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
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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