Inter-lamellar crystallization in poly(tetramethylene oxide)

High molecular weight poly(tetramethylene oxide) crystallizes isothermally from the bulk to a final crystallinity level of approximately 50%. Further crystallization can be induced in this material by cooling. This effect has been studied by differential scanning calorimetry (d.s.c.) and small angle X-ray scattering (SAXS). The additional crystalline material has a lower melting point than the original and its presence causes a pronounced decrease in the small angle spacing (correlation function maximum). The propensity to crystallize further at low temperatures decreases with increasing secondary crystallization under the original isothermal conditions. Additional crystallinity can also be induced, without temperature change, by cleaving chains by prolonged exposure to an X-ray source. These facts are explained in terms of the additional crystallinity occurring by growth of new thin lamellae between the original isothermally grown lamellae. The new lamellae grow preferentially in the thicker amorphous regions, which are reduced in size and number by secondary crystallization. The radiation damage effects indicate that amorphous chain constraint as well as available space is an important factor inhibiting crystallization between preformed lamellae.