DOE-Driven Synthesis of Bio-based Itaconate Polyester: A Solvent-Free and Catalyst-Free Approach

Abstract

Producing polymeric products from renewable raw materials is desirable to reduce reliance on petrochemical-based materials. To date, toxic acrylic monomers and their derivatives are most commonly used in applications such as UV-crosslinked materials. Itaconate compounds are considered as potential “green alternatives” for acrylic compounds because of their similar chemical structure. For this, in this work, the DOE-based optimization of itaconate-based prepolymer derived from bio-based precursors - poly(dodecamethylene-co-hexamethylene itaconate) (abbreviation: PDDHItc) via catalyst-free and solvent-free polycondensation reaction from commercially available 1,6-hexanediol (1,6-HD), 1,12-dodecanediol (1,12-DDD), and itaconic anhydride (IAn) was performed. To date, to the best of our knowledge, no other examples of the synthesis of such a binary polyester have been reported. To optimize the reaction conditions (molar fraction of 1,12-DDD in the reaction system, time, and temperature of the prepolymer synthesis), the Design of Experiments (DOE) method, specifically a Box-Behnken plan, was used to limit the number of experiments and avoid conducting reactions under extreme conditions. The three selected product properties were as follows: percentage conversion of carboxyl groups -COOH, percentage of unreacted unsaturated C = C double bonds, and a complex variable related to the viscosity and appearance of the prepolymer. The obtained prepolymer was a viscous resin (𝜂 = 16.2 Pa ∙ s (25 °C), 3.2 Pa ∙ s (36.6 °C)) with an M_w of 1505 g/mol. The specific molecular weight, along with the structural irregularity introduced by the co-diol system, was strategically targeted to prevent premature crystallization and to achieve a viscosity range compatible with future solvent-free, UV-curable formulations. While actual validation of UV-crosslinking and 3D printing remains the subject of future studies, the successful preservation of reactive pendant C = C double bonds and the tailored rheological profile establish this PDDHItc prepolymer, derived from bio-based precursors and synthesized under catalyst-free, solvent-free conditions, as a promising base material for additive manufacturing applications.