Dynamic mechanical behavior of some partially crystalline poly‐α‐olefins

Internal friction (Q−1) and dynamic elastic storage modulus have been measured as functions of temperature (80°K. and higher) for partially crystalline samples of poly(pentene‐1) (PP1), poly(3‐methylbutene‐1), (P3MB1), and poly(4‐methylpentene‐1) (P4MP1); a resonance technique at audiofrequencies was used. Two internal friction peaks at 145°K. (γ) and 290°K. (β) and a final upswing in Q−1 at 335–345°K. (α) in conjunction with associated modulus dispersions are exhibited by PP1, the mechanical loss spectrum being similar to that reported previously for poly(butene‐1) except that the final upswing for PP1 occurs at lower temperatures. Both P3MB1 and P4MP1 have small Q−1 damping peaks near 150°K. (γ). The latter polymer also has a peak of considerable magnitude at 335–340°K. (β) and an upswing in Q−1 at 425–435°K. (α). The former polymer shows a broad dispersion commencing at about 320°K. (β). Owing to the absence of a sizable transition below the principal amorphous transition starting at about 325°K., the modulus for P3MB1 exhibits the least variation with temperature in the range of 80–325°K. among the poly‐α‐olefins with aliphatic side chains, including polyethylene and polypropylene, that have been studied by this method. It is suggested that the γ and β loss peaks and associated modulus changes are the consequence of the onset of motion in the amorphous regions, involving small and large number of chain segments, respectively.