavior of growing chains of poly (meth) acrylate guanidines in aqueous solutions [Text] / Kh. Kh. Sapaev., S. Yu. Khashirova., N. A. Sivov., Yu. A. Malkanduev // III All-Russian Scientific and Practical Conference “New Polymer Composite Materials”. - Nalchik: KBSU, 2007. - P. 149 - 153.
- Sapaev, Kh. Kh. Radical polymerization of nitrogen-containing diallyl monomers [Text] / Kh. Kh. Sapaev., S. Yu. Khashirova., Yu. A. Malkanduev // Materials of the All-Russian scientific and practical conference of young scientists, graduate students and students. - Grozny.: ChSU, 2008. - P. 154 - 162
- Sapaev, Kh. H. Modification of cellulose with biocidal polyelectrolytes [Text] / Kh. Kh. Sapaev., S. Yu. Khashirova., Yu. the situation in the North Caucasus: problems and ways to solve them.” - Grozny.: ChSU, 2008. - P. 414 - 419.
- Sapaev, Kh. Kh. Copolymers of guanidine-containing ionogenic monomers are effective biocidal polymers [Text] / Kh. Kh. Sapaev., S. Yu. Khashirova., Yu. A. Malkanduev // Materials of the All-Russian scientific and practical conference “Ecological situation in the North Caucasus : problems and ways to solve them.” - Grozny: ChSU, 2008. - P. 419 - 424.
- Sapaev, Kh. Kh. Chemical modification of cellulose with guanidine methacrylate [Text] / Kh. Kh. Sapaev., S. Yu. Khashirova., Yu. A. Malkanduev // Bulletin of ChSU. - 2008 - No. 2. - P. 50 - 53.
- Sapaev Kh.Kh. Study of biocide-toxicological characteristics of new polyacrylamide flocculants [Text] / Kh.Kh. Sapaev., S.S. Baker., S.Yu. Khashirova., Yu.A. Malkanduev // Journal “Plastic Masses”. - 2008. - No. 5, - P. 53-54.
The author considers it his duty to express great gratitude to N.A. Sivov, Candidate of Chemical Sciences, Head of the Laboratory of the Chemistry of Polyelectrolytes and Surface-Active Polymers of the Institute of Chemical Chemistry of the Russian Academy of Sciences. for assistance and scientific advice during the dissertation work.
Lecture outline:
1. Radical polymerization.
2. Ionic polymerization
The vast majority of high-molecular compounds are obtained as a result of polymerization and polycondensation reactions.
Polymerization
Polymerization is a process for producing polymers in which the construction of macromolecules occurs by sequential addition of molecules of a low molecular weight substance (monomer) to the active center located at the end of the growing chain. For polymerization, the stages of initiation and chain growth are mandatory.
Initiation - This is the transformation of a small fraction of monomer molecules M into active centers AM*, capable of attaching new monomer molecules. For this purpose, pathogens are introduced into the system ( initiators I or catalysts) polymerization. The initiation of polymerization can be represented as follows:
If one monomer participates in polymerization, then we get homopolymers, if two or more then copolymers. Depending on the nature of the active center, there are radical And ionic polymerization And copolymerization.
Radical polymerization
Radical polymerization always proceeds by a chain mechanism. The functions of active intermediates in radical polymerization are performed by free radicals. Common monomers that undergo radical polymerization include vinyl monomers: ethylene, vinyl chloride, vinyl acetate, vinylidene chloride, tetrafluoroethylene, acrylonitrile, methacrylonitrile, methyl acrylate, methyl methacrylate, styrene, and diene monomers (butadiene, isoprene, chloroprenidr.).
Radical polymerization is characterized by all the signs of chain reactions known in the chemistry of low molecular weight compounds (for example, the interaction of chlorine and hydrogen in the light). Such signs are: the sharp influence of a small amount of impurities on the speed of the process, the presence of an induction period and the course of the process through a sequence of three stages dependent on each other - the formation of an active center (free radical), chain growth and chain termination. The fundamental difference between polymerization and simple chain reactions is that at the growth stage, the kinetic chain is embodied in the material chain of a growing macroradical, and this chain grows to form a polymer macromolecule.
