Highly living polymer with over 100 kg/mol molecular weight is very difficult to achieve by controlled/living radical polymerizations since the unavoidable side reactions of irreversible radical termination and radical chain transfer to monomer reaction become significant. We will report that over 500 kg/mol polystyrene with high livingness (~90%) and narrow molecular weight distribution (PDI~1.2) could be synthesized by a facile two-stage reversible addition-fragmentation transfer emulsion polymerization. The monomer conversion reaches over 90% within about 10 hours. We will also touch on the polymerization kinetics. It is revealed that the high livingness of the product should be ascribed to extremely low initiator concentration and the dramatic reduction in irreversible radical chain transfer to monomer reaction rate. The polymerization rate remains high even at very low initiator concentrations. As the initiator concentrations is decreased to very low levels, both molecular weight distribution (PDI) and particle size distribution (PSD) unexpectedly broaden in an accelerating rate due to the slow activating/deactivating rates between particles with and without a radical inside. The two-stage monomer feeding policy can much decrease PDI. It is estimated that the rate constant of the irreversible radical chain transfer to monomer reaction (CM) should be only about 1/6 to 1/4 of the well-accepted value in the conventional radical polymerization.

To achieve well-defined and highly-living polystyrene over 500 kg/mol with high polymerization rates via a two-stage RAFT emulsion polymerization

254th National Meeting (2017)

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