Low‐Temperature Relaxation of Some Polyamides

The low-temperature relaxation process of polycaprolactam, methyl-substituted poly-caprolactams, and other linear polyamides was studied by dielectric methods in the temperature range from – 140°C. to +50°C., and in the frequency range from 100 cps to 10 Mc./sec. In some of these polymers the temperature dependence of the complex shear modulus of elasticity was also measured at a frequency of about 1 cps. The methyl substituent provokes an increase of relaxation times of dielectric dispersion in poly-γ-methylcaprolactam and a decrease of relaxation times in poly-ϵ-methylcaprolactam. This decrease is ascribed to the increase in steepness of the potential barrier owing to a close attachment of dipole to the methyl-substituted group. Irrespective of its position, the methyl substituent has been found in all cases to cause an extension of the distribution of relaxation times of shear modulus towards lower temperatures, as compared with the dispersion of nonsubstituted polyamides. The dependence of the widths of the distribution of dielectric relaxation times upon the temperature and the degree of crystalline arrangement have been discussed. For the copolymer of caprolactam. 7-aminoheptanoic acid, and aminoundecanoic acid, which possess the same concentration of polar groups per unit of chain length as poly(hexamethylene sebacamide), a narrower distribution of relaxation times has been found. On the basis of ideas concerning low-temperature dispersion it is possible to explain also higher relaxation times of low-temperature dispersion occasioned by low molecular weight substances by an increase of the mean friction factor.