Definition - What does Polybutene mean?

Polybutene is a type of polymeric molecule composed of 1-butene, 2-butene and isobutylene, which are all isomers of butene (non-cyclic C4H8), a basic hydrocarbon with four carbon atoms. From these three building blocks there are three possible types of repeating units in polybutene:

  • -[CH2CH(CH2CH3)]x-
  • -[CH(CH3)CH(CH3)]y-
  • and -[CH2C(CH3)2]z-

derived from 1-butene, 2-butene and isobutylene, respectively and where x, y and z represent various numbers of each repeating unit in one particular molecule of polybutene.

Although polybutene formulations may vary in the molecular weight of the polymers, polybutene refers to the relatively low molecular weight polymers that are liquids at room temperature and pressure. Polybutenes are often used as plasticizers, adhesives, chemical intermediates for gasoline additives, and sealants. Although industrial applications are found in boosting properties such as adhesion, anti-rust and water repellency in coatings, polybutene is also often used in cosmetics such as lipstick formulations.

Corrosionpedia explains Polybutene

Being the name for a family of related molecules, the exact physical properties of polybutene such as density, viscosity, average molecular weight and refractive index varies from each specific polybutene product. Nonetheless, polybutenes are typically odorless and colorless. Polybutene should not be used to refer to higher molecular weight relatives, such as polybutylene (polybutene-1). To clarify the distinction, polybutene products may have average molecular weights from the hundreds to thousands of grams per mol, but polybutylene type formulations may have average molecular weights in the hundred of thousands to even millions of grams per mol.

The lower molecular weight of polybutene is one reason why polybutenes are liquids. Another reason come from the randomness in its repeating unit composition. Polybutene is prepared from a mixture of butene isomers, which share the same molecular formula (C4H8) but vary in the connectivity of the four carbon atoms and the location of a single carbon-carbon double bond. 1-Butene is linear with a formulation of CH2=CHCH2CH3. 2-Butene is also linear with a formulation of CH3CH=CH=CH3. Isobutylene has a branched structure and a formula of CH2=C(CH3)2. Along the long central carbon atom chain in a polybutene molecule, these various starting butenes create repeating units with different kinds of branches (ethyl -(CH2CH3), methyl -(CH3) and dimethyl –(CH3)2). The randomness of these components along the chain make two polybutene molecules difficult to pack together nicely, thus lowering the melting point of the compound.

The large non-polar surface area created by these long carbon chains and ease of mixing being a liquid give polybutene its sought after adhesive properties. Being non-polar, polybutenes stick well to other non-polar compounds and do not mix well with water, making them water repellent. The combination of water repelling and sealant properties make polybutenes suitable for corrosion prevention applications.

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