Degradable Star Polymers with High "Click" Functionality

Degradable polyester-based star polymers with a high level of functionality in the arms were synthesized via the "arms first" approach using an acetylene-functional block copolymer macroinitiator. This was achieved by using 2-hydroxy-ethyl 2'-methyl-2'-bromopropionate to initiate the ring-opening polymerization (ROP) of caprolactone monomer followed by an atom transfer radical polymerization (ATRP) of a protected acetylene monomer, (trimethylsilyl)propargyl methacrylate. The hydroxyl end-group of the resulting block copolymer macroinitiator was subsequently crosslinked under ROP conditions using a bislactone monomer, 4,4'-bioxepanyl-7'-dione, to generate a degradable core crosslinked star (CCS) polymer with protected acetylene groups in the corona. The trim ethyl silyl-protecting groups were removed to generate a CCS polymer with an average of 1850 pendent acetylene groups located in the outer block segment of the arms. The increased functionality of this CCS polymer was demonstrated by attaching azide-functionalized linear polystyrene via a copper (I)(I)-catalyzed cycloaddition reaction between the azide and acetylene groups. This resulted in a CCS polymer with "brush-like" arm structures, the grafted segment of which could be liberated via hydrolysis of the polyester star structure to generate molecularbrushes. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1485-1498, 2009