Synthesis Of Phenyl POSS And Thermal Properties Of Its Modified Membranes

Cage-type phenyl POSS has a rigid aromatic hydrocarbon structure,making its corresponding material system with excellent heat resistance,flame retardant and mechanical properties.The composite material formed by the phenyl POSS modified silicone resin has a very broad application prospect.However,there are still some scientific problems to be solved in the preparation of phenyl POSS with high degree of polymerization and high purity,such as long reaction cycle and low yield.At the same time,in the aerospace applications,the doping of phenyl POSS-modified silicone resins and the further improvement of the heat resistance of the resulting composite films still need to be explored.In this paper,the effects of different catalysts（alkali,F-,mixed catalysts）and different solvents（ethanol,toluene,dichloromethane）on the synthesis of phenyl POSS were studied.Finally,a multi-step hydrolysis synthesis method for the synthesis of high polyphenyl POSS was summarized,in which F ion was used as a catalyst.The ethanol used in the first step of hydrolysis and the dichloromethane used in the second step of hydrolysis can be used to synthesize cage-type phenyl POSS with higher degree of polymerization and higher purity.When the phenyl POSS modified silicone resin is formed into a composite material,physical film doping is poor due to physical doping,so that the organic silicon resin is modified using a chemical doping method.The cage-type phenyl POSS structure whose reaction mechanism was incompletely polymerized was analyzed by mass spectrometry and XPS to modify the silicone resin by dehydration condensation of Si-OH.Comparing TBAF and acid-catalyzed different types of silicone resins,the optimal results of the acid-catalyzed phenyl POSS/amino silicone composites were summarized based on their film forming effect and TG-DSC analysis of heat resistance.The heat resistance of the composite film is 200°C higher than the ther mal decomposition temperature of a single silicone and can be cured at room temperature.The composite film layer was modified by using low-temperature glaze and adding two high emission components of MoSi₂ and CoO₂.The composite film that promotes the formation of Phenyl POSS/Silicone composites on the surface of thermal insulation tiles can be applied to aerospace vehicle thermal protection systems.Before applying the coating on the substrate,the heat-insulating tile needs to be coated with a transition layer.Through SEM analysis,the use of the transition layer not only improves the loose porous structure of the heat-insulating tile surface.Moreover,due to its permeation to the substrate,the binding force between the substrate and the composite material can be increased,and the film layer and the substrate can be more closely combined.The transition layer used in this experiment is a POSS60:POSS50mass ratio of 2:1.The low-temperature glaze and high emission component modified Phenyl POSS/Silicone resin were analyzed by XRD,SEM,thermal shock resistance,TG,macroscopic morphology of the coating,and firing mechanism.The optimum firing temperature for the composite film is 1000°C.The optimum ratio of low-temperature glaze,high-emission component and composite material is low-temperature glaze:the mass ratio of composite material is 3:1,and the high-emission component Mo Si₂ and CoO₂ each account for 1%of the coating mass fraction.The composite coating formed on the surface of the heat-insulating tile has good heat resistance and can withstand high temperatures above 1000°C.The emissivity reaches 0.9,which is 0.4 more than the average emissivity of the original coating.