Abstract

Polymer gels that are in equilibrium with excess solvent(s) are three-component systems consisting of cross-linked polymer networks, solvent(s) in gels, and solvent(s). We have developed a method for the determination of densities of the polymer and solvent components in gels by using a specifically designed pycnometer. The method was applied to the cross-linked poly(N-isopropylacrylamide) and water system from 3.0 to 50.0 °C. From the densities of the polymer and solvent components, we have evaluated the total volume of gel per unit mass of the cross-linked polymer (solid) [v(gel)/mp], the ratio of mass of polymer (or solvent) versus mass of gel [mp/m(gel) or ms/m(gel)], and the number of solvent molecules per polymeric residue at various temperatures. The determination revealed how contraction of the total volume of gels is related to temperature dependences of these quantities as follows: (1) The total volume at 3.0 °C [v(gel)/mp = 32.61 cm3/(1.0 g of mp)] continuously decreased to a value 10.59 cm3 a...

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