Analysis of the composition of polycarboxylic acids obtained by catalytic hydrocarboxylation of polybutadienes

Abstract

Infra-red (IR) spectroscopy, conductimetric titration, ¹H and ¹³C nuclear magnetic resonance (NMR) spectroscopies have been assessed for their reliability in determining the composition of polymers obtained by hydrocar-boxylation of polybutadienes. ¹H NMR data can be successfully applied to the analysis of polymers that have been selectively hydrocarboxylated on only the terminal C atoms of the pendant double bonds or of polymers that have phenyl end groups. For polymers that have H, OH or CO₂H termination and which have been hydrocarboxylated in a non-selective manner, it is necessary to use a combination of ¹H and ¹³C NMR spectroscopies with due allowance being made for the different receptivities of different kinds of carbon atoms. Conductimetric titrations give information on the overall conversion of double bonds to carboxylic acids but not on the detailed microstructure of the polymer. Problems are encountered in some cases because of precipitation of the polymer during the titration as a partial sodium salt. IR spectroscopy is not suitable for analysis of these polymers because of large background absorption in the appropriate region.