Multi-objective synthesis optimization and kinetics of a sustainable terpolymer†

Abstract

The properties of polymers are primarily influenced by their monomer constituents, functional groups, and their mode of linkages. Copolymers, synthesized from multiple monomers, offer unique material properties compared to their homopolymers. Optimizing the synthesis of terpolymers is a complex and labor-intensive task due to variations in monomer reactivity and their compositional shifts throughout the polymerization process. The present work focuses on synthesizing a new terpolymer from styrene, myrcene, and dibutyl itaconate (DBI) monomers with the goal of achieving a high glass transition temperature (T_g) in the resulting terpolymer. While the copolymerization of pairwise combinations of styrene, myrcene, and DBI have been previously investigated, the terpolymerization of all three at once remains unexplored. Terpolymers with monomers like styrene would provide high glass transition temperatures as the resultant polymers exhibit a rigid glassy state at ambient temperatures. Conversely, minimizing styrene incorporation also reduces reliance on petrochemical-derived monomer sources for terpolymer synthesis, thus enhancing the sustainability of terpolymer usage. To balance the objectives of maximizing T_g while minimizing styrene incorporation, we employ multi-objective Bayesian optimization to efficiently sample in a design space comprising 5 experimental parameters. We perform two iterations of optimization for a total of 89 terpolymers, reporting terpolymers with a T_g above ambient temperature while retaining less than 50% styrene incorporation. This underscores the potential for exploring and utilizing renewable monomers such as myrcene and DBI, to foster sustainability in polymer synthesis. Additionally, the dataset enables the calculation of ternary reactivity ratios using a system of ordinary differential equations based on the terminal model, providing valuable insights into the reactivity of monomers in complex ternary systems compared to binary copolymer systems. This approach reveals the nuanced kinetics of terpolymerization, further informing the synthesis of polymers with desired properties.