Molecular Motions in Low Molar-Mass Alkyl Amides: Models for Molecular Motions in Polyamides. (Reannouncement with New Availability Information).

摘要

Four model amides containing 3-18 linear alkane chains attached to the amide nitrogen and carbonyl were synthesized. Molecular motions of the amides crystallized from solution were analyzed by solid-state NMR, FTIR, and DSC. Each amide showed one or two submelting transitions by DSC with the transition enthalpy varying with respect to segment chain lengths. For the propamide (delta H = 6 J/g) being an order of magnitude less than the transition enthalpy for the stearamide (delta H = 49 J/g). Variable-temperature solid-state 13 C NMR (100.6 MHz) of the stearamide showed a discontinous change in chemical shift of the all-trans interior CH2's from ca 33.2 ppm to ca 32.8 ppm on heating through the sub-melting transition. This change reflects a crystal-crystal transformation involving a change of ca 60 deg. in the orientation of the all-trans methylene chain with respect to the amide plane and an increase in the librational motion of the alkane segment without complete rotational freedom (rotator phase formation).