Mechanisms of reversible thermal deformation of oriented polymers

Reversible thermal deformation coefficients (TDCs) of oriented samples of a flexible-chain polymer (polyethylene) and of a number of rigid-chain polym ers were measured in the longitudinal and transverse directions near room t emperature. The same samples were used to measure the TDCs of crystallites by x-ray diffraction. The magnitudes of the TDCs of macroscopic oriented sa mples and of constituting crystallites and the characteristics of the therm al deformation of flexible-chain and rigid-chain polymers are compared. A c onclusion is made that the mechanisms that determine thermal deformation in the longitudinal and transverse directions for the flexible-chain and rigi d-chain polymers are different. (C) 2001 MAIK "Nauka/Interperiodica".