Syntheses Of Polyhedral Oligomeric Silsesquioxanes And Their Applications In Methyl Silicone Resin

Methyl silicone resin is a class of organic/inorganic hybrid materials with highly cross-linked net-structure, which combined comprehensive properties of inorganic and organic materials. However, Methyl silicone resin has many disadvantages such as low hardness. Polyhedral oligomeric silsesquioxanes (POSS) are a special class of the oligomeric silsesquioxanes with three-dimensional structure, which are also organic/inorganic hybrid materials. POSS can be introduced into polymeric system by chemical bonding or physical blending to improve the comprehensive performances of polymeric composites.At present, there are a few literatures about POSS modified methyl silicone resin, most of which did research on the thermal stability of the modified methyl silicone resin. In this thesis, POSS were mainly introduced into Methyl silicone resin by chemical bonding. And a series of novel methyl silicone resin/POSS hybrid materials were prepared. The structure of resin/POSS hybrid materials was researched by Fourier infrared (FT-IR), Nuclear magnetic resonance (NMR), X-ray diffraction (XRD); the surface morphology of the hybrid materials was researched by scanning electron microscopy (SEM) and atomic force microscope(AFM); the properties of the hybrid materials was researched by thermal gravity analysis, contact angles (CA), pencil hardness analysis, UV-visible spectrophotometer(UV) and adhesion tester.1. Syntheses and characterization of POSSIn the thesis, octavinyl-POSS (Vinyl-POSS) and octachloropropyl-POSS (Chloropropyl-POSS) were prepared through hydrolysis-condensation reaction. Octa[(trimethoxysilyl)ethyl]-POSS(OPS) and divinyl-hexa[(trimethoxysilyl)ethyl]-POSS(DVPS) were prepared based on controlling the ratio of Vinyl-POSS and trimethoxysilane by hydrosilylation. Octa(N-propylimidazolyl)-POSS(Im-POSS) was firstly synthesized based on Chloropropyl-POSS by substitution of the functional groups. It was found by thermal gravity analysis that in nitrogen atmosphere, Vinyl-POSS possessed the property that was prone to sublimate at high temperature, resulting in low char yield.Chloropropyl-POSS melted firstly in higher temperature, then decomposed and charred, which finally resulted in a lot of residues(45.9%). Hence, they exhibited good thermal stability. The decomposition of OPS and DVPS at high temperature accompanied with microcrystalline sublimate, though it had a lot of residues(56.6%,64%), which indicated good thermal stability. The decomposition of Im-POSS at high temperature was complicated, but it also had high residues(51%), which also indicated good thermal stability.2. Syntheses and characterization of POSS/Methyl silicone resin hybrid materialsThe content of this part can be divided into two parts:(1) The properties of POSS/methyl silicone resin with different OPS adding amount;(2) The properties of silicone resin filled fumed silica sol join with OPS and DVPS separately.(1) Kinds of modified methyl silicone resin with different amount of OPS addition were prepared. The structure and properties of the cured film were studied. The results show that there were auto-reactive agglomeration among OPS during its reaction with methyl silicone resin; the decomposition or condensation of OPS cage vertices resulted in lower thermal stability compared with pure methyl silicone resin; the hardness increased from3H to7H with the increasing of OPS addition amount due to the active cross-linking points in OPS which was characterized by pencil hardness analysis; the average transmittance were above92%, higher than glass whose transmittance is91.74%, indicating that methyl silicone resins and modified methyl silicone resin possessed good transparency, and there are varying degrees of increased transmittance effect; the contact angles of silicone resin prepared in this research were all more than90°, that is, both methyl silicone resin and modified silicone resin are hydrophobic due to hydrophobic methyl group.(2) The conventional modifiers-nano-silica sol were joined with POSS to modify methyl silicone resin. Afterwards, the structure and properties of the cured film were studied. Results showed that, the hardness of methyl silicone resin increased from3H to9H. And the heat stability increased compared with those modified with pure OPS.3. The increased transmittance effect of POSS-based silicone resinFirstly, OPS/SiO2/methyl silicone resin and DVPS/SiO2/methyl silicone resin which were hybrid materials were prepared. The transmittance, surface morphology, hardness, adhesion and hydrophobic property of the films were researched. The results show that there were a large amount of-OH, Si-O-Si network structure and a few non-decomposition methyl on the film surface after heat treatment.; The surface of methyl silicone resin films were porous with a lot of uniform small particles; both methyl silicone resin and modified methyl silicone resin exhibited excellent increased transmittance effect with a maximum transmittance of97%; the transmittance of modified methyl silicone resin was slightly higher than ordinary methyl silicone resin; the film was hydrophobic with good adhesion to glass at hardness9H.Secondly, the amount of silica sol and the OPS addition was modified in order to improve the increased transmittance effect. The increased transmittance effect, molecular structure, hardness and adhesion properties of the film were also studied. The results showed that the modified methyl silicone resin films with small pores after material ratio adjustment possess loose surface; the transmittance increased to98%with the increasing of nano-silica sol; the film transmittance reached maximum (more than99%) when OPS content is10%-20%with a certain amount of nano-silica sol, the hardness of the film increased from HB to3H with the increasing of OPS; and the hardness of the film was6H when OPS content is50%.