Effect of crosslinking networks on strain-induced crystallization in polyamide 1012 multiblock Poly(tetramethylene oxide) copolymers

Abstract The effect of the chemical crosslinking network structure within a poly(amide-b-ether) segmented multiblock copolymer based on crystalline polyamide 1012 hard segments and amorphous poly(tetramethylene oxide) (PTMO) soft segments on its microstructural evolution and mechanical properties during uniaxial deformation has been investigated. The chemical crosslinking process in the molten state of poly(amide-b-ether) is monitored by rheological measurements, and the crosslinking density (ν) after isothermal treatment at different temperatures is further determined. The effect of the ν on the microstructural evolution during uniaxial deformation has been quantitatively studied via in situ wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS), and Fourier transform infrared spectroscopy (FTIR). The increasing ν has a weak effect on the onset of PTMO strain-induced crystallization (SIC) and mainly affects the lamellae-fibril transition in polyamide 1012, the orientation behaviors of the hard-, soft-segments and PTMO SIC at large deformations. For samples with a high ν, both highly oriented PTMO SIC and oriented molecular segments enable the material to withstand high stresses without fracturing. The ultimate strain-at-break and breaking strength increased with the increasing ν.