β-Pinene-Based Polyester from Renewable Feedstock with Elastomeric Behavior

The utilization of biobased feedstocks in the production of polyesters is a promising opportunity as the industry focuses more and more on sustainability. Terpenes are naturally derived and inexpensive feedstocks that do not compete with agricultural land and can be transformed into a variety of biobased polymers. In particular, the bicyclic monoterpenes α-pinene, β-pinene, and 3-carene are promising candidates for high-value polymer materials when incorporating their cyclic unit in the backbone of polymers. In this work, we propose a straightforward synthesis, transforming β-pinene into nopinone lactone (NopL) via ozonolysis followed by a Baeyer-Villiger reaction without further skeletal rearrangement. Ring-opening polymerization of the lactone monomer was achieved using yttrium-bis(phenolate) and indium-salan complexes as catalysts at different monomer-to-catalyst ratios, yielding tunable molecular weights up to 105 kg·mol^-1 and maintaining narrow polydispersities. The cyclobutane ring introduced in the polymer main chain induces higher rigidity in the resulting poly(nopinone lactone) (pNopL), yielding a thermally highly stable amorphous polymer with a glass transition temperature above room temperature (T_g = 23 °C). Mechanical studies show elastomeric behavior with a high elongation at break of 559 ± 46%. Incorporation of p(NopL) as a soft building block in triblock polymers (TBPE) with syndio-polyhydroxybutyrate (PHB) was successful, and stress-strain measurements showed the beneficial influence of the terpene-based polyester on the elasticity of ABA-type polymers.