ABSTRACT
For many years, polyethers, such as [---cH2CH(R)(}-]n, were considered to be excellent candidates for elastomers, in the expectation that the oxygen atom would contribute greatly to chain flexibility and thus enhance elastomeric behavior (Price, 1961 ). Poly(propylene oxide), with its low cohesive energy between chains, should be a superior elastomer, but the known methods of polymerizing propylene oxide gave only low molecular weight liquid polymers, not the desired high molecular weight polymer. Such liquid propylene oxide polymers could be made largely hydroxyl-ended and then converted to a rubbery polyether urethane by reaction with dior polyisocyanate. These polyurethane-type propylene oxide rubbers are widely used for lowdensity foams and other fabricated articles in which a propylene oxide-based polyol is chainextended and crosslinked during fabrication with di-or polyisocyanates (Price, 1958). This chapter discusses only polyether elastomers that are of sufficiently high molecular weight to be processed and fabricated by conventional rubber equipment and that are then crosslinked (i.e., vulcanized) in a separate step. The preparation of such polyether elastomers required the development of new catalyst systems, specifically coordination catalysts, for polymerizing propylene oxide and other epoxides.
