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 °C, the diblock copolymer dissolved in water as a unimer with a hydrodynamic radius (Rh) of ca. 10 nm. Above CAT the diblock copolymers formed polymer micelles with an Rh 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 Rh of the CCL polymer micelles remained at ca. 40 nm regardless of temperature.