SYNDIOTACTIC 1,2-POLYBUTADIENE WITH CO-CS2 CATALYST SYSTEM .3. H-1-NMR AND C-13-NMR STUDY OF HIGHLY SYNDIOTACTIC 1,2-POLYBUTADIENE

The **1H- and **1**3C-NMR spectra of highly crystalline syndiotactic 1,2-polybutadiene (s-PB) are discussed in order to clarify the mechanism of butadiene polymerization with cobalt compound-organoaluminum-CS//2 catalysts. Cis opening of the double bonds in the syndiotactic polymerization is affirmed by the study of the copolymer from perdeuteriobutadiene and cis,cis-1,4-dideuteriobutadiene. cis-1,4-dideuteriobutadiene. S-PB (mp 210 degree C) has 99. 7% 1,2 units, 0. 3% isolated cis-1,4 units, and 99. 6% syndiotacicity. Polymer ends (2-methyl-3-butenyl group and conjugated diene structure) are also determined. The differences in free energy of activation between 1,2 and cis-1,4 propagation and between syndiotactic and isotactic propagation are 14. 0 and 9. 6 kcal/mol, respectively, for Co(acac)//3-AlEt//3-AlEt//2Cl-CS//2, and 6. 7 and 5. 7 kcal/mol, respectively, for the aluminum-free Co(C//4H//6)(C//8H//1//3)-CS//2 system. The conformation of s-PB in o-dichlorobenzene at 150 degree C is described by the sequence (tt)//1//. //6(gg)(tt).