The Cure of Carboxy‐terminated Diene Polymers and the Role of a Polymer‐supported Catalyst

Abstract

Both infrared spectroscopy and wet chemical techniques reveal that the terminal acid groups of carboxyl-terminated polybutadiene behave in the same manner as in representative low molecular weight dilute solution systems. Contrary to previous expectations the chromium(III)-catalysed epoxy chain extension shows third-order character, and the slow progress of reaction at high conversions can be rationalised on simple kinetic grounds and without recourse to considerations of limited functional group accessibility. The parallels between bulk polymer and classical solution reactions anticipate the effectiveness of a system in which the catalyst is also a polymer: the synthesis and evaluation of two such catalysts are described. Whilst gel times are no slower for the polymer-catalysed cures, product properties may be actually improved, thus, the unreinforced product of a liquid nitrile rubber cure may achieve a tensile strength of 4.5 MPa when the initial catalyst is chromium(III) supported on the same polymer, an improvement which can be rationalised in terms of classical concepts of polymer reactivity and step growth processes.