Sequence Structure of Styrene-Butadiene Copolymer Determined by Ozonolysis-HPLC Method

Abstract

The configurational sequence of styrene units and the arrangement of styrene and 1,2-butadiene units in styrene-butadiene copolymers were characterized by 1H- and 13C-NMR analysis of the ozonolysis products which were separated by a combination of GPC and HPLC. The ozonolysis products from diad and triad styrene sequences flanked by 1,4-butadiene units showed two and three peaks in HPLC, respectively, reflecting the diad and triad tacticity. The probability of racemic addition was found to be 0.56 and 0.58 for radical and anionic SBR, respectively. The ozonolysis products from styrene-1,2 sequences were separated into three fractions by HPLC. The first and second fractions were assigned to a 1,4-1,2 styrene-1,4 (VS) structure differed only in cotacticity. The third fraction was considered to be a mixture of the meso and racemic forms of the l,4-styrene-l,2-l,4 (SV) sequence. The GPC fraction corresponding to a sequence consisting of two styrenes and one 1,2 units was separated into four peaks by HPLC. Both large peaks contained SSV + VSS structures, where one peak consisted of meso configurations with respect to the two styrene units, and the second peak contained racemic styrene alignments. The two small peaks were SVS with the separation due to cotacticity. Based on the intensity of HPLC peaks, it was deduced that the addition of a 1,2 unit after the styrene terminal predominated the addition of a styrene unit after the 1,2 terminal.

Quantitative Analysis of Sequence Length Distribution of 1,2 Units in Polybutadienes by Ozonolysis−GPC Method

“…It is, consequently, clear that the 1,2 and 1,4 additions of 1,3-butadiene monomer occur randomly in anionic polymerization. The ozonolysis-GPC method was also applied to cis-1,4 polybutadiene to detect the diad sequence of 1,2 units which was not found by 13 C NMR measurement due to the low relative intensity and overlapping with other signals. Table 5 shows theoretical and experimental mole fractions of 1,4-(1,2) n -1,4 sequences for cis-1,4 polybutadienes prepared with a coordination catalyst.…”

“…The experimental mole fraction of 1,4-(1,2) 2 -1,4 sequence of cis-1,4 polybutadienes was significantly higher than the theoretical value, providing a short blocky distribution in these polymers. The ozonolysis-GPC method was shown to be a powerful technique for detecting a sequence that is a minor component, such as the diad sequence of 1,2 units in cis-1,4 polybutadiene that was not detected by 13 C NMR measurement.…”

“…1 Several approaches have been developed for the determination of the sequence distribution of the isomeric units. 13 C NMR spectroscopy provides quantitative information on the distribution of diad to triad sequences. The diad sequence distribution of cis-1,4, trans-1,4 and 1,2 units determined by 13 C NMR showed a good agreement with those assumed on the basis of Bernoulian statistics for polybutadienes from anionic and radical initiators as well as those from Co-Al catalysts.…”

“…13 C NMR spectroscopy provides quantitative information on the distribution of diad to triad sequences. The diad sequence distribution of cis-1,4, trans-1,4 and 1,2 units determined by 13 C NMR showed a good agreement with those assumed on the basis of Bernoulian statistics for polybutadienes from anionic and radical initiators as well as those from Co-Al catalysts. 2 13 C NMR studies on hydrogenated polybutadienes also have shown that racemic sequences of 1,2 units longer than 3.7 are necessary to crystallize syndiotactic 1,2 polybutadiene.…”

“…We have established a novel method for the analysis of the sequence distribution of styrene and styrene−1,2 units in styrene−butadiene copolymers (SBR) by the GPC analysis of ozonolysis products. − This ozonolysis−GPC method has proven to be a powerful tool for analysis of the entire sequence distribution from short to long sequences in commercial SBRs. , The method was applied to the analysis of the sequence distribution of 1,2 units in polybutadiene by GPC measurement of ozonolysis products, which were transformed into trifluoroacetates after reductive degradation of the ozonide with LiAlH 4 . A commercial polybutadiene showed GPC peaks corresponding to 1,4−1,4 and 1,4−(1,2) n −1,4 sequences from n = 1 to 9 using a refractive index (RI) detector.…”