Synthesis of butyl acrylate-styrene block copolymers in emulsion by reversible addition-fragmentation chain transfer : effect of surfactant migration upon film formation

The synthesis of block copolymers in an environmentally friendly medium was carried out in emulsion polymerizations through the reversible addition-fragmentation chain transfer process, using a transfer active xanthate (MADIX) agent, under batch and starved-feed conditions. First, ab initio experiments were carried out to prepare a seed of PBA dormant chains (i.e., poly(butyl acrylate) (PBA) polymer attached with a transfer active xanthate). The n and polydispersity were predicted accurately with numerical simulations and equations derived by Müller from the method of moments. Those seeds were then used in a second-stage polymerization under starved-feed and batch conditions to prepare composite polymer colloids of block PBA-co-poly(styrene). Under starved feed conditions, approximately 90% of total polymer consisted of blocks, whereas under batch conditions only 70% consisted of blocks, which is proposed to be due a higher entry efficiency and thus greater termination rate. The films of these latexes were examined by atomic force microscopy. Surfactant migration to the surface increased with an increase in the amount of MADIX, resulting from a combination of a smaller particle size and a lower average molecular weight.