Catalyst-controlled sustainable crosslinking reaction for green itaconate polyester coatings

Abstract

In the context of a bio-based circular economy, replacing fossil raw materials with renewable alternatives has become a major trend. Platform chemicals such as itaconic acid and 2.5-furandicarboxylic acid can now be produced from sugars or lignocellulose and used to synthesize fully bio-based polyesters e.g. poly(ethylene 2.5-furandicarboxylate) with thermomechanical and barrier properties comparable to conventional polyesters. Life cycle assessments indicate that these bio-based polymers emit significantly less greenhouse gas than their fossil-derived counterparts, and thermomechanical testing and degradation studies confirm their practical suitability. Current crosslinking methods typically rely on melamine and isocyanates, which pose toxicological and ecological disadvantages. We propose using itaconic acid as a renewable crosslinking component to address these issues, with the crosslinking reaction tailored through catalyst selection. In our work, the incorporation of itaconic units into the polyester was confirmed by SEC (size-exclusion chromatography), 1 H-NMR (nuclear magnetic resonance spectroscopy), ATR-FTIR (attenuated total reflectance-Fourier-transform infrared spectroscopy) analysis. Thermal/mechanical properties were characterized by DSC (differential scanning calorimetry) and DMTA (dynamic mechanical analysis). In situ ATR-FTIR and rheology reveal that network formation proceeds via two competing mechanisms: radical C–C crosslinking and oxa-Michael (C–O–C) addition. Catalyst choice dictates the dominant pathway. Brønsted acids (DBSA, MSA) reduce the apparent reaction order to ~ 0.6, whereas a radical initiator (di-tert-butyl peroxide, DTBP) enhances radical crosslinking (apparent order ~ 1.7). In contrast, Lewis acids and metal salts (e.g. AlCl 3 , Zn(OAc) 2 ) suppress covalent gelation, favouring coordinative and supramolecular interactions over permanent covalent crosslinks. In coating tests, selected itaconate-containing formulations achieved an optimal balance of hardness, adhesion (crosscut = 0), and solvent resistance, with pendulum hardness values reaching 94–105 when catalyzed by MSA (methanesulfonic acid)/DBSA (dodecylbenzene sulfonate)/DTBP. These results demonstrate that the network architecture and thus the functional properties of itaconic acid–based renewable polyester coatings can be precisely controlled through targeted selection of catalysts and matrices. This approach offers a promising strategy for developing sustainable, high-performance bio-based coating materials.