Synthesis and self-assembly of new amphiphilic thermosensitive poly(N-vinylcaprolactam)/poly(d,l-lactide) block copolymers via the combination of ring-opening polymerization and click chemistry

Abstract

New amphiphilic thermosensitive poly(N-vinylcaprolactam)/poly(e-caprolactone) (PNVCL-b-PCL) block copolymers were synthesized by click reaction with alkynyl-terminated poly(N-vinylcaprolactam) (PNVCL-C ≡ CH) and azido-terminated poly(e-caprolactone) (N3-PCL). The structures of the polymers were determined by proton nuclear magnetic resonance spectroscopy (1H NMR) and gel permeation chromatography (GPC) measurements. The fluorescence technique was used to determine the critical micelle concentrations (CMC) of copolymer solutions. The factors affecting the lower critical solution temperature (LCST) of the copolymers were studied by UV-visible analysis. The diameters and distribution of the micelles were characterized by dynamic light scattering (DLS), and their shapes were observed by transmission electron microscopy (TEM). The results showed that these copolymers could self-assemble into nano-micelles in water. The CMC values of the copolymer solutions and the sizes of micelles reduced with increasing proportion of hydrophobic parts. TEM images demonstrated that the micelles are all spherical. On the other hand, the UV–visible measurements showed that these block copolymers exhibit a reproducible temperature-responsive behavior with a LCST that is tunable by block composition.