page_title: Cationic polymerization
section_title: Lewis acids/Friedel-Crafts catalysts
hierarchical_section_title: Cationic polymerization / Synthesis / Initiation / Lewis acids/Friedel-Crafts catalysts
caption_attribution_description: English: lewis acid initation
context_page_description: Cationic polymerization is a type of chain growth polymerization in which a cationic initiator transfers charge to a monomer which then becomes reactive. This reactive monomer goes on to react similarly with other monomers to form a polymer.
  The types of monomers necessary for cationic polymerization are limited to alkenes with electron-donating substituents and heterocycles. Similar to anionic polymerization reactions, cationic polymerization reactions are very sensitive to the type of solvent used. Specifically, the ability of a solvent to form free ions will dictate the reactivity of the propagating cationic chain.
  Cationic polymerization is used in the production of polyisobutylene and poly.
context_section_description: Lewis acids are the most common compounds used for initiation of cationic polymerization. The more popular Lewis acids are SnCl₄, AlCl₃, BF₃, and TiCl₄. Although these Lewis acids alone are able to induce polymerization, the reaction occurs much faster with a suitable cation source. The cation source can be water, alcohols, or even a carbocation donor such as an ester or an anhydride. In these systems the Lewis acid is referred to as a coinitiator while the cation source is the initiator. Upon reaction of the initiator with the coinitiator, an intermediate complex is formed which then goes on to react with the monomer unit. The counterion produced by the initiator-coinitiator complex is less nucleophilic than that of the Brønsted acid A⁻ counterion. Halogens, such as chlorine and bromine, can also initiate cationic polymerization upon addition of the more active Lewis acids.
caption: Initiation with boron trifluoride (coinitiator) and water (initiator)
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