Cooling and annealing properties of copolymer‐type polyacetals and its crystallization behavior

Copolymer‐type polyacetals (POMs) that have been cooled at seven different rates from the melt at 180°C to the solid at 23°C show average spherulite diameters from 10 to 25 μm on an etched fracture surface using scanning electron microscopy (SEM). The wide‐angle X‐ray diffraction (WAXD) of POM displays a degree of crystallinity ranging from 60 to 66% by applying the two‐phase model. From studies of mechanical properties, physical properties, and dielectric dissipation factor (tan δ), we found that POM with a faster cooling rate shows looser packing and smaller spherulites on the fracture surface than that with a slower cooling rate. This conclusion is in agreement with the observations made on SEM and WAXD. DSC measurements were used to measure the heat of fusion, melting point, and crystallization temperature of POMs. An equilibrium melting temperature was estimated from the Hoffman–Weeks plot. The overall crystallization kinetics of POMs were analyzed by the Avrami equation. Results for the Avrami exponent n, between 2 and 3, indicate small disklike spherulites following nucleation growth kinetics. Annealing the cooled POM at 150°C results in recrystallization featuring a significant increase in the average diameter of spherulites in SEM.