Polyisobutylene and butyl rubber are two materials based on polymers polymerized from isobutylene. 56 Polyisobutylene is not reactive after manufacture, so it has been used as a modifier in various types of adhesives and sealants. Butyl rubber is polymerized by adding isoprene to isobutylene. This addition creates a small amount of unsaturation in the polymer, making the material crosslinkable. Additionally, chlorinated and brominated versions of this material are available. Polyisobutylene has a low glass transition temperature of -60°C, so it is expected to be flexible at low temperatures. Due to their structure, polyisobutylene and butyl rubber are expected to have high air permeability and moisture resistance, making these materials ideal for polyisobutylene sealant formulations. Polyisobutylene has a wide molecular weight range from 45 000 to 2 110 000.
A common form of butyl sealant is tape form. The tape is coated on release paper and rolled onto a core. Tape can be formulated to have a certain tack. These materials are expected to spread over the surface of an adherend and form a seal substantially immediately after application to another adherend. These materials have been used in glass applications, appliance manufacturing, and automobile manufacturing.
Butyl sealants are also formulated for hot melt applications. These materials are formulated with high levels of tackifiers to produce solid sealants in stick, granule or block form. The application temperature is about 180°C. This type of sealant is already used in the manufacture of insulating glass, where the high barrier properties of polyisobutylene can be exploited.