CC BY
43
UDC 542.9:628.34
M. D. Goldfein, N. V. Kozhevnikov, N. I. Kozhevnikova, G. E. Zaikov
KINETICS AND MECHANISM OF POLYMER DISPERSION FORMATION ON BASED OF (METH)ACRYLATES. PART 2
Keywords: emulsion polymerization, alkyl acrylates, metacrylic acid, acrylonitrile, ammonium persulfate, kinetics, mechanism.
The aim of the present work was to establish the kinetics and mechanism of joint emulsion polymerization of methyl acrylate with metacrylic acid (MAA) or acrylonitrile, which underlies production of many commercial acrylic polymeric dispersions. The emulsion polymerization of methyl methacrylate (MMA) and copolymers with acrylonitrile (AN) and methacrylic acid (MAA) was studied. Also some aspects of kinetics and mechanism of polymeric latexes formation processes in absence of emulsifier were investigated.
Ключевые слова: эмульсионная полимеризация, алкилакрилаты, метакриловая кислота, акрилонитрил, персульфат аммония,
кинетика, механизм.
Цель данной работы заключалась в изучении кинетики и механизма реакции эмульсионной сополимеризации метилакрилата с метакриловой кислотой (MAR) или акрилонитрилом, являющейся основой производства многих промышленных акриловых полимерных дисперсий. Изучена эмульсионная полимеризация метилметакрилата (ММА) и его сополимеров с акрилонитрилом (AH) и метакриловой кислотой (МАК). Также исследованы некоторые аспекты кинетики и механизма процессов формирования полимерных латексов без эмульгатора.
1 Introduction
Emulsion polymerization of vinyl monomers is always characterized by a rather sophisticated mechanism, because the emulsion system contains several phases and elementary reactions are localized in its various zones. The process is more complicated while joint polymerization of several monomers. In contrast to a reaction in block or in solution, emulsion copolymerization depends not only on the character of chemical interaction of comonomers with growing radicals but also on factors influencing the topochemistry of the process, the number of PMP formed, and their stabilization. At copolymerization of monomers with different solubility in water, the nucleation mechanism may switch. The influence of comonomers on emulsion polymerization is determined by their distribution in the phases and their affecting the processes in each of them. Besides, the parameters of reactivity of some monomers are medium-dependent [1]. The aim of the present work was to establish the kinetics and mechanism of joint emulsion polymerization of methyl acrylate with metacrylic acid (MAA) or acrylonitrile, which underlies production of many commercial acrylic polymeric dispersions.
2 Experimental
The emulsion polymerization of the following monomers was studied: methyl acrylate (MA), ethyl acrylate (EA), butyl acrylate (BA), methyl methacrylate (MMA), and their copolymerization with acrylonitrile (AN) and methacrylic acid (MAA). These monomers were thoroughly purified (releasing from the stabilizer, drying, distilling under reduced pressure in an inert gas, and recondensation in vacuum).
The polymerization initiator, ammonium persulphate (APS), was purified by recrystallization from its water-alcohol solution.
The following surfactants were used as emulsifiers:
- sulfated oxyethylated alkylphenol S-10, which is a reaction product of the nonionic wetting agent OP-IO (monoalkylphenyl ether of polyethylene glycol CnH2n+rCaH4-(OC2H4)m-OH , where n = 8-10, m = 10-12) with concentrated sulfuric acid followed by neutralization with ammonia [2];
- Neonol AP9-12S, an analog of S-10, oxyethylated nonylphenol sulfate with an ethoxylation degree of 12;
- sodium lauryl sulfate (LS).
Since polymerization is accompanied by volume effects, dilatometry fully conforms to the specified requirements to rate estimation [3]. There exists proportionality between the volumetric changes of the polymerizate during the reaction and the weight monomer-to-polymer conversion degree, determined by the densities of the monomer and polymer: AK _pn- pM AP , K Pn Po
where AV and AP are the changes in volume of the polymerizate and the weight of the monomer during polymerization, Vo and Po the initial volume and
weight of the monomer, pm and pp the densities of the
monomer and polymer at the polymerization temperature.
