Phenyl Propyl Polysiloxane‐Modified Epoxy Resin III: The Reaction Condition, Phase Structures, and Macroproperties

ABSTRACT Polysiloxanes are known to significantly enhance the toughness and thermal stability of epoxy resins. However, unsatisfactory grafting or copolymerization often occurs due to compatibility issues between the two materials, resulting in noticeable phase separation and a significant reduction in strength. In this paper, the copolymerization extent of epoxy resin with polysiloxanes was enhanced through solution polymerization by refining the synthesis process. The investigation explored the impact of polymerization process parameters on the reaction extent, phase structure, and mechanical properties. The results of refractive index and epoxy value showed that the extent of copolymerization ceased to increase after a 3‐h reaction duration at 15°C, 25°C, and 40°C. The results of FTIR and NMR showed that the lower the reaction temperature, the higher the extent of copolymerization. The toughness and strength of the resins copolymerized at 15°C increased simultaneously, while the strength of the resins copolymerized at 40°C decreased. The SEM results showed that the higher the extent of copolymerization, the finer the size of the second phase of the resins and that controlling the size of the second phase to an average of about 600 nm is the key to the strengthening of the resins. It is found that a low temperature is more favorable for the occurrence of a copolymerization reaction between polysiloxanes and epoxy resin, and it is pointed out that the relationship between the extent of reaction, phase structure, and macroscopic properties is an important guide for the work on siloxane‐modified epoxy resins.