Study On Preparation And Properties Of Phosphorus-Containing Poly(Arylene Ether)and Polyimide Materials For Atomic Oxygen Erosion Resistance

After the recent development in the aerospace industry, the larger number of spacecrafts was launched into Low-Earth Orbit (LEO). However, the rough and harsh environment in LEO due to presence of Atomic Oxygen (AO) is still a big threat for spacecraft manufactures. Polymeric materials are treated by a number of extreme factors, causing polymers erosion and, as the result, reducing their physical and chemical properties. Actually, the most damaging factor for polymeric materials is bombardment materials surfaces by the stream of AO. To prolong spacecraft's functional lifespan, it's essential to develop new polymeric materials with high resistance to AO.In our china, not too much research has been done in this field. Most of inorganic materials possess very good resistance to AO. Using of inorganic protective coverings, such as SiO2 or A12O3, can offer outstanding protection, but because of the absence of flexibility these are open for appearance of cracks. Through these cracks particles of AO can approach polymeric material. So, nowadays, major focus of researchers is to modify the organic materials to adopt the harsh space environments. At present, there are three types polymer including fluoropolymer, silicone containing polymer and phosphorus polymer, which demonstrates good performance against AO erosion. Especially, FEP Tefoln (one of fluoropolymer) and silicone resin have been applied in the spacecraft, showed good resistance to AO in short-term exposure experiment.However, in the long-term space exposure experiments and LDEF exposure experiments it has been found that under the ultraviolet irradiation for long time, the reaction rate of fluoropolymers with AO increased rapidly. At the same time, because of the synergistic effect of thermal cycling, vacuum ultraviolet and AO, the silicone resin express poor mechanical property, and susceptible to aging, cracking, leading to a serious decline for material properties and volatilizing dark brown condensate production, which will pollute the optical devices and solar power systems in surroundings. Therefore, polymers containing fluorine and silicon are unable to meet the requirements of long-term spacecraft in LEO. In short-term and long-term space exposure experiments, it was proved that the structure of benzene phosphorus oxide containing polymers showed excellent performance to resistance AO erosion, long-term stability in the space environment.The purpose of this paper is to design and prepare a series phosphorus-containing polymer films, expected to obtain one or more high-performance polymer materials, which not only can meet the performance requirements of spacecraft but also be well adapted to low-Earth orbit space environment.Polyarylether(PAE) with high heat and environmental resistance, better chemical and thermal stability, become one type of important special engineering plastics. This paper first describe the synthesis of 4,4'-bis(fluorophenyl) phenyl phosphine oxide(BFPPO) by Grignard reagent using bromo-fluorobenzene and Dichlorophenylphosphine oxide. Then two polymers PAEPO and 6F-PAEPO containing triphenylphosphine oxide were synthesized by the nucleophilic substitution reaction in base catalysis. BFPPO and Bis-A were monomers used for the synthesis of PAEPO wihle BFPPO and Bis AF were used for 6F-PAEPO.The molecular structure of the two polymers were characterized by FTIR, NMR. Due to the introduction of triphenylphosphine oxide structure, the polymers exhibited more excellent thermal stability, mechanical property, organic solubility, optics trasmittance and flame resistance compared with nomal PAE, the presence of fluorine in 6F-PAEPO was help to improve the thermal,organic solubility and optics trasmittance performance of the polymer. However, the glass transition temperature(Tg) of two kinds of PAE were only between 200-211℃, at 120"C high temperature, the maximum strength is less than 33 MPa and mechanical properties reduced roughly. However, in the temperature range of-150℃to 120℃, variation of the value of CTE is comparatively large. So these shortcomings make it unfit for LEO harsh environment.Polyimide is the class of organic polymer material that has been reported with the highest thermal performance among the polymers, A new phosphorus-containing diamine, bis[4-(3-aminophenoxy)phenyl]benzenephosphorous oxide(m-BAPPO), was successfully synthesized through the nucleophilic substitution reaction with BFPPO and m-aminophenol. A series of random copolymers were prepared from m-BAPPO,4,4'-diaminodiphenyl ether (ODA) and 3,3',4,4'-Biphenyl tetracarboxylic dianhydride (s-BPDA) in apolar aprotic solvent. According to m-BAPPO content for the total diamine, the name of co-polyimides were PPI-0, PPI-20, PPI-40, PPI-60, PPI-80andPPI-100, respectively. The basic properties were studied, the results showed that as the phosphorus-containing diamine content increased, light transmission properties of copolymer films improved, but the thermal, thermal stability and mechanical properties of polymers decreased. However, the co-polyimide still showed better performance than phosphorus containing PAE materials. It was found that small amount of phosphorus-containing diamine help the polyimide to improve flame retardant properties.Manufacturing cost of phosphorus-containing diamine is high and mechanical properties of pure m-BAPPO based polyimide are not good. So double coating technology is used to apply the polyimide. By controlling the temperature of the thermal imidization, the phosphorus-containing polyimide was succeed in grow on one side of the traditional polyimide which has been applied to the spacecraft. By controlling the polyamide acid viscosity and the thickness of wet films, the thickness of each layer in the composite film achieved precise controllable. The mapping scanning of SEM-EDX on the cross section measured and confirm the thickness of each layer. Especially, film of PPI_PI-10 showed excellent mechanical properties and low CTE, conld compare favorable with the traditional polyimide.To investigate the AO resistant performance of the phosphorus-containing polymer films in space environment, all the phosphorus-containing polymer films were tested in atomic oxygen environment ground simulation experiment for 8 hours (flux of 2.14-2.62×1020 atoms/cm2). It is found that the phosphorus-containing PI showed better resistance performance to atomic oxygen than the phosphorus-containing PAEs, and phosphorus-containing polyimide composite film showed the best AO resistant performance, whose erosion rates (Ey) less than one third of Kapton film. Especially, composite film of PPI_PI-10 express both a excellent basic performance and good enough AO resistent performance, is expected to be a candidate material applied as the surface materials of spacecraft in low earth orbit.Finally, the phosphorus-containing co-polyimide films were getting a AO exposure experiment as long as 32 hours together, to study change of the erosion rate of the polymer over time. The surface of co-polyimides were analysed by SEM, EDX and XPS to study the change of morphology and elemental composition before and after AO erosion. The mechanism of AO reaction with triphenylphosphine oxide containing PI was explained on the basis of above results, it was surmised that a layer of dense polyphosphate network was generated when the phosphorus-containing polyimide films were eroded by the attack of atomic oxygen, preventing sublayer polymer from the AO erosion.