Polymerization was carried out in special glass dilatometers of original design. The main elements of such a dilatometer are a measuring capillary, a reaction vessel, and a filling system providing the opportunity of releasing the monomer and dispersion medium from dissolved gases before polymerization. To avoid the influence of oxygen on the processes studied, the water-soluble and oil-soluble components of the reaction system were separately freed from dissolved air by multiple freezing (liquid nitrogen), high vacuum pumping, and thawing in vacuo with subsequent
transfusions through the measuring capillary into the reaction vessel of the dilatometer. The tool filled with inert gas was then placed into a water bath over an electrical magnetic stirrer. The desired temperature was maintained via an ultrathermostat.
The estimation of the number and size of the resulting latex particles formed in the reaction was made by classical theory of emulsion polymerization [4] and turbidity spectrum method.
The classical theory establishes the nature of the influence of the concentration of initiator In and emulsifier E just on the number of particles in the emulsion N, which, starting from the second (fixed) stage of the reaction, was considered to be independent of the conversion degree and, for micellar nucleation, is described by: N = K[Inf 4[Ef 6. The emulsion polymerization rate is determined by the number of
particles, the average number n of radicals, and the monomer concentration [M]p therein:
W = kp n [M]pN/NA.
The turbidity spectrum method [5] based on the determination of the wavelength exponent in Angstrom's equation z = const 2~v, describing the spectral dependence of the turbidity .zof colloidal solutions within a relatively narrow wavelength range. Turbidity is the coefficient in the exponent of Bouguer's
law I = Ioe~z'1, where l is the scattering layer
thickness (the cuvette length) characterizing the ability of the disperse system to reduce the intensity of the incident light due to scattering. Turbidity depends on the number N of scattering centers, their sizes and optical properties: z = Nw2K(a,m),
where K(a,m) is the scattering efficiency factor (or scattering coefficient), a = 2m-no/l the relative size of a particle, m = n/no their relative refractive index (r the radius of a particle, 2the wavelength of light, n and no the refractive indices of a particle and the dispersion medium). The wavelength exponent u is a function of a and m and can be found by measuring the slope of the straight portion of the graphic dependence of turbidity (or absorbance) D = lg (Io/I) = z •1/2.303 on 2
in the log-log coordinates.
It is possible to determine the parameters of the dispersion particles from the found wavelength exponent with the known dependences u(a,m) and K(a,m) on the relative size and the relative refractive index. These relationships for a discrete set of m according to the formulae of G. Mie's light scattering theory [6] were calculated [5]. However, these dependencies have an oscillating character for monodisperse systems. The allowance for the actual polydispersity of colloidal systems is typically provided by a graphical smoothing on the principle of symmetry of the oscillating curves plotted for specific values of the relative refractive index m. It is more convenient to use approximate analytic expressions for the characteristic functions of light scattering [7]. This approach allows computer processing of experimental data. Besides, due to the fact that the relative refractive
index of the particles may continuously vary during the experiment (e.g., as the polymerization depth increases, the monomer-polymer ratio in the particles varies and, therefore, their spectral characteristics do as well), the table data calculated for a discrete set of m turn out to be inapplicable.
The mean radius and number concentration of particles in dispersed systems were calculated by the formulae [5]:
r = a2m/2mio , N =4n.T(Xm)no2/XjK(a,m)a2, where 2m is the middle of the wavelength range in the
togarkhrnc scale (2 = -j2max2rnm ).
The allowance for refractive index dispersion was made in accordance with the approaches to this problem developed in Ref. [8]. In this paper it is shown that the theoretical value of the wavelength exponent uo, which is calculated by the approximate equations with
r and N, and which corresponds to systems with negligible dispersion is related to the experimental parameter u by a relation like: uo = u + Au, where Au = kou + 2m(k - ko)/(m - 1) when u > 2 and Au = kou + um(k - ko)/(m - 1) when u < 2.
