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May 12, 2023
Organosilicone epoxy resins with different chain lengths were synthesized using double Si-H terminated silica fume and vinyl epoxy resin as raw materials. The effects of the main chain length of silica fume on cationic polymerization and thermal discoloration, as well as the effect of catalyst concentration on thermal and UV discoloration were investigated.
Polysiloxane has poor compatibility with epoxy resin and is not easy to blend, so direct copolymerization reaction is adopted for modification. Copolymerization is to use the active end groups on the organic silicon, such as tibial group, amino group, pendant group, vinyl group and oxy group, to react with the epoxy group and light group in the epoxy resin to generate graft or block polymers, so as to solve the problem of compatibility, and introduce stable and flexible Si-0 chains into the curing structure to improve the fracture toughness of the epoxy resin. The copolymer modified resin can observe a very fine two-phase separation structure under high magnification (23000 times) SEM. There are several ways to prepare epoxy modified silicone resin.
The epoxy group on the phenolic resin is converted to allyl group, and then the epoxy resin is hydrosilylated with the hydrosilyl oil containing terminal group H and side group H. The side group Si-H has a better stress reduction effect than the end group Si-H. When there is more side group Si-H, heat resistance and impact resistance are better. Especially for the sample HS8 CMw=6000 of Si-H on the side substrate, the encapsulated component can withstand 4100 repeated impacts between -65 ° C and 150 ° C, with only 50% cracking, while the unmodified component can withstand only 750 cycles.
Then, by blending the polymer with bisphenol A epoxy resin at room temperature, a modified resin with good compatibility can be prepared. Through scanning electron microscopy (SEM), it can be observed that as the amount of polysiloxane containing epoxy groups increases, the fracture surface of the sample becomes rough, and the dispersion of polysiloxane in the epoxy resin matrix becomes more uniform; However, the weight loss curve shows that during the curing process, due to the different reactivity of the two, phase separation occurs when the amount of polysiloxane containing epoxy groups is too high; From the analysis of viscoelasticity spectrum, when the mass halo ratio of polysiloxane containing epoxy group to bisphenol A type epoxy resin is 1:10, polysiloxane can be well dispersed in the continuous phase of the epoxy resin matrix, and the toughening effect is the best.