Saccharide effect on the deswelling process of the thermosensitive poly(N-isopropylacrylamide) gel

The kinetic parameters of deswelling and the change of a lower critical sol ution temperature (LCST) for poly(N-isopropylacrylamide) get, poly(NIPAAm) gel, were investigated in the presence of glucose and other sugars as hydro philic probes. The enthalpy of activation (DeltaH(double dagger)) and the e ntropy of activation (AS) for deswelling were influenced by the concentrati on of additive sugars. Plots of DeltaH(double dagger) against T DeltaS(doub le dagger) fell on a straight line, of which the slope was approximately 0. 91-0.94. This result shows a compensation effect of the free energy of acti vation (AG) concerning the relationship between Al-P and AS' for deswelling of poly(NIPAAm) gel. The molecular interaction between sugar and water clu sters involved with the polymer is responsible for the compensation effect between DeltaH(double dagger) and DeltaS(double dagger). The equatorial hyd roxy groups of sugar molecules interact easily with water clusters around t he hydrophobic isopropyl groups (the iceberg) to form hydrogen bonds, which give rise to change the situation of polymer hydration. A decrease of the LCST has close connections with the number of equatorial hydroxy groups of sugars as additives. The LCST decrease in sugar solutions was regarded as t he situation change of polymer hydration in the iceberg.