RAFT surfactant-free cationic emulsion polymerization of styrene: effect of hydrophobicity of block macro-RAFT agent

The effect of the hydrophobicity of block copolymer macro-RAFT agents on the controllability of RAFT surfactant-free cationic emulsion polymerization of styrene was investigated. Three different copolymers, poly(dimethyl aminoethyl acrylate) (PDMAEA), poly(dimethyl aminoethyl acrylate-co-styrene)-b-(butyl acrylate) (P(DMAEA-co-St)-b-PBA) and poly(dimethyl aminoethyl acrylate-co-styrene)-b-(hexafluorobutyl acrylate) (P(DMAEA-co-St)-b-PHFBA), which had different hydrophobicity in their hydrophobic segments, were synthesized and used as the macro-RAFT agents. When P(DMAEA-co-St)-b-PHFBA and P(DMAEA-co-St)-b-PBA were used as macro-RAFT agents, the RAFT surfactant-free cationic emulsion polymerization of styrene underwent very fast. But when the PDMAEA was used as the macro-RAFT agent, no polymerization of styrene was observed. The controllability of styrene polymerization with P(DMAEA-co-St)-b-PHFBA as the RAFT agent showed much better than that with P(DMAEA-co-St)-b-PBA as the macro RAFT agent. This was ascribed to hydrophobicity difference of the hydrophobic segment between P(DMAEA-co-St)-b-PHFBA and P(DMAEA-co-St)-b-PBA macro-RAFT agents. A mechanism explanation for the controllability of emulsion polymerization was proposed. The location of the active trithiocarbonate group of the macro-RAFT agent in micelle was supposed to be a key factor affecting the controllability of RAFT surfactant-free cationic emulsion polymerization of styrene. The hydrophobicity of the RAFT agent and nature of medium had impact on the location of the active trithiocarbonate group of the macro-RAFT agent in micelle and affected the polymerization controllability.