High Performance Cyanate Ester Resins Toughened By Unique Polysiloxane@Polyimide Core-shell Microspheres

High performance thermosetting resin（HPTR） has been considered as key fundamental material in many cutting-edge industrial fields such as electrical information, new energy research, aerospace and so on. Existing heat resistantthermosetting resins（TR） have high heat resistance and high rigidity, as well as great brittleness. The usual toughening methods would significantly decrease the strength and modulus of materials. As a result, it is still a challenge to develop a new and efficient toughening method to prepare novel HPTRs which can meet the needs of advanced industrial applications.Cyanate ester（CE） resin is the representative of heat resistant TRs, itslow dielectric constant and loss are the most properties different from other TRs, so it is quiet essential to maintain this advantage when toughening CE resin,this no doubt increasesthe difficulty of modifying CE resin. The thesis aims at solving the problem and developing a new method to obtain high performance CE resins with excellent dielectric properties, high heat resistance, high toughness and rigidity.In this thesis, the idea of developing high performance CEresins by usinghigh heat resistant core-shell microspheres was proposed.This project started from synthesizing heat resistant core-shell microspheres, and focused on investigating structure-property relationship.The main work of this thesis includes following two aspects:First, octamethylcyclotetrasiloxane（D4） was chosen as monomer, methyltrimethoxysilane（MTMS） as cross-linking agent, silane coupler（KH-560） as functional group. These materials were used to synthesize a kind of core-shell microsphere with epoxy groups on surface by emulsion polymerization. Then using different feeds of pyromelliticdianhydride（PMDA） and 4, 4’-diaminodiphenyl ether（ODA）, two kinds of polysiloxane@polyimide core-shell microspheres with different diameters are obtained, diameters of which are 150 nm（PSi@PI） and 220 nm（PSi@PI₁）. And then a series of PSi@PI/CE（PSi@PI1/CE） resins were prepared and their thermal, mechanical and dielectric properties were systemically studied. Results show that PSi@PI/CE resins have the best comprehensive properties.The impact strength and fracture toughness of 2PSi@PI/CE（with 2wt%PSi@PI） are 1.72 and 1.68 times of those of CE resins, respectively. Crack pinning and micro-cracking are the main toughening mechanisms. The initial decomposition temperature（Tdi） and glass transisiton temperature（Tg） of 2PSi@PI/CE are 450 oC and 300 oC, about 4-14 ℃ higher than that of CE resin, respectively. Moreover, compared to CE resin, PSi@PI/CE resin has lower dielectric constant and loss.Second, another PSi@PI₀ with the diameter of 4μm was synthesized by homo-polymerization. A series of PSi@PI₀/CE resins were prepared and their integrated performances were systemically studied. The results show that PSi@PI₀ has better toughening effect on CE resin than PSi@PI. The impact strength and fracture toughness of 2PSi@PI₀/CE are 1.95 and 1.87 times of those of CE resin, respectively. The main toughening mechanismsare are crack pinning and micro-cracking. But the rigidity and heat resistance are poorer than those of CE resin.