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Mechanism of Coupling Agent

1、Monoalkoxy type

    Monoalkoxy titanates form chemical bonds at the interface between inorganic powders and matrix resins. It is generally believed that only one isopropoxy group is a hydrolytic group coupled with hydroxyl groups on the surface of inorganic substances, so a monolayer can be formed on the surface of inorganic pigments and fillers. There are no multi-molecular membranes at the interface.

    It still has the chemical structure of titanate. In the presence of excess coupling agent, the surface energy changes and the viscosity decreases greatly. Titanate molecules can be coupled in the matrix resin phase due to the trifunctional and ester transfer reactions of the coupling agent. This is convenient for the modification of titanate molecule and the selection of filling polymer system.

    This kind of titanate is suitable for filling systems with high moisture content, such as clay, talc and so on. In these systems, apart from the coupling reaction between monoalkoxy group and hydroxyl group on the surface of filler, pyrophosphate group can also be decomposed to form phosphate group, which binds a part of water.

3、Chelating type
    This kind of coupling agent is suitable for non-polar filler with high moisture content and water-containing resin system, such as wet silica, clay, talc, aluminium silicate, water treatment glass fiber, carbon black, etc. Moreover, the coupling agent has excellent hydrolysis stability in high humidity system, and shows good coupling effect in this state.

4、Coordination type
    This kind of coupling agent can avoid the side reaction of tetravalent titanate in some systems, such as transesterification reaction in polyester, reaction with hydroxyl group in epoxy resin, reaction with polyol or cyanate ester in polyurethane, etc. This kind of coupling agent is suitable for many filler systems and has good coupling effect. Its coupling mechanism is similar to that of monoalkoxy type.