Facile Synthesis of Triple-Stimuli (photo/pH/thermo) Responsive Copolymers of 2-Diazo-1,2-naphthoquinone-Mediated Poly(N-isopropylacrylamide-co-N-hydroxymethylacrylamide)

A series of poly(N-isopropylacrylamide-co-N-hydroxymethylacrylamide) P(NIPAM-co-NHMA) copolymers were firstly synthesized via free radical polymerization. Then, the hydrophobic, photosensitive 2-diazo-1,2-naphthoquinone (DNQ) molecules were partially and randomly grafted onto P(NIPAM-co-NHMA) backbone through esterification to obtain a triple-stimuli (photo/pH/thermo) responsive copolymers of P(NIPAM-co-NHMA-co-DNQMA). UV-vis spectra showed that the lower critical solution temperature (LCST) of P(NIPAM-co-NHMA) ascended with increasing hydrophilic comonomer NHMA molar fraction and can be tailored by pH variation as well. The LCST of the P(NIPAM-co-NHMA) went down firstly after DNQ modification and subsequently shifted to higher value after UV irradiation. Meanwhile, the phase transition profile of P(NIPAM-co-NHMA-co-DNQMA) could be triggered by pH and UV light as expected. Thus, a triple-stimuli responsive copolymer whose solution propel-ties could be, respectively, modulated by temperature, light, and pH, has been achieved. These stimuli-responsive properties should be very important for controlled release delivery system. (c) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2763-2773, 2009