Design, Preparation And Application Of Novel Carborane-based Thermosets With High Performance

With the rapid development of aerospace industry, higher requirements are put forward for the high-performance polymers. These high-performance polymers should have excellent integrated properties, such as good processing characteristics, high mechanical strength, high thermal stability, high thermal conductivity, high electric insulating strength, excellent dielectric properties and low thermal expansion coefficient etc, thus make it impossible for one type of material to meet these harsh requirements. Since last decades, inorganic/organic hybrids have attracted great attentions worldwide because they combine the advantages of both inorganic and organic phases, and show some new unique properties which are not possessed by either inorganic or organic phase. Polybenzoxazine resins, benzocyclobutene resins, cyanate ester resins and epoxy resins are some representative sorts of high-performance thermosetting resins, and are considered to be the most promising resins for fabricating high-performance polymer matrix composites. Unfortunately, some performances of these resins still need to be improved to meet the harsh requirements of the increasing development of aerospace industry. Therefore, it is a great importance in both theory and application to develop novel high-performance thermosetting resins.Inorganic/organic hybrids have combined the advantages of both inorganic and organic phases, which provide an effective route for developing new materials. Among them, the icosahedral carboranes have attracted great interest owing to their unique structure and properties. Carborane-based polymers have been prepared as advanced materials with unique thermostabilities, which have potential applications in the researches of advanced matrix resins, ceramic precursors, oxidation resistance coatings and neutron-absorbing materials. Unfortunately, the synthetic routes of carborane-based polymers are relatively complicated, which restrict the development and application of carborane-based polymers. In order to overcome the drawbacks of present thermosetting resins and meet the requirements of high-performance for aerospace materials, this dissertation focuses on the study of novel carborane-based thermosets through simple synthetic process with high yield, mainly including three aspects as follows:.(1) By means of molecular design, diazidomethyl m-carborane was synthesized from m-carborane molecule followed by hydroxymethylation, esterification and nucleophilic substitution. Diacetylene bisbenzoxazine was prepared by Mannich reaction of paraformaldehyde, propargylamine and bisphenol A. We demonstrated that benzoxazine with m-carborane moieties in the main-chain could be prepared by click reaction. Meanwhlie, the traditional polybenzoxazine precursor was also prepared through click reaction of diazidomethyl p-benzene and diacetylene bisbenzoxazine as a control. The benzoxazine groups were shown to undergo thermally activated ring-opening reaction and form crosslinked networks. The cured carborane-based polybenzoxazine showed high Tg and excellent thermo-oxidative stability. The results demonstrate great promise for carborane-based polybenzoxazines as a new generation of space-survivable materials.(2) By means of molecular design, bis(hydroxydimethylsilyl)-m-carborane was prepared by chemical modification of m-carborane, and then reacted with chlorodimethylsilane in the presence of excessive triethylamine to obtain bis(hydriodimethylsilyl)-m-carborane, and benzocyclobutene compound with vinyl group was synthesized through the cross coupling reaction of benzocyclobutene functional Grignard reagent and vinyldimethylchlorosilane with higher yield. Dibenzocyclobutene-functional m-carborane was synthesized in the first place by one-step hydrosilylation reaction. The benzocyclobutene groups were shown to undergo thermally activated ring-opening reaction and form crosslinked networks. The cured carborane-based benzocyclobutene resin was of high thermal stability. Due to a combination of high thermal stability and boron-riched structure, the as-prepared resin has potential application in future neutron shielding fields such as aerospace and nuclear power station. The cured carborane-based benzocyclobutene resin with shape memory property could be further fabricated into space-efficient neutron shielding garments which are lightweight and have a small packing volume.(3) By means of molecular design, bis(hydriodimethylsilyl)-m-carborane was prepared on a large scale, which was then reacted with eugenol and allyl glycidyl ether by hydrosilylation to obtain phenolic functional m-carborane and epoxy functional m-carborane with high yield. Cyanate ester functional m-carborane was synthesized by a cyanogen halide-phenol method with phenolic hydroxy functional m-carborane and cyanogen bromide as materials. These precursors are promising for preparing high-performance thermosets.