1. Temperature Dependence of Density of Polymer Gels: 2. Poly[N-(1,3-dioxolan-2-ylmethyl)-N-methyl-acrylamide] Networks -Water or -Alcohol System


Densities of the polymer and solvent components in gels made of poly[N-(1,3-dioxolan-2-ylmethyl)-N-methyl-acrylamide (DIOMMA)] networks and water, methanol or ethanol were determined from 5 °C to near bp of the respective solvents. From the densities, we have evaluated the following quantities at various temperatures (T): (1) the volume of gels [νsp(gel)] occupied by one single polymeric residue and its associated solvent molecules; (2) mass of solvent in gels per one polymeric residue; (3) the ratio of mass of polymer or solvent vs mass of gels; and (4) the number of solvent molecules per one polymeric residue (Nsp). The results in νsp(gel)(T) revealed the following: (A) νsp(gel) in the hydrogel decreased with increasing it up to 55 °C. This is essentially caused by a loss of water from the gel system. The increase in νsp(gel) beyond 55 °C is brought about by conformational changes in the polymer together with a further inclusion of solvents into gels. (B) Alcohol environments gave the thermally reversed trend in νsp(gel)(T) against the hydrogel. (C) Several changes in the gradient of the plot of νsp(gel) vs T for the gel made of ethanol indicated some conformational changes in the polymer at specific temperatures. These temperatures exactly matched with changes in spin-lattice relaxation times for the OH proton of ethanol that is present in gels. Altogether, the above differences in their thermal behaviors of various gels were elucidated in terms of strengths and modes of the intermolecular polymer-polymer, polymer-solvent, and solvent-solvent interactions that are modulated by thermal motions of molecules.



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© 2001 American Chemical Society (ACS), All rights reserved.

Publication Date

01 Jan 2001