Real-Time Raman Monitoring of Photopolymerization in Rubber-Acrylate Networks for Assessing the Impact of Initiator Concentration on Grafting, Kinetic and Thermal Stability

UV-induced polymerization is a widely adopted technique in materials science, valued for its rapid curing, low energy consumption, and ability to produce polymers with tunable properties. Central to this process are photoinitiators that generate free radicals upon exposure to UV light to initiate polymerization. This study investigates the effect of varying 2,2-dimethoxy-2-phenylacetophenone (DMPA) concentrations on the polymerization kinetics, grafting efficiency, grafting yield, and final properties of a polymer synthesized by grafting ethylene glycol methyl ether acrylate (EGMEA) onto 25% mole epoxidized natural rubber (ENR), forming P(EGMEA3-g-ENR1). The polymerization process and kinetics were monitored in real time using in situ Raman spectroscopy, enabling precise tracking of chemical changes, initiation points, curing time, and the overall progress of grafting. Thermal properties and degradation behavior were analyzed by using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The results revealed that an optimal DMPA concentration of 1.5 mol % yielded the highest grafting efficiency and grafting yield. Excessive concentrations of photoinitiators led to premature chain termination and grafting yield, while insufficient DMPA concentrations hindered monomer conversion, lowering grafting efficiency and compromising polymer integrity. These findings underscore the importance of optimizing photoinitiator concentrations for achieving the desired material properties and enhancing the efficiency of UV-induced graft polymerization. Importantly, this work aims to improve the performance and processability of natural-rubber-based polymers for energy-storage applications. By optimizing the UV-grafting process and tailoring polymer properties, the study supports the development of rubber-derived materials suitable for use in battery components, particularly as binders or solid polymer matrices in lithium-ion and solid-state batteries.This work addresses a significant knowledge gap, as similar studies on rubber-based polymers have not been previously reported.