Abstract

Novel temperature- and pH-responsive ABA-type triblock copolymers, P(DEAEMA-co-MEO2MA-co-OEGMA)-b-PEG-b-P(DEAEMA-co-MEO2MA-co-OEGMA), composed of a poly(ethylene glycol) (PEG) middle block and temperature- and pH-sensitive outer blocks, were synthesized by atom transfer radical polymerization (ATRP). The composition and structure of the copolymer were characterized by 1H NMR and gel permeation chromatography (GPC). The temperature- and pH-sensitivity, micellization, and the sol–gel transitions of the triblock copolymers in aqueous solutions were studied using transmittance measurements, surface tension, viscosity, fluorescence probe technique, dynamic light scattering (DLS), zeta-potential measurements, and transmission electron microscopy (TEM). The lower critical solution temperature (LCST) of the triblock copolymer, which contains a small amount of a weak base group, (N,N-diethylamino) ethyl methacrylate (DEAEMA), can be tuned precisely and reversibly by changing the solution pH. When the copolymer concentration was sufficiently high, increasing temperature resulted in the free-flowing solution transformation into a micellar gel. The sol-to-gel transition temperature (Tsol–gel) in aqueous solution will continue to decrease as solution concentration increases.

Highlights

  • While chemically cross-linked polymer gels are being widely used and continuously evaluated, there is a growing interest in stimuli-responsive block copolymer aqueous micellar gels [1,2,3,4,5,6,7,8]

  • The peak at 2.4 ppm is attributed to poly(ethylene glycol) (PEG), it is replaced by the peak at 1.8 ppm which is attributed to Br–PEG–Br

  • Because the lower critical solution temperature (LCST) of P2 aqueous solution was 37.5 ◦°C, which is very close to the body temperature, P2 was chosen as a representative was 37.5 C, which is very close to the body temperature, P2 was chosen as a representative to discuss some properties of the ABA triblock copolymers

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Summary

Introduction

While chemically cross-linked polymer gels are being widely used and continuously evaluated, there is a growing interest in stimuli-responsive block copolymer aqueous micellar gels (namely, physically cross-linked gels) [1,2,3,4,5,6,7,8]. These physically cross-linked gels, responsive to temperature, pH, light, salt, and magnetic or electric fields have received considerable attention [8,9,10,11,12,13,14,15].

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