Synthesis of poly(tetrahydrofuran)-b-polystyrene block copolymers from dual initiators for cationic ring-opening polymerization and atom transfer radical polymerization

A dual initiator (4-hydroxy-butyl-2-bromoisobutyrate), that is, a molecule containing two functional groups capable of initiating two polymerizations occurring by different mechanisms, has been prepared. It has been used for the sequential two-step synthesis of well-defined block copolymers of polystyrene (PS) and poly(tetrahydrofuran) (PTHF) by atom transfer radical polymerization (ATRP) and cationic ring-opening polymerization (CROP). This dual initiator contains a bromoisobutyrate group, which is an efficient initiator for the ATRP of styrene in combination with the Cu(O)/Cu(II)/N,N,N',N",N"-pentamethyldiethylenetriamine catalyst system. In this way, PS with hydroxyl groups (PS-OH) is formed. The in situ reaction of the hydroxyl groups originating from the dual initiator with trifluoromethane sulfonic anhydride gives a triflate ester initiating group for the CROP of tetrahydrofuran (THF), leading to PTHF with a tertiary bromide end group (PTHF-Br). PS-OH and PTHF-Br homopolymers have been applied as macroinitiators for the CROP of THF and the ATRP of styrene, respectively. PS-OH, used as a macroinitiator, results in a mixture of the block copolymer and remaining macroinitiator. With PTHF-Br as a macroinitiator for the ATRP of styrene, well-defined PTHF-b-PS block copolymers can be prepared. The efficiency of PS-OH or PTHF-Br as a macroinitiator has been investigated with matrix-assisted laser desorption/ionization time-of-flight spectroscopy, gel permeation chromatography, and NMR. (C) 2003 Wiley Periodicals, Inc.