Emulsion terpolymerization of St/MMA/BuA: Modeling of composition, number of particles and the influence of n-DDM on the molecular weights

•Systematic study of gel effect in batch, semicontinuous and seeded processes.•Simple mathematical kinetic modeling with a good fitting to experimental data.•Analysis of the dependence of mass transfer of n-DDM on the feed monomer composition.•Simulation of the behavior of number of particles in emulsion terpolymerization.•Contribution to the design of process strategies to emulsion terpolymerization.

The influence of n-dodecyl mercaptan (n-DDM) on the molecular weights distribution of the styrene/methyl methacrylate/butyl acrylate (St/MMA/BuA) terpolymer was studied. First, a kinetics emulsion terpolymerization model based on Nomura’s model for copolymerization was developed. The predicted data by this model was compared with those obtained for batch, semicontinuous polymerization, as well as seeded experiments for the St/MMA/BuA system. A composition near to the unitary azeotrope of methyl methacrylate (MMA) was calculated and used to estimate the Mw of a terpolymer uniform in composition synthesized by a seeded process. It was established that a higher proportion of BuA makes the model of weight fraction of polymer Wp in the particle more suitable for simulating the gel effect on the propagation rate coefficient kp. Likewise, this model of gel effect upon kp is significant for both the semicontinuous processes with lower monomer addition rate and the seeded process.

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