Differences between ab initio emulsion and miniemulsion polymerization of styrene mediated by an alkenyl-functionalized amphiphilic RAFT agent

Abstract

An alkenyl (butene)-functionalized amphiphilic macromolecular reversible addition fragmentation chain transfer (macro-RAFT) agent was designed as both surfactant and polymerization mediator for ab initio emulsion and miniemulsion polymerization of styrene (St), intending to synthesize polymer nanoparticles with alkenyl-enriched surfaces. However, the pendent alkenyl units exhibited unexpectedly higher reactivity in ab initio emulsion polymerization than they did in solution polymerization. Their copolymerization with St resulted in depletion of alkenyl groups, positive deviation of molecular weights, broad molecular weight distributions, and limiting conversions. Miniemulsion polymerization was superior to ab initio emulsion polymerization in its ability to prepare alkenyl-functionalized nanoparticles. Consumption of alkenyl groups happened, but only within the nucleation period. In spite of positive deviation of molecular weights and broad molecular weight distributions, the final particles were characteristics of alkenyl functionalities confined to the particle surfaces. Thus, PSt nanoparticles with alkenyl-enriched surface were obtained via miniemulsion polymerization.