Synthesis of star-shaped poly(epsilon-caprolactone)-b-poly(styrene) block copolymer by combining ring-opening polymerization and atom transfer radical polymerization

摘要

Newly designed star-shaped block copolymers made of poly(B-caprolactone) (PCL) and polystyrene (PS) were synthesized by combining ring-opening polymerization (ROP) of epsilon-caprolactone (CL) and atom transfer radical polymerization (ATRP) of styrene (St). The switch from the first to the second mechanism was obtained by selective transformation of "living" radical sites. First, tri- and tetrafunctional initiators were used as an initiator for the "living" ring opening polymerization (ROP) of epsilon-caprolactone producing a hydroxyl terminated three or four arm star-shaped polymer. Next, the OH end groups of PCL star branches were derivatized into 2-bromoisobutyrate groups which gave rise to the corresponding tri- and tetrabromoester ended-PCL stars; the latter served as macroinitiators for the ATRP of styrene at 110 degrees C in the presence of CuBr/2,2-bipyridine (Bipy) catalyst system affording star-shaped block copolymers PCLn-b-PSn (n = 3 or 4). The samples obtained were characterizated by H-1-NMR spectroscopy and GPC (gel permeation chromatograph). These copolymers exhibited the expected structure. The crystallization of star-shaped block copolymers was studied by DSC (differential scanning calorimetry). The results show that when the content of the PS block increased, the T-m of the star-shaped block copolymer decreased.