Experimental and Theoretical Study on Bulk Suspension Polymerizations of Styrene in the Presence of Styrene-b-Butadiene Diblock Copolymers

LUCIANI, C. V.; DIAZ DE LEÓN, R.; MORALES, G.; ESTENOZ, D. A.; MEIRA, G. R.

Los Cocos, Prov. de Córdoba, Argentina

Congreso; III Simposio Argentino-Chileno de Polímeros (Archipol’05); 2005

High-Impact Polystyrene (HIPS) is a heterogeneous material produced via bulk or combined bulk-suspension processes, in which the styrene (St) monomer is polymerized in the presence of 5-10% w/w of an elastomer [polybutadiene (PB) or St-b-butadiene (Bd) diblock copolymers (BC)]. The bulk processes involve 2 main stages: Prepolymerization and Finishing. The Prepolymerization is carried out at lower temperatures, with a chemical initiator, and under well-stirred conditions. Initially, the process is homogeneous, but the thermodynamic incompatibility between the produced free PS and the preexistent PB chains determines a phase separation, with a discontinuous PS-rich phase and a continuous PB-rich phase. Then, the phase inversion takes place, and the particle morphology is developed. In the Finishing, the temperature is increased to reduce the viscosity and to promote the thermal monomer initiation. Also, the stirring is eliminated to avoid destroying the morphology. In the combined bulk-suspension process, the Finishing stage is carried out in the presence of an aqueous suspension medium and under well-stirred conditions. Numerous mathematical models have been developed that describe the HIPS process and are capable of predicting the molecular structure of the reacting mixture in one or two phases. In Luciani et al. (2003), we presented a model that predicts the HIPS morphology produced in a bulk polymerization of St in the presence of PB. In this work, the model is extended to simulate a bulk-suspension process when a St-Bd BC is used as the base rubber.