Synthesis and characterization of well-defined polystyrene and poly(ε-caprolactone) hetero eight-shaped copolymers

Well-defined hetero eight-shaped copolymers composed of polystyrene (PS) and poly(epsilon-caprolactone) (PCL) with controlled molecular weight and narrow molecular weight distribution were successfully synthesized by the combination of ring-opening polymerization, ATRP, and click reaction. The synthetic procedure involves three steps: (1) preparation of a tetrafunctional PS and PCL star copolymer with two PS and two PCL arms using the tetrafunctional initiator bearing two hydroxyl groups and two bromo groups; (2) synthesis of tetrafunctional star copolymer, (alpha-acetylene-PCL)(2)(omega-azido-PS)(2), by the transition of terminal hydroxyl and bromo groups to acetylene and azido groups through the reaction with 4-propargyloxybutanedioyl chloride and NaN3 respectively; (3) intramolecular cyclization reaction to produce the hetero eight-shaped copolymers using click chemistry under high dilution. The H-1 NMR, FTIR, and gel permeation chromatography techniques were applied to characterize the chemical structures of the resulted intermediates and the target polymers. Their thermal behavior was investigated by DSC, and their crystallization behaviors of PCL were studied by polarized optical microscopy. The decrease in chain mobility of the eight-shaped copolymers restricts the crystallization of PCL and the crystallization rate of PCL is slower in comparison with their corresponding star precursors. (C) 2008 Wiley Periodicals, Inc.