Effects of comonomer and termonomer content and thermal history on dynamic mechanical properties of polyoxymethylene

Dynamic mechanical measurements at 100 cps were made on homo‐, co‐, and terpolymers of oxymethylene in the temperature range from −150°C to the crystalline melting point. The comonomer (ethylene oxide) content was varied from 0 to 5.1 wt.‐%; the terpolymer contained a small amount of a rigid non‐crystallizable termonomer. The combined effect of the structural changes and variations in crystallization conditions and annealing provided a range of crystallinity, corresponding to densities of 1.396 to 1.435 g/cm 3 . The γ‐loss peak located at −60°C remained unaffected by these variations in structure and thermal history. However, the size of the β‐loss peak increased uniquely with decreasing density, regardless of how the density was attained. The loss temperature increased from 0 to lO°C on going from a density of 1.396 to 1.435 g/cm 3 . The incorporation of a rigid chemical unit raised this temperature by 17°C. The α‐relaxation centered at about 130°C became more prominent with an increase in crystallite size and perfection. A correlation between dynamic mechanical and tensile elongation properties has been obtained.