Effect of branching on dynamic mechanical properties of polyethylene

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 CH 2 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.