Toughening polyisoprene rubber with sacrificial bonds: The interplay between molecular mobility, energy dissipation and strain-induced crystallization

Abstract

Sacrificial bonds have been utilized to improve the mechanical properties of self-reinforced rubbers with strain-induced crystallization (SIC) behavior. However, the influence of sacrificial bonds on the SIC behavior under quasistatic and dynamic processes is rarely reported. Herein, weak hydrogen bonds and strong metal coordination bonds are introduced as sacrificial bonds to toughen polyisoprene rubber (IR). Compared with the sample containing only hydrogen bonds, the further introduction of coordination bonds form denser network and impose stronger restriction on the molecular mobility, leading to higher energy dissipation. The hydrogen bonds suppress the crystallization rate and crystallinity of SIC, due to the suppressed molecular mobility and orientation of amorphous chains. By contrast, the coordination bonds lead to smaller onset crystallization strain and partially recovered crystallinity, as they are difficult to relax during stretching and thus can maintain a higher degree of chain orientation. However, under dynamic cyclic loading, both the hydrogen and metal coordination bonds obviously retard the SIC and reduce the crystallinity after the first loading cycle, which is unfavorable for the dynamic mechanical properties. Despite this fact, the synergistic effect of SIC and energy dissipation significantly improves the quasistatic mechanical properties of the modified IR containing both hydrogen and metal coordination bonds.