Chlorobutyl

Chlorobutyl refers to a class of halobutyl rubbers in which chlorine atoms have been introduced into a butyl rubber backbone. The most common member is chlorobutyl rubber (CIIR), produced by chlorination of polyisobutylene-based or butyl rubber polymers to impart chlorine functionality. Bromobutyl rubber, a related family, uses bromine instead of chlorine. These materials are part of the broader category of halobutyl rubbers and share similar properties with enhanced gas impermeability compared with unhalogenated butyl rubber.

Production and structure

Chlorobutyl is produced by chemically chlorinating a butyl-type polymer, typically polyisobutylene with a small amount of residual unsaturation. The chlorine incorporation changes the polymer’s polarity and crosslinking behavior, improving impermeability to gases and certain chemicals. The exact chlorine content and distribution depend on the manufacturing process and desired properties.

Properties

Chlorobutyl rubbers exhibit low gas permeability, making them well suited for barriers in packaging and tire inner liners. They have good resistance to weathering and ozone, modest chemical resistance to fuels and solvents, and favorable aging stability. The halogenated structure enables effective crosslinking during vulcanization, contributing to elasticity and resilience in molded and extruded products.

Applications

The primary use of chlorobutyl rubber is in tire inner liners and various sealing and gasket applications where gas impermeability is critical. It is also employed in pharmaceutical closures, medical tubing, and other gaskets and seals that benefit from chemical resistance and low permeability.

Safety and handling

As a halogenated elastomer, chlorobutyl requires standard industrial hygiene practices during processing. Decomposition or combustion can release halogenated compounds and sulfur or hydrogen halides, so appropriate ventilation and controls are important.

See also: butyl rubber, bromobutyl rubber.