DEFORMATION-BEHAVIOR OF POLY(ETHER ESTER) THERMOPLASTIC ELASTOMERS AS REVEALED BY SMALL-ANGLE X-RAY-SCATTERING

The scattering behaviour of thermoplastic elastomers based on poly(ether ester) (PEE) under stress is studied. Bristles of PEE consisting of poly(butylene terephthalate) as hard segments and polyethylene glycols (M(w) = 1000) as soft segments in a ratio of 50/50 wt% are drawn five times and then annealed with fixed ends. Small angle X-ray scattering (SAXS) measurements are carried out with single bristles subject to stress and with deformations up to 200%. The increase of long spacing L is directly proportional to strain epsilon (up to epsilon = 100%) supporting an affine deformation mechanism. At epsilon = 75 and 100% two long spacings L1 and L2 are observed, L2 being close to the initial L1(0) and remaining constant with further increase in epsilon up to epsilon = 200%. The L values measured after removal of the stress (up to epsilon = 30%) revert almost to those obtained without stress; further increase in the deformation of the samples leads to a decrease in L values. The effect of stress on the scattering intensity is similar. A model is proposed to explain the scattering behaviour under stress. The affine increase of L with epsilon is related to the reversible deformation of the amorphous regions. Further increase in epsilon leads to the elimination of the interfibrillar contacts since tie molecules are pulled out. As a result relaxation of some microfibrils occurs and a second long spacing with a value close to that of the initial one is observed. A microscopic picture of the deformation mechanism and the influence of tie molecules on L are discussed.