Light scattering studies of insulin solutions at pH 1.9 and 2.6 in 0.1 M NaCl and NaHzP04 permit the evaluation of equilibrium constants governing the equilibria among monomers, dimers, and trimers. The variation of the constants appears to be explicable in terms of changes in the electrostatic repulsion. Measurements in the range of 20" to 40" C lead to the determination of the corresponding heats and entropies. These are found to be surprisingly low and suggest that increased solvation of the monomer with respect to the dimer is taking place.

A13C CP/MAS NMR study of furfuryl alcohol resins is reported. A conformational rigidity is found for uncured or less cured resins. The contents of methylol groups and dimethylene ether linkages are found to be very small. It is postulated that cross-linking involves the breaking of methylene bridges in the curing process. Further confirmation is given that the major cross-linking processes that occur during curing involve linkages with bridging CH2 groups, rather than substitution at the 3-and 4-positions of furan rings in the resins.

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SynopsisAn examination has been made of the capability of conventional infrared analysis to define the structure of urea-formaldehyde (UF) polymers in the cured, crosslinked state. Proton NMR and infrared measurements of model compounds and uncured UF polymers were combined with infrared observations during polymer cure. The existing interpretation of UF polymer infrared spectra was clarified and a partial confirmation of the UF polymer cure mechanism obtained. However, it was concluded that conventional infrared possesses distinct limitations for defining the UF cure process in great detail, and it is hoped that the new solid-sample NMR methods will prove capable of the desired structural determination in the cured state.