Sol-Gel Transition Behavior of Amphiphilic Comb-Like Poly[(PEG-b-PLGA)acrylate] Block Copolymers

Abstract

The effects of comb-like amphiphilic block copolymer architectures on the physical properties such as sol-gel transition and micellization behaviors with the change of temperature and pH were examined. Comb-like poly((poly(ethylene glycol)-b-(poly(lactic acid-co-glycolic acid))acrylate-co-acrylic acid) (poly((PEG-b-PLGA)A-co-AA)) copolymers were synthesized by coupling of poly(acrylic acid) (PAA) with two different kinds of PEG-b-PLGA diblock copolymers to investigate the effects of the number of branches and hydrophilicity/hydrophobicity on the sol-gel transition and micellization. The molecular weights and chemical structures were confirmed by GPC and (1)H NMR. The number of PEG-b-PLGA branches was gradually deviated from the feed molar ratio with increasing the molecular weight and the number of branches and due to the bulkiness of PEG-b-PLGA. Poly[(PEG-b-PLGA)A-co-AA] aqueous solutions showed thermosensitive sol-gel transition behavior, and the gelation took place at lower concentration with increasing the number of branches and PLGA chain length due to the increase of hydrophobicity. The temperature, at which abrupt increase of viscosity by dynamic rheometer appeared, was also in good agreement with sol-gel transition by tube-titling method. The CIVIC, calculated from UV-Visible spectroscopy using DPH as hydrophobic dye, also decreased with increasing the number of PEG-b-PLGA branches and PLGA chain length with same reason. The micelle size was increased with increasing temperature at the initial stage, however, decreased with further increase of temperature, since the micelles were, first, aggregated by hydrophobic intermolecular interaction, and then fragmented by dehydration of PEG segments with increasing temperature. PH-sensitive PAA backbone played a key role in physical properties. With decreasing pH, sol-to-gel transition temperature, CIVIC values, and micelle size were decreased because of the increase of hydrophobicity resulting form non-ionized acrylic acid. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1287-1297, 2010