The quantities k and ko describe the refractive index dispersion of the dispersed phase n(2) and the dispersion medium no(2) and represent their logarithmic derivatives with respect to wavelength. The values of the parameter k are proposed [9] to be evaluated from the inverse relative dispersion S and the refractive index at the wavelength corresponding to the yellow line of sodium nD. Approximating n(2) by Cauchy's
binomial formula, we obtain:
k{I) = (nD -1)(V + V) / riDS{AF2 -Ac2) =
,
where 2 = [ 2f~2 + 2c~2 /2]~1/2 = 552.4 nm is the
middle of the spectral interval in the 1/2 coordinates between the F and C lines.
The relation for k(2) was used for the final
polymer dispersion when the conversion q approached 100%, and the latex particles were composed of polymer entirely. However, this approach is inapplicable in analysis of the properties of latex particles depending on the polymerization depth, as the particles consist of the polymer and monomer with their varying ratio depending on q. In the absence of monomer droplets, when almost all the monomer and polymer are in the latex particles, the refractive index of the scattering centers can be estimated through the corresponding values for the monomer nm and polymer np, in view of the volume ratio 9 of the monomer and polymer in a particle, calculated, in turn, from the conversion degree: n = (pnm + np)/(1 + 9).
But the values of S for such particles are unknown.
It has been shown [8] that the parameter k( 2)
can also be estimated based only on nD, since for more than 100 samples of polymers it is described by a
general dependence approximated as: - k( X) = Bo +
B1(nD - 1.4) + B2(nD - 1.4)2, where Bo = 0.01675, B1 = -0.026858, and B2 = 0.780829. The use of this approximation requiring the knowledge of nD, within the range nm -r- np (in the case of MA polymerization it is 1.4040-1.4725) to assess the value of k, apparently gives wrong results, since when nD = 1.4 - Bo/2B2 = 1.4172, this function has a minimum, which contradicts our experimental data. The dependence of k on the refractive index in this range of its values can be more accurately represented by linear interpolation between the values calculated for the monomer and polymer.
The parameter ko for the medium in the case of aqueous dispersions can be obtained from direct spectral measurements of no(X). Approximation of the data from Ref. [10] for no(X) of water at 20°C by Cauchy's tripartite formula gives ko = -0.0155 (X = 552.4 nm).
Turbidity spectra were recorded on a SF-26 spectrophotometer. The value Xcp=X = 552.4 nm was selected as the wavelength mid-range, and measurements were performed with a constant logarithmic step AlgX= 0.02.
The polymer dispersion formed by the emulsion polymerization of acrylates (the monomer concentration is 10-20%, the initiator is ammonium persulfate, APS) have relatively high optical density; therefore, they were diluted with water before measuring turbidity. However, it turned out that the results of measurements, and, in particular, the wavelength exponential in Angstrom's equation and the reduced turbidity (the turbidity multiplied by the dilution R) depended on the dilution (Fig. 1), especially at its relatively small values. These dependencies are not observed at high dilutions. These data indicate that in sufficiently concentrated dispersions there is multiple secondary scattering due to which more (as compared with single scattering) light passes through the cuvette and reaches the receiver as if to reduce the turbidity of the system. The theory underlying the turbidity spectrum method does not account for multiple light scattering. Therefore, to estimate the parameters of the dispersion it is necessary to dilute it to such an extent that the reduced turbidity becomes independent of R and remains constant at any dilution, which serves as the criterion of no multiple scattering [9].
The obtained data have allowed us to estimate the contribution of multiple light scattering at different dilution degrees, since the proportion of multiply scattered light at the exit of the cell T2 can be expressed [9] through the reduced turbidity at the given dilution (tR) and infinite dilution (tR)m = lim (tR):
R—
T2 = I2/I = 1 - 10 D"A, where D - D1 =
l . (tR) - (tR)m 2.303 R '
(I) being the intensity of light transmitted through the dispersion, which consists of the intensity I1 weakened due to single scattering, and the additional intensity I2 arising due to multiple scattering of radiation in the direction of the receiver).
