Research On The Properties Of Crosslinked Polystyrene Synthesized By γ-ray Radiation

With the development of high-power pulse technology, large high-power pulse devices in vacuum were increasingly popular in national defense, military area, high-tech researches and other realms. Insulator stack is an important part of pulse devices. Its compressive strength can influence the working range of device directly. In the international scope, crosslinked polystyrene(CLPS) was the first choice of making insulator stacks. But the production process of this kind of material was not mature in China up to now. There still had some problems, like low rate of product, weak properties of material, were waiting for being solved.In this work, the linear polystyrene prepolymer was synthesized firstly using styrene(St) as monomer and benzoyl peroxide(BPO) as initiator. Then it was mixed with divinyl benzene(DVB), the crosslinker, in a certain percentage. The mixture was radiated in γ-ray to finish the crosslinking copolymerization and to synthesize crosslinked polystyrene. Initial reaction procedure of the polymerization system has been analyzed by testing the exothermic properties in curing process of materials. Influence of radiation on structure of material has been studied by scanning electron microscope(SEM) and fourier transform infrared spectroscopy(IR), etc. And the influence of radiation dose, radiation dose rate and content of crosslinker on the properties of CLPS materials have been explored according to their static mechanical properties, dynamic mechanical properties, thermal properties, dielectric properties and surface flashover characteristics in vacuum.The main research results are summarized as follows: During the initial period of γ-ray radiation, the polymerization of linear polystyrene prepolyme system accorded the dynamics of polymerization of pure styrene. There was a linear, positive correlation was found between reaction conversion and radiation dose. Compared to the CLPS materials synthesized by thermal polymerization, the γ-ray-radiated samples had better structural density and higher crosslink density. Radiation improved the mechanical properties of materials, especially the tensile strength, bending strength and impact strength. The mechanical properties increased at first and decreased later with the increasing radiation dose and dose rate. When the radiation dose was 19 kGy and the radiation dose rate was 40 Gy/min, CLPS materials got the best mechanical properties. There is an increase in the storage modules of CLPS materials with increasing radiation dose, while the loss factor was contrary. According to the storage modules, crosslink densities were calculated. They were increased at the range of 12~22 kGy, as the radiation dose increased. Compared to the thermal-polymerization simples, the glass transition temperatures(Tg) and thermal decomposition temperatures of CLPS materials synthesized by γ-ray radiation were higher. The γ-ray decreased the dielectric constant and dielectric loss of the materials, which would be increased by the addition of initiators. The vacuum surface flashover performances of CLPS materials increased at first and decreased then with the increasing radiation dose. And the best surface flashover characteristic was got when the radiation dose was 19 kGy. The increase content of crosslinker in this system made the mechanical strength and flashover strength of the materials increased first and then decreased. And the mechanical strength and flashover strength were at the maximum when the content of crosslinker was 2 wt%.