Abstract

There have been significant interests in recent years for incorporating dynamic bonds into polymer materials for achieving multiple functionalities, such as self-healing, recycling, stimuli-responsiveness, and so on. Nevertheless, the impact of dynamic bonds on the polymer dynamics is actually less explored. In this study, we investigate a self-healing solid-liquid elastomer (SLE), which is a dual-crosslinked network made by coupling a permanently crosslinked polydimethylsiloxane (PDMS) network with polyborosiloxane (PBS) via abundant dynamic boron/oxygen dative bonds. Proton double-quantum (DQ) NMR reveals that the crosslinking degree is reduced while the structural heterogeneity of network is enhanced with increasing PBS content, i.e. increasing the content of dynamic boron/oxygen dative bonds. Rheological experiments clearly reveal two chain relaxation modes in the SLE samples with a characteristic relaxation time of around 2.1s and 11.8s, corresponding to the relaxation of coupled PBS and PDMS chains, respectively. The master curves obtained from variable-temperature frequency-dependent rheological experiments also reveal enhanced heterogeneity of chain relaxation with increasing PBS content. Finally, the impact of boron/oxygen dative bonds on the Rouse dynamics is further revealed by fast-field-cycling (FFC) NMR experiments, where the spin-lattice relaxation rate (R1) of all SLE samples follows the same power law of R_1 (ω)∝ω^(-0.33). Nevertheless, the incorporation of PBS did slightly increase the energy barrier of Rouse dynamics. Our study well demonstrates a combined use of rheology and solid-state NMR spectroscopy can provide piercing insights into the interplay of crosslinking structures and dynamics of polymer materials.