Carboxidation of Polybutadiene Rubber

Unlike PE, many polymers have ahigh concentration of the internal C=C bonds. The carboxidation of such materials led to quite unexpected results. This can be illustrated by the carboxidation of cis-1,4-polybutadiene rubber (poly-BD) studied in detail by Dubkov et al. [180]. The concentration of C=C bonds in this rubber is 250 bonds per 1000 carbon atoms. Possible oxygen content in the poly-BD can reach up to 23 wt%, if all C=C bonds are transformed into the C=0 groups. 

An estimation based on NMR data showed that the route 1 comprises 95% and route 2 only 5% of the total carboxidation rate. These data are close to the carboxidation results of 2-butene, for which the non-cleavage route was found to be 92% and cleavage route 8% [173]. However, in distinction to the individual alkene, where the cleavage route only slightly decreases the selectivity for ketone, in the case of poly-BD, as we shall see below, this route may have dramatic consequences even at a 5% contribution. 

The carboxidation degree exhibits a dramatic effect on the consistency of the resulting samples. At the introduction of small amounts of oxygen (0.2-0.8 wt%), the rubber retained its consistency, but became sticky. At an oxygen content of 1.6 wt%, the material became fluid and lost the ability to retain its shape. At oxygen contents of 5.0 wt% or more, the samples turned into a bright viscous liquid. 

For the most oxygenated sample, the carboxidation reaction may be presented by (7.19), having huge stoichiometric coefficients compared to conventional chemical reactions  

Sample no. (see Fig. 7.8) Carboxidation condition (P n20 =2.5 MPa) Oxygen content (wt%) xc=c (%) MJM deav Number of monomeric units in a fragment Consistency of sample 

---