Why liquid silicone can be widely used in various fields?

1.Introduction of liquid silicone rubber with addition molding

liquid silicone rubber with addition molding is composed of vinyl polysiloxane as the basic polymer, polysiloxane with Si-H bond as the cross linking agent, in the presence of platinum catalyst, at room temperature or heating under the cross linking vulcanization of a class of silicone materials. Different from condensed liquid silicone rubber, molding liquid silicone vulcanization process does not produce by-products, small shrinkage, deep vulcanization and no corrosion of the contact material. It has the advantages of wide temperature range, excellent chemical resistance and weather resistance, and can easily adhere to various surfaces. Therefore, compared with the condensed liquid silicone, the development of liquid silicone molding is faster. At present, it has been more and more widely used in electronic appliances, machinery, construction, medical, automobile and other fields.

2.Main Components

Base Polymer

The following two linear polysiloxane containing vinyl are used as base polymers for the addition of liquid silicone. Their molecular weight distribution is wide, generally from thousands to 100,000-200,000. The most commonly used base polymer for additive liquid silicone is α,ω -divinylpolydimethylsiloxane. It was found that the molecular weight and vinyl content of basic polymers could change the properties of liquid silicone.

cross-linking agent

The crosslinking agent used for adding molding liquid silicone is the organic polysiloxane containing more than 3 Si-H bonds in the molecule, such as linear methyl-hydropolysiloxane containing Si-H group, ring methyl-hydropolysiloxane and MQ resin containing Si-H group. The most commonly used are linear methylhydropolysiloxane of the following structure. It is found that the mechanical properties of silica gel can be changed by changing the hydrogen content or structure of cross linking agent. It found that the hydrogen content of the crosslinking agent is proportional to the tensile strength and hardness of silica gel. Gu Zhuojiang et al. obtained hydrogen-containing silicone oil with different structure, different molecular weight and different hydrogen content by changing the synthesis process and formula, and used it as crosslinking agent to synthesize and add liquid silicone.

catalyzer

In order to improve the catalytic efficiency of catalysts, platinum-vinyl siloxane complexes, platinum-alkyne complexes and nitrogen-modified platinum complexes were prepared. In addition to the type of catalyst, the amount of liquid silicone products will also affect the performance. It found that increasing the concentration of platinum catalyst can promote the cross-linking reaction between methyl groups and inhibit the decomposition of the main chain.

As mentioned above, the vulcanization mechanism of the traditional additive liquid silicone is the hydrosilylation reaction between the base polymer containing vinyl and the polymer containing hydrosilylation bond. The traditional liquid silicone additive molding usually requires rigid mold to manufacture the final product, but this traditional manufacturing technology has the disadvantages of high cost, long time, and so on. Products often do not apply to electronic products. The researchers found that a series of silicas with superior properties can be prepared by novel curing techniques using mercaptan – double bond addition liquid silicas. Its excellent mechanical properties, thermal stability and light transmittance can make it applied in more new fields. Based on the mercapto-ene bond reaction between branched mercaptan functionalized polysiloxane and vinyl terminated polysiloxane with different molecular weight, silicone elastomers with adjustable hardness and mechanical properties were prepared. Printed elastomers show high printing resolution and excellent mechanical properties. The elongation at break of silicone elastomers can reach 1400%, which is much higher than reported UV curing elastomers and even higher than the most stretchable thermal curing silicone elastomers. Then ultra-stretchable silicone elastomers were applied to hydrogels doped with carbon nanotubes to prepare stretchable electronic devices. Printable and processable silicone has broad application prospects in soft robots, flexible actuators, medical implants and other fields.