Synthesis of mikto-topology star polymer containing one cyclic arm

Journal of Polymer Science Part A: Polymer Chemistry

http://onlinelibrary.wiley.com/doi/10.1002/pola.26226/abstract

Well-defined mikto-topology star polystyrene composed of one cyclic arm and four linear arms was synthesized by a combination of atom transfer radical polymerization (ATRP) and Cu-catalyzed azide-alkyne cycloaddition (CuAAC) click reaction.
First, the bromine-alkyne α,ω-linear polystyrenes containing four hydroxyl groups protected with acetone-based ketal groups were synthesized by ATRP of styrene using a designed initiator.
Then, the bromine end-group was converted to the azide and the linear polystyrene was cyclized intra-molecularly by the CuAAC reaction.
The four hydroxyl groups were released by deprotection and then esterified with 2-bromoisobutyryl bromide to produce a cyclic polymer bearing four ATRP initiating units.
By subsequent ATRP of styrene to grow linear polymers with the cyclic polystyrene as a macroinitiator, the mikto-topology star polymers were prepared.