The initiation of radical polymerization is reduced to the creation of free radicals in the reaction medium capable of starting reaction chains. The initiation stage includes two reactions: the formation of primary free radicals of the initiator R* (1a) and the interaction of the free radical with the monomer molecule (16) to form the radical M*:
Reaction (1b) proceeds many times faster than reaction (1a). Therefore, the rate of polymerization initiation is determined by reaction (1a), as a result of which free radicals R* are generated. Free radicals, which are particles with an unpaired electron, can be formed from molecules under the influence of physical influence - heat, light, penetrating radiation, when they accumulate energy sufficient to break the π-bond. Depending on the type physical impact per monomer upon initiation (formation of the primary radical M*), radical polymerization is divided into thermal, radiation and photopolymerization. In addition, initiation can be carried out due to the decomposition into radicals of substances specially introduced into the system - initiators. This method is called real initiation.
Thermal initiation lies in self-initiation at high temperatures of polymerization of pure monomers without introducing special initiators into the reaction medium. In this case, the formation of a radical occurs, as a rule, due to the decomposition of small amounts of peroxide impurities, which can arise during the interaction of the monomer with atmospheric oxygen. In practice, the so-called block polystyrene is obtained in this way. However, the method of thermal initiation of polymerization has not found wide distribution, since it requires large expenditures of thermal energy, and the polymerization rate in most cases is low. It can be increased by increasing the temperature, but this reduces the molecular weight of the resulting polymer.
Photoinitiation polymerization occurs when the monomer is illuminated with the light of a mercury lamp, in which the monomer molecule absorbs a quantum of light and goes into an excited energy state. Colliding with another monomer molecule, it is deactivated, transferring part of its energy to the latter, and both molecules turn into free radicals. The rate of photopolymerization increases with increasing irradiation intensity and, unlike thermal polymerization, does not depend on temperature.
Radiation initiation polymerization is in principle similar to photochemical. Radiation initiation consists of exposing monomers to high energy radiation (γ -rays, fast electrons, α - particles, neutrons, etc.). The advantage of photo- and radiation-chemical methods of initiation is the possibility of instant "turning on and off" radiation, as well as polymerization at low temperatures.
However, all these methods are technologically complex and may be accompanied by side undesirable reactions in the obtained polymers, such as degradation. Therefore, in practice, chemical (material) initiation of polymerization is most often used.
Chemical initiation is carried out by introducing into the monomer medium low-molecular unstable substances containing low-energy bonds - initiators that easily decompose into free radicals under the influence of heat or light. The most common radical polymerization initiators are peroxides and hydroperoxides (hydrogen peroxide, benzoyl peroxide, hydroperoxides mpem-butyl and isopropylbenzene, etc.), azo- and diazo compounds (azobisisobutyric acid dinitrile, diazoaminobenzene, etc.), potassium and ammonium persulfates. Below are the decomposition reactions of some initiators.
Peroxide tert-butyl(alkyl peroxide):
The activity and applicability of radical polymerization initiators is determined by the rate of their decomposition, which depends on temperature. The choice of a particular initiator is determined by the temperature required for polymer synthesis. Thus, dinitrile of azobiisobutyric acid is used at 50-70 ° C, benzoyl peroxide - at 80-95 ° C, and peroxide tert- butyl - at 120-140°C.
Redox systems are effective initiators that make it possible to carry out the process of radical polymerization at room and low temperatures. Peroxides, hydroperoxides, persulfates, etc. are usually used as oxidizing agents. Reducing agents are salts of metals of variable valence (Fe, Co, Cu) in the lowest oxidation state, sulfites, amines, etc.
Self-test questions:
1. What substances are the initiators of radical polymerization?
2. What does the initiation of radical polymerization come down to?
3. Types of initiation.
4. What is polymerization?
Lecture 6. Copolymerization.
