文摘

The phase transition temperatures (T p) of poly(N-isopropylacrylamide-co-2-acrylamidoglycolic acid) (P(NIPAAm-co-AmGc)) and P(NIPAAm-co-AmGc)/poly(dimethylaminoethyl methacrylate) (PDMAEMA) complex were monitored to investigate the effects of pH, comonomer composition, and complex formation. P(NIPAAm-co-AmGc) was synthesized via free radical polymerization with AmGc molar fractions of 0.04, 0.08, 0.16, and 0.25; the corresponding ratios of dimethylaminoethyl methacrylate (DMAEMA) and AmGc in the P(NIPAAm-co-AmGc)-16/PDMAEMA complex were 0.3, 0.7, 1.0, 2.0, and 4.0, respectively. Our results indicated that the T p of P(NIPAAm-co-AmGc) increased as the mole fraction of AmGc increased and was higher at pH 4 than at pH 3 and pH 7. For the P(NIPAAm-co-AmGc)-16/PDMAEMA complex, the lower critical solution temperature (LCST) was observed from 23 to 48?°C, and the upper critical solution temperature (UCST) was detected above 63?°C at pH values of 3, 4, and 7. The aggregation rate of the polymer chains was determined from the slope of the turbidity change in a plot of LCST versus temperature. As the T p was lower, aggregation occurred faster in P(NIPAAm-co-AmGc)-16 but slower in the P(NIPAAm-co-AmGc)-16/PDMAEMA complex at pH 7. Aggregation was not observed during the cooling scan or, at least, was less evident than in the heating scan because the hydrophobic attractive interactions during the cooling scan were not sufficient to offset the electrostatic repulsion between ionic groups at high temperatures.