Free‐radical polymerization with long‐chain branching: Batch polymerizations of vinyl acetate in t‐butanol

Abstract

SynopsisVinyl acetate was batch polymerized a t 60°C in t-butanol solution. Conversion and molecular weights were measured as functions of time for several initiator and solvent concentrations. Although the overall rate constant depends somewhat on solvent concentration, the reaction is first order in monomer concentration up to a t least 60% conversion and one-half order in the concentration of initiator. Molecular weights were independent of initiator concentration, confirming that the polymerization is transfer dominated. Measurements of A?u and A?, , versus conversion were used to establish the individual transfer constants. All are independent of solvent concentration, except C,,, the polymer transfer constant, which decreases systematically with increasing solvent concentration.

Transient Behavior and Gelation of Free Radical Polymerizations in Continuous Stirred Tank Reactors

“…[25] Results obtained by the method here described present an excellent agreement with the experimental data, specially taking into account that no fitting of rate parameters was done. The improved results obtained by this [15,16] for polymerization of vinyl acetate in a CSTR. method comparatively to the Monte Carlo simulation are, in our opinion, explained by the elimination of the assumption of negligible initiation and termination reaction rates relatively to propagation and transfer.…”

“…In fact, for this system the use of inappropriate models, namely the lack of consideration of the existence of poly-radicals and neglect of radical outflow can lead to the divergence of the second moment of CLD and therefore to the prediction of gelation contrary to experimental evidence, as stated by Tobita. [25] The experimental data and chosen operation conditions can be found in works by Chatterjee et al [15,16] namely with y S ¼ 2, C M ¼ 2.46 Â 10 À4 , C P ¼ 1.30 Â 10 À4 , C S ¼ 0.34 Â 10 À4 , and K 2 ¼ 0.66, which are also the same parameters used by Tobita with the goal of comparison with his Monte Carlo simulations. [25] In Figure 6, comparisons between these experimental results and the predictions of two versions of the method of the moments, Monte Carlo simulation, and the present method are presented.…”

“…[25] In Figure 6, comparisons between these experimental results and the predictions of two versions of the method of the moments, Monte Carlo simulation, and the present method are presented. The predictions of method of moments 1 were obtained according to Chatterjee et al [15,16] and method of moments 2 is based on an improved version of this method. [21] The inability of both methods of moments to calculate the second order (or higher) moment of CLD is clear.…”

“…Some attempts in the inclusion of initiation, termination, and inhibition effects in the models have also not been well succeeded. [14] Other sets of experimental data were obtained in batch and continuous reactors with especial care about the elimination of inhibition periods, [15,16] but the same inconsistencies above identified between model predictions and experimental observations have remained.…”

A New Look at Kinetic Modeling of Nonlinear Free Radical Polymerizations with Terminal Branching and Chain Transfer to Polymer

“…22,23 The results obtained in those simulations demonstrate a fairly good agreement with experimental results of several other previous works. 9,[24][25][26][27] In those cases, we have considered the situation where transfer to polymer can occur in two different sites in the molecules. Then the formation of saponified and nonsaponified branches can also be simulated.…”