Low-Energy Ultrasound-Triggered Frontal Polymerization for Scalable and High-Performance Polyolefins

There is an urgent demand to develop energy-saving synthesis methods to alter the traditionally energy-intensive and environmentally polluting production of polyolefins. This work introduces an innovative method for synthesizing high-performance polyolefins using low-energy ultrasound-driven frontal ring-opening metathesis polymerization (U-FROMP). Focusing on the polymerization of dicyclopentadiene (DCPD) and 1,5-cyclooctadiene (COD), we investigated the optimal ultrasound power to evaluate its effects on frontal temperature, velocity, energy consumption, and mechanical properties, as well as the new mechanism of ultrasound-driven frontal polymerization (FP). Nuclear magnetic resonance (NMR) revealed improved efficiency of Grubb's catalyst during the initiation period due to PCy3 ligand release, enabling ring-opening metathesis polymerization (ROMP) at lower temperatures, supported by dynamic differential scanning calorimetry (DSC) analysis of U-FROMP, showing reduced exothermic heat. Using COD as a model system with better solubility after polymerization, we demonstrated ultrasound's impact on polymer regioselectivity and molecular weight, with U-FROMP samples showing increased trans content and higher molecular weights. This study advances the green synthesis of engineering plastics, enhancing the scalability of FP via a multi-ignition strategy and improving polymer ductility by preventing high-temperature spikes and degradation.