Rubber, Polyisoprenes and Allied Compounds. V. The Chemical Linking of Rubber and of Other Olefins with Phenol-Formaldehyde Resins

Abstract

Abstract Rubber combines readily with maleic anhydride up to a limit of one molecule of the latter per isoprene unit of the former. The comparative ease of occurrence of this reaction made it seem feasible to use maleic and similar unsaturated anhydrides (or acids) as a means of linking rubber chemically with various types of hydroxylic compound, the ethylenic carbon pairs of the maleic molecules serving to form C—C links with the rubber, and the anhydro groupings to form ester links with hydroxy compounds. Although it was possible to carry out this linking process successfully in a number of examples, the combination of rubber with phenol-formaldehyde resins could be much more satisfactorily effected if the rubber-maleic anhydride compound was not preformed, but, instead, a somewhat oxidized rubber together with maleic anhydride, phenol, and formaldehyde were simply heated together until resin formation occurred. Subsequently, it was found that considerably oxidized rubber (oxygen, approximately 10–13%; M, 3000–4000) reacted more readily than slightly oxidized rubber, the product being a thermosetting resin of Bakelite type, remarkable in possessing valuable residual thermoplastic properties. Investigation of the chemical reaction by which this resin is produced has given rather unexpected results in the field of additive reactions, and has thrown new light on the process of resinification.