Vitrification: Versatile Method To Modulate Properties of Myrcene-Based Rubbers

We report bio-derived vitrimeric rubbers with weldability and excellent reprocessability. Reversible-deactivation radical copolymerization of the commercially available terpene-based β-myrcene with 10 to 30 mol % (2-acetoacetoxy)ethyl methacrylate (AAEMA) afforded linear prepolymers, which were cross-linked in a single step treatment with difunctional amine, the vegetable oil-derived Priamine 1075, or trifunctional amine tris(2-aminoethyl)amine (TREN). Decoupling the networks' backbone structure and cross-linkers led to high tunability of the vitrimers' final mechanical and rheological properties using prepolymer composition, molecular weight, nature and concentration of cross-linker, and cross-linking density. Glass transition temperature (Tg) of the vitrimers ranged between −49 and −5 °C, while the average elongation and stress at break ranged from ∼83% and 0.18 MPa to ∼30% and 1.68 MPa, respectively from the lowest, 0.12 mol/L, to the highest, 0.98 mol/L, cross-linking densities. The characteristic features of dynamic vinylogous urethane-vitrimers were confirmed over at least three reprocessing cycles by grounding and hot-pressing at 110 °C. No appreciable changes in the ATR-FTIR spectra, Tg, decomposition temperatures, tensile properties, and storage modulus were observed due to reprocessing. Furthermore, the incorporation of 5 mol % epoxy-based glycidyl methacrylate into the prepolymer led to the formation of a network with dual static and dynamic cross-links. Compared to the counterpart network with solely dynamic cross-links, the addition of static cross-links decreased creep by 75% and imparted shape memory effects. This work shows that combining vitrimer chemistry with myrcene is a facile and inexpensive, yet highly versatile method to not only modulate and compensate for the poorer mechanical properties of brush-like terpene-based elastomers but also provides a potential platform for recyclable biobased rubbers with more sophisticated functionalities.