Thermo-responsive behavior of hybrid core cross-linked polymer micelles with biocompatible shells

Poly(2-(methacryloyloxy)ethyl phosphorylcholine)-b-poly(N-isopropylacrylamide-co-2-(N,N-dimethylamino)ethyl methacrylate) (pMPC-b-p(NIPAM/DMA)) was synthesized via reversible addition-fragmentation chain transfer (RAFT) controlled radical polymerization. Below the critical aggregation temperature (CAT), i.e., about 40 degrees C, the diblock copolymer dissolved in water as a unimer with a hydrodynamic radius (R-h) of ca. 10 nm. Above CAT the diblock copolymers formed polymer micelles with an R-h of ca. 40 nm, composed of a p(NIPAM/DMA) core and biocompatible pMPC shell due to hydrophobic self-aggregation of the thermo-responsive p(NIPAM/DMA) block. The pendent 2-(N,N-dimethylamino)ethyl group of DMA in pMPC-b-p(NIPAM/DMA) reduced HAuCl4 to form gold nanoparticles (AuNPs) and could attach to their surfaces. The cores of these polymer micelles could be cross-linked above CAT by HAuCl4, which upon being reduced generated AuNPs as cross-linking points to form core cross-linked (CCL) polymer micelles, as confirmed by UV-vis absorption and dynamic light scattering measurements. The CCL polymer micelles absorbed visible light at 532 nm because of surface plasmon resonances of the AuNPs. The R-h of the CCL polymer micelles remained at ca. 40 nm regardless of temperature. (c) 2011 Elsevier Ltd. All rights reserved.