MICELLIZATION OF THERMO- AND PH-RESPONSIVE BLOCK COPOLYMER OF POLY(N-ISOPROPYLACRYLAMIDE)-BLOCK-POLY(4-VINYLPYRIDINE)

摘要

Micellization of double-hydrophilic block copolymers under the influence of a given external stimulus, such as a change in pH, temperature or ionic strength, has attracted considerable interests due to their potential application in areas such as biomimetic chemistry, molecular switch, and controlled drug delivery. Very recently, the double-hydrophilic copolymers in which both of the hydrophilic blocks are stimuli-responsive also have been extensively studied for various applications. We report here the micellization of a novel double-hydrophilic copolymer of poly(N-isopropylacrylamide)-block- poly(4-vinylpyridine) (PNEPAM-b-P4VP) consisting of a thermo-responsive block of PNIPAM and a pH-responsive block of P4VP. The block copolymer PNIPAM-b-P4VP could respond to both temperature and pH, i.e., a water-soluble copolymer under appropriate conditions (T < 36°C and pH < 4.7) can form micelles with a PNIPAM core at a higher temperature or micelles with a P4VP core at a higher pH, while keeping the other conditions constant. The transformation process is summarized in scheme 1. The range of temperature and pH of response and the stability of this system is suitable for use in the biomedical fields and the concept may be applied to other block copolymer systems that can respond to stimuli such as changes in pH, temperature, ionic strength and presence of bioactive species.