Self−healing performance and reprocessing behaviors of FPPU and BPPU elastomers. (IMAGE)
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The stress−strain diagrams of pristine and healed (a) FPPU and (b) BPPU films. (c) The self-healing efficiency (SHE) of elastomers at several temperatures, showing the enhancement of SHE with temperature increase, while the SHE of the FPPU elastomer was consistently higher than BPPU elastomer. (d) Representative illustrations of molecular evolution (original, cut, healed) of the healing process of FPPU and BPPU strips. (e) The photographs of FPPU (left) and BPPU (right) pieces before and after reprocessing, showing the reprocessing of FPPU elastomer was more facile than the BPPU elastomer. The stress−strain diagrams of pristine, first, and second reprocessing films of (f) FPPU and (g) BPPU elastomers. (h) The recovery efficiency of tensile strength of two elastomers at various reprocessing cycles, where the tensile strength recovery rate of FPPU was 1.5 times that of BPPU, showing FPPU elastomer was more processable than BPPU elastomer. (i) The τ* fitted lines and determined the Ea of the FPPU and the BPPU from the slope, showing Ea of the FPPU elastomer was lower than determined for the BPPU elastomer, which was the prerequisite for fast network rearrangement. (j) The dissociation degree of the phenol−carbamate bonds of FPPU and BPPU determined from -NCO/C6H6 ratio from 25 to 150 °C. (k) The conversion rate of small molecule model compounds AC and AB from 0 to 15 min (interval: 5 min) at 40 °C (Taking AC as an example: conversion ratio = [AC]t/[AC]0, [AC]0 = integral area of 1H NMR spectra at 0 min, [AC]t = integral area of 1H NMR spectra at t min).
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