Combining atom-transfer radical polymerization and ring-opening polymerization through bifunctional initiators derived from hydroxy benzyl alcohol - Preparation and characterization of initiators, macroinitiators, and block copolymers

摘要

A simple, one-step procedure has been developed for the preparation of bifunctional initiators capable of polymerizing monomers suitable for atom-transfer radical polymerization (ATRP) and ring-opening polymerization (ROP). These bifunctional initiators were employed for making narrow disperse poly(styrene) macroinitiators, which were subsequently used for the ROP of various lactides to yield poly(styrene-block-lactide) copolymers. Thermogravimetric analysis (TGA) of these block copolymers are interesting in that it shows a two-step degradation curve with the first step corresponding to the degradation of poly(lactide) segment and the second step associated with the poly(styrene) segment of the block copolymer. This nature of the block copolymer makes it possible to estimate the block copolymer content by TGA in addition to the H-1 NMR spectroscopic analysis. Thus, this study for the first time highlights the possibility of making porous materials by thermal means which are otherwise obtained by base hydrolysis. The bifunctional initiators were prepared by the esterification of 3-hydroxy, 4-hydroxy, and 3,5-dihydroxy benzyl alcohols with alpha-bromoisobutyryl bromide and 2-bromobutyryl bromide. A mixture of products was obtained, which were purified by column chromatography. The esterified benzyl alcohols were employed in the polymerization of styrene under copper (Cu)-catalyzed ATRP conditions to yield macroinitiators with low polydispersity. These macroinitiators were subsequently used in the ROP Of L-, DL-, and mixture of lactides. The formation of block copolymers was confirmed by gel permeation chromatography (GPC), spectroscopic and thermal characterizations. The molecular weight of the block copolymers was always higher than the macroinitiator, and the GPC chromatogram was symmetrical indicating the uniform initiation of ROP by the macroinitiators. (c) 2007 Wiley Periodicals, Inc.