Synthesis of Dendron Functionalized Core Cross-linked Star Polymers.
The preparation of dendron functional initiators capable of initiating polymerization by atom transfer radical polymerization is described. Polyester dendrons up to the fifth generation were synthesized by the divergent route using acetonide-protected 2,2-bis(methoxy)propionic acid. These dendrons were functionalized, at the focal point, with a single -bromoisobutyrate group, thus forming a dendron functional macroinitiator. A library of highly branched, 3-dimensional, dendron functional core cross-linked star (CCS) polymers were prepared from these macroinitiators by varying generation number and polystyrene chain length, followed by reaction with divinyl benzene, utilizing the “arm first” approach. The number of arms of the star polymer was shown to decrease with increasing dendron size; a generation 1 functional polymer prepared CCS polymers with 27 arms, and a generation 5 functional polymer prepared CCS polymers with 19 arms. The length of the polystyrene linear segment had a drastic effect on the formed CCS polymers; with as little as 5 styrene units attached to a generation 5 initiator, CCS polymers with 37 arms were produced, with 290 units of styrene, CCS polymers with 8 arms were prepared.