The structure and mechanical properties of polyoxymethylene polymerized in the solid state

Abstract

Polyoxymethylene specimens with single crystal texture were produced by irradiation of needle-shaped trioxane crystals subsequently post-polymerized at fixed temperatures between 30 and 60°C. A clear dependence of polymer conversion on irradiation dose and polymerization temperature was revealed. The polymer morphology consisted of mutually aligned fibrils, half of which were chain-extended crystallites with their molecular axes coincident with the specimen axis. The remaining fibrils consisted of folded chains in a “twin” configuration.

The degree of order in the specimens was analysed in terms of the arcing of X-ray diffraction spots. There existed an intrinsic level of misorientation of molecules which depended on the post-polymerization temperature, plus a misalignment due to displacement of fibrils on the removal of unreacted monomer. Finally, the mechanical properties were investigated and the Young's modulus was found to approach closely its theoretical limit at the conversion maximum. The results are interpreted on the basis of a simple morphological model.