Polyisobutylene is a typical saturated linear polymer. The main body of the molecular chain does not contain double bonds, there are no long side chains, no asymmetric carbon atoms, and the structural units are connected by a regular sequence from beginning to end.
In its undeformed state, polyisobutene is an amorphous polymer. At room temperature, high molecular weight polyisobutene chains crystallize during stretching, and in the crystalline region, every 8 structures repeat to form a helical chain structure. Due to the spatial interlocking of the two methyl groups on the alternating carbon atoms of the polymer chain, the polymer chain does not exhibit a planar sawtooth model, and the bond angle of the carbon in - CH2- increases significantly, transforming from 109.5 ° in tetrahedral form to 123 °, resulting in the aforementioned helical chain structure.
According to the raw materials used in polymerization, polymers made from pure isobutene (≥ 99%) are called polyisobutene, while polymers made from mixed light C4 fractions containing isobutene, other olefins (1-butene, cis-2-butene, and anti-2-butene), and alkanes (n-butane, isobutane) are commonly known as polybutene due to the presence of a small amount of n-butene (≤ 5%) structural units embedded in their polyisobutene polymer chains. The structure and properties of commercial polybutene and polyisobutene with the same molecular weight are basically the same.
Due to chain transfer reactions and chain termination reactions, polyisobutene chains typically contain unsaturated double bonds at their ends. According to the chemical structure of the terminal double bond, polyisobutene can be divided into ordinary polyisobutene and reactive polyisobutene. The terminal alpha olefin content of ordinary polyisobutene is less than 15%, and the other structures are mainly beta olefins and internal olefins; Reactive polyisobutene refers to polyisobutene with a terminal alpha olefin structure content of over 70%. Commercially available reactive polyisobutene typically has an alpha olefin structure content of over 80%.
