Self-association of poly(N-isopropylacrylamide) and its complexation with gelatin in aqueous solution

摘要

The association of poly(N-isopropylacrylamide) (PNIPAM) above its low critical solution temperature (LCST, approx. 32°C) leads to stable aggregates instead of the expected precipitation, which could be attributed to the microphase inversion of the PNIPAM chains. A laser light scattering study showed that the lower association temperature and higher PNIPAM concentration resulted in larger low density interchain aggregates with a cluster structure, while the higher association temperature and lower PNIPAM concentration led to spherical aggregates formed mainly through the packing of individual collapsed chains. Above approx. 32°C, the intrachain coil-to-globule transition competes with the interchain association. Gelatin was encaptured/complexed into the PNIPAM aggregates and the complexation was completely reversible as the temperature varied. The PNIPAM/gelatin complexes with the highest molar mass and density were formed when the PNIPAM/gelatin weight ratio was in the range 1-2 and the temperature was close to approx. 32°C. This would be the optimum condition for the concentration of a dilute protein solution follows by the ultracentrifugation of the PNIPAM-protein complexes.