In this paper, one LCST-type thermoresponsive poly(ionic liquid) (PIL), poly(tetrabutylphosphonium styrenesulfonate) (P[P-4,P-4,P-4,P-4][SS]), was introduced to poly(N-isopropylacrylamide) (PNIPAM) by two different ways, mixing and copolymerization. Interestingly, they show distinct thermoresponsive phase transition behaviors, evidenced by temperature-variable H-1 nuclear magnetic resonance and Fourier transform infrared in combination with the perturbation correlation moving window (PCMW) technique. The PNIPAM/P[P-4,P-4,P-4,P-4][SS] mixture exhibits a sharp and drastic phase transition, similar to that of pure PNIPAM. In the statistical copolymer, PNIPAM-co-P[P-4,P-4,P-4,P-4][SS], the thermosensitivity of P[P-4,P-4,P-4,P-4] [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-4,P-4,P-4,P-4][SS]. Our findings improving our understanding of the interaction between LCST-type polymers with distinct structures perspective for preparing thermoresponsive materials with linear phase transition behavior. should be conducive to and provide a new