Dynamic mechanical characterization of relaxations in poly(oxymethylene), miscible blends,and oriented filaments

Multifrequency dynamic mechanical analysis (DMA) data were obtained for molded poly(oxymethylene) (POM) and its blends from-150°C to 150°C. Because of the high crystallinity, the assignment of the glass transition in POM has been controversial in the literature. Low and high glass transition temperature (T _g) phenolated compounds, including poly(vinyl phenol), were found to be miscible with POM. The shift of the β transition in the POM blends favors an assignment of the β transition detected at ?3°C(1 Hz), not the ?80°C γ transition, as the T _g in semicrystalline POM because the latter is invariant with diluent. The peak at the β transition in pure POM is weak and can only be seen clearly by DMA measurements on samples that have not “aged” at ambient temperature. This is further evidence that the β transition arises from a cooperative glass-transition-like motion. The γ transition is not influenced by aging because it is due to a concerted localized main chain motion. The β transition of an oriented POM filament can be seen in the DMA flexural loss spectrum at-18°C (1 Hz), but not in a tensile loss spectrum. The broad a relaxation was detected at about 110°C (1 Hz) in molded POM and its blends, while it was shifted to about 135°C in the higher crystallinity, oriented system. The α peak is also independent of diluent, consistent with a crystalline origin for this transition, as was proposed earlier.