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.
1H- and 13C-NMR Analysis of a Series of 1,2-Diaryl-1H-4,5-dihydroimidazoles