Structure Design And Performance Study Of Heat-Resistant Polymers Containing Carborane

Icosahedral carboranes,carbon-containing polyhedral boron-cluster compound(C2B10H12),have special thermal stability,high chemical resistance and excellent electrochemical property.Polymers containing the carborane unit within the backbone exhibit appreciable enhancement in their solubility,oxidative stability,char yield at high temperature,and ceramic yield.In order to improve the thermal-oxidative stability of common high performance polymers,here several carborane-containing polymers and thermosetting resins were prepared from these carborane-containing monomers and compounds.The application of these polymers and monomers in thermosetting resins,oxidation protection system,and ceramic precursor was explored in this work.The main contents of this work are listed as follows:A novel carborane-containing acetylenic monomer with trimethylsilylethynyl as crosslinking group was synthesized.Thermosetting mechanism of CBTMS confirmed by FT-IR was Diels-Alder reaction between the Ph-C=C group and the C?C group.Non-isothermal DSC tests were conducted and the activation energy of the curing reaction of CBTMS was calculated through Kissinger's and Ozawa's methods.The excellent thermal stability of thermoset derived from CBTMS was confirmed by TGA,which was attributed to the incorporation of inorganic elements,boron and silicon.High thermo-oxidative stable ceramic was obtained by heat treatment of thermosetting resin derived from CBTMS at 1000? in air.In order to improve the thermal and thermo-oxidative stability of the polyimide materials,one novel acetylenic monomer(APCB)containing carborane with highly thermal and thermo-oxidative stability was synthesized and used as the thermal copolymerization component with acetylene-terminated imide monomer(m-EFDA).The processability of the acetylene-terminated imide monomer was significantly improved by the addition of APCB.According to DMA analysis,the cured sample showed a higher Tg with the increase content of APCB.Based on TGA tests,the blends with more content of APCB showed a better thermal and thermo-oxidative stability.Additionally,APCB-50 and APCB-100 exhibited excellent thermo-oxidative aging stability confirmed by oxidative aging study.Carborane-containing polyarylether ketone(PCBEK)was prepared and PCBEK exhibits high thermo-oxidative and thermal stability.A series of polymer coatings with PCBEK and APCB were successfully utilized to construct effective oxidation protection coatings for carbon fibers by solution coating,drying,and curing.According to TGA tests,carbon fiber sample with polymer coating exhibited a better oxidation resistance.The good oxidation resistance of the coating mainly relied on the production of boron oxide protective layer from oxidation of the carborane groups,which was confirmed by XRD,FT-IR and XPS.Furthermore,CB4/C ceramic coatings could be easily prepared via heating treatment of polymer-based coatings under argon at 1300? for 2 h.The carbon fiber sample with ceramic coating exhibited high thermo-oxidative stability.Under the optimized polymerization condition,a poly(phenylene-carborane)(PPB)with moderate number-average molecular weight was successfully synthesized.Based XRD test,the crystalline character of PPB prevented the further increase of molecular weight of PPB during the polymerization.According to DSC test,the glass transition temperature and melting point of PPB were all above its decomposition temperature(450?).Based on TGA test,PPB exhibited excellent thermal and thermo-oxidative stability.PPB has proven to be excellent sing-source precursor to boron-carbide/carbon ceramic materials with a ceramic yield>90%.Boron carbide as well as graphite crystals in the ceramics were confirmed by TEM,XRD,and Raman analysis.