Fig. 1 - Dependence of the wavelength exponent (24) and the reduced turbidity of the dispersions (1, 5, 6) obtained by MA emulsion polymerization (50°C) with the monomer concentration of 10 (2, 4-6) and 20% (1, 3) on the dilution prior to measuring turbidity. The emulsifier (1%) is LS (1-3, 6) and Neonol (4, 5); [APS] x 103 = 2 (2, 4-6) and 36 mol/l (1, 3)
The effect of multiple light scattering quickly decreases with increasing dilution (Fig. 2).
The necessary dilution degree depends on the dispersion properties, in particular, it is higher when sulfated oxyethylated alkylphenols (C-10, nonoxynol-9-12) are used as an emulsifier in comparison with sodium lauryl sulfate (LS), and it also depends on the monomer content in the initial emulsion.
T2
Fig. 2 - Dependence of the fraction of multiple light scattering at X = 552 nm at the cell outlet with l = 0.1 cm on the dilution degree of the dispersion obtained by MA polymerization of 20% (1) and 10% (2, 3) with LS (1, 3) and Neonol (2) as the emulsifier. [APS] x 103 = 2 (2, 3) and 36 mol/l (1); 50 0C
Dilution simultaneously facilitates washing of the latex particle surface from the emulsifier molecules stabilizing them, whose refractive index differs from the corresponding quantities of the monomer or polymer, which, in the absence of dilution, introduces an additional uncertainty into the results. Therefore, polymer dispersions are pre-diluted with water by 100-
200 times and measurements are usually performed in 0.3-cm cuvettes with the value of transmittance maintaining within the range of 0.2-0.8.
Thus, our studies have shown that the turbidity spectrum method can be applied not only to the final polymer dispersions resulting from the emulsion polymerization of acrylic monomers but also to the emulsion systems arising in the course of the reaction at various conversions. It is necessary to take into account multiple (secondary) light scattering, and the dependences of the scattering properties of particles on the polymerization depth, those of the refractive indices of the particle and medium on wavelength. Under these conditions, the turbidity spectrum method can be used in kinetic studies of this reaction.
3 Results and Discussion
Emulsion Copolymerization Methyl Acrylate with Some Hydrofilic Monomers
At emulsion copolymerization of MA with AN or MAA, the composition of the comonomers influences not only the properties of the latexes formed and the reaction rate but also the character of the dependence of rate on time or conversion depth [11]. E.g., increasing the MAA content retards polymerization and increases the value of conversion qmax, at which the maximum (for the given conditions) reaction rate Wmax is achieved (Fig. 3). Meanwhile, the data on equilibrium solubility of MA in its monomer [12] point to that disappearance of monomer drops and the end of the constant rate plateau on the kinetic curves (finishing the second stage of emulsion polymerization) should be observed as early as at q = 16%.
The dependence of the rate of emulsion copolymerization on the composition of the monomers is due, on the one hand, to changes in the reaction rate in PMP, and, on the other hand, to changes of the amount of latex particles in the emulsion. The latter fact is determined by the influence of the monomer composition of the processes of nucleation and flocculation.
q (%)
Fig. 3 - Rate of emulsion copolymerization of MA with MAA as a function of conversion depth. [MAA] = 0 (1), 4 (2), 8 (3) and 14 % of [M] (4); [APS] = 2 x 10-3 mol/l; [Neonol] = 1 %; 60 0C
In the presence of MAA, in spite of the low coefficient of its water-monomer phase distribution [2], the concentration of the monomer dissolved in water increases. Judging by the values of MA-MAA copolymerization constants [13], the reaction in water proceeds with the predominating participation of acid molecules, and with a relatively low rate characteristic of MAA polymerization in low-acidic aqueous solutions [14]. The high content of MAA units in the oligomeric radicals formed in water elongates the chain length at which they can generate particles by the homogeneous nucleation mechanism, and hinders micellar nucleation (due to the poor solubility of oligomeric MAA-containing radicals in the monomers). As a result, MAA increases the probability of radical interaction in the aqueous phase, which leads to termination of reaction chains, a decrease in the number of PMP and an increase of their sizes.
