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 MARC W. WEIMER, 1,2 JEAN M. J. FRE ´ CHET, 1,2 IVAN GITSOV 1,2,3 1 Department of Chemistry, University of California, Berkeley, California 94720-1460 2 Baker Laboratory, Department of Chemistry, Cornell University, Ithaca, New York 14853-1301 3 Department of Chemistry, SUNY College of Environmental Sciences & Forestry, Syracuse, New York 1321-2786 Received 12 June 1997; accepted 10 October 1997 ABSTRACT: The self-condensing vinyl polymerization of 4- ( chloromethyl ) styrene using metal-catalyzed living radical polymerization catalyzed by the complex CuCl / 2,2 -bi- pyridyl has been attempted. Given the unequal reactivity of the two potential propagat- ing species in this system, a variety of polymerization conditions were tested to optimize the extent of branching in the products. Typical reaction conditions included polymer- ization in the bulk, or preferably in chlorobenzene solution, with catalyst to monomer ratios in the range 0.01 – 0.30, temperatures of 100 – 130°C, 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.  1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 955–970, 1998 Keywords: hyperbranched; self-condensing vinyl polymerization; metal catalyzed; living radical ular weight characteristics, a high number of func- INTRODUCTION tional units, and novel architectures. 1 Dendrimers 2 represent a new class of perfectly branched macro- The expansion of new technologies is creating a growing interest in polymers of well-defined molec- molecules of particular interest since they possess these features. However, industrial production of dendrimers is limited due to the current require- Correspondence to: J. M. J. Fre ´chet ment for multistep reactions and the intermediate Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 36, 955–970 (1998)  1998 John Wiley & Sons, Inc. CCC 0887-624X/98 / 060955-16 purification steps that are needed to create such 955 8g70 97122p / 8G70$$122P 02-19-98 09:32:30 polcal W: Poly Chem