Microstructural evolution underlying the ternary stages of the elastic behaviors for poly(ether‐b‐amide) copolymer elastomers

Abstract

Three stages of elastic behavior were observed during cyclic deformations for poly(ether‐b‐amide) (PEBA) segmented copolymers based on crystalline hard segments of polyamide 12 (PA12) and amorphous soft segments of poly(tetramethylene oxide) (PTMO). The underlying microstructural evolution was characterized by a combination of in situ Fourier transform infrared spectroscopy (FTIR), wide‐angle X‐ray diffraction (WAXD), and small‐angle X‐ray scattering (SAXS) technologies. The γ–α″ phase transition of crystalline PA12 occurred upon stretching, and the orientation of the α″ phase was less reversible under larger strains. PTMO chain orientation cannot be restored to the initial state, contributing to plastic deformation. Driven by the entropy effect, the strain‐induced crystallization of PTMO can fuse during sample retarding, exerting little influence on the residual strain. For PEBA with a shore D hardness of 35 D, the long period (L) can be restored to the initial L after the sample was unloaded until system fibrillation. The tie molecules between adjacent oriented lamellae can be by drawn out high stress in a PEBA material with a shore D hardness of 40 D, and the relaxation led to a second long period. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 855–864

Crystal Structure and Mechanical Properties of Uniaxially Stretched PA612/SiO2 Films

“…Notably, the intensity of diffraction peak of (100) planes in the unstretched films (ε = 1) is much lower than the stretched counterparts. This should be ascribe to the twisting and rotation of crystal lamellae caused by the stretching [34]. As shown in Figure 6, the c axes of α phase, which is parallel to the direction of molecular chains, show preference orientation along the MD after stretching.…”

Microphase separation/crosslinking competition-based ternary microstructure evolution of poly(ether-b-amide)

“…The crystallinity of PA12 crystals ( X c ) was calculated by the normalized Δ H m,HS with the fraction of PA12 HS dividing by the fusion enthalpy of perfect PA12 crystals (246 J g −1 ). 40 The results are listed in Table 1 .…”

“…The weight fraction of PA12 segments (W PA ) of the studied elastomers determined by 1 H NMR are list in Table 1. 28,40 The thermal properties of the three studied copolymers were determined by differential scanning calorimetry (DSC Q2000, TA instruments). The instrument was calibrated with indium before measurements.…”

“…As the applied strain increased, the segmental chains' orientation, the crystalcrystal transition, and strain-induced crystallization can occur. [37][38][39][40] Studying the microstructural evolution under the external elds is important for a better understanding of the macroscopic properties of the segmented copolymers. To date, the phase diagram of multi-block copolymers cannot be predicated well due to the more complex segmental interactions.…”

Structural origin for the strain rate dependence of mechanical response of fluoroelastomer F2314

“…The hard domains are either glassy or crystalline at room temperature, whereas the soft domains are usually in the rubbery state and endure major deformation . Imposing deformation on TPEs may induce complex structural evolutions simultaneously, such as deformation of microphase‐separated domains, crystallization in soft domains, melting or phase transition in hard domains, and so forth . These structural evolutions can be tracked with in situ small‐ and wide‐angle X‐ray scattering (SAXS/WAXS) techniques .…”