Effect of side methyl from mixed diamine chain extenders on microphase separation and morphology of polyurethane fiber

Abstract

Polyurethane fiber (PUF) can be used as self-adaptive material in the field of nuclear physics and its properties depended on the molecular structure. To explore the effect of side methyl on its degree of microphase separation (DPS) and morphology for PUF, ethanediamine and 1,2-propylene diamine with different molar ratio were used as mixed diamine chain extenders (MDCEs) to fabricate PUF. The effect of side methyl content on the H-bond, crystallinity, DPS and mechanical performance were investigated with FTIR, XRD, AFM, SAXS, universal tensile machine (UTM) and DMA, respectively. The results of FTIR and XRD revealed that the hydrogen bonds (H-bonds) and crystallinity increased with the decrease of side methyl content on account of the reduction effect of steric hindrance. Furthermore, due to the stronger H-bonds and higher crystallinity in hard segment domain (HD), the DPS of PUF was enhanced with the increasing molar ratio of MDCEs in the aspect of the ordered structure in soft segment domain and the enlarged HD. Therefore, PUF showed more excellent mechanical performances with the improved DPS. The elongation at break extended from 482% to 557%. Static stress relaxation rate V increased while static stress relaxation ratio R decreased. Furthermore, Tg,s of soft segment moved to the low temperature direction. These results demonstrated how the microstructure-to-properties of PUF could be influenced by side methyl from MDCEs.