The effect of chain branching on the dynamic mechanical properties of polyethylene within the temperature region 80 to 380°K. has been studied using an apparatus which drives rod‐like specimens in their transverse modes. The results for three types of polyethylene having 3.2, 1.6, and less than 0.1 branches per 100 carbon atoms of the main chain are compared and discussed. Experimental results indicate that all of the three main dispersion regions (α, β, γ) characteristic of polyethylene are affected to some extent by branching. The β region, starting near 230°K., decreases with decreased branching, and for polyethylene which has negligible branching it is almost entirely absent. This suggests a direct relation between the number of branch points and the size and shape of this peak. The γ dispersion region near 170°K. appears sharper and shifted to higher temperatures with decreased branching, this being attributed to a narrowing of the relaxation times associated with the movement of a small number of CH2 units. The α dispersion region near 370°K. is also shifted to higher temperatures with decreased branching in accord with the shift of melting temperature with degree of crystallinity.

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The damping, resonant frequency, and dynamic elastic storage modulus of five polyamides have been investigated at resonant frequencies ranging from 100 to 2000 cycles/sec. at temperatures in the 100 to 450°K. region. Specimens of poly(hexamethyleneadipamide) containing 0, 0.9, 3.3, and 6.4 wt.‐% water were studied and it was found that with increasing water content: the loss peak and associated modulus dispersion at 170°K. in the dry material decreased; the loss peak and modulus dispersion at 370°K. in the dry material shifted to lower temperatures reaching a value of 280°K. for 6.4% water; a third damping peak appeared at 240 to 245°K. and the modulus in the 150 to 250°K. region increased while above and below this range the reverse was true. A poly(hexamethylene adipamide) specimen containing 10.5 wt.‐% methanol exhibited one broad peak at about 255 to 260°K. Dry specimens of poly(hexamethylene sebacamide), poly(decamethylene sebacamide), 17% N‐methylated poly(decamethylene sebacamide), and 58% N‐methylated poly(decamethylene sebacamide) were also investigated. For the latter three specimens the principal amorphous transition shifted from 340 to 285°K. and the area under the loss peak increased greatly in going from 0 to 58% N‐methylation, while the low temperature transition remained at 160 to 170°K. essentially unchanged. Of the five polymers studied the 17% N‐methylated poly(decamethylene sebacamide) exhibited the highest apparent modulus in the 110 to 160°K. region; and at all temperatures below the principal amorphous transition this material had a higher modulus than the unmethylated parent polymer.