Synthesis Of Crosslinked Polysiloxane Hybrid Material And Its Application In Coating

Nuclear energy is considered as one type of clean energy and plays an important role in national economy. The reactor pressure vessel (RPV), which is core component in nuclear power station, generally contacts rigid circumstance. In detail, the shell of RPV is in the media of high temperature and high moisture, with high concentration of Cl-(3.0mg·L-1). In that case, there is a high chance for metal shell to be corroded, inducing its security is reduced. For that reason, it is necessary to develop a polymeric coating with high performance, in order to extend the service life of RPV. Herein, the coating binder should be selected from thermal and irradiation resistant and anti-corroded, high performance polymers. Among these candidates, the high crosslinked poly(methylphenylsiloxane)(methylphenyl-silicone resin) exhibits thermal and irradiation resistance, and possesses excellent solubility in conventional solvents. So this polymer is widely used as film material of this protective coating. The industrial synthetic process (hydrolysis and condensation of chlorosilanes), however, is very complex, long-termed and yields large amount of waste acid. In addition, because of the flexible molecular segments, the polysiloxane molecules tend to experience chain mobility at high temperature, which induce an unzipping degradation. To realize an optimization of synthetic process and an improvement on thermal stability on the basis of conventional process of PMPS, a novel process named reversed-hydrolysis was used in the hydrolysis of poly(methylphenylsiloxane); in addition, rigid inorganic particles modified with organic groups were imported into hybrid system. This modification is used to generate obvious steric interaction, furthermore, to restrain the thermal mobility of polysiloxane molecules and to retard the primary degradation process. In this paper, the structural characterization was measured by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR) and gel-permeation chromatography (GPC) and the thermal stability was researched by thermal geometric analysis (TGA), iso-thermal weight loss and TGA coupled with FTIR. The performances of prepared products were studied by mechanical tests of coating films, electrochemical impedance spectroscopy (EIS) and Co60gamma-irradiation. The work in this paper contains three parts as follows:1. Poly (methylphenylsiloxane) is successfully prepared via reversed-hydrolysis, and several factors in the process were optimized. According to the results of FTIR, NMR and GPC, the structure of prepared products, which are generally the same with the one via conventional method, contain methyl and phenyl groups linked with backbones with=Si-OH as terminated groups. It was found that the reaction system is of homogeneous phase at primary period, in which HCl generated by hydrolysis induced the rearrangement of intermediates and the uniformization of structural units in ultimate products. Compared to conventional method, reversed-hydrolysis significantly reduces the reaction time, which is only1/6to1/10of conventional process. Thus the effectivity of preparation could be enhanced, and the its cost could be saved. According to the investigation on water amount, heating persavation time and agitation rate/gel time, the product could be obtained at an optimized condition:5-7of water/Si-Cl, no more less than2.5h of heating preservation time,100r·min-1of agitation rate and72s of gel time. In our research, when R/Si and Ph/R is1.4,0.5respectively, the prepared coating film exhibited satisfied performance; especially show an excellent mechanical properties. TGA data indicated that the process of weight loss is close to the case of conventional polysiloxane product.2. With the view of molecular design, the hybrid material was successfully prepared by the combination of such crosslinked polysiloxane and organic functionalized SiO2particles (MQ silicone resin). For insuring the compatability, the hetero-condensation between different functional groups linked with silicon atoms is used to form stable chemical bonds between the two components. The research was found that the grafted reaction is available for silanol prepolymer (hydrolysate of chlorosilanes) and MQ silicone resin containing residual=Si-OEt groups, to yield a uniform, transparent hybrid product. According to the results of FTIR, NMR and GPC, the structure of prepared hybrid products show the units of polysiloxane and modified silica particles. When the content of modified silica reaches15wt%, and the M/Q arrives at0.5, the coating film prepared by hybrid products exhibit satisfied film-forming performance and thermal mechanical performance after calcinating at350℃for2h. Compared to neat polysiloxane, TGA data indicates that the residual ratio was significantly increased, and the primary degradation temperature was increased by approximate100℃. It could be found that the importation of modified silica retards the primary degradation process. The residual ratio from TGA data of prepared hybrid products is70wt%, which is much more than the value of pure component (55wt%).3. To develop a synthetic route of organic-inorganic interpenetrating network hybrids, in order to improve thermal stability and mechanical strength of objective material, the phenylene-silica was imported into hybrid system to form PMPS/phenylene-silica interpenetrating network hybrid material via two-step sol-gel process. In this paper, the structure and performance as a binder were researched in detail; especially the Co60gamma-irradiation effects on the hybrid products and coating films were discussed. FTIR and29Si-NMR data of phenylene-silica and ultimate products reveal the importation of phenylene into the structural units of silica, and the hybrid products contain the phenylene-silica frameworks in their structure. TGA data shows satisfied primary degradation temperature (Td5) up to500℃, which is150℃higher than pure polymer. Compared to the previous work, the products in this part show a significantly retarded Td5. DTGA data indicate restraint of primary degradation process due to phenylene-silica. The degradation mechanism of typical hybrid product was detected by TGA-FTIR, indicating three steps during the period of thermal degradation:the elimination of cycle obligomers (430-580℃), the deprivation of phenyl groups (450-680℃) and methyl groups (620-850℃), among which the former two are due to concerted reaction, whereas the latter one is caused by free radical reaction. Provided significantly increased degradation temperature, the hybrid films could maintain the mechanical performance after calcinating at400℃for2h. The excellent results cannot be realized by pure PMPS and prepared PMPS/SiO2hybrid products. The hybrid products also exhibit excellent tensile behavior and even a degree of toughness, showing tensile strength of25.9±1.7MPa and elongation at break of5.97±1.02%, because the phenylene-silica framework compensates low inter-molecular interactions of polysiloxane. The EIS data reveal high resistance of coating film up to1010Ohm·cm2, which has no obvious change during30days, reflecting a satisfied impermeability. In order to be used as protective coating on RPV, we firstly investigate the Co60gamma-irradiation effect of hybrid products. FTIR study reveals that their structure shows no significant change after1.6×105Gy of irradiation, with only a bit increase of crosslinking degree. The TGA and TGA-FTIR data of the irradiated samples indicate that gamma-irradiation has not produced a adverse effect in the thermal stability of hybrid product, and a good level of thermal properties were maintained. The tensile samples after irradiation could preserve90%of strength. The coating films also exhibit advanced thermal mechnical performance after irradiation.