Importance of active-site reactivity and reaction conditions in the preparation of hyperbranched polymers by self-condensing vinyl polymerization: Highly branched vs. linear poly[4-(chloromethyl)styrene] by metal-catalyzed “living” radical polymerization
✍ Scribed by Marc W. Weimer; Jean M. J. Fréchet; Ivan Gitsov
- Publisher
- John Wiley and Sons
- Year
- 1998
- Tongue
- English
- Weight
- 362 KB
- Volume
- 36
- Category
- Article
- ISSN
- 0887-624X
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✦ Synopsis
The self-condensing vinyl polymerization of 4-(chloromethyl)styrene using metal-catalyzed living radical polymerization catalyzed by the complex CuCl/2,2 -bipyridyl has been attempted. Given the unequal reactivity of the two potential propagating species in this system, a variety of polymerization conditions were tested to optimize the extent of branching in the products. Typical reaction conditions included polymerization in the bulk, or preferably in chlorobenzene solution, with catalyst to monomer ratios in the range 0.01-0.30, temperatures of 100-130ЊC, and reaction times from 0.1 to 32 h. Polymers with weight average molecular weights between 3 1 10 3 and 1.6 1 10 5 and different extents of branching are formed as evidenced by size-exclusion chromatography, light scattering, and NMR analysis of the reaction products. The influence of reaction conditions on the molecular weight and branching of the resulting polymers is discussed in detail. In sharp contrast to an earlier report, the weight of evidence suggests that, at a catalyst to monomer ratio of 0.01, an almost linear polymer is obtained, while a high catalyst to monomer ratio favors the formation of a branched structure. As a result of the unequal reactivity of the primary and secondary benzylic halide reactive sites, growth occurs by a modified self-condensing vinyl polymerization mechanism that involves incorporation of the largely linear vinyl-terminated fragments formed early on in the polymerization into the vinyl polymer, to afford an irregularly branched structure. Chemical transformations involving the numerous benzylic halide functionalities of the highly branched polymer have been investigated.