Lecture outline:
1.Copolymerization
2. Technical methods for carrying out homo- and copolymerization.
Copolymerization
Copolymerization is the production of high molecular weight substances from a mixture of two or more monomers, which are called comonomers, and the substance itself - copolymer. Macromolecules of copolymers consist of elementary units of all monomers present in the initial reaction mixture. Each comonomer imparts its own properties to the copolymer it is part of, and the properties of the copolymer are not a simple sum of the properties of the individual homopolymers. Thus, the content of a small amount of styrene in polyvinyl acetate chains increases the glass transition temperature of the latter, eliminates the property of cold flow and increases its surface hardness.
The laws of copolymerization are much more complex than the laws of homopolymerization. If in homopolymerization there is one type of growing radical and one monomer, then in binary copolymerization, which involves only two monomers, there are at least four types of growing radicals. Indeed, if two monomers A and B interact with free radicals R" generated during the decomposition of the initiator, primary radicals are formed, one of which has a terminal unit A, and the second - B:
Each primary radical can react with both monomer A and monomer B:
The ratio of the rate constant of the reaction of each radical with its “own” monomer to the rate constant of the reaction with the “foreign” monomer is called copolymerization constants or relative activities monomers:
The values of r A and r B determine the composition of the macromolecules of the copolymer to a greater extent than the ratio of monomers in the initial reaction mixture. For example, in a vinyl acetate (A)-styrene (B) pair, the copolymerization constants are r A = 0.01, r B = 55. This means that when a copolymer is produced by polymerization in bulk and solvent, the macromolecules contain significantly more styrene units than vinyl acetate. If the relative activities of comonomers are close to unity, then each radical interacts with both “its own” and “foreign” monomer with equal probability. The inclusion of monomers in the chain is random in nature, and statistical copolymer. This copolymerization is called perfect. An example of a system close to ideal is the butadiene-styrene pair.
Copolymerization reactions can occur by either a radical or an ionic mechanism. In ionic copolymerization, the copolymerization constants are influenced by the nature of the catalyst and solvent. Therefore, copolymers obtained from the same comonomers at the same initial ratio in the presence of different catalysts have different chemical compositions. Thus, a copolymer of styrene and acrylonitrile, synthesized from an equimolar mixture of monomers in the presence of benzoyl peroxide, contains 58% styrene units. At the same time, during anionic copolymerization on a C 6 H 5 MgBr catalyst, the content of styrene units in macromolecules is 1%, and during cationic polymerization in the presence of SnCl 4 - 99%.
In practical terms, interesting block- And vaccinated copolymers. In the macromolecules of these copolymers there are long sections of units of each comonomer.
Block copolymers are prepared by different methods. Firstly, during anionic polymerization of one monomer, the resulting “living” chains, that is, macroanions, can initiate the polymerization of another monomer:
Secondly, with intense mechanical action on a mixture of different polymers, chain destruction occurs and macroradicals are formed. Macroradicals interact with each other to form a block copolymer.
Block copolymers can also be formed from oligomers due to the interaction of end groups.
Graft copolymers are usually obtained by the interaction of a monomer with a polymer and, less commonly, by the interaction of two different polymers with each other. Since these processes use a chain transfer reaction with the conversion of polymer molecules into macroradicals, atoms or groups with increased mobility (for example, bromine) are often introduced into the macromolecules, which accelerates the value transfer reaction. Thus, if the reaction medium contains a polymer based on the CH 2 =CHX monomer, the CH 2 =CHY monomer and an initiator, the process of formation of the graft copolymer proceeds as follows. First, the middle macroradical appears:
This macroradical then initiates polymerization of the monomer to form side branches:
The production of block and graft copolymers is almost always accompanied by the formation of a tomopolymer from the monomer present in the reaction zone.
Radical sonolimerization usually initiated in the same ways as radical polymerization. It is characterized by the same mechanisms of growth, chain termination and transmission.
Let's consider the copolymerization of two monomers M, and M 2. If the activity of growth radicals is determined only by the type end link then four elementary growth reactions should be taken into account:
The corresponding rates of elementary stages of chain growth can be written as
The kinetics of the chain growth reaction determines the composition of copolymers and the entire complex of their chemical and physical-mechanical properties. The model, which takes into account the influence of the terminal link on the reactivity of the active center in relation to monomer molecules and considers four elementary reactions of a growing chain with different types of terminal link (M*) with the monomer (M (), is called "end link model" copolymerization. This model was independently proposed in 1944 by American chemists F. Mayo and F. Lewis. Kinetic processing of the given scheme in a quasi-stationary approximation makes it possible to establish the relationship between composition of copolymers And composition of the initial mixture of monomers, those. an equation that describes the composition of the “instant” copolymer, as well as the composition of the copolymer formed at the initial conversions, when changes in monomer concentrations can be neglected.
