Emulsion polymerization. IV. Experimental verification of the theory based on slow termination rate within latex particles

Abstract

SynopsisA large body of data shows that the time dependence of conversion fits the equation P = At2 + Bt in the interval where, according to the Smith-Ewart model, the relationship should be linear. For latexes of very small particle size the Smith-Ewart linear relationship (P = Bt) is often observed, and for latexes of very large particle size the conversion was found to be proportional to te. The experimental value of parameter B was in good agreement with independent theoretical predictions. From A and B the ratio between termination and propagation constants was calculated and was in the 5-200 range. Independent estimates of this ratio give the same order of magnitude. These independent estimates are from the literature and are obtained from the increase in conversion rate at catalyst post-addition during emulsion polymerization or from emulsion polymerization initiated by intermittent irradiation or from homogeneous polymerization in the presence of inert polymers of high viscosity. The conversiontime curves describing the whole conversion process generally have sigmoid shape. The molecular weight is often found to pass through a maximum as the conversion increases. In one experiment this maximum coincided with the calculated maximum in the average number of radicals per particle &. The variation of experimental molecular weights with conversion accurately followed the theoretical predictions. The deviation from the Smith-Ewart model was often significant. The value of & was not 0.5, as the Smith-Ewart model requires it to be, but often reached values much larger, as large as 10.The particle size distribution broadened with increasing conversion and became increasingly skew. Numerous data taken from the literature are in good quantitative or qualitative agreement with the theory proposed in Part I11 and for these data the observed deviations from the Smith-Ewart theory are readily explainable. The new data obtained with styrene, n-butyl methacrylate, and methyl methacrylate are also in quantitative agreement with the new theory. One experiment involving methyl methacrylate is analyzed in great detail. The variation of time, of &, of molecular weight, of average particle size, and of particle size distribution with conversion are reported. The molecular weight distribution is also calculated from the conversion dependence of molecular weight.

The SCOPE dynamic model for emulsion polymerization II. Comparison with experiment and applications

“…The number average molecular weights predicted by the model simulations are also consistent with an earlier result reported by GardonZ1 for the number average molecular weight of MMA homopolymer (4.11E6) as well as other results previously reported in the literature. 7,8,21, 22 In summary, the SCOPE model qualitatively predicts every major trend noted in the experiments. It reliably predicts the conversion at any time to within 15 wt % over a wide range of initiator concentrations, monomer concentrations, particle concentrations, and monomer compositions.…”

“…As stated above, number average molecular weight predictions made by SCOPE exhibit good agreement with the results of several experimental investigations. 3,7,8,21, 22 These experimental studies indicate that transfer-to-monomer largely controls the molecular weight. Test calculations carried out using different transfer-to-monomer rate constants indicated this to be the case.…”

Population Balance Model for Miniemulsion Polymerization, 2

“…Gardon defined skewness as the exponent, s of the radius such that the particle size distribution expressed in the size parameter (radius) s is most nearly Gaussian. [5] If s ¼ 1, the radii have symmetrical distribution. If s < 1, the distribution is skewed, in that relatively small number of particles have small radii and a larger number of particles are in the large particle radius range.…”

An Advanced Approach on the Study of Emulsion Polymerization: Effect of the Initial Dispersion State of the System on the Reaction Mechanism, Polymerization Rate, and Size Distribution of Polymer-Monomer Particles

“…Later on, these ideas have been modified by Gardon [17][18][19][20][21][22][23] A more general review of topochemistry and kinetics of polymerization of the latex were presented by 14]. Agreeing with Harkins-Yurzhenko's ideas concerning particles formation, Medvedev, nevertheless, has proposed that micelles have properties of swarms, and an exchange of molecules and radicals between (a) micelles themselves, and (b) micelles and polymer particles takes place.…”