PTFE specimens with a crystallinity of 42 % were uniaxially stretched at 473 K resulting in draw ratios between 1 and 4. The degree of molecular orientation was obtained by X-ray wide angle and birefringence measurements. The thermal expansion coefficients and the Young's moduli both parallel and perpendicular to the draw direction were measured in the temperature range from 100 to 400 K. The thermal expansion behaviour turned out to be dependent upon the molecular orientation in a sensitive manner and could be explained by a simple model of structure changes caused by the deformation processes.

Mechanical tests of prestressed and nonprestressed specimens show that prior stressing often signijicantly changes the stress-strain curve of amorphous and partly crystalline Specimens subjected to a prior mechanical stress show a Jla#er stress-strain curve (even with a "kink") than those not previously stressed. The original properties of prestressed specimens can be restored by tempering (at least in the range of small elongations). Specimens made of ABS react differently: After certain longterm prior stresses, followed by short-term tensile tests, brittle fracture occurs.