Fabrication of Recyclable Polyisoprene Elastomers with Tuneable Mechanical Properties by Incorporating Dynamic Bonds and Separated Polystyrene Phase

Recently, various associative dynamic bonds have been introduced into vitrimers to make the materials recyclable. However, for the high-molecular-weight diene vitrimers, there is a big challenge to endow the rubbers with great intrinsic recyclability without sacrificing their mechanical properties. Herein, a series of copolymers consisting of polystyrene (PS) blocks and hydroxyl-functionalized polyisoprene blocks are synthesized. After being modified and cross-linked, diene vitrimers PS_xIM₂ (x = 0, 1, 2, 3) and PS₂IM_y (y = 1, 2, 3) were prepared, where the contents of styrene units or hydroxyl groups were changed gradually. The resulting samples possess both a dynamic covalent network consisting of vinylogous urethane bonds and a physical network consisting of phase-separated polystyrene domains. The experimental results show that the flow of PS phases above T_g,PS effectively accelerates the rearrangement of dynamic covalent networks, so that the exchange activation energy (E_a) and topological freezing transition temperature (T_v) of the samples decrease with the increase of the PS phase content, giving the samples superior recyclability and self-healing ability. The increase of cross-link density can further improve the recycling performance of the samples, where the toughness recovery ratio of PS₂IM₃ can reach 100%. Especially for PS₂IM₂, it showed much better recycled mechanical properties compared with other diene vitrimers reported. With the existence of T_g,PS and T_v, PS₂IM₂ also possesses sensitive thermally triggered shape memory performance. Our works provides a broader idea for the recycling of diene vitrimers.