Synthesis and sol-gel transition of novel temperature responsive aba triblock-graft copolymers based on PCL and PEG analogues

Abstract

Novel hydrophilic, temperature responsive, and biodegradable ABA tribl°Ck-graft copolymers, [poly(ɛ-caprolactone)-g-poly(2-(2-methoxyethoxy) ethyl methacrylate-co-oligo(ethylene glycol) methacrylate)]-b-poly(ethylene glycol)-b-[poly(-caprolactone)-g-poly(2-(2-methoxyethoxy) ethyl methacrylate-co-oligo(ethylene glycol) methacrylate)] ([PCL-g-P(MEO2MA-co-OEGMA)]-b-PEG-b-[PCL-g-P(MEO2MA-co-OEGMA)]) (tBGs), were synthesized via a combination of ring-opening polymerization (ROP) of ɛ-caprolactone (ɛCL) and α-chloro-ɛ-caprolactone (αClɛCL) in the presence of PEG and atom transfer radical polymerization (ATRP) of MEO2MA and OEGMA. Temperature responsive P(MEO2MA-co-OEGMA) graft chains on the hydrophobic PCL block of PCL-b-PEG-b-PCL not only improved the solubility of PCL-b-PEG-b-PCL in water, but also endowed it with temperature sensitivity. The synthesized temperature responsive triblock-graft copolymers formed well-defined core-shell micelles as the temperature was above their LCST (ca. 35 °C), with hydrophilic PEG block as shell, P(MEO2MA-co-OEGMA) graft chains on the PCL block and hydrophobic PCL block aggregates as core. The micellization induced by temperature for the tBGs in aqueous solutions had been investigated by transmittance measurement, laser particle size measurement, 1HNMR in D2O, DLS and TEM. For a given tBG5 aqueous solution (30 wt%), a weak hydrogel was available at 35 °C, and its sol-gel transition temperature gradually decreased with increasing concentration. In addition, the tBG5 hydrogels loaded with anethole were used for hydrophobic drug release, and in vitro the sustained release of anethole from the tBG5 hydrogels was examined, which is a significant for anethole for their biomedical applications.