Well-Tailored Dynamic Liquid Crystal Networks with Anionically Polymerized Styrene-Butadiene Rubbers toward Modulating Shape Memory and Self-Healing Capacity

Abstract

Well-tailored construction of liquid crystal networks (LCNs) with simultaneous molecular mobility and mechanical enhancement is desirable. Since the properties of polymeric materials are largely a result of the molecular compositions of polymer chains, in the present work, we demonstrate the tuning compositional synthesis of anionically polymerized random styrene-butadiene rubbers (r-SBRs) with well-controlled 75 wt % butadiene (Bd) contents that offer molecular mobility. Microstructural 1,2-olefins of 51.5–64.0 mol % were designed to attach 50 mol % SiH-terminated mesogenic moieties (M) along Bd units using hydrosilylation. As mechanical strength usually conflicts with high molecular mobility, an integrated design derived from the orderly LC stacking and simultaneous crosslinking in various ratios of the dynamic 2(6-isocyanatohexylaminocarbonylamino)-6-methyl-4[1H]-pyrimidinone (UPy-NCO) and permanent hexamethylene diisocyanate (HMDI) along 1,4-olefins of Bd units offers necessary mechanical strength and molecular mobility, resulting in a series of dynamic LCNs (r-SBR-g-[M·HMDI·UPy]). LC textures, phase transitions, self-healing/welding, and shape memory capacities were comprehensively studied. All LCNs showed LC textures in POM around Tᵢ (42–53 °C), which definitely contributed to both mechanical performance and molecular mobility due to the 50 mol % orderly LC stacking. Ureidopyrimidinone (UPy) that forms a dynamic H-bond is beneficial for the temporary shape fixity ratio (Rf), recyclability, and self-healing/welding ability while decreasing the shape recovery ratio (Rᵣₑc) because UPy can increase breaking elongations but sacrifice the mechanical strength. However, HMDI that forms a covalent crosslink showed the contrary effect, as HMDI can effectively enhance the mechanical strength but reduce the chain mobility. It is evidenced that r-SBR45k-g-[M-0%, 2%] can hardly undergo shape recovery (Rᵣₑc = 0) despite Rf = 92.6%, while with regard to r-SBR45k-g-[M-10%, 2%], Rᵣₑc greatly increased to 100%, but Rf decreased to 46.2%. All LCNs showed a higher than 82% self-healing/welding efficiency, with an exception of r-SBR-g-[M-10%, 2%]. This indicated the cooperative effect of molecular compositions on the properties. The well-tailored construction of polymer chain architecture through quantitative synthesis proves to be a powerful strategy for manipulating properties.