Synthesis and multiple responsiveness study of Poly(N-isopropylacrylamide) containing azopyridine

Abstract

Environmentally sensitive polymer materials exhibit diverse properties due to their ability to respond to external environmental changes such as light, temperature, pH, and et al. These responses lead to corresponding alterations in their structure or state, resulting in unexpected performance. In this study, azo pyridine groups were introduced into the end groups and side chains of PNIPAM to synthesize two distinct polymer structures (PNIPAM-AZO and P (NIPAM-co-PAZO-co-OEGMA). This integration enables the polymers to respond to multiple stimuli, including temperature, light, pH, and gas (CO₂). A comprehensive investigation of the properties of these multi-responsive polymer materials was conducted. The findings reveal that the presence of azo pyridine units enables both polymers to modulate the (lower critical solution temperature) LCST of PNIPAM through UV, pH, and CO₂, with a maximum temperature adjustment of 13 °C when CO₂ is introduced. This modulation range is influenced by the azo pyridine content in the polymer. Notably, when azo pyridine is present only at the polymer end group, the maximum LCST regulation range is limited to 3 °C. Moreover, the LCST of the two polymers can also be adjusted by pH. In the presence of carbonate ions, the protonation of azo pyridine by carbonic acid increases the solubility of the polymer and enhances the LCST. Introducing argon gas removes CO₂, thereby restoring the polymer's solubility and LCST to their neutral condition levels. By alternately introducing CO₂ and argon gas, the LCST of the polymer exhibits cyclic changes.