Assumptions required for the conclusion copolymer composition equations(dependence of the copolymer composition on the composition of the monomer mixture) include:
- 2) reactivity of M* and M: * does not depend on R p;
- 3) quasi-stationary condition: the concentrations of M* and M* remain constant if the rates of their mutual transformation are the same, i.e. V p |2 = K r 21;
4) low conversions.
The rates of conversion of monomers during copolymerization are described by the equations
where from, and t 2 - concentration of monomer units in the copolymer.
The ratio of the rates of these reactions leads to the expression
Taking into account the stationary condition for the concentrations of radicals, it is easy to obtain the following expression, which characterizes at the initial stages of the transformation, when changes in the concentrations of monomers [M,] and [M2], can be neglected, the dependence of the composition of the resulting copolymer on the composition of the monomer mixture:
Where k iV k 22 are the rate constants for the addition of its monomer by the radical; kvl, k. n are the rate constants of addition of a foreign monomer by a radical; g, = k n /k l2 , r 2 = k 22 /k 2l- copolymerization constants, depending on the chemical nature of the reacting monomers.
Often instead of concentrations, the corresponding mole fractions are used. Let us denote by /, and / 2 mole fractions of comonomers in the mixture, and through F ( And F 2- mole fractions of units M ( and M 2 in the copolymer:
Then, combining expressions (5.28)-(5.30), we obtain
The dependence of the composition of copolymers on the composition of the monomer mixture is conveniently characterized by a composition diagram (Fig. 5.1). At r(> 1 and r 2 1 copolymer is enriched with Mj units (curve 1) at r x 1 and r 2 > 1 copolymer is enriched with M units; (curve 2). If r, = r 2 = 1, then the composition of the copolymer is always equal to the composition of the original mixture (direct 3).
Rice. 5.1.
If r( r ( > 1 and r 2 > 1, then there is a tendency towards separate polymerization of monomers in the mixture (curve 5). If the composition curve intersects the diagonal of the composition diagram, then at the intersection point called azeotropic, the composition of the copolymer is equal to the composition of the comonomer mixture.
The properties of binary copolymers depend on the average composition of the copolymer, its compositional heterogeneity and the distribution of monomer units in macromolecules. With the same composition, the distribution of links along the chain can be different (block, statistical, alternating or gradient). The composition of an individual macromolecule may differ from the average composition of the entire sample, which leads to compositional heterogeneity of the copolymer. A distinction is made between instantaneous and conversion heterogeneity of copolymers. Instant compositional heterogeneity arises as a result of the statistical nature of the process. Conversion compositional heterogeneity is caused by a change in the composition of the monomer mixture during copolymerization (except for azeotropic copolymerization), its contribution to the overall compositional heterogeneity is much higher than the contribution of instantaneous heterogeneity.
During copolymerization at deep stages of transformation, the composition of the monomer mixture (except in the case of azeotropic copolymerization) continuously changes during the course of the reaction: the relative content of the more active monomer decreases, and the less active one increases (Fig. 5.2).
Rice. 5.2. Dependence of the copolymer composition on the composition of the monomer mixture for cases of one-sided enrichment (curve1: r,> 1; r 2 2: r x 1; r 2 > 1)
For the same composition of the monomer mixture (Fig. 5.2, point A) products are formed with different contents of the first component: corresponding in the first case - point IN at the second point D". During the reaction, the mole fraction M will constantly change: in the first case it will decrease, in the second it will increase. At the same time, the instantaneous compositions of the resulting copolymers will change: in the first case, there will be a constant depletion of the copolymer in Mp units; in the second, an enrichment in M units. In both cases, products of different “instant” compositions accumulate, which leads to the emergence of conversion compositional heterogeneity of the resulting copolymer. However, the average composition of the final product in both cases will be the same: at 100% conversion it is equal to the composition of the monomer mixture and corresponds to the point WITH.
