The accuracy of 13C nuclear magnetic resonance (13C NMR) measurements has been examined by using 14C-labeled ethylenepropylene (EP) copolymers. The monomer compositions calculated from the methylene and methine resonances are in agreement with those determined by radioassay within a relative error of 4%. These results indicate that the NOES are uniform, at least for such carbons, and, therefore, the monomer sequence distributions obtained are sufficiently reliable. Monomer reactivity ratios, rl (ethylene) and rz (propylene), have been calculated from the dyad distribution and the monomer feed composition. The observed triad distribution, compared with that calculated by a first-order Markovian scheme using rl and r2, shows the peculiarity that ethylene tends to copolymerize either in alternation or in runs.ABSTRACT: Two samples of poly(viny1 bromide) were prepared and purified. Sample A was synthesized by radical polymerization of vinyl bromide at 35 "C, and sample B was obtained by extraction of sample A with dioxane at room temperature. Both samples had an isotactic content (determined by I3C NMR) of 46%. Molecular weight averages were calculated from viscometric measurements in THF solutions and were found to be 52 100 and 27 400 for samples A and B, respectively. Dielectric measurements were performed in solutions of both samples in dioxane and 1-methylnaphthalene at several temperatures, and dipole ratios D, = (fi2)/xm2 were found to be 0.53 and 0.45 in dioxane and 1-methylnaphthalene, respectively. No noticeable dependence of D, with molecular weight was found; the variation of D, with temperature was too small to allow an accurate determination of its temperature coefficient. A rotational isomeric state model was derived and used to calculate dipole and characteristic (C, = (P)o/nF) ratios. Theoretical values of both D, and C, are in