Particle Size Limits of RAFT Living Emulsion Polymerization, with Xanthate-Based Transfer Agent

Abstract

With a xanthate-based low activity RAFT (reversible addition–fragmentation chain transfer) agent, the living emulsion polymerization system follows zero-one kinetics and particles are smaller than their characteristic cross over diameter. The size and kinetic limitations in RAFT emulsion were investigated by using the concept of crossover size, based on a mechanistic approach. The main reason for these limitations is attributed to the low transfer constant, which tends to render desorption of a radical from particles difficult, the incoming z-mer has a higher probability to propagate relative to the addition process in RAFT equilibrium. In contrast, the living mini-emulsion polymerization follows either zero-one or pseudo-bulk kinetics, depending on the initial droplet size and reaction conditions.