Linear polyethylene (Lupolen 6041 D) and a polyethylene fraction (PE 2
000) were investigated by WAXS at temperatures 8 K < T < 293 K. From t
he position and integral widths of the reflections the lattice constan
ts (and expansion coefficients) and lattice distortions are determined
. Lattice distortions are of the strain type, induced by inherent stre
sses. They increase with decreasing temperature up to similar to 50 K
and then to lower temperatures a decrease is observed. This is explain
ed by the decrease of the thermal expansion coefficients. For PE 2000
for some reflections a minimum in the integral widths at T similar to
38 K occurs. The explanation of this effect is given by the occurence
of a stress induced martensitic transformation (orthorhombic to monocl
inic) of part of the material. The corresponding weak reflections are
observed.