Aliphatic polyolefins polyisobutylene

The principal polyolefins are low-density polyethylene (ldpe), high-density polyethylene (hope), linear low-density polyethylene (lldpe), polypropylene (PP), polyisobutylene (PIB), poly-1-butene (PB), copolymers of ethylene and propylene (EP), and proprietary copolymers of ethylene and alpha olefins. Since all these polymers are aliphatic hydrocarbons, the amorphous polymers are soluble in aliphatic hydrocarbon solvents with similar solubility parameters. Like other alkanes, they are resistant to attack by most ionic and most polar chemicals their usual reactions are limited to combustion, chemical oxidation, chlorination, nitration, and free-radical reactions. 

The abovementioned materials can be mixed with one another. A series of other polymers and resins can also be added if the substances listed in 1 to 4 form the bulk of the material. Additional materials are PE, PP, low molecular weight polyolefins, polyterpenes (mixtures of aliphatic and cycloaliphatic hydrocarbons produced by polymerisation of terpene hydrocarbons), polyisobutylene, butyl rubber, dammar gum, glycerine and pentaerythritol esters of rosin acid and their hydration products, polyolefin resins, hydrated polycyclopentadiene resin (substance mixtures manufactured by thermal polymerization of a mixture mainly composed of di-cyclopentadiene with methylcyclopentadiene, isoprene and piperylene which is then hydrogenated). 

Polyisobutylene consists of saturated hydrocarbons, so that PIB exhibits a chemical resistance similar to that of other polyolefins because of its non-polar character. It has excellent resistance to water, aqueous solutions of inorganic salts and alkalis and acids unless they are also oxidants. Due to its non-polar character, polyisobutylene dissolves at room temperature in aliphatic, aromatic, and chlorinated hydrocarbons. Polyisobutylene is degraded by halogens and strong oxidants [32]. Table A.7 (Appendix) compiles the chemicals resistance of PIB. 

The solubility of crystalline polymers is rather less than for amorphous polymers. Polyethylene and isotactic polypropylene have much less miscibility in potential solvents than that exhibited by amorphous aliphatic polymers such as polyisobutylene or ethylene-propylene copolymer. This is associated with the necessity of the heat of mixing overcoming the heat of fusion of the crystalline lattice. The aliphatic hydrocarbon solvents, which dissolve amorphous polymers such as polyisobutylene, have small heats of mixing which carmot disrupt the crystalline lattices of polyolefins. The amorphous regions of the semi-crystaUine polyolefins are swollen by aliphatic hydrocarbon solvents and their mechanical properties are lowered, but they do not dissolve. It is only when the temperature approaches the polymer s melting point that dissolution occurs. 

---