Briefly describe the three principles of crosslinking agents changing polymer properties

Crosslinking technology and its applications actually originated from human primitive inventions. In ancient times, clay was added with water to make ceramics, gelatin was added with water to make sweet Dim sum, leather was softened with whale oil, asphalt was used as floor covering material, nitrocellulose was added with tar as roof material, etc. Water, whale oil, tar, etc. in the above products played a plasticizing role, and they were called cross-linking agents in the above products respectively. Crosslinking agents can alter the properties of polymers, and it is generally believed that:

1. Crosslinking agents isolate the distance between polymer macromolecules, weakening the intermolecular forces between polymer molecules, i.e. weakening the van der Waals forces between resin molecules;

2. The addition of non-polar crosslinking agents to non-polar polymers blocks the polar portions between polymer molecules, preventing polar connections and disrupting dipole dipole interactions between polymer molecules;
3. Crosslinking agents are used to bond with resins through dipole forces, rather than chemical forces.

Therefore, any substance that can be uniformly mixed with resin, does not undergo chemical reactions during mixing, can change certain properties of the resin after mixing, can be retained in plastic products for a long time, and can change the properties of plastic products can be used as a crosslinking agent. Substances with these functions are mostly liquid organic compounds or low melting point solids. They must have polarity, be compatible with the resin, stay in the resin for a long time, have good performance, high efficiency, and low cost for the resin.