Structure-property relations of poly(propylene oxide) block copolymers with monodisperse and polydisperse crystallisable segments

Abstract

Segmented block copolymers with poly(propylene oxide) and crystallisable segments were synthesized and their structure-property relations studied. As crystallisable segments, amide units based on poly( p-xylylene terephthalamide), were used. The length of the amide segment was varied and these segments either had a monodisperse or random length distribution (polydisperse). The poly(propylene oxide) used was end capped with 20 wt% ethylene oxide (EO-tipped) and had a molecular weight of 2300 g/mol ( M n, incl. EO-tips). These segmented block copolymers are model block copolymers to gain insight in the structure-properties behaviour of related semi-crystalline segmented block copolymers, like polyether(urethane–urea)s. The morphology of the polyether(ester–amide)s (PEEA) was studied with TEM, the thermal properties with DSC and DMTA and the crystalline structures with WAXD. The elastic behaviour of the block copolymers was investigated in tensile and compression. Phase separation in PEEA's with crystallisable, short and monodisperse amide segments occurred by crystallisation, while with crystallisable random amide segments phase separation occurred through liquid–liquid demixing in combination with crystallisation. With short monodisperse amide segments, morphology of dispersed ribbons with a high aspect ratio was observed. PEEA's containing these monodisperse amide segments had higher moduli and better elastic properties as compared to PEEA's with random length amide segments. Increasing the length of the monodisperse amide segment increased the modulus and decreased the compression set of the corresponding blockcopolymers.