Effect of γ-irradiation on the melting behaviour of poly(trioxane)

Abstract

Poly(trioxane) obtained by radiation-induced polymerization in the solid state, was subjected to 1 Mrad γ-rays and the change in melting behaviour and the thermogravimetric curve examined. Little structural change in the X-ray scattering patterns was observed. The heating curve of as-polymerized poly(trioxane) exhibited a double endothermic peak under a high polymer yield, but the endotherm on the higher temperature side disappeared at a heating rate lower than 8° C min⁻¹. On irradiating over 25 krad, or rolling, the endotherm was again absent even at heating rates above 16° C min⁻¹. The endotherm at higher temperatures is interpreted as being due to superheating caused by entropy restriction. The irradiation or rolling causes chain scission at a selective point in the crystallites. These scissions reduce the superheatability of a poly(trioxane) with a high polymer yield. The lamellar-type poly(oxymethylene) crystal was also studied for comparison.