Curing Mechanisms of an Allyl‐Functionalized Preceramic Polymer With Radical Initiators: Kinetics and Thermodynamics

This study investigates the thermal curing behavior of allyl‐functionalized SMP‐10, a preceramic polymer used as a silicon carbide (SiC) precursor in ceramic matrix composites (CMCs). The relatively high curing temperature of SMP‐10 may pose a significant processing challenge, as it can impact quality, microstructure, and performance of the composite. However, the allyl group enables radical‐initiated crosslinking pathways. To address this, the effect of radical initiators, dicumyl peroxide (DCP) and Luperox 101, on lowering the curing temperature was examined. Using non‐isothermal differential scanning calorimetry (DSC) at heating rates of 0.5, 1, 2.5, 5, and 10/min, the behavior of pure SMP‐10 and systems with 2 wt.% initiator was monitored. Kinetic analysis was performed using Kissinger and Ozawa peak‐based methods, model‐free isoconversional methods (Kissinger–Akahira–Sunose [KAS], Flynn–Wall–Ozawa [FWO], and Starink) and model fitting method (Master plot). The results showed that the initiators significantly lower the onset curing temperature. However, the apparent activation energy () increases from approximately 116–122 kJ/mol for pure SMP‐10 to 141–153 kJ/mol for the system with DCP and 155–156 kJ/mol for the system with Luperox 101. To better understand this trend, transition state theory was applied. It was found that the acceleration is not driven by a reduction in the enthalpic barrier, but rather by a shift in the entropy of activation (), from negative values in the pure system (approximately J/) to large positive values with initiators (approximately 77 J/ for DCP and 85 J/ for Luperox). The results suggest that curing in the presence of initiators proceeds through a dissociative transition state that is entropically more favorable, leading to a lower Gibbs free energy of activation (). These findings provide a basis for developing more efficient low‐temperature curing strategies for advanced CMC processing.