Synthesis and characterization of temperature-sensitive cellulose-graft-poly(N-isopropylacrylamide) copolymers

Abstract

A new series of cellulose-graft-poly(N-isopropylacrylamide) (cellulose-g-PNIPAM) copolymers were prepared by atom transfer radical polymerization (ATRP) of N-isopropylacrylamide monomers from a cellulose-based macro-initiator, which was homogeneously synthesized in an ionic liquid 1-allyl-3-methylimidazolium chloride (AmimCl). The composition of cellulose-g-PNIPAM copolymers could be adjusted by altering the feeding ratio and reaction time. The resultant copolymers with relatively high content of PNIPAM segments (molar substitution of PNIPAM ≥ 18.3) were soluble in water at room temperature. Aqueous solutions of cellulose-g-PNIPAM copolymers exhibited clear temperature-sensitive behavior, and their sol-to-gel phase transition properties were investigated by dynamic light scattering (DLS) and UV measurements. Compared with pure PNIPAM, the cellulose-g-PNIPAM copolymers possessed higher lower critical solution temperatures (LCST) in a range from 36.9 °C to 40.8 °C, which are close to normal human body temperature, and could be tuned by adjusting the content of PNIPAM segments in copolymers. Spherical structure of cellulose-g-PNIPAM copolymers formed at temperatures above LCST and its morphology was observed by TEM and SEM. These novel cellulose-g-PNIPAM copolymers may be attractive substrates for some biomedical applications, such as drug release and tissue engineering.