During copolymerization with a tendency to alternate (see Fig. 5.1, curve 4) for an arbitrary composition of the initial monomer mixture, there are two composition regions on the composition curve: one lies above the diagonal and the second lies below this diagonal. They are separated by the azeotrope point ( ), which is located at the intersection of the composition curve with the diagonal. With the exception of the azeotrope point, during copolymerization the instantaneous compositions of the copolymer change along a curve to the right. Thus, in this case, copolymerization at deep conversions leads to compositionally heterogeneous products.
An exception is the azeotropic copolymerization of a monomer mixture, during which the compositions of the copolymer and monomer mixture do not change during the reaction and remain equal to the initial composition of the monomer mixture until the monomers are completely exhausted. The invariance of the copolymer composition during azeotropic copolymerization leads to the production of homogeneous products, the compositional heterogeneity of which is minimal and is associated only with its instantaneous component. The condition for the formation of an azeotropic composition has the form
The values of G[ and g 2 can be determined experimentally. Knowing them makes it possible to predict the composition of the copolymer and the distribution of monomer units in the chains for any ratio of monomers in the mixture. Values of r, and g 2 during radical copolymerization and, therefore, the composition of the copolymer usually weakly depends on the nature of the solvent and changes very little with temperature.
The exceptions are:
- 1) phenomena associated with donor-acceptor interactions of reagents. If one of the monomers turns out to be a strong donor and the other a strong acceptor, alternating copolymers are formed (styrene - maleic anhydride, r, = 0 and g 2 = 0);
- 2) co-polymerization of ionic monomers depending on pH (acrylic acid - acrylamide, pH = 2, g, = 0.9 and g 2 = 0.25; pH = 9, g, = 0.3 and g 2 = 0, 95);
- 3) co-polymerization of the “polar monomer - non-polar monomer” pair in polar and non-polar solvents (bootstrap effect, styrene - n-butyl acrylate, g = 0.87 and g 2 = 0.19 in weight and g, = 0.73 and g 2 = 0.33 in DMF; 2-hydroxymethyl methacrylate - tert- butyl acrylate, g, = 4.35 and g 2= 0.35 in mass and g, = = 1.79 and g 2 = 0.51 in DMF);
- 4) heterophasic co-polymerization. In heterophase copolymerization, selective sorption of one of the monomers by the polymer phase can lead to a deviation from the composition characteristic of homogeneous copolymerization of the same solution (styrene - acrylonitrile: copolymerization in bulk and in emulsion; MW A - N-vinylcarbazole in benzene g, = 1 ,80 and g 2 = 0.06, in methanol g, = 0.57 and g 2 = 0,75).
Consideration of the quantities r, and g 2 within the framework of the theory of ideal radical reactivity leads to the conclusion that r, r 2 = 1, i.e. the rate constants for the addition of one of the monomers to both radicals are the same number of times greater than the rate constants for the addition of the other monomer to these radicals. There are a number of systems for which this condition is well realized experimentally. In such cases, monomer units of both types are randomly located in macromolecules. Most often, g., 1, which is associated with polar and steric effects, which determine the tendency for the alternation of monomer units M and M 2 in macromolecules. In table. Table 5.12 shows the values of copolymerization constants for some pairs of monomers. Conjugation with a substituent reduces the activity of the radical to a greater extent than it increases the activity of the monomer, so a monomer that is more active in copolymerization turns out to be less active in homopolymerization.
To quantitatively characterize the reactivity of monomers in radical copolymerization, a zero-empirical
Radical copolymerization constants for some monomers
scheme Q-e, proposed in 1947 by American chemists T. Alfrey and K. Price. Within the framework of this scheme it is assumed that
Where P Q- parameters corresponding to the conjugation energies in the monomer and radical according to the theory of ideal radical reactivity. Quantities e ( And e 2 take into account the polarization of the reacting monomers. Then
Using this scheme, it was possible to evaluate the relative reactivity of monomers and the role of polar factors for a large number of pairs of copolymerizing monomers.
