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Determination of the Critical Chain Length of Oligomers in Dispersion Polymerization.

The critical chain length (jcrit) in dispersion polymerization is systematically investigated utilizing low molecular weight poly(methyl methacrylate) oligomers synthesized by catalytic chain transfer polymerization. The solubility of these oligomers in methanol/water media of different compositions and at different temperatures has been visually determined. The results show that the solubility of the oligomers increases with increasing methanol fraction and increasing temperature. The constructed solubility map allows for an estimate of jcrit as a function of these important polymerization parameters. Furthermore, it is found that the value of jcrit changes with the concentration of the oligomers in the methanol/water medium, an important consideration for understanding the nucleation stage of a dispersion polymerization. The obtained results have been successfully correlated to earlier data reported on the dispersion polymerization of methyl methacrylate.