Butyl Rubber

Abstract

Butyl rubber and other isobutylene polymers in wide use include various homopolymers and copolymers. Low levels of unsaturation for subsequent cross‐linking are incorporated by copolymerization with isoprene. Halogenation at the unsaturation site provides additional cross‐linking mechanisms and covulcanization with highly unsaturated elastomers. Polymers containing star branches, conjugated‐diene sites, divinylbenzene, and brominated p ‐methylstyrene have also been synthesized. Isobutylene polymers are polymerized by a cationic mechanism, using a Brønsted acid as an initiator and a Lewis acid as a coinitiator, eg, water and aluminum chloride. Molecular weights range from several hundred for terminally unsaturated polybutenes to over a million for elastomer grades. The T g of polyisobutylene is about −70°C, and the polymer is amorphous in the unstrained state. The polymers exhibit a broad damping peak and a low plateau modulus. They display an exceptionally low permeability to gases, and are widely used as air retention barriers in tires. Optimum physical properties are obtained by compounding with carbon black and other fillers. Various mechanisms are used to cross‐link the compounds into elastomeric vulcanizates. Sulfur is used to provide polysulfidic cross‐links, while resin and zinc oxide cure systems give carbon–carbon cross‐links. Besides inner tubes and innerliners, butyl rubbers are used in blends to improve cut‐growth resistance and wet‐skid resistance. Blends with thermoplastic resins improve toughness. Polyisobutylenes enjoy extensive use as adhesives and caulks, and are chemically modified for use in lubricants as dispersants.

Highly exo‐olefinic polyisobutene synthesized using a recyclable acid

“…Cationic polymerization 1,2 is key to the production of a variety of products vital to modern‐day life. These include butyl rubber, 3,4 polyisobutene (PIB), 5,6 polybutenes, 7,8 various synthetic lubricants, 9,10 terpenic resins, 11,12 hydrocarbon resins, 13 and poly(vinyl ethers) 14,15 . The technique is the oldest known method for polymer synthesis and the first to employ a renewable monomer 16 .…”

Indefinitely active aqueous cationic polymerizations, part I: Low cost, recyclable initiator systems

“…Regardless, the cationic mechanism is the primary means of producing a number of commodity products including: synthetic lubricants, hydrocarbon resins, terpene polymers, polyisobutene, poly(vinyl ethers), and butyl rubber . Great effort has been made to synthesize them in a more benign manner .…”

Pilot Plant Study on the Polymerization of Isobutene Using Silica-Supported Methylaluminoxane

“…Isobutene (IB)-based polymers play a vital role in modern society and are used in a broad array of applications ranging from tires, lubricants, adhesives, and pharmaceutical devices. − Such polymers are produced exclusively by a cationic mechanism, − which has many shortcomings from a sustainability perspective. , A few include the requisite use of cryogenic temperature (T) and halogenated solvents for the production of the high-molecular-weight (MW) polymer and the generation of acid waste streams upon workup. The MW–T profile can be enhanced by using initiator systems containing weakly coordinating anions (WCAs), whereas heterogeneous acids can be readily reclaimed. , …”