Polybutene

Polybutene and polyisobutylene are liquid oligomers widely used as plasticizers for high-molecular weight polymers, such as polyethylene, and as carriers and lubricants. They are not to be confused with the high molecular weight polymer polybutene-1.

The liquid is clear and colourless, and is sold in many different grades. The grades are determined mainly by molecular weight, with the higher molecular weight grades having increasing viscosity. The oligomer degrades at high temperature (upwards of 350 °C) to form monomer isobutene by chains unzipping from the chain ends.

Polybutene is similar to but different from polyisobutylene (PIB). Polybutene is typically made from cat cracker mixed C4s (after the stream is Merox treated to remove sulfur and amines, and contain 1-butene, 2-butene, and isobutylene. Ethylene steam cracker C4s are also used as supplemental feed for polybutene. On the other hand, PIB is produced from essentially pure isobutylene made in a C4 complex of a major refinery. The presence of isomers other than isobutylene can have several effects including: 1) lower reactivity due to steric hindrance at the terminal carbon in, e.g., manufacture of polyisobutenyl succinic anhydride (PIBSA) dispersant manufacture; 2) the molecular weight—viscosity relationships of the two materials may also be somewhat different.

The reaction is an acid catalyzed carbocationic polymerization typically using aluminum chloride or hydrogen halide acid such as HF. So called "high reactivity" polybutene or PIB is produced using purified isobutylene feedstock and strong acid catalyst such as HF or HF with promoter.

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