No abstract

Polymer gels that are in equilibrium with excess solvent(s) are three-component systems consisting of crosslinked 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)/m p ], the ratio of mass of polymer (or solvent) versus mass of gel [m p /m(gel) or m s /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)/m p ) 32.61 cm 3 /(1.0 g of m p )] continuously decreased to a value 10.59 cm 3 at 33.5 °C. This decrease is essentially brought about by a loss in the mass of water from the gel system to liquid water; (2) The above change corresponds to the changes in m p /m(gel) and m s /m(gel) from their original values 3.055% and 96.94% at 3.0 °C to 9.417% and 90.58% at 33.5 °C, respectively; and (3) The ratio of m p /m(gel) vs m s /m(gel) asymptotically approached 4.5 vs 5.5 above 34.0 °C. The changes in both quantities caused a further shrinkage in total volume but held to less than several percent of the original value (2.017 cm 3 at 50 °C). The number of water molecules per unit polymeric residue changed from 199 (3 °C) to 60.4 (33.5 °C) and then to 7.28 (50 °C).

The contribution of intramolecular vibrations to the observed structure of liquid water J. Chem. Phys. 82, 5289 (1985); 10.1063/1.448606 Ultrasonic measurements and liquid structure of DMSO-water mixture Proton spin-lattice relaxation times (T 1) of water and dimethyl sulfoxide (DMSO) in H20-DMSO (I), H 2 0-DMSO-d 6 (II), and D 2 0-DMSO (IV) systems at 9.8, 18.7,29.9, and 41.4°C exhibited minima near 0.65 mole fraction of water (X H,O)' The depth of the minimum, relative to T 1 values at higher and lower X H,O' increased as the temperature was lowered. The intramolecular contribution to the relaxation of DMSO protons was always greater than the intermolecular DMSO-DMSO contribution and the former showed a minimum at X D 0::::0.6 as compared with the latter's minimum at X D,0::::0.4-0.6. There is almost no contrib~tion to water proton T 1 from the interaction of water protons-DMSO protons in the DMSO·rich mixtures, while this contribution is rather significant in the DMSO·poor mixtures. The proton chemical shifts of water with reference to DMSO protons (over a temperature range of -60-45'C) moves to higher fields with rising temperatures, and this temperature dependence is affected considerably by the changes in composition. All these experimental results suggest the presence of strong intermolecular interactions between water and DMSO molecules that contribute to the "structuring" of this binary mixture. The structure of this liquid system is very sensitive to composition and temperature.In this work the dynamic liquid structure of DMSOwater mixtures was investigated by measuring T 1 , T 2 , and chemical shift values of the protons of both compo-

No abstract

Nmr parameters are given for pyridine in a variety of solvents. Using several sets of a-electron wave functions together with symmetry MO's for the u electrons, diamagnetic and paramagnetic contributions to the proton and carbon-1 3 shifts were evaluated. Paramagnetic shifts were calculated by the methods of McConnell, (11) S. Castellano, C. Sun, and R. Kostelnik, J . Chem. Phys., 46, 327 (1 9 67). 944 (1968).