The high rate of polymerization in the particles can also be maintained after exhaustion of monomer drops due to the creation of favorable conditions for coexistence of several growing polymeric radicals in PMP and the appearance of gel effect, which becomes stronger with the growing initiation rate. This affects the shape of the kinetic curves, being a cause of the observed increase of qmax (Fig. 4). At MA-AN copolymerization, the reduction of the reaction rate is also observed, however, the conversion degree at which the maximum rate is achieved decreases in comparison with homopolymerization (Fig. 4), which is evidence of decreasing the gel effect.
%гйх (%)
iAPSl x 103 (mo№ Fig. 4 - Dependence of the conversion depth, at which the maximum rate of emulsion homopolymerization (2) and copolymerization of MA with MAA (8 %) (1) and with AN (8 %) (3) is achieved, on the initiator concentration. [Neonol] = 1%; 600C
As well as at homopolymerization, the number of particles in the emulsion depends on the conversion degree. The character of this dependence is influenced by the emulsifier as well as the comonomer. Earlier [15] it was noted that in the case of Neonol, which is partially dissolved in acrylates, a gradual rise of the number of particles occurs when the conversion degree increases, which is caused by extraction of the emulsifier dissolved in the monomer drops and PMP.
But at high conversion degrees, the amount of particles begins to decrease due to flocculation proceeding at the third stage of the reaction. When sodium lauryl sulfate (almost insoluble in the monomer) is used, no additional feed of the reaction solution with the emulsifier in the course of polymerization takes place and no increase in the number of PMP is observed (Fig. 5, curve 4).
Similar regularities have also been found while studying MA-AN copolymerization. The reduction of the number of PMP occurs as late as at the very end of the reaction at high conversion degrees, while during almost the whole third stage of the process the number of particles gradually increases (Neonol as emulsifier, curve 2) or almost does not change (LS, curve 3). Comparison of these data allows us to conclude that AN reduces flocculation at the third polymerization stage. Moreover, at copolymerization with AN, more stable dispersions are formed and the amount of coagulum decreases in comparison with MAA-containing monomer systems.
N/N16
0 20 40 60 80 100
q (%)
Fig. 5 - Changes in the number of particles in emulsion at the third stage of emulsion homopolymerization (4) and copolymerization of MA with MAA (8 %) (1) and AN (8 %) (2, 3). Emulsifier (1 %): LS (1, 3, 4) and Neonol (2); [APS] = 0,25 x 10-3 mol/l; 60oC
Flocculation of particles at the third stage of polymerization plays a more important role while usage of monomer-soluble emulsifiers (Neonol), which is due to the formation of new particles in such conditions in the course of reaction. This flocculation entails an extremal dependence of the number of particles N100 in the final polymeric dispersion (when q tends to 100%) on the APS concentration, which is characteristic of polymerization of (met)acrylates in the presence of this emulsifier. At homopolymerization with LS, only gradual increase in N100 with the initiator content was observed [16]. However, at MA-MAA copolymerization, this extremal dependence of the number of particles was found with LS as well (Fig. 6). Therefore, this comonomer attaches LS-containing systems such kinetic properties which are characteristic of Neonol-containing systems. They feature an increase in the number of PMP not only at the first stage of the process but also at higher conversion degrees. However, the cause of the appearance of such an effect at copolymerization with LS (emulsifier) differs from that
proposed for the case with Neonol. At MA-MAA copolymerization, the termination probability of reaction chains in the aqueous phase increases, which leads to the formation of water-soluble surfactant molecules with micelle-forming properties and promoting nucleation [17]. I.e. oligomers appear which play the role of their "own" emulsifier. As a result, one of the possible mechanisms of particle stabilization is realized, characteristic of emulsifier free emulsion polymerization [17]. Owing to the bimolecular chain termination , the formation of such oligomeric radicals continues during the whole reaction, which results in the formation of new PMP. However, the appearance of new particles in the course of polymerization (due to extraction of the emulsifier dissolved in the monomer to the aqueous phase from the drops and PMP, or due to the appearance of an "own" emulsifier at interaction of oligomeric radicals in water), which have a poorly protected surface, promotes flocculation.
