The modification of polyoxymethylene structure by the action of high pressures for various degrees of hydrostaticity

Abstract The effect of high pressures on polyoxymethylene (POM) crystals consisting of folded and extended chains has been studied by IR spectroscopy. A phase transition from hexagonal to orthorhombic was observed in the POM with extended chains at ca. 75 kbar pressure. The deviation from hydrostaticity and appearance of tangent stresses in the polymer results in an essential change in chain conformation. Hydrostatic pressure hardly affects the crystals with folded chains but they are transformed into crystals with extended chains by shearing strain under pressure. It is assumed that this transformation is due to mechano-chemical rupturing of stressed loops and a chain transfer reaction on the surface of folding of adjacent lamellar crystallites.