Poly(N-isopropylacrylamide)

Poly(N-isopropylacrylamide) (variously abbreviated PNIPA, PNIPAM, PNIPAAm, NIPA, PNIPAA or PNIPAm) is a temperature-responsive polymer that was first synthesized in the 1950s. It can be synthesized from N-isopropylacrylamide which is commercially available. It is synthesized via free-radical polymerization and is readily functionalized making it useful in a variety of applications.

PNIPA dissolves in water, however, when these solutions are heated in above their cloud point temperature, they undergo a reversible lower critical solution temperature (LCST) phase transition from a soluble hydrated state to an insoluble dehydrated state. Although it is widely believed that this phase transition occurs at 32 °C (90 °F), the actual temperatures may differ 5 to 10 °C (or even more) depending on the polymer concentration, molar mass of polymer chains, polymer dispersity as well as terminal moieties. Furthermore, other molecules in the polymer solution, such as salts or proteins, can alter the cloud point temperature.

Since PNIPA expels its liquid contents at a temperature near that of the human body, PNIPA copolymers have been investigated by many researchers for possible applications in tissue engineering and controlled drug delivery.