Quantitative analysis of sequence length distribution of 1,2 units in polybutadienes by ozonolysis-GPC method

The sequence distribution of 1,2 units in commercial and laboratory produced polybutadienes, containing 1,2 units from 0.5 to 87%, was analyzed by an ozonolysis-GPC method. Ozonides from polybutadiene were converted to trifluoroacetates by reduction with LiAlH4, followed by esterification with trifluoroacetic anhydride. The trifluoroacetates derived from 1,4-1,4 and 1,4-(1,2)(n)-1,4 sequences, from n = 1 to 7, were observed as respective GPC peaks using an refractive index detector. The relative intensities of these peaks were converted to the concentration of each sequence by using correction factors determined with model compounds and by direct weighing of each peak. Polybutadienes prepared by anionic polymerization showed a sequence distribution of 1,2 and 1,4 units corresponding to Bernoulian statistics, whereas the 1,4-(1,2)(2)-1,4 sequence was significantly higher than the theoretical value for 1,2 units in cis-1,4 polybutadiene.