Cross-Linking Mechanism of the Butadiene–Maleic Anhydride Copolymerization

With the expansion of ethylene production, butadiene will face a crisis of overcapacity by 2025. Converting it into high-value functional copolymers is more desirable. A butadiene–maleic anhydride copolymer is an amphiphilic alternating copolymer with potential applications in adhesives, emulsifiers, composite compatibilizers, and so forth. However, the unpredictable cross-linking reaction limits its research and industrial production. In this paper, the structural differences between linear and cross-linked copolymers are identified by Raman and nuclear magnetic resonance spectroscopy, and the transformation process from linear to cross-linked copolymers is investigated. We demonstrate that the cross-linking process is caused by the 1,2-unit vinyl (>2%) at a high copolymer concentration of 500 mg/mL. We reveal the cross-linking mechanism and identify the critical factors in this process. This work provides a theoretical basis for guiding the production of conjugated diolefin–maleic anhydride copolymers with a controllable gel fraction and improving the efficient utilization of butadiene.