Unusual Phase Transition Behavior of Poly(<i>N</i>‑isopropylacrylamide)-<i>co</i>-Poly(tetrabutylphosphonium styrenesulfonate) in Water: Mild and Linear Changes in the Poly(<i>N</i>‑isopropylacrylamide) Part

Abstract

In this paper, one LCST-type thermoresponsive poly­(ionic liquid) (PIL), poly­(tetrabutylphosphonium styrenesulfonate) (P­[P<sub>4,4,4,4</sub>]­[SS]), was introduced to poly­(<i>N</i>-isopropylacrylamide) (PNIPAM) by two different ways, mixing and copolymerization. Interestingly, they show distinct thermoresponsive phase transition behaviors, evidenced by temperature-variable <sup>1</sup>H nuclear magnetic resonance and Fourier transform infrared in combination with the perturbation correlation moving window (PCMW) technique. The PNIPAM/P­[P<sub>4,4,4,4</sub>]­[SS] mixture exhibits a sharp and drastic phase transition, similar to that of pure PNIPAM. In the statistical copolymer, PNIPAM-<i>co</i>-P­[P<sub>4,4,4,4</sub>]­[SS], the thermosensitivity of P­[P<sub>4,4,4,4</sub>]­[SS] is largely suppressed, resulting in a linear, mild, and incomplete phase transition, which has never been reported before. This abnormal phenomenon is shown to arise from the outstanding hydration ability of P­[P<sub>4,4,4,4</sub>]­[SS]. Our findings should be conducive to improving our understanding of the interaction between LCST-type polymers with distinct structures and provide a new perspective for preparing thermoresponsive materials with linear phase transition behavior

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