From Molecular Structure to Macroscopic Performance: Insights into Polycarbosilane Curing

Curing protocols critically influence the structure and properties of crosslinked polymer networks, yet their impact on nanoscale structural features remains poorly understood. Here, polycarbosilane (PCS) networks are used as a model system to investigate curing-induced structural evolution across multiple techniques. PCS networks were prepared via Pt-catalyzed hydrosilylation reaction at progressively higher curing temperatures, and their macroscopic properties were correlated with molecular-level changes using a combined experimental-computational approach. Mechanical testing revealed a transition from flexible to brittle behavior with increasing curing temperature, while dynamic mechanical thermal analysis (DMTA) and swelling experiments showed a continuous increase in glass transition temperature (T_g) and crosslink density. Positron annihilation lifetime spectroscopy (PALS) provided direct insight into network development and revealed a redistribution toward larger free-volume populations despite the higher crosslink density. Molecular dynamics (MD) simulations qualitatively supported this trend by demonstrating reduced segmental mobility and the formation of fewer but larger geometric free volume domains at high conversion, thereby explaining both the increase in free volume and the onset of brittleness. This integrated approach highlights the strong influence of curing temperature on both network architecture and macroscopic performance. Beyond PCS, the methodology provides a generalizable framework for analyzing structure-process-property relationships in highly crosslinked polymer networks.