Synthesis of Block Copolymers of Styrene with D,L-Lactide by the Sequential Controlled Cationic Polymerization and Ring-Opening Anionic Polymerization

Abstract

The cationic polymerization of styrene initiated by the system 2-chloro-2-phenylpropane–TiCl4–pyridine is studied in a mixture CH2Cl2–n-hexane at a temperature of –80°С. It is shown that under these conditions polymerization occurs via the living mechanism at [monomer]: [initiator] ≤ 100. The method of preparing polystyrenes with terminal primary hydroxyl groups (Mn = 4000–10000 g/mol) by the sequential controlled cationic polymerization of styrene and the in situ alkylation of 4-phenoxy-1-butanol by polystyrene macrocations is proposed. The resulting functionalized polystyrenes are used as macroinitiators of anionic-coordination ring-opening polymerization of D,L-lactide in the presence of tin bis(2-ethyl hexanoate) [Sn(Oct)2] in toluene at 80°С. Copolymers polystyrene-block-poly(D,L-lactide) with the controlled length of the poly(D,L-lactide) block (Mn = 10000–17000 g/mol) and a relatively low molecular-weight distribution (Mw/Mn = 1.6–1.8) are synthesized. Formation of the block copolymers is confirmed by 1Н NMR spectroscopy, gel-permeation chromatography, and atomic force microscopy.