A mathematical model is presented that simulates the polymerization of styrene in the presence of polybutadiene (PB) for producing high-impact polystyrene (HIPS) via the heterogeneous bulk process. The model follows the polymerization in two phases; and calculates in each phase the main reaction variables and the molecular structure of the three polymeric components: free polystyrene (PS), unreacted PB, and graft copolymer. Two polymerizations (at 90 and 120°C) were carried out and simulated. The model was validated with measurements of the monomer conversion, the grafting efficiencies, and the average molecular weights.

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SYNOPSISIn our previous publication the detailed molecular macrostructure generated in a solution polymerization of styrene (St) in the presence of polybutadiene (PB) at 6OoC, was theoretically calculated. In this work, an extended kinetic mechanism that incorporates monomer thermal initiation, chain transfer to the rubber, chain transfer to the monomer, and the gel effect is proposed, with the aim of simulating a bulk high-impact polystyrene (HIPS) process. The mathematical model enables the calculation of the bivariate weight chainlength distributions (WCLDs) for the total copolymer and for each of the generated copolymer topologies and the univariate WCLDs for the free polystyrene (PS), the residual PB, and the crosslinked PB topologies. These last topologies are characterized by the number of initial PB chains per molecule; copolymer topologies are characterized by the number of PS and PB chains per molecule. The model was validated with published literature data and with new pilot plant experiments that emulate an industrial HIPS process. The literature data correspond to a dilute solution polymerization at a constant low temperature with chemical initiation and a bulk polymerization at a constant high temperature with thermal initiation. The new experiments consider different combinations of prepolymerization temperature, initiator concentration, and solvent concentration. One of the main conclusions is that most of the initial PB is transformed into copolymer. For example, for a prepolymerization temperature of 12OOC with addition of initiator, the experimental measurements indicate that the final total rubber mass is approximately three times higher than the initial PB. Also, according to the model predictions, the final weight fractions are: free PS, 0.778; graft copolymer, 0.220; initial PB, 0.0015; and purely crosslinked PB, 0.0005. The final graft copolymer exhibits the following characteristics: average molecular weights, Mn,c = 492,000 and Mw,c = 976,000; average weight fraction of St, 0.722; and average number of PS and PB branches per molecule, 5.19 and 1.13, respectively. 0 1996JohnWiley & Sons, Inc.

ABSTRACT:In this study, we investigated the synthesis of high-impact polystyrene through a series of (batch and bulk) polymerizations of styrene in the presence of 6 wt % polybutadiene. The reactions with rubber involved three stages: dissolution, prepolymerization, and finishing. The prepolymerizations were isothermal (at 70°C) and nonisothermal (with an initial heating period from 70 to 120°C). Purely thermal reactions were compared with chemically initiated polymerizations involving tert-butyl peroctoate (TBPO), 2,2Ј-azobisisobutyronitrile (AIBN), and their mixtures. Most prepolymerizations involved a stirring rate of 125 rpm. The particle morphology was mainly determined by the evolution of the grafting efficiency, stirring rate, and system viscosity during prepolymerization. In the nonisothermal prepolymerizations with pure AIBN, the grafting efficiency was lower than in equivalent prepolymerizations without an initiator, yielding unstable emulsions and a poor final morphology. In the nonisothermal prepolymerizations with pure TBPO, a large amount of graft copolymer was produced early in the prepolymerization, yielding a submicrometer core-shell morphology. The particle size and morphology could be controlled by the appropriate adjustment of the recipe and the prepolymerization conditions.

SYNOPSISThis work studies the bulk and nonisothermic polymerization of styrene (S) using mixtures of mono-and bifunctional initiators. The effects on polymerization rate and on molecular weight averages after changes in the global initiator concentration and in the nature of the initiator mixtures were experimentally and theoretically analyzed. The mathematical model was adapted from the literature to admit initiator mixtures and to simulate the applied temperature profiles. Compared to the standard use of monofunctional initiators, the use of initiator mixtures that include bifunctional initiators presents the advantage of reducing the polymerization time, while not deteriorating the final polymer quality. The simulation program accurately describes the evolution of conversion, but exhibits some deviations with the average molecular weights. 0