Butyl rubber commercial grades

A somewhat different approach to the production of thermoplastic polyolefin rubbers has been adopted by Allied Chemical with their ET polymers. With these materials butyl rubber is grafted on to polyethylene chains using a phenolic material such as brominated hydroxymethyl phenol. The initial grades of these polymers, which were introduced commercially towards the end of the 1970s, had polyethylene butyl rubber ratios of 50 50 and 75 25. Both low-density and high-density polyethylene-based varieties were produced. 

Several partially cross-linked butyl rubbers are commercially available. The more tightly cross-linked grades are designed for butyl tapes. On the other hand, various depolymerized butyl rubbers and butyl/plasticizers blends are also available. 

Commercial grades of HR (butyl rubber) are prepared by copolymerising small amounts of isoprene with polyisobutylene. The isoprene content of the copolymer is normally quoted as the mole percent unsaturation , and it influences the rate of cure with sulphur, and the resistance of the copolymer to attack by oxygen, ozone and UV light. The polyisobutylene, being saturated, however, naturally confers on the polymer an increased level of resistance to these agencies when compared to natural rubber. Commercial butyl rubbers typically contain 0.5-3.0% mole unsaturation. 

Butyl rubbers are copolymers of isobutylene with a small amount of isoprene, synthesized by low temperature cationic polymerization. Commercial grades of HR are distinguished by unsaturation content (0.6-2.2 mole %) and by molecular weight (viscosity). 

Table 1. Commercial Grades of Butyl Rubber and Polyisobutylene Polymers.

Chlorobutyl rubber is prepared by chlorinating the regular butyl polymer under controlled conditions so that reaction is primarily by substitution and little of the unsaturation originally present in the macromolecule is lost. The chlorine is believed to enter the molecule at the highly reactive ally lie position, one carbon removed from a double bond. Approximately 1.2 wt % chlorine is present in the commercial grades of Exxon chlorobutyl. The chlorine... 

Commercial production of uniform, high quality, chlorinated butyl rubber was first achieved by the Exxon Chemical Co. in 1961. Since then, chlorobutyl rubbers have become firmly established in the rubber industry, and market demand continues to grow. Exxon and its affiliates were the only suppliers of chlorobutyl until 1979, when Polysar Ltd entered the market with competitive grades. 

The IISRP listings also include two crosslinked, one brominated and two chlorinated grades of butyl rubber, but three additional grades of halobutyl rubber have become commercially available since the listings were compiled. 

The acrylic rubbers were first introduced commercially in 1948 by B. F. Goodrich. This was a direct consequence of earlier work by the Eastern Regional Laboratory of the United States Department of Agriculture which issued a number of patents and publications in the 1940s. This laboratory also introduced two materials on a small scale, Lactoprene EV and Lactoprene BN. The EV was a copolymer of ethyl acrylate and 2-chloroethyl vinyl ether and the BN a copolymer of butyl acrylate and acrylonitrile. The Goodrich product Hycar PA-21, later renumbered Hycar 4021 may be considered as a direct descendant of Lactoprene EV whilst Hycar 2121X38 was a descen-dent of the BN grade. 

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