Study Of Crystalline Polysilsesquioxanes

Over the last decade,the preparation of organic-inorganic hybrid materials from polyhedral oligomeric silsesquioxane(POSS) has attracted much attention.Owing to their excellent properties,POSS will be widely used in aeronautics,space,electronics, optics,medicine and material fields in the future.However,the synthetic routes and starting materials of POSS are limited,the reaction time is long and the yields are unsatisfactory.Moreover,the crystalline properties of POSS are not deeply investigated.All these need to be improved to promote the further study of POSS.So, it is very necessary to carefully study the synthetic routes and crystalline properties of POSS.In this thesis,four kinds of crystalline polysilsesquioxanes were prepared by acid-catalyzed hydrolytic condensation of low concentration functional triethoxysilanes without organic solvent.The reactions are mild and need no organic solvent.The crystalline properties of the products were investigated using TEM, electron diffraction,XRD.The thermal stability of the products was characterized by TGA.The main results obtained are described as follows:1.Crystalline poly(n-propylsilsesquioxane) was prepared by acid-catalyzed hydrolytic condensation of low concentration n-propyltriethoxysilane.The Influence of reaction time,monomer concentration and catalyst on the morphology of the product was studied.The triangular crystalline lamellae were easily formed when monomer concentration was low.Increasing monomer concentration went against the formation of them.The ammonia-catalysed product was short rods with poor crystallinity.The diffraction spots arranged regularly on a hexagonal array,which indicated the crystal system might be hexagonal and the product might be (n-C₃H₇SiO_1.5)₈.XRD showed that a little crystal existed in the product when monomer concentration was low.2.Crystalline poly(γ-chloropropylsilsesquioxane) was prepared by acid-catalyzed hydrolytic condensation of low concentration γ-chloropropyltriethoxysilane.The Influence of reaction time,monomer concentration and catalyst on the morphology of the product was studied.The triangular crystalline lamellae were observed when monomer concentration was low and they had clear edges of 0.2μm.Increasing monomer concentration went against the formation of them.The ammonia-catalysed product was amorphous spherelike grains.The diffraction spots arranged regularly on a hexagonal array,which indicated the crystal system might be hexagonal and the product might be(γ-ClC₃H₆SiO_1.5)₈.XRD showed that the product were amorphous on the whole.3.Crystalline poly(γ-aminopropylsilsesquioxane) hydrochloride salt was prepared by acid-catalyzed hydrolytic condensation of low concentrationγ-aminopropyltriethoxysilane.The Influence of reaction time,monomer concentration and catalyst on the morphology of the product was studied.The crystalline products were short rods,hemicycle lamellae and so on.The ammonia-catalysed product was amorphous.The diffraction spots arranged regularly on a hexagonal array,which indicated the crystal system might be hexagonal and the product might be (γ-ClNH₃C₃H₆SiO_1.5)₈.XRD showed that little crystalline matter existed in the product.4.Crystalline poly(methylsilsesquioxane) was prepared by acid-catalyzed hydrolytic condensation of low concentration methyltriethoxysilane.The Influence of reaction time,monomer concentration and catalyst on the morphology of the product was studied.The crystalline products were spherelike grains,short rods and so on. Increasing monomer concentration went against the formation of crystalline product. The ammonia-catalysed product was crystalline.There were two sets of diffraction spots arranging regularly on a hexagonal array,which indicated the possibility of hexagonal crystal system and there minght be(CH₃SiO_1.5)₈ in the product.XRD showed that little crystalline matter existed in the product.5.TGA indicated that poly(methylsilsesquioxane),poly(n-propylsilsesquioxane), poly(γ-chloropropylsilsesquioxane) and poly(γ-aminopropylsilsesquioxane) hydrochloride salt exhibited two-step decomposition in the range of room temperature to 800℃.The thermal stability of poly(n-propylsilsesquioxane), poly(γ-chloropropylsilsesquioxane),and poly(γ-aminopropylsilsesquioxane) hydrochloride salt fell gradually.