Synthesis of Densely Grafted Cylindrical Polymer Brushes

Densely grafted cylindrical polymer brushes with more than one side chains on each repeating unit of backbone were synthesized by copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction via grafting-onto method. The ketal-protected monomer, 2, 2-bis-(hydroxymethyl) propyl methacrylate (bis-MPMA) was prepared and polymerized by reversible addition-fragmentation chain transfer (RAFT) mediated radical polymerization to yield linear polymer backbone with narrow distribution of molecular weight. The polymer backbone with two hydroxyl groups at each repeating unit was obtained after deprotection under acid condition. Then the hydroxyl groups were converted to alkyne groups by reacting with 4-pentynoic anhydride. Azido-terminated poly (ethylene oxide) (PEO) or polystyrene (PS), which were obtained by post-polymerization modification,were coupled with the alkyne groups on the backbone by CuAAC reaction. The grafting ratio and structure of the obtained polymer brushes were characterized by size exclusion chromatography (SEC) and nuclear magnetic resonance (NMR). The reaction efficiency of PEO113-N-3 and PS18-N-3 in CuAAC was 85.1% and 78.0%, and the grafting ratios were 64.7% and 54.6%, respectively. The denseness of the alkyne groups on the polymer backbone or the steric hindrance of the polymer side chains may be holdback of the grafting.