Poly(isobutylene) has the chemical properties of saturated hydrocarbon compounds, and the side chain methyl groups are tightly and symmetrically distributed. It is a polymer with unique properties. The aggregation state and properties of polyisobutylene depend on its molecular weight and molecular weight distribution. When the viscosity-average molecular weight is in the range of 70,000-90,000, polyisobutylene undergoes a transition from a volatile liquid to an elastic solid. Generally, according to the molecular weight of PIB, it is divided into the following series: low molecular weight polyisobutylene (number average molecular weight = 200-10,000); medium molecular weight polyisobutylene (number average molecular weight = 20,000-45,000); high molecular weight polyisobutylene (number average molecular weight = 75,000-600,000); ultra-high molecular weight polyisobutylene (number average molecular weight greater than 760,000).
Air tightness
One of the outstanding features of PIB is its excellent air tightness. Due to the presence of two substituted methyl groups, the molecular chain moves slowly and the free volume is small. As a result, low diffusion coefficient and gas permeability are produced.
Solubility
PIB is soluble in aliphatic hydrocarbons, aromatic hydrocarbons, gasoline, cycloalkanes, mineral oils, chlorinated hydrocarbons, and carbon monosulfide; it is partially soluble in higher alcohols and phenols, or swells in solvents such as alcohols, ethers, esters, ketones, and animal and vegetable oils, and the degree of swelling increases with the increase of the solvent carbon chain length; it is insoluble in lower alcohols (such as methanol, ethanol, isopropanol, ethylene glycol, and co-glycol), ketones (such as acetone, methyl ethyl ketone), and glacial acetic acid.
Chemical resistance
PIB is resistant to acids and alkalis. Such as ammonia water, hydrochloric acid, 60% hydrofluoric acid, lead acetate aqueous solution, 85% phosphoric acid, 40% sodium hydroxide, saturated salt water, 800} sulfuric acid, 38% sulfuric acid + 14% nitric acid, but cannot resist strong oxidants, hot weak oxidants (such as 60% potassium permanganate), some hot concentrated organic acids (such as 373K acetic acid) and halogens (fluorine, chlorine, bromine).