Was taken as the standard monomer styrene with meanings Q = 1, e= 0.8. When copolymerizing styrene with other monomers (M), the latter were characterized by their Q values and e~, which made it possible to predict the behavior of these monomers in copolymerization reactions with other monomers, for which values were also established Q And e.
For active radicals, the activity of monomers depends on resonance factors. With the increase Q constant k l2 increases. For inactive radicals (styrene, butadiene), the activity of monomers depends on polarity. In table. 5.13 shows the values of Qn e some monomers.
Table 5.13
ValuesQAndesome monomers
UDC 541.64:547.32:547.371
RADICAL COPOLYMERIZATION OF STYRENE AND UNSATURATED GLYCIDIL ETHERS
M.A. Chernigovskaya, T.V. Raskulov
Angarsk State Technical Academy,
665835, Irkutsk region, Angarsk, st. Tchaikovsky, 60, [email protected]
Binary radical copolymerization of unsaturated glycidyl ethers (alli-glycidyl ether, vinyl glycidyl ether of ethylene glycol) with styrene in toluene was studied. The copolymerization constants and microstructure of the resulting copolymers were calculated. It has been established that the composition of the copolymers depends on the structure of the unsaturated glycidyl ether. Allyl glycidyl ether copolymers, regardless of the composition of the initial monomer mixture, are close in structure to alternating ones. When copolymerizing styrene with vinyl glycidyl ether of ethylene glycol, the latter is characterized by lower reactivity. Il. 2. Table. 3. Bibliography 14 titles
Key words: radical copolymerization; styrene; allyl glycidyl ether; vinyl glycidyl ether of ethylene glycol.
RADICAL COPOLYMERIZATION OF STYRENE AND UNSATURATED GLYCIDYL ETHERS
M.A. Chernigovskaya, T.V. Raskulova
Angarsk State Technical Academy,
60, Chaikovskogo St., 665835, Angarsk, Irkutsk Region, 665835 Russia, [email protected]
The radical copolymerization of styrene and unsaturated glycidyl ethers (allyl glycidyl ether, ethylene glycol vinyl glycidyl ether) was examined in toluene solution. The reactivity ratios and parameters of copolymer microstructure were calculated. It was found that copolymer composition depends on unsaturated glycidyl ethers structure. Copolymers of styrene and allyl-glycidyl ether have an alternative structure. Ethylene glycol vinyl glycidyl ether has less reactivity than styrene in copolymerization. 2 figures. 3 tables. 14 sources.
Key words: radical copolymerization; styrene; allyl glycidyl ether; ethylene glycol vinyl glycidyl ether. INTRODUCTION
One of the promising directions is the synthesis of copolymers with active functional chemistry of high-molecular compounds being groups. As monomers
For such syntheses, epoxy compounds and, in particular, unsaturated glycidyl ethers (UGEs) are of increasing interest. Copolymers containing NGE units are of interest for theoretical studies, since the simultaneous presence of an oxirane ring and oxygen atoms in the side chain in the composition of NGE makes it possible to exhibit complex formation effects.
On the other hand, such polymers provide the broadest opportunity for directed modification by carrying out polymer-analogous reactions along oxirane rings and, therefore, open the way to the production of materials, including composites, with a predetermined valuable set of properties.
The range of NGEs used in radical copolymerization reactions is quite wide, but the most studied at present are methacrylic acid derivatives (for example, glycidyl methacrylate), allyl glycidyl ether (AGE), as well as vinyl glycidyl ethers of glycols (for example, vinyl glycidyl ether ethylene glycol (EGE)). AGE and VGE seem to be the most interesting as modifiers for industrial polymers, since due to their low reactivity they should be included in the polymers in limited quantities, without changing the overall set of properties of the base polymer.
The traditional areas of use of these compounds in copolymerization processes are discussed in detail in the works. Recently, epoxy-containing copolymers are increasingly used for the production of various nanomaterials and nanocompositions [for example, 5,6], as well as functional polymer composite materials. Therefore, the study of copolymerization processes of NGE, including AGE and VGE, with basic industrial monomers is of undoubted scientific interest.
