Stimuli sensitive interpenetrating polymer networks composed of poly(N-isopropylacrylamide) and hydrophilic polymers

Abstract

The stimuli sensitive interpenetrating polymer networks composed of poly(N-isopropylacrylamide) (PNIPAM) and hydrophilic polymers were studied in aqueous solution with the variation of temperature/pH. Cloud point measurement, differential scanning calorimetry (DSC), compression modulus, and FT-IR (Fourier transform-infrared) spectra were measured to understand phase transition caused by molecular interaction. To observe the temperature-induced phase transition, semi-interpenetrating networks (semi-IPNs) composed of poly(N-isopropyl acrylamide) and various linear hydrophilic polymers were obtained via aqueous redox polymerization. With the formation of semi-IPNs, the lower critical solution temperature (LCST) was shifted to lower temperature, probably due to the intermolecular interaction such as hydrogen bond in the gel network. Cloud point measurement and FT-IR show that the formation of hydrogen bond in the semi-IPNs played an important role in the shift of LCST. Also, the shift of LCST was observed with the variation of functional group and molecular weights of linear hydrophilic polymers, probably due to the increase of hydrogen bonding and network entanglement between polymer chains. To understand a swelling/deswelling/swelling behavior of interpenetrating polymer networks (IPNs) composed of PNIPAM gels and poly(acrylic acid) (PAA) gels and to investigate the mutual influence of pH/temperature, the IPNs were synthesized by a sequential redox polymerization with N-isopropylacrylamide as the temperature-sensitive component and with acrylic acid as the pH-sensitive component. The IPNs showed mutual sensitivity of pH/temperature with a significant change of volume. This sensitivity resulted from a hydrophobic aggregation induced by hydrogen bonding at a lower pH and from a swelling of PAA separated by dehydrogen bonding interaction at a higher temperature. Also, the multi-interaction between molecules such as hydrogen bonding and hydrophobic interaction may se...