Explanation

The network macromolecule formed by chemical bond connection between macromolecule chains is also called network polymer or three-dimensional polymer. thermosetting resin (such as phenolic, epoxy, unsaturated polyester, etc.) and vulcanization rubber belong to crosslinked polymer. Generally, crosslinked polymer are insoluble and non melting, and they have excellent dimensional stability. For example, vulcanization is the process of forming sulfur bridges in natural rubber. After vulcanization, the molecular chains cannot slide, thus giving rubber the reversible elastic deformation ability. polyethylene can be crosslinking by radiation or chemical methods. After crosslinking, polyethylene's bating point and strength are significantly improved, so it can be used in the manufacturing of electrical connectors, cables and wire insulation sleeves. The degree of crosslinking of macromolecule materials will affect its performance. rubber with low degree of crosslinking (sulfur content less than 5%) usually has good elasticity, while rubber with high degree of crosslinking (sulfur content 20% -30%) has poor elasticity. With the increase of degree of crosslinking, the mechanical strength and hardness of materials will also increase, and eventually lose elasticity. The degree of crosslinking can usually be expressed by the average molecular weight of the chain between two adjacent crosslinking points. The higher the degree of crosslinking, the lower the corresponding average molecular weight. Another representation is the crosslinking point density, which represents the percentage of crosslinking structural units in the total structural units, that is, the probability of crosslinking of each structural unit. The degree of crosslinking of materials can be estimated by measuring the swelling degree and mechanical properties.

Classification