Cationic effect of an ionic copolymer with a temperature-responsive charateristic on the LCST value: A broad LCST spectrum of 35 to 46 °C

Abstract

A series of stimuli-responsive copolymers (p-NIBIm) of N-isopropylacrylamide (NIPAAm) and 1-butyl-3-vinyl imidazolium bromide (BVIm) with various BVIm monomer concentrations such as 5, 10, 15, and 20 mol% were synthesized by radical copolymerization. The different concentrations of the imidazolium moiety within the resulted copolymer chain were determined by 1H NMR analysis. The LCST (lower critical solution temperature) values of the copolymers that were checked by UV-Vis spectrophotometer increased with the increasing concentration of the imidazolium moiety and were ranged from 36 up to 46 °C. According to the increasing concentration of the imidazolium moiety, the p-NIBIm copolymers also showed increasing zeta potential values (from +3.4 up to +21.3 mV) at pH 7, increasing initial and final micelle sizes (from 211.5 to 69.1 and from 325.4 to 171.2 nm), respectively, at 25 and 50 °C, and increasing contraction levels of micelle volumes between 25-50 °C (from 2.69×10-18 up to 8.67×10-18 cm3). These results demonstrate that it is possible to tune the LCST value of a temperature-responsive copolymer only by changing the imidazolium unit (BVIm) concentration within the copolymer chain. Moreover, p-NIBIm10 and 15 among the prepared copolymers could demonstrate high applicability in various endeavors such as on a target drug or in a gene delivery system.