Sustainable Rubbers from Terpene: Synthesis, Characterization and Properties

Development of sustainable rubbers not only entails inclusion of renewable monomers, but also a judicious choice of green manufacturing methodology. The acyclic monoterpene β-myrcene, having a conjugated double bond, resembles the chemical structure of various petro based unsaturated hydrocarbons and is thus quite interesting. We have employed environmentally benign emulsion polymerization method to prepare elastomers from β-myrcene. Apart from polymyrcene, series of copolymers were also synthesized. From the spectroscopic measurement, it was found that the persulfate initiated polymyrcene possesses 3,4 and 1,2 vinyl defects along with 1,4 microstructures, whereas the redox polymyrcene contains solely 1,4 addition products. The copolymers however contained only 1,4 microstructures of the polymyrcene unit. The reactivity ratio of the monomers was determined and a plausible mechanism of the emulsion copolymerization was provided. All the synthesized homo and copolymers registered sub ambient glass transition temperature, reasonably good thermal stabilities over the individual homo-polymers and pseudoplastic flow behaviour. Molecular dynamics simulation was employed to visualize the spatial distribution of macromolecular chains. After conventional sulphur vulcanization, the rubber showed a tensile strength of 6.4 MPa and 400% elongation at break. The present study would thus pave a green tarmac for synthesizing terpene-based elastomers as a sustainable material of the future.