Initiators based on poly(ethylene glycol) for starting heterophase polymerizations: generation of block copolymers and new particle morphologies

Abstract

Radical heterophase polymerizations with poly(ethylene glycol) radicals lead to the formation of block copolymer particles where the block copolymer architecture and the particle morphology depend on the number of radicals per poly(ethylene glycol) chain, the radical termination mode, and the polarity of the monomer, respectively. The thermal decomposition of symmetrical poly(ethylene glycol) azo-initiators following the classical recipes of Heitz results in one radical per poly(ethylene glycol) chain whereas the number of radicals can be adjusted between one or two in the redox system poly(ethylene glycol)/cerium ions. The polymerization of styrene results in latex particles with an almost spherical morphology, consisting of block copolymers, only. In case of a methyl methacrylate polymerization the latex morphology depends on the architecture of the block copolymers formed. Heterophase polymerization with poly(ethylene glycol) azo-initiators in oligo(ethylene glycol) (average molecular weight 200 g mol -1 ) instead of in water results in particles with random shape and a strongly indented interface which is explained by the surface tension between polymers and solvent being close to zero.