Nano Co-Continuous Structure Poly(imide-siloxane)/Phenolic Hybrid Resin Fabricated by Copolymerization for the Thermal Protection System

Organic–inorganic hybridization is an important way to improve the ablation resistance of phenolic resin (PR). However, it is difficult to form a continuous inorganic liquid film on the resin surface during ablation, thus limiting the further improvement of ablation performance. In this work, a new poly(imide-siloxane) (PIS) was designed by introducing imide rings and terminal ethoxy groups into the main chain of silicone, and then it was introduced into PR. The imide rings can increase the polarity of the chain, and the terminal ethoxy groups can react with hydroxyl groups in PR, which can improve the compatibility of PIS with PR. SEM and AFM showed that nano co-continuous and sea-island structures of hybrid resins were prepared, respectively. Then, the influence of different structures on thermal stability and ablation-resistant properties was investigated by using TGA, tube furnace heat treatment, and oxyacetylene ablation test. Compared to the sea-island structure, the nano co-continuous structure of resin can form a continuous and dense SiO2 film in situ, giving the resin superior thermal stability and ablation-resistant properties. The present work provides an available way to manipulate hybrid resin's phase structure and develop high-performance ablation-resistant resin in aerospace applications.