Nanocomposites of a Silicon-containing Arylacetylene Resin with Octakis(dimethylsiloxy)octasilsesquoixane

Nanocomposites（PMSEPE/Q8M8^H） were prepared via solution blending of octakis（dimethylsiloxy）octasilsesquoixane（Q8M8^H） into poly（dimethylsilyleneethynylenephenyleneethynyle ne）（PMSEPE）. PMSEPE/Q8M8^H nanocomposites were characterized by Fourier transform infrared（FT-IR） spectroscopy, rheological measurement, differential scanning calorimetry（DSC）, scanning electron microscopy（SEM） and thermal gravimetric analysis（TGA）. The experimental results show that the hydrosilylation reaction in PMSEPE/Q8M8^H nanocomposites occurs slowly exceeding 180 ℃. PMSEPE/Q8M8^H nanocomposites can be cured at temperatures less than 260 ℃ and the cube structure of Q8M8^H keeps stable during the curing process. POSS domains are evenly dispersed in the cured nanocomposite. However, serious aggregation of POSS occurs at 15% Q8M8^H content. The thermal and thermooxidative stabilities of PMSEPE/Q8M8^H nanocomposites obviously depend on the content of Q8M8^H. The incorporation of Q8M8^H can effectively enhance the thermal and thermooxidative stabilities of cured PMSEPE. PMSEPE/Q8M8^H nanocomposites can be the candidates for applications in high temperature environment.

Preparation and Characterization of Cyano-Silicon-Containing Arylacetylene Resins and Their Composites:Dual Enhancement Strategy Involving Physical Interfacial Interactions and Chemical Crosslinking

Silicon-containing arylacetylene (PSA) resins have broad application prospects because of their excellent heat resistance.However,improving their mechanical properties and interfacial bonding with reinforcement fibers while maintaining heat resistance is a challenge in engineering applications.Here,poly(diethynylbenzene-methylsilyl-3-benzonitrile)(DEB-CN) and poly(diethynylbenzene-methylsilyl-3,6-diethynylcarbazole-3-benzonitrile)(DEC-CN) were synthesized via an isopropylmagnesium chloride lithium-chloride complex (i-PrMgCl·LiCl),overcoming the compatibility problem between cyano groups and Grignard reagents.The cyano and alkyne groups in the resin underwent cyclization to form pyridine,catalyzed by the-NH-moiety in DEC-CN,resulting in extremely high thermal stability (5%weight loss temperature:669.3°C,glass transition temperature>650°C).The combination of cyano dipole-dipole pairing and hydrogen bonding greatly enhanced the resin-fiber interface properties,while the generated pyridine promoted stress relief in the crosslinked network,substantially improving the mechanical properties of the cyano-silicon-containing arylacetylene resin composites.The flexural strength of quartz fiber cloth/DEC-CN composites was 298.2 MPa at room temperature and 145.9 MPa at 500°C,corresponding to 84.0%and 127.6%enhancements,respectively,over the cyano-free counterpart.These cyano-silicon-containing arylacetylene resins exhibited a dual reinforcement mechanism involving physical interfacial interactions and chemical crosslinking,achieving a good balance between thermal stability and mechanical properties.

CHARACTERIZATION OF A MODIFIED SILICON-CONTAINING ARYLACETYLENE RESIN WITH POSS FUNCTIONALITY

A modified silicon-containing arylacetylene resin with a well-defined organic-inorganic POSS functionality was successfully synthesized by Huisgen azide-alkyne 1,3-dipolar cycloaddition. The POSS hybridized resin exhibits excellent thermal properties which were characterized by differential scanning calorimetry （DSC） and thermogravimetric analyses （TGA）. Scanning electron microscope （SEM） was used to characterize fracture surface of the hybridized polymer. The results show that phase separation occurs. The POSS moieties are aggregated each other in the polymer to form 200-400 nm domains.

SYNTHESIS AND CHARACTERIZATION OF POLY[(METHYLSILYLENE ETHYNYLENEPHENYLENEETHYNYLENE)-CO-(DIMETHYLSILYLENE ETHYNYLENEPHENYLENEETHYNYLENE)]S

A series of poly[（methylsilylene ethynylenephenyleneethynylene）-co-（dimethylsilylene ethynylenephenyleneethynylene）]s were synthesized by the incorporation of various ratios of methylsilylene to dimethylsilylene units into the polymer chain backbone. The resultant copolymers were soluble in a variety of common organic solvents at room temperature. The copolymers were characterized by FT-IR, ^1H-NMR, GPC, rheological analysis, differential scanning calorimetry （DSC） and thermogravimetric analysis （TGA）. The results showed that the copolymers exhibited good processability and cured at low temperatures like 200℃. The curing reactions involved in hydrosilylation of Si-H and alkyne groups and the polymerization of alkynes. Td5 （5% weight loss） of the cured copolymers ranged from 629℃ to 686℃, and the decomposition residues of cured copolymers at 1000℃ ranged from 88.1% to 90.9% under nitrogen. Thermal stability of the copolymers increased with the introduction of methylsilylene traits into polymer chains. The cured copolymers were sintered at 1450℃, and the results of X-ray diffraction analysis showed that β-SIC was formed in the sintered products.

Investigation on poly[(methylsilylene ethynylene phenylene ethynylene)-co-(tetramethyldisiloxane ethynylene phenylene ethynylene)]

Poly[(methylsilylene ethynylene phenylene ethynylene)-co-(tetramethyldisiloxane ethynylene phenylene ethynylene)]was synthesized by polycondensation reaction of m-diethynylbenzene magnesium reagent with 1,3-dichlorotetramethyldisiloxane and dichloromethylsilane.The copolymer was characterized by FT-IR,~1H NMR,differential scanning calorimetry and thermogravimetric analysis.The results show that the copolymer exhibits good processability and cures at low temperatures.The cured copolymer shows high thermal stability.