Tripropylene, also known as propylene trimer, is usually sold as a mixture of structural isomers of nonene. This mixture is obtained by oligomerization of propene:
In this process, two double bonds are lost and one is retained as illustrated by the isomer shown in the figure. The reaction is catalyzed by acids, such as polyphosphoric acid. A variety of catalysts have been explored. The reaction proceeds via the formation of a carbocation ((CH<sub>3</sub>)<sub>2</sub>CH<sup>+</sup>), which attacks another propylene unit, generating a new carbocation, etc. This kind of process affords mixtures (C<sub>3</sub>H<sub>6</sub>)<sub>n</sub>.
Like other alkenes, propylene trimer is used as an alkylating agent. A number of surfactants and lubricants are produced by alkylation of aromatic substrates.