The sequence distribution of styrene-butadiene copolymer initiated with n-butyllithium in toluene was investigated by GPC measurements of ozonolysis products in relation to the time-conversion and time-copolymer composition relationships. Rapid increase of conversion and styrene content in the copolymer was observed from about 75% conversion after the consumption of almost all of the butadiene. GPC analysis of the ozonolysis products showed three peaks corresponding to 1-3 styrene sequences flanked by 1,4-butadiene units for the copolymers obtained below 75% conversion. A broad peak due to long styrene sequences was observed in addition to the peaks due to 1-4 styrene sequences for the copolymers obtained above 75% conversion. The average number of styrene units in the long styrene sequence increased from 43 to 65 with increase of conversion from 89% to 100%. The sequence distribution of styrene units determined from the ozonolysis-GPC measurement was in good agreement with that calculated by monomer reactivity ratios.
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.
ABSTRACT:A study was made on the isomeric structure of trimethyl-cyclododecatriene (TMCDT) prepared by oligomerization of isoprene with (C5H8) 2 Mg-AlC13-TiC14-CH3SCH3 as a catalyst. The 1 H and 13 C NMR spectra of this compound showed the presence of one cis and two trans double bonds. The partial ozonolysis of TMCDT followed by the reductive degradation to alcohols gave three products corresponding to a linear trimer and two dimers of isoprene. These products were fractionated by liquid chromatography. 13 C NMR measurements showed these partial ozonolysis products to be 5-methyl-cis-5-decene-2,9-diol, 5-methyl-trans-4-nonene-1,8-diol, and 5,8-dimethyl-trans,cis-4,8-tridecadiene-1, 12-diol, indicating that one of the trans isoprene units was linked to the other isoprene units in a head-to-head and tail-to-tail fashion. This was also confirmed by an infrared measurement of hydrogenated TMCDT. The TMCDT was concluded to be 1 ,5,9-trimethyl-cis,trans,trans-1 ,5, 1 0-cyclododecatriene.
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