Ozone and its Reactions with Diene Rubbers

Abstract

The reactions of ozone with 1,4-cis- polybutadiene (SKD); Diene 35 NFA (having the following linking of the butadiene units in the rubber macromolecules: 1,4-cis (47 %), 1,4-trans (42 %), 1,2- (11 %); 1,4-cis-polyisoprene (Carom IR 2200), 1,4-trans-polychloroprene (Denka M 40), and 1,4-trans- polyisoprene have been investigated in CCl 4 solutions. The changes of the viscosity of the polymer solutions during the ozonolysis have been characterized by the number of chain scissions per molecule of reacted ozone (φ). The influence of the conditions of mass-transfer of the reagents in a bubble reactor on the respective φ values has been discussed. The basic functional groups-products from the rubbers ozonolysis have been identified and quantitatively characterized by means of IR-spectroscopy and 1 H NMR spectroscopy. A reaction mechanism that explains the formation of all identified functional groups has been proposed. It has been shown that the basic route of the reaction of ozone with elastomer double bonds - formation of normal ozonides - does not lead directly to a decrease in the molecular mass of the elastomer macromolecules, because the respective 1,2,4-trioxolanes are relatively stable at ambient temperature. The most favourable conditions for ozone degradation emerge when the cage interaction between Criеgee's intermediates and respective carbonyl groups does not proceed. The amounts of measured different carbonyl groups have been used as an alternative way for evaluation of the intensity and efficiency of the ozone degradation. The thermal decomposition of partially ozonized diene rubbers has been investigated by DSC. The respective values of the enthalpy, the activation energy and the reaction order of the 1, 2, 4-trioxolanes have been determined.