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 degrees C to 150 degrees 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 beta transition in the POM blends favors an assignment of the beta transition detected at -3 degrees C (1 Hz), not the -80 degrees C gamma transition, as the T-g in semicrystalline POM because the latter is invariant with diluent. The peak at the beta 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 beta transition arises from a cooperative glass-transition-like motion. The gamma transition is not influenced by aging because it is due to a concerted localized main chain motion. The beta transition of an oriented POM filament can be seen in the DMA flexural loss spectrum at -18 degrees C (1 Hz), but not in a tensile loss spectrum. The broad a relaxation was detected at about 110 degrees C (1 Hz) in molded POM and its blends, while it was shifted to about 135 degrees C in the higher crystallinity, oriented system. The alpha peak is also independent of diluent, consistent with a crystalline origin for this transition, as was proposed earlier.