The purpose of this work was to study the binary radical copolymerization of styrene (St) with AGE and VGE.
EXPERIMENTAL PART
For the synthesis of copolymers, we used commercial St produced by OJSC AZP (purity
99.8%) with constants: p = 0.906 g/ml, 1bp = = 145 °C, AGE (product of the company "AShsI") with constants: p = 0.962 g/ml, ^ip = 154 °C, n20 = = 1, 4330, and WGE obtained at the Institute of Chemical Chemistry of the Siberian Branch of the Russian Academy of Sciences, purified to chromatographic purity
99.9% with the following constants: p = 1.038
g/ml, ^ip = 204 °C, = 1.4310.
Copolymerization was carried out in a toluene solution at a temperature of 60°C and a tenfold excess of solvent. Azo-bis-isobutyric acid dinitrile was used as an initiator in an amount of 1 wt%. The resulting copolymers were isolated by precipitation with isobutanol, purified by reprecipitation with isobutanol from acetone, and dried to constant weight.
The composition of the resulting products was determined according to elemental analysis (C, H), functional analysis (content of epoxy groups) and IR spectroscopy. The content of epoxy groups in the copolymers was determined by back titration with hydrochloric acid according to. Relative viscosity was determined for 1% solutions in cyclohexanone at 25 °C.
THE DISCUSSION OF THE RESULTS
Depending on the composition of the initial mixture, the resulting copolymers are solid powdery or amorphous substances of white color, highly soluble in polar solvents.
The fact that copolymerization occurs in the systems studied was confirmed using turbidimetric titration data. For example, in the turbidimetric titration curves of St - VGE copolymers (Fig. 1), one inflection is observed, which indicates the formation of copolymers, and not a mixture of two homopolymers. A similar picture is observed for St-AGE copolymers.
In the IR spectra of NGE, an absorption band is observed in the region of 1620-1650 cm-1, characteristic of a double bond. The presence of an oxirane ring is confirmed by the presence of absorption bands in the spectrum in the following regions: 765 and 915 cm-1, related to asymmetric stretching vibrations of the epoxy ring; 1230 cm-1, related to symmetrical stretching vibrations of the epoxy ring; 3060 cm-1, corresponding to vibrations of the methylene group in the epoxy ring.
In the IR spectra of the copolymer, there are no absorption bands characteristic of a double bond, which confirms that the copolymerization process occurs along the vinyl or allylic groups. In the absorption regions characteristic of the oxirane ring and alkyl groups, the spectra of the copolymers are identical to the spectra of the original NGE.
Experimental data obtained as a result of studying copolymerization processes in the St - VGE and St - AGE systems are presented in table. 1.
It was assumed that the studied NGE
O 0.2 0.4 0.6 0.8 1.0
Precipitator volume, ml
Rice. 1. Dependence of the optical density of solutions of St - VGE copolymers on the volume of added precipitant (methanol). Content of VGE in the initial mixture (% mol.): 1 - 10; 2 - 25; 3 - 50
Table 1
General principles of copolymerization of St - NGE in toluene solution _(DAK1 wt.%, 60°C, 2 h)__
No. Composition of the initial mixture, % mol. Composition of the copolymer, % mol. Exit, %
St OGE St NGE
System St - AGE
1 95 5 36,36 63,64 3,7
2 90 10 55,14 44,86 12,6
3 70 30 47,16 52,84 32,4
4 50 50 92,32 7,68 20,2
5 30 70 46,73 53,27 19,8
6 10 90 60,13 39,87 19,3
System St - VGE
1 90 10 91,98 8,02 68,5
2 75 25 79,93 20,07 56,7
3 50 50 67,95 32,05 46,2
4 25 75 55,08 44,92 38,1
5 10 90 46,45 53,55 32,5
have lower reactivity in radical copolymerization than Art. Such a picture is indeed observed for St-VGE copolymers. They are enriched with St units throughout the studied range of initial mixtures, while the content of VGE units in the composition of the copolymers increases symbatically with its amount in the monomer mixture (Table 1).