[APS] x 103 (mol/l) Fig. 6 - Number of particles in the polymeric dispersion formed at emulsion copolymerization of MA with MAA (5%) as a function of the initiator concentration. [LS] = 1 %; 50 оС
Possibly, the oligomers with surfactant properties, playing the role of an "own" emulsifier, are formed at copolymerization with AN as well. But the effect of increasing the number of particles in this case is weaker than at copolymerization with MAA, and it is compensated by weak/poor flocculation, which results in the independence on conversion degree (Fig. 5).
The specific reaction rate in the particle w=W/(N[M]part) at the conversion degree corresponding to the attainment of the total maximum rate of polymerization, in the MA-AN system is lower than at homopolymerization of MA. Providing for the polymerization constants kp of MA and AN having close values [18], one can conclude on a reduction of the average number of radicals in PMP and a poorer gel effect at copolymerization with AN. This is possible at faster chain termination in the particles in comparison with homopolymerization. Really, AN raises the termination rate since the constant of this reaction kt for AN is almost two orders of magnitude higher than that for acrylic esters [18]. The influence of the gel effect reduces at decreasing the concentration of the initiator,
and at its low content in the systems with AN the gel effect is almost not observed. This is evidenced by the independence of the specific rate in the particles on the conversion depth in these conditions (Fig. 7, curve 3), whilst in the case of homopolymerization (curve 2), this value grows at the third stage of the reaction almost twice.
The increase in the specific rate of polymerization in the particles with the conversion depth at copolymerization with MAA speaks for a strong gel effect (Fig. 7, curve 1). However, in contrast to MA homopolymerization, it appears at high conversion degrees only. This is reflected on the shape of the kinetic curves: the reaction rate rises at higher conversion degrees and its maximum values are attained at the final stage of polymerization. As was already noted, MAA is more actively, in comparison with acrylic esters, participates in the reaction of copolymerization in both aqueous and organic medium (judging by the values of copolymerization constants). However, the growth constant of MAA polymerization in block or in an organic solvent is much lower than in water, and lower that for acrylic esters [19]. This must entail a reduction of the polymerization rate, a decrease in the molecular mass of the polymer and viscosity in the particles. Hence, the conditions for the appearance of gel effect at copolymerization with MAA are created only at high conversion degrees, when the reaction in PMP accelerates, and much stronger than in the case of homopolymerization (Fig. 7).
w/w 1Й
0 20 40 60 80 100
q (%)
Fig. 7 - Variation of the specific reaction rate in particles at the third stage of emulsion homopolymerization (2) and copolymerization of MA with MAA (8%) (1) and AN (8%) (3). [APS] = 0.25 x 10-3 mol/l; [LS] = 1 %; 600C
The increase in the maximum rate of MA homopolymerization with the APS concentration occurs to some degree within various ranges of the initiator concentration. As a result, the plot of the dependence of the rate on the initiator concentration in the log coordinates (which is used for determination of the order of the reaction by initiator n) looks as a broken line with inflexion point (Fig. 8).
