Catalytic chain transfer mediated emulsion polymerization : compartmentalization and its effects on the molecular weight distribution

We present the first population balance calculations which encompass the complete molecular weight distribution (MWD) to discuss the implications of both radical and catalytic chain transfer agent (CCTA) compartmentalization in a catalytic chain transfer (CCT) mediated emulsion polymerization system. Compartmentalization effects are attributed to reduced frequencies of entry and exit of the CCTA (bis[(difluoroboryl)dimethylglyoximato]cobalt(II) or COBF). Two limiting scenarios were identified. In instances of fast CCTA entry and exit, monomodal MWDs are obtained governed by a global CCTA concentration. In instances of slow entry and exit, bimodal MWDs are obtained; one peak can be attributed to the generation of a bimolecular termination product produced in polymer particles devoid of CCTA, while a transfer-derived peak can be attributed to polymer particles containing one or more CCTA molecules. We present theoretical evidence that experimentally observed multimodal MWDs ( Macromolecules 2009, 42, 7332-7341) originate from a reduced mobility of the CCTA and that when viscosity is high in the polymer particles, compartmentalization of the CCTA becomes important.