(1) Chemical properties of NR

General Reactivity of Alkenes NR, BR, IR, SBR, NBR, CR are all diene rubbers. There are thousands of double bonds on each macromolecule, and the π bond in the double bond is essentially the same as the π bond in the double bond of the small molecule olefin. The π electron cloud is distributed above and below the atomic plane and is an electron source, which is a Lewis base. An electrophilic ion addition reaction can be carried out with an electrophile such as a halogen or a hydrohalic acid. The reaction is carried out in two steps: first forming an intermediate, a positive carbon ion; then completing the reaction. The rate of this addition reaction depends on the structure of the positive carbon ions.

(2)Natural rubber reactivity

The above several reactions are the basis for the vulcanization, aging, protection and chemical modification of NR and unsaturated rubber. The NR molecular chain has an average of one double bond per four carbon atoms. Ion or radical addition can occur, and an a-H reaction can also occur. This depends mainly on the reaction conditions. Of course, the actual vulcanization, aging and protection are quite complicated. The modification of maleimide in the presence of NR organic peroxide vulcanization, oxidation and initiator is mainly a-H reaction, and NR has three a-H positions a, b and c.

A large number of practices have shown that the vulcanization and thermal oxidation of sulfur promoters, and the electrophilic ionic addition reaction of HC1 are all NR>BR>CR. analyse as below.

There is no substituent on the double bond carbon atom, and the electron cloud density on the double bond is normal and is not polarized.

The double bond carbon atom pushes the methyl group of the electron, not only the electron cloud density on the double bond is larger than usual, the double bond is activated, and the double bond is polarized.

The double bond is connected to a relatively electron-negative chlorine atom. The electron cloud density on the double bond is smaller than usual, the double bond activity is decreased, and it is polarized.