Synthesis And Modification Of Thermo-Degradable Controllable Phosphorus, Silicon-Containing Cycloaliphatic Epoxy Resins

The cured conventional epoxy resins have three-dimentional network structure. They are infusible and insoluble, and usually have high thermal decomposition temperature, which make the dismantlement and recovery of the waste electronic products to be very difficult. In this paper, thermal unstable phosphorus-containing groups were incorporated into the molecular structure of epoxides to confer reworkable function on cycloaliphatic epoxy resins. A novel phosphorus-containing, tri-functional liquid cycloaliphatic epoxy resin (Epo-phosphite) was designed and synthesized. Its chemical structure was confirmed by FTIR,1HNMR and31P NMR methods, and the epoxide was cured by MHHPA. The properties of the cured product were investigated by curing kinetic analysis, DSC, TGA, FTIR, LOI and shear strength test detailedly. The tests showed that the cured epoxides owned a Tg of178℃, and displayed a rapid decomposition when the temperature rose to237℃, which was much lower than that of the commercial cycloaliphatic epoxy resin ERL-4221(316℃). Moreover, the residues of degradation could be removed easily, making it convenient to do the thermo-reworking operation. Besides, with the introduction of phosphorus, the cured samples had a better fire resistance with a LOI value of23.2, which was24%higher than that of ERL-4221. In addition, due to the tri-functional structure, the new product had an excellent shear strength of5.67MPa, which was almost1.7times as that of the di-functional ERL-4221.To further improve the reworkability and other properties of the phosphorus-containing epoxy resins so as to fulfill different demands, Epo-phosphite was modified by copolymerization with a silicon-containing epoxide Epo-silicon by varying their ratios. After curing with MHHPA, a series of copolymers with different contents of phosphorus and silicon were prepared, and the cured products were characterized by the same method mentioned above. It was found that Tg of the copolymerized epoxides could be raised to190℃, and the degradation temperature was controllable from from237℃to313℃by varying the proportion of Epo-silicon, providing a wider choice for different use condition. On the other hand, the flame resistance was improved from23.2to25.1, when the proportion of Epo-silicon reached40%as a result of the phosphorus-silicon synergistic effect. Furthermore, Epo-silicon also facilitated the mechanical property of the cured epoxy resins so that the shear strength enhanced from5.67to6..63MPa.