SynopsisButadiene is polymerized by cobalt compound-organoaluminum-CSz catalysts to give highly crystalline syndiotactic 1,2-polybutadiene (s-PB) having melting point up to 216OC. An aluminum-free catalyst, CO(C4H6)(C8H13)-CS2, is also effective. Syndiotactic polymerization with C O ( C~H~) ( C~H~& C S~ is not interrupted by the addition of protic substances such as water and alcohol, but is influenced by donor or acceptor substances. The donor molecule, e.g., dimethylsulfoxide or dimethylformamide, decreases the stereoregularity, i.e., syndiotacticity and 1,2 content. An acceptor molecule of organoaluminum with appropriate acidity such as AlEt3-AlEtzCl or tetraethylaluminoxane increases the molecular weight, stereoregularity, and yield of the polymer. In the presence of CSz a mixture of cis-PB and s-PB was obtained by using Co(octoate)z-AlEtzCl-HzO, with molar ratio H20/Co less than unity. In the case of HzO/Co > 1, only cis-PB was obtained. By the addition of donor substances such as ester, ether, nitrile, and U t 3 , s-PB was obtained even when H20/Co > 1. The amount and ratio of cis-PB and s-PB are dependent upon the nature and amount of the additives. [43& = [7]gg&,, = 8.18 x 1 0 -5~~o . w a Polymerization conditions: benzene 860 mL, butadiene 85 g, at 4OoC with HzO (variable)-AlEta (3.0 mmol)-Co(acac)3 (0.045 mmol)-CSz (0.13 mmol) as the catalyst.

SynopsisThe 'Hand '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 compoundorganoaluminum-C& catalysts. Cis opening of the double bonds in the syndiotactic polymerization is affirmed by the study of the copolymer from perdeuteriobutadiene and cis,cis-l,4-dideuteriobutadiene. S-PB (mp 21OOC) has 99.7% 1,2 units, 0.3% isolated ck-l,4 units, and 99.6% syndiotacticity.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 ck-l,4 propagation and between syndiotactic and isotactic propagation are 14.0 and 9.6 kcal/mol, respectively, for Co(acac)3-AlEt3-AlEt2Cl-CS2, and 6.7 and 5.7 kcal/mol, respectively, for the aluminum-free CO(C&)(C&~)-CS~ system. The conformation of s-PB in o-dichlorobenzene at 150°C is described by the sequence (tt)l.fj(gg)(tt).

Highly crystalline syndiotactic 1,2‐polybutadiene (s‐PB) having melting point (mp) up to 216°C was obtained by using a Co(acac)3‐AIEt3‐CS2 catalyst. The polymer with mp 208°C was found to have 99.7% 1,2 content and 99.6% syndiotacticity by 1H and 13C‐NMR measurements. The s‐PB can be molded by addition of a stabilizer such as 2,6‐di‐t‐butyl‐4‐hydroxymethylphenol into fiber, film, and various shaped articles. The physical properties presented in the present article include stress‐strain and dynamic mechanical behavior. The highly crystalline syndiotactic 1,2‐polybutadiene was applied to a carbon fiber and UBEPOL VCR (cis‐1,4‐polybutadiene reinforced by fibrous syndiotactic 1,2‐polybutadiene).

SynopsisA mechanism is proposed for the polymerization of syndiotactic 1,2-polybutadiene (s-PB) with soluble cobalt-organoaluminum-CS2. The proposed active species have structures which consist of side-on coordination of CS2 to cobalt, anti-r-ally1 growing end, cisoid bidentate coordination of butadiene, and activation by complex formation with organoaluminum at the nonbonded sulfur of the coordinated CS2. This proposal is based on findings for the aluminum-free catalyst CO(C.&)(C&I~&CS~. It is tentatively interpreted that syndiotactic 1,2 polymerization proceeds under the influence of the side-on coordinated CS2, by which the reactivity between the terminal carbons of butadiene and the C3 of the s-ally1 end is enhanced.

ABSTRACT:The monomer unit sequence distribution in partly epoxidized trans-1,4-polyisoprene was determined by the 13 C NMR spectrometry available. Epoxidation of polymer was carried out by peracid prepared in situ from hydrogen peroxide and a small amount of formic acid, and the epoxy content in the modified polymer was determined by 1 H NMR. The 13 C NMR spectra of the partly epoxidized trans-! ,4-polyisoprene exhibited new signals both in the olefinic and aliphatic carbon regions, in addition to the signals due to the original trans-! ,4-polyisoprene. Each signal, except for the methyl carbon signals, was interpreted in terms of the dyad or triad of trans-!,4 and epoxidized units, taking into consideration the results from the signal assignments made by offresonance decoupling techniques and lanthanide shift reagent experiments. The monomer unit sequence distribution in partly epoxidized trans-1,4-polyisoprene determined by 13 C NMR agreed very closely with that calculated on the basis of the random distribution of trans-! ,4 and epoxidized isoprene units. These results suggest that the site of the epoxy group formed is not affected by such groups previously formed in polyisoprene.