Synthesis of well-defined cyclodextrin-core star polymers

The synthesis of 81-arm methyl methacrylate (MMA) and styrene star polymers is reported. The copper (I)-mediated living radical polymerization of MMA was carried out with a cyclodextrin-core-based initiator with 21 independent discrete initiation sites: heptakis[2,3,6-tri-O-(2-bromo-2-methylpropionyl]-beta -cyclodextrin. Living polymerization occurred, providing well-defined 81-arm star polymers with predicted molecular weights calculated from the initiator concentration and the consumed monomer as well as low polydispersities [e.g., poly(methyl methacrylate) (PMMA), number-average molecular weight (M-n) = 55,700, polydispersity index (PDI) = 1.07; M-n = 118,000, PDI = 1.06; polystyrene, M-n = 37,100, PDI = 1.15]. Functional methacrylate monomers containing poly(ethylene glycol), a glucose residue, and a tert-amine group in the side chain were also polymerized in a similar fashion, leading to hydrophilic star polymers, again with good control over the molecular weight and polydispersity (M-n = 15,000, PDI = 1.03; M-n = 36,500, PDI = 1.14; and M-n = 139,000, PDI = 1.09, respectively). When styrene was used as the monomer, it was difficult to obtain well-defined polystyrene stars at high molecular weights. This was due to the increased occurrence of side reactions such as star-star coupling and thermal (spontaneous) polymerization; however, low-polydispersity polymers were achieved at relatively low conversions. Furthermore, a star block copolymer consisting of PMMA and poly(butyl methacrylate) was successfully synthesized with a star PMMA as a macroinitiator (M-n = 104,000, PDI = 1.05). (C) 2001 John Wiley & Sons, Inc.