Poly N-isopropylacrylamide (PIPAAｍ) is an unique polymer that exhibits thermally reversible soluble-insoluble changes in aqueous solution in response to temperature changes across LCST (lower critical solution temperature) of 32 degrees celsius.

Polymer chains of acrylamide hydrate to expand in water below the LCST, while isopropyl group dehydrating to form compact, insoluble conformations above the LCST.

Please take a look at the right photo. The solution in the right hand side tube is white. This is due to the temperature being over 32°C. On the other hand, the solution in the left hand side tube is crystal clear, suggesting the temperature being lower than 32°C. The polymer changes its characteristics dramatically across the LCST of 32°C.