The present application provides a composition for the production of a polymer, the composition comprising (i) an epoxidized oil with an iodine value of at least 100; and (ii) a polymer with multiple epoxide-reactive groups. The composition may further comprise a filler, such as spent coffee grounds. The components are available from renewable or waste 5 feedstocks. Also provided are processes for the production of polymers from the composition, and polymers produced therefrom. Polymer, which may be vitrimer type dynamic thermosets in particular, contain a highly crosslinked polymer network with excellent mechanical properties, while allowing for reversible cross-linking and subsequent thermo-reforming and re-use multiple times. The polymers may be fully plant-derived and 0 compostable, addressing an unmet need for biocompatible and sustainable plastics.