4+1 gW,
0,0 0,5 1,0 1,5 2,0
4+lg[APS]
Fig. 8 - Dependence of the rate of emulsion homopolymerization and copolymerization of MA with MAA on the initiator concentration. [MAA] = 0 (1), 4 (2), 8 (3), and 14 % of [M] (4); [Neonol] = 1 %; 600C
The value ni found at relatively small initiator concentrations (lower than at the point of inflection) has turned out to be higher than the theoretically expected value 0.4, and in the range of its relatively high content - lower than 0.4. This dependence is determined by the influence of the initiator on the number of particles in the emulsion, subject to flocculation processes, and also by influencing the reaction rate in PMP, which grows owing to the strengthened gel effect. That is why at relatively low initiator concentrations, when flocculation is still weak, the strengthening of the gel effect with [APS] determines a sharper (than following the classical concept) dependence of the rate on the initiator concentration. At a high initiator content, the strengthening of flocculation reduces the value of ni.
The presence of comonomers affects the character of this dependence. The reaction order by initiator ni estimated in the range of relatively low APS concentrations reduces at increasing the content of MAA but increases with the AN concentration. Within the range of the initiator concentrations, higher than at the kink, the comonomers raise ni in comparison with that observed at homopolymerization. As a result, at copolymerization with MAA the differences in ni values before and after the point of inflection become weaker and at relatively high MAA concentrations (14 %) the kink on the log Wmax - log [APS] curve disappears (Fig. 8).
The slight decrease in ni at copolymerization with MAA (low [APS]) points to the weaker dependence of the gel effect on the initiation rate in the presence of this monomer. On the contrary, AN reduces the gel effect but raises the degree of its dependence on [APS], which entails a growth of n. The increase in the order by initiator at its relatively high content under the action of the studied comonomers speaks for flocculation moderation at the initial stages of polymerization. This leads to a growth of the APS concentration corresponding to the point of inflection.
The studies made have enabled a number of regularities of emulsion copolymerization of methyl acrylate with some hydrophilic monomers to be established. The effects revealed are explained by a
concept of several nucleation mechanisms, gel effect, bimolecular breakage of oligomeric radicals in the aqueous phase, the appearance of surfactant oligomers acting as emulsifiers, flocculation of polymer-monomer particles and the influence of polymerization conditions (initiator concentration, emulsifier nature) and the composition of monomers on the said processes.
4 Conclusion
The kinetics and mechanism of the emulsion polymerization of (meth) acrylates and their copolymerization with hydrophilic monomers (methacrylic acid, acrylonitrile) in the presence of various emulsifiers (sodium lauryl sulfate, sulfated oxyethylated alkylphenols) were studied. It has been shown that the kinetics and mechanism of emulsion polymerization contradict to the classical concepts of this reaction due to a variety of nucleation mechanisms, the presence of several growing radicals in the polymer-monomer particles, the manifestation of gel effect, flocculation of the particles at different stages of polymerization, the partial solubility of some of the tested emulsifiers in the monomer, interactions between radicals in the aqueous phase, resulting in the formation of surfactant oligomers that act as a "self' emulsifier as well as chain termination. These effects lead to the number of particles and the reaction rate therein depending on the conversion degree, the influence of polymerization conditions on the kinetic orders by the emulsifier and initiator concentrations.
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© M. D. Goldfein - Doctor of Chemistry, Full Professor, Saratov State University, Saratov, Russia, N. V. Kozhevnikov - Doctor of Chemistry, Full Professor, Saratov State University, Saratov, Russia, N. I. Kozhevnikova - Ph.D., Associate Professor, Saratov State University, Saratov, Russia, G. E. Zaikov - Doctor of Chemistry, Full Professor, Plastics Technology Department, Kazan National Research Technological University, Kazan, Russia, abzaldinov@mail.ru.
© М. Д. Гольдфейн - доктор химических наук, профессор, Саратовский государственный университет, Саратов, Россия, Н. В. Кожевников - доктор химических наук, профессор, Саратовский государственный университет, Саратов, Россия, Н. И. Кожевникова - кандидат химических наук, доцент, Саратовский государственный университет, Саратов, Россия, Г. Е. Заиков - доктор химических наук, профессор, кафедра Технологии пластических масс, Казанский национальный исследовательский технологический университет, Казань, Россия. abzaldinov@mail.ru.
