Dimerization and Polymerization
Olefins can react with themselves to give molecules of variable length. If two molecules (monomers) bond, a dimer is obtained. If the chains formed are short, they are called oligomers, and if they are long (thousands of monomer units), polymers.
Polymers are very important from the industrial point of view because they are profusely used to create almost all objects and tools essential for our everyday life (synthetic fibers for textiles, bottle making, pipes, almost anything...).
Polymerization can be effected by different methods, involving the usual studied reaction intermediates: carbocations, carbanions and radicals. Efficient catalysts have been also developed.
Cationic polymerization
Protonation of an olefin produces an electrophilic carbocation that can be attacked by the π cloud of another molecule.
Anionic polymerization
Electron-poor olefins, i.e. those with electronegative substituents, undergo anionic polymerization.
Radical polymerization
If a radical initiator, such as a peroxide, is introduced into the reaction, polymerization proceeds through radicals.
Catalysed polymerization
Metal catalyzed polymerization of olefins allows for a control of both length and stereochemistry of the final polymer. This is paramount to industrially condition the polymer final properties. The discovery of such metal catalyst was the subject of the Nobel Prize won by their inventors.
Karl Waldemar Ziegler (1898-1973): German chemist, professor at the Halle University, in 1943 was promoted to the direction of the Max Planck Institute for Coal Research. He discovered the procedure to produce polyethylene at low pressure with linear structure. Nobel Prize of Chemistry (shared with Natta) in 1963.
Giulio Natta (1903-1978): Director of the department of Industrial Chemistry at the Polytechnic Institute in Milan. From 1950 he exclusively devoted his research efforts to the chemistry of macromolecules. In 1954 he synthesized a highly crystalline polypropylene, based in part in Ziegler's work. He is the father of the idea about tacticity. Nobel Prize of Chemistry (shared with Ziegler) in 1963.