One-pot synthesis of branched poly(styrene-divinylbenzene) suspension polymerized resins

Spherical particulate polymer resins have become ubiquitous support materials in both solid phase synthesis and in the heterogenizing of homogeneous catalysts. In the former case lightly cross-linked so-called gel-type species are favored whereas in the latter so-called macroporous species are finding increasing utility. Despite the success of these materials, mass transfer limitations can lead to poor performance, and in this context there is still a need for improvement in the morphology of these species. One potential advancement would be resins with a highly branched backbone architecture since such a molecular level structure would in principle generate a large proportion of functional groups near chain ends or at least on mobile chains anchored to the main matrix by a single linkage. In addition a high level of chain ends relative to that in conventional resins might lead to novel solvation characteristics. We now report a facile one-pot suspension polymerization which allows synthesis of both branched gel-type and branched macroporous resins. The procedure is an adaptation of our earlier reported methodology for producing soluble branched vinyl polymers and involves use of controlled levels of a free radical chain transfer agent which functions in effect to limit chain growth and in combination with a cross-linking comonomer leads essentially to branched backbone architectures. The system styrene/divinylbenzene/dodecanethiol has been probed in detail, and a range of experimental conditions have been identified which lead to branched gel-type and branched macroporous resins. The structure of these has been evaluated from solvent swelling data, dry state surface area measurements, and inverse size exclusion chromatographic data.