For copolymers St - AGE observed
different picture. For any composition of the initial monomer mixture, the content of St and AGE units in the copolymers is almost the same and ranges from 40 to 64 mol.%, which indicates the formation of products close to alternating (Table 1).
As an analysis of literature data shows, AGE is characterized by processes of alternating copolymerization with quite
table 2
General patterns of copolymerization of VC - NHE in a solution of toluene
(DAK 1% wt., 60 °C, 2 h)
The composition of the initial mixture, mol%. Composition of the copolymer, % mol. Yield, % Viscosity [G|], dl/g
VKh NGE VKH NGE
VX - AGE system
95,0 5,0 96,79 3,21 3,19 0,20
90,0 10,0 93,92 6,08 2,88 0,15
85,0 15,0 87,92 10,58 2,56 0,08
73,7 26,3 76,19 23,81 2,69 0,04
30,1 69,9 44,69 55,31 2,48 0,04
VX - VGE system
95,0 5,0 95,55 4,45 3,78 0,29
90,0 10,0 92,44 7,56 3,45 0,26
80,0 20,0 88,44 11,56 3,01 0,22
75,0 25,0 78,79 21,21 2,91 0,17
25,0 75,0 36,62 63,38 2,23 0,13
a wide range of monomers [for example, 11, 12]. This is explained by the formation of charge transfer complexes between AGE and the second comonomer, in which AGE plays the role of a donor. However, a study of the binary radical copolymerization of AGE with VC, carried out by the authors, did not reveal the formation of alternating copolymers (Table 2).
The formation of alternating copolymers during the copolymerization of AGE with St can be associated with the formation of charge transfer complexes between the epoxy group of AGE and the aromatic ring of styrene. The resulting complex then plays the role of an “individual monomer” in copolymerization, which leads to the production of products of alternating structure.
Product yields are generally decreasing
with an increase in the content of low-active monomer units in the composition of copolymers (Table 1), which is due to an increase in the concentration of NGE in the initial mixture of comonomers. Increasing the concentration of a low-active monomer increases its content in the copolymer, but reduces the total rate of chain growth and, consequently, reduces the yield of the product and its molecular weight. This reasoning is confirmed by the values of the relative viscosity of copolymer solutions (for example, St-AGE) and their dependence on the content of esters in the initial mixture (Fig. 2).
The calculation of the relative activity constants of monomers (copolymerization constants) for the studied systems was carried out using different methods. System copolymerization constants
Rice. 2 Dependence of the relative viscosity of St-AGE copolymers on the AGE content in the initial mixture
Table 3
Copolymerization constants and average block lengths of St ^^ _and NGE ^2) units in copolymers_
System M1 m1 r Li L2
System St - AGE 0.70 0.47 r1 = 0.09 1 1
0.50 0.92 r2 = 0.05 21 1
0.75 0.20 n1 = 1.13 ± 0.09 n2 = 0.22 ± 0.02 10 1
System St - VGE 0.50 0.32 9 1
St - AGE was calculated based on functional analysis data using the nonlinear least squares method in the MathCAD 11 Enterprise Edition package, which allows calculations to be carried out using any sets of experimental data. The copolymerization constants for the St-VGE system were calculated using the standard Fineman-Ross and Kelen-Tudos methods using the Mortimer and Tidwell experimental design method. The values of copolymerization constants are presented in table. 3. Based on the values of the copolymerization constants, the parameters of the microstructure of the copolymers were determined, which are also given in Table. 3.
The obtained values of the copolymerization constants confirm the previously made conclusion about the different reactivity of NGE in the processes of copolymerization with St. For the St - AGE system, the values of the calculated copolymerization constants are close to zero, which is typical for alternating copolymers. Calculation of the microstructure of these copolymers showed that, regardless of the composition of the initial mixture, almost strictly alternating products are obtained (Table 3).
The values of the relative activity constants for St - VGE copolymers indicate a lower reactivity of VGE in radical copolymerization compared to St. VGE is present in the data structure of the co-
polymers only in the form of single units, and the length of blocks of St units in copolymers naturally decreases with a decrease in the proportion of St in the original mixture.
Thus, the structure of the copolymers St and NGE can apparently be reflected by the following formula:
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