Polybutene

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

Properties

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.

Production

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 hinderance 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.

Structure

The repeat unit is in case of 1-butene:

-[-CH₂-CH(CH₂CH₃)-]_n-

The repeat unit in case of 2-butene is:

-[-CH(CH₃)-CH(CH₃)-]_n-

One of the end units in the polymer chain contains a double bond, allowing reactivity with other compounds to provide functional chemistry mainly for lubricant additives for engine oils, fuels and greases.

Oxidation

But the same double bond makes the molecule sensitive to oxidation when hot liquid is exposed to air. The polymer degradation reaction produces aldehydes and ketones, which are the further oxidised to carboxylic acids. This causes loss of tack and makes the material soluble in water.

Applications

It is used in two broad areas: 1) as a chemical intermediate for additives used in engine oils, gasoline and greases, and 2) formulations based on its physical performance characteristics. It is used in preparation of polybutenyl succinic anhydride (PIBSA), a dispersant / VI improve in engine oils. Industrial applications include, sealants, adhesives, extenders for putties used for sealing roofs and windows, coatings, polymer modification, tackified polyethylene films, personal care, polybutene emulsions. Hydrogenated polybutenes are used in a wide variety of cosmetic preparations, such as lipstick and lip gloss. It is used in adhesives owing to its tackiness. In addition it is used as a smoke inhibitor in two stroke engine fuels, where the benefit derives from the polymer decomposing (unzipping) at temperatures below the combustion temperature.

Also see

• Polybutene-1
• Oligomers

Bibliography

• Decroocq, S and Casserino, M, Polybutenes, Chapter 17 in Rudnick (Ed), Synthetics, Mineral Oils, and Bio-Based Lubricants: Chemistry and Technology, CRC Press (2005), Print ISBN: 978-1-57444-723-1, eBook ISBN: 978-1-4200-2718-1.zh:聚丁烯