Solvent-initiator compatibility and sensitivity of conversion of styrene homo-polymerization

Efforts were made to synthesize polystyrene (PS) using free radical solution polymerization. Four common solvents with dissimilar polarities, acetone, chloroform, benzene and toluene, with two different initiators, were selected. The homo-polymerization was conducted in an ace round-bottom pressure flask of diameter 62 mm, with a thermo well, which housed the thermometer. The reaction temperature was maintained at 120°C using a heater with a temperature controller, coupled with a magnetically driven stirrer. One hundred experimental runs of 8 different groups were carried out. Polymerization was conducted in the mass concentration of 0.1 g for each initiator [benzoyl peroxide (BPO) and its blend]. The key parameter considered is the volume ratio of monomer to solvents under different types of solvents, initiators and reaction time. Initially, there was an increase in conversion with the solvent volume and time, until a certain point where there was a gradual decline in monomer conversion. Polymerization rate and monomer conversion were observed to be higher in polar solvents (acetone). Further presented in this study is the macromolecular architecture (molecular weight) and micro-structure of some of the solution polymerized monomer. A kinetic model was also presented to predict the conversion with time profile of the polymerization process. Molecular weight determined were between acceptable ranges while the model presented though with considerable error margin but seems to respond just fairly at extremely low monomer conversion. Similar response was observed from earlier model reported in literature when tested with our experimental data.