Molecular control of polystyrene in the reverse iodine transfer polymerization (RITP) – Suspension process

The reverse iodine transfer polymerization (RITP)-suspension polymerization of styrene was carried out in the presence of molecular iodine (I2) using AIBN as an initiator and polyvinylalcohol (PVA) as a stabilizer under argon atmospheres at 70 °C for 10 h in the absence of light. The effect of iodine and styrene contents on the molecular characteristics was investigated. The result was summarized into three categories; (1) the two different polymerizations, the emulsion and suspension, simultaneously occurred in the RITP-suspension polymerization. (2) The emulsion fraction decreased, whereas the suspension fraction increased with the I2 content from 0 to 0.25 mmol, resulting in the decreased molecular weight of the resultant polymer from 320,000 to 59,000 g/mol, respectively. This was arisen from the higher reaction rate of the RITP-suspension polymerization due to the better solubility of AIBN in the monomer droplet in the suspension phase than in the micelle in the emulsion phase upon the increased I2 content. (3) As the styrene content increased up to 40 wt% under fixed I2 content, the suspension fraction dominated, resulting in the reduced molecular weight from 59,000 to 38,000 g/mol, respectively. This was rationalized that the temperature increment upon the relatively small amount of solvent, which means due to the large amount of monomer, induced the rapid polymerization in the monomer droplets where the suspension polymerization was favorable. Thus, the RITP-suspension process dramatically decreased the molecular weight of PS not only by the presence of I2, but also by the dominated suspension fraction.