Synthesis of polystyrene microgel with a hyperbranched polyglycerol scaffold as core: Effect of shell congestion

Two hyperbranched polyglycerols (PG) ( 1a : M n = 2000, 1b : M n = 8000), both with 61% of the overall hydroxyl groups being transformed into trithiocarbonates ( 2a , 2b , with 16 and 65 OH groups being replaced by trithiocarbonates, respectively), can be used as a reversible addition‐fragmentation chain transfer (RAFT) agent. Polymerization of styrene mediated by 2a /2b was in a living manner, resulting in star‐like, amphiphilic, core‐shell structured polymers with 16 arms ( 3a ) and 65 arms ( 3b ), respectively. It was found that for system mediated by 2b , more serious side reaction (radical–radical coupling) occurred than that by 2a , most probably due to their difference in shell congestion. A shell‐crosslinked polymer could be prepared in the presence of divinylbenzene via a one‐pot route at solid content up to 20%, but analysis proved the crosslinking was incomplete. Furthermore, the 65‐arm‐star polymer ( 3b) more tended to undergo macroscopic rather than intramolecular crosslinking than the 16‐arm‐star polymer ( 3a ) did. The phenomenon might again be attributed to their difference in shell congestion. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007