tBHBMA: a novel trifunctional acrylic monomer for the convenient synthesis of PAA-g-PCL well-defined amphiphilic graft copolymer

A series of well-defined amphiphilic graft copolymers, consisting of a hydrophilic poly(acrylic acid) (PAA) backbone and hydrophobic poly(epsilon-caprolactone) (PCL) side chains, was synthesized by the combination of reversible addition-fragmentation chain transfer (RAFT) polymerization and ring-opening polymerization (ROP). A new acrylate monomer containing a ROP initiation group, tert-butyl(2-((4-hydroxybutanoyloxy)methyl)acrylate), was first prepared using tert-butyl acrylate as the starting material, and it was homopolymerized by RAFT in a controlled way to give a well-defined homopolymer bearing ROP initiation group in every repeating unit. This homopolymer directly initiated ROP of epsilon-caprolactone to provide well-defined poly(tert-butyl acrylate)-g-poly(epsilon-caprolactone) graft copolymers via the grafting-from strategy without post-polymerization functionality transformation. Finally, the hydrophobic poly(tert-butyl acrylate) backbone was selectively hydrolyzed in an acidic environment without affecting the PCL side chains to afford poly(acrylic acid)-g-poly(epsilon-caprolactone) amphiphilic graft copolymers possessing the hydrophilic PAA backbone and equally distributed hydrophobic PCL side chains. The self-assembly behavior of the obtained amphiphilic graft copolymers and pH-sensitivity of the resultant micelles were investigated by fluorescence spectroscopy, DLS, and TEM. DSC and XRD analysis showed the crystallization behavior of poly(acrylic acid)-g-poly(epsilon-caprolactone) graft copolymers.