Both the main chain and side chains (or side groups) of silicone rubber can be modified through chemical reactions. Generally, silicone rubber is prone to main chain breakage and side group oxidation reactions at high temperatures, which reduces performance. Therefore, modifying the main chain, side chain (or side group) structure of silicone rubber is an effective way to improve its performance. .

1.1 Chemical reaction modification

1.1.1 Main chain modification

The introduction of aromatic structures or other large steric hindrance groups in the main chain of silicone rubber can significantly improve its heat resistance. Introducing phenylene, phenylene ether, cyclodisilazyl, carbadecyl and cage icosahedral carbodecyl into the main chain of silicone rubber, huge steric hindrance can be achieved. The effective shielding of adjacent groups improves the stability of adjacent groups, effectively suppresses the occurrence of cyclization degradation reactions, and further improves the heat resistance of silicone rubber. The card decaborane modified silicone sealant can be used for a long time below 400 ℃.

Silicone rubber and aminopropyltriethoxysilane (APTES) introduce amino groups into the molecular backbone through copolymerization, which can greatly improve the surface energy and adhesion of silicone rubber, and the added carbon black can further improve the adhesion. . Based on functionalized polyorganosiloxane, it is reacted with styrene (St), acrylic acid (AA), methyl methacrylate (MMA) and butyl acrylate (BA), etc. under the initiation of potassium persulfate (KPS). The copolymerization to obtain the main chain modified polyorganosiloxane can effectively improve the adhesive performance of silicone rubber.

Modification of the main chain of the silicone rubber can also be performed by a block copolymerization method. The preparation of polysiloxane and PU (polyurethane) and PS (polystyrene) multiblock copolymers has been extensively studied. Through the esterification polycondensation reaction between low Mr (relative molecular mass) prepolymers, modified silicone rubber block copolymers with controllable segment lengths can be obtained. A series of nylon 6-b-polysiloxane (PA6-b-PDMS) multi-block copolymers with different structures can also be obtained by two extremely incompatible systems of nylon 6 and silicone rubber. It can be used as a compatibilizer to modify PA6 / silicone rubber blending system, which can greatly improve the performance of the blend.

Liu Yufeng et al. Used polycondensation to introduce polysilsesquioxane (POSS) into the polysiloxane molecular chain, so that POSS is evenly dispersed in the silicone rubber at the molecular level. The introduction of POSS increases the rigidity of the polysiloxane molecular chain and hinders the entanglement and slip orientation of the molecular chain, thereby effectively improving the elastic modulus and thermal stability of the copolymer.

1.1.2 Side chain (or side group) modification

The chemical modification of the side chain (or side group) structure effectively improves the thermal stability of the silicone rubber. The heat resistance and oxygen stability of different pendant silicone rubbers are not the same. Usually it is phenyl silicone rubber> methyl silicone rubber> ethyl silicone rubber> propyl silicone rubber. Tang Bin et al. Discussed the heat resistance of different side group structures (such as dimethyl, methylphenyl, dimethyldiphenyl, and methyltrifluoropropyl) to RTV (room temperature vulcanization) silicone foaming sealants. It is found that the heat resistance of the methyl group on the side group is better than that of trifluoropropyl group.

He Yeming and others examined different end-capping agents [such as tetramethoxysilane (TMOS), methyltrimethoxysilane (MTMS), methyltriethoxysilane (MTES), vinyltrimethoxysilane (VTMO), and Effects of vinyl triethoxysilane (VTEO) on the properties of silicone rubber matrix. Studies have shown that: TMOS and VTMO have a better capping effect on the 107 glue, which is characterized by excellent heat resistance.

After being catalyzed by Me4NOH (tetramethylammonium hydroxide), methyl phenyl vinyl silicone rubber is prepared. After introducing white carbon black and iron tin oxide as a reinforcing agent and a heat-resistant agent, a heat-resistant type can be obtained. Silicone Rubber. Compared with methyl vinyl silicone rubber, the introduction of phenyl into the molecular side chain destroys the regularity of the molecular structure of dimethylsiloxane, thereby reducing the crystallization temperature and glass transition temperature (Tg) of the silicone rubber. Furthermore, the high and low temperature application range of the material is expanded.

Araki et al. Used alkoxysilane compounds and their partially hydrolyzed polycondensates as cross-linking agents and organic titanium compounds as catalysts, and introduced alkane chains containing 1 to 10 carbon atoms in the main chain and side groups of the polyorganosiloxane. , To obtain a building sealant with good storage stability.

Sakamoto et al introduced groups such as alkane chain, —S— and —NH— into the main chain of polysiloxane, and introduced alkane containing 1 to 12 carbon atoms into the side chain. The properties and moisture resistance are significantly improved, and the cured adhesive can still maintain excellent physical properties after 180 days of storage.