Block copolymers offer the potential of tuning product properties for applications in biomedical engineering to specialty products. Living free radical polymerisation with reversible addition–fragmentation chain transfer (RAFT) is the most promising. RAFT is facilitated by compounds such as Z-C(=S)S-R. For block copolymer synthesis, we prepared polystyrene and polybutyl acrylate homopolymers with predetermined molecular weights at the first stage. Emulsion polymerization was performed under batch conditions at controlled temperature and 350 rpm agitation speed. Latex particles containing macro-RAFT agent with a targeted molecular weight of 9194 g/mol were obtained.

In the second stage, the entire styrene (100g) was added to 260g PBA seed latexes (24.45% solids) obtained from the first stage to produce b-PBA-co-PSt. Water (190g) and SDS (0.15g) added to the mixture were stirred overnight at 100 rpm. After 2 hours, batch emulsion polymerization of styrene in PBA seeds was started by adding 0.15g KPS (in 10g water at reaction temperature) under nitrogen pressure. In stage II, styrene was polymerized in 200g PBA seeds (24.45% solids) obtained from the first stage.

Our results showed that the choice of blocking sequence is important in reducing the influence of terminated chains on the distributions of polymers obtained. We found that polymerizing styrene followed by the active butyl acrylate monomer resulted in pure block copolymer with low polydispersity shown by our size exclusion chromatography and nuclear magnetic resonance (1H-NMR) measurements. We demonstrated that living polymerization can be approached via semi-batch emulsion polymerization under starved-feed conditions with production of high purity block copolymers.