Investigation on synthesis of high vinyl polybutadiene with iron-based catalysts I. Effect of triphenyl phosphate

1,3-Butadiene (BD) polymerization catalyzed by iron (2-ethyl hexanoate)(3)(Fe)-triisobutyl aluminium (Al)-triphenyl phosphate (P) was investigated, in regard to different phosphorous compounds, n(P)/n(Fe) and n(Al)/n(Fe) ratios, catalyst preparation method and reaction temperature. Though the addition of triphenyl phosphine, triethyl phosphite, triphenyl phosphite, triethyl phosphate or tributyl phosphate as a ligand to the catalyst system gave rise to oil-like oligomers, the addition of dialkyl phosphite (diethyl phosphite and diphenyl phosphite) or triphenyl phosphate as a ligand produced polybutadiene with high I 2-unit contents. The activity of the iron-based catalyst with triphenyl phosphate remarkably promoted with the increase of the reaction temperature from 0 to 50 degreesC. The optimum activity achieved at n (Fe) : n (P) : n (Al) = 1: 4: 25 with an addition order of BD + Fe + P + Al. The polydispersity index was 2.50 and the unimodal GPC curve of the polymer indicated that the catalytic system involved a single active site at 50 degreesC. According to the results of NMR, XRD, GPC and DSC, the product polymer possessed high 1,2- unit content (95%), high syndiotacticity (95%), high crystallinity (68%), high molecular mass (M-n = 7.4 x 10(5)), and high melting point (189 degreesC) . Regardless of reaction conditions, the 1,2-unit content and syndiotacticity of the polymer obtained at 50 degreesC stayed around 95%, indicating the high stability of stereospecificity of the catalyst.