The properties of cyanoalkyl groups are first manifested in the thermal stability of polymers. If the methyl group is replaced by an ethyl group or a propyl group in the dimethylpolysiloxane, the thermal stability drops drastically. If the cyano group is added to the carbon atom, the thermal stability will drop even more. And if the CN-group is in the β- or γ-position, the thermal stability will be significantly increased. Therefore, the γ-cyanopropyl group-containing co-case has good thermal stability like dimethylpolysiloxane. Increasing the number of -CH2 groups between nitrile groups and silicon atoms will further reduce the effect of CN-groups on polymer properties.
The content of cyanoalkylsiloxane or the concentration of nitrile groups in the copolymer can adjust two properties: solvent resistance and cold resistance. As the nitrile content increases, the swelling resistance of the rubber in the solvent increases. When the CN-group concentration is greater than 20%, the swelling rate of the rubber armpit is less than that of the best dimethylpolysiloxane; and when the CN-group concentration is greater than 359, its swelling index is the same as that of the most solvent-resistant organic Rubber is the same.
The regularity of the rubber structure is destroyed when the alkyl group is introduced, which greatly reduces the brittleness temperature and improves the cold resistance. However, when the content of CN-group continues to increase, the intermolecular interaction increases, and the flexibility of the chain is limited due to the influence of the strong polar group CN, which increases the brittle temperature. However, even in the case of a relatively high content of CN-groups, the brittleness temperature is still lower than that of dimethylpolysiloxane. The nitrile silicone rubber containing 65% cyanopropyl methylsiloxane has a brittleness temperature of -95°C, while the nitrile rubber with the same oil resistance has a brittleness temperature of not lower than -30°C. On the other hand, if the nitrile silicone rubber is compared with the cold-resistant phenyl silicone rubber, it can be seen that when the cold resistance is equal, the stability of the phenyl silicone rubber against hydrocarbon solvents is much lower than that of the CN-containing In this way, in the manufacture of nitrile silicone rubber, by adjusting the type and amount of raw materials and the conditions of the polycondensation reaction, copolymers containing different types, different contents and different proportions of cyanoalkyl groups can be obtained. Copolymers with very different properties