Linear and semicyclic amphiphilic diblock copolymers .1. Synthesis and structural characterization of cyclic diblock copolymers of poly(hydroxyethyl vinyl ether) and linear polystyrene and their linear homologues

We recently proposed a new method allowing the controlled synthesis of ring-shaped polymers with predictable molar masses and narrow molar mass distribution. The cyclization is based on a unimolecular ''end-to-end'' coupling reaction of an heterodifunctional linear polymer precursor. In this paper, this methodology is applied to the synthesis of semicyclic block copolymers comprising a cyclic hydrophilic block on which a linear hydrophobic polymeric tail is attached, i.e., a cyclic diblock copolymer of poly(hydroxyethyl vinyl ether) and linear polystyrene. The general strategy for the synthesis involves three main steps: (i) preparation of a linear alpha-acetal-gamma-styrenyl-poly(chloroethyl vinyl ether-block-styrene) precursor, (ii) intramolecular coupling involving the activation and reaction of the two complementary functions under high dilution, yielding the cyclized poly(CEVE) block, and (iii) substitution by hydroxy functions of the chloro side groups of poly(CEVE) block in order to form the amphiphilic semicyclic diblock copolymer. The corresponding linear diblock copolymer, with the same block length, DP,, and molar mass distribution, was simultaneously obtained using steps i and iii. The synthesis and characterization of these new diblock copolymers of controlled dimensions is described.