Kinetics of High-Temperature Bulk Thermal Polymerization of Methyl Styrene

Methyl styrene monomer is a styrene derivative, created by the methyl group(s) substituted on the benzene ring. Polymethyl styrene has similar properties as with polystyrene (PS) but a lower density and higher glass transition than PS. The knowledge of polymerization kinetics allows us to construct complex polymeric architectures with different polymerization techniques and controlling their polymerization conditions. The aim of this study is to study the kinetics of free radical polymerization of methyl styrene (64% meta- and 36% para-methyl styrene isomers) in the temperature range of 80-140°C, using second- and third-order thermal initiation models and moment equations.

All polymerization runs were carried out through the ampoule method. Bulk thermal polymerization of methyl styrene was established in the range of 80-140°C and conversions were measured gravimetrically. Modeling of methyl styrene polymerization was simulated by MATLAB and moment equations. Moment equations were obtained by using the polymerization reaction. The assumed models for the initiation step of polymerization included second- and third-order in the monomer.

The theoretical results obtained from both initiation methods showed good agreement with the experimental results acquired from the gravimetric method. Also, it was demonstrated that the third-order model has better adaptation with experimental results of conversion than the second-order model. The similar results were obtained for modeling of average molecular weights. It was revealed that the gel effect had stronger effect on the average molecular weight than monomer transfer. This effect was more significant for weight average molecular weight than number average molecular weight. On the other hand, an ideal polymerization model, with no gel effect assumptions and having the same rate constants throughout, does not make good agreement with the experimental results.