Sol–gel transition of novel temperature responsive ABA triblock copolymer P(MEO2MA-co-HMAM)-b-PEG-b-P(MEO2MA-co- HMAM)

Abstract

A well-defined temperature responsive ABA triblock copolymer, poly(2-(2-methoxyethoxy) ethyl methacrylate-co-N-hydroxymethyl acrylamide)-b- poly(ethylene glycol)-b-poly (2-(2-methoxyethoxy) ethyl methacrylate-co-N- hydroxymethyl acrylamide) [P(MEO2MA-co-HMAM)-b-PEG-b-P(MEO2MA-co- HMAM)], was synthesized by atom transfer radical polymerization (ATRP). The synthesized triblock copolymer was characterized by 1H nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR) spectroscopy and Gel Permeation Chromatography (GPC). The aqueous solution phase behaviors of the triblock copolymers were investigated by UV transmittance measurements, surface tension measurement, laser particle size and viscosity analysis. The micellization of temperature responsive triblock copolymer was investigated by fluorescence probe technique, dynamic light scattering (DLS) and transmission electron microscopy (TEM). The results showed that the molecular weight of the poly(ethylene glycol) (PEG), the N-hydroxymethylacrylamide (HMAM) content, and the degree of polymerization (DP) of the P(MEO2MA-co- HMAM) block for the synthesized triblock copolymers could all affect the lower critical solution temperature (LCST) of the triblock copolymer aqueous solution. The higher the molecular weight of the PEG and the HMAM content for a given triblock copolymer are, the higher the LCST of its aqueous solution. The higher the DP of the P(MEO2MA-co-HMAM) block is, the lower the LCST of the copolymer aqueous solution. Sol–gel transition temperature (T sol-gel) for the triblock copolymer determined by vial inversion test further indicated that it is dependent on the molecular weights of the PEG, the DP of the P(MEO2MA-co-HMAM) blocks and the concentration of the copolymer aqueous solution. Copolymer hydrogels loaded with bovine serum albumin (BSA) were used for the release study. The results revealed that 1) the hydrogels had sustained release for the BSA, 2) the release rate for the BSA is dependent of the length of the PEG chain, and 3) the longer the PEG chain is, the faster the release rate of the hydrogel for the BSA.