Dual-Functional Telechelic Phosphonium Silicate Accelerators with Thermal Latency and Stress-Relieving Properties for Epoxy Resin

The chemorheological and internal stress control of epoxy resins is critical for improving the reliability of advanced packaging. Here, a series of dual-functional thermal latent accelerators, tetraphenylphosphonium bis (2,3-dioxy-naphthalene)(3-(ethylthio)propyl)silicate-terminated polymethylphenylsiloxane (P-PMPSi_n), were designed and synthesized to improve the curing and internal stress management of epoxy packaging materials. A comprehensive investigation was conducted to evaluate the catalytic activity of these P-PMPSi_n accelerators in epoxy/phenolic resin systems, along with their effects on the thermal and mechanical properties and internal stress performance of the cured resins. Comparative analyses were performed against monomeric accelerators, triphenyl phosphine (TPP) and tetraphenylphosphonium bis(2,3-dioxy-naphthalene)methylsilicate (P-Si-Me), and the commodity stress-relief additive, carboxyl-terminated butadiene–acrylonitrile liquid rubber (CTBN). It was found that the ionic phosphonium silicate moiety in P-PMPSi_n accelerators resulted in their latency and catalytic activities comparable to those of the monomeric phosphonium silicate accelerator P-Si-Me. Notably, P-PMPSi_n accelerators exhibited delayed gelation in the uncured epoxy while simultaneously enhancing the cross-link density and glass-transition temperature (T_g) of the cured resins compared to the commercially available TPP accelerator. Meanwhile, the incorporation of flexible polymethylphenylsiloxane segments in P-PMPSi_n accelerators significantly reduced the elastic modulus and internal stress in the cured resins relative to the monomeric accelerator systems and CTBN-modified formulation. The stress-relieving mechanism was attributed to the formation of a dispersed polysiloxane particle phase within the epoxy matrix, which effectively mitigated internal stresses through enhanced molecular mobility and phase separation.