Steric Stabilization of Thermally Responsive N-isopropylacrylamide Particles by Poly(vinyl alcohol)

摘要

Poly(vinyl alcohol) (PVA) was used as a steric stabilizer for the dispersion polymerization of crosslinked poly(N-isopropylacrylamide) (PNIPAM) in water. A series of reactions were carried out using PVA of varying molecular weight and degree of hydrolysis. Under appropriate conditions, PNIPAM particles of uniform and controllable size were produced using PVA as the stabilizer. The colloidal stability was investigated by measuring changes in particle size with temperature in aqueous suspensions of varying ionic strength. For comparison, parallel colloidal stability measurements were conducted on PNIPAM particles synthesized with low molecular weight ionic surfactants. The PVA provides colloidal stability over a wide range of temperature and ionic strength, whereas particles produced with ionic surfactants flocculate in moderate ionic strength solutions upon collapse of the hydrogel as temperature is increased. Experimental results and theoretical consideration indicate sterically stabilized PNIPAM particles resulted from grafting of PVA to the PNIPAM particle surface. The enhanced colloidal stability afforded by PVA allows the temperature responsive PNIPAM particles to be used under physiological conditions where electrostatic stability is ineffective.