Poly(ethylene oxide)-block-polystyrene copolymers obtained by radical polymerization involving chain-transfer processes

Abstract

Poly(ethyl oxide)-block-polystyrene (PEO-PSt) block copolymers were prepared by radical polymerization of styrene in the presence of iodoacetate-terminated PEO (PEO-I) as a macromolecular chain-transfer agent. PEO-I was synthesized by successively converting the OH end-group of α-methoxy ω-hydroxy PEO to chloroacetate and then to the iodoacetate. The chain-transfer constant of PEO-I was estimated from the rate of consumption of the transfer agent versus the rate of consumption of the monomer (Ctr,PEO-I = 0.23). Due to the involvement of degenerative transfer, styrene polymerization in the presence of PEO-I displayed some of the characteristics of a controlled/'living' process, namely an increase in the molecular weight and decrease of polydispersity with monomer conversion. However, because of the slow consumption of PEO-I due to its low chain-transfer constant, this process was not a fully controlled one, as indicated by the polydispersity being higher than in a controlled polymerization process (1.65 versus <1.5). The formation of PEO-PSt block copolymers was confirmed by the use of size-exclusion chromatography and 1H NMR spectroscopy. © 2004 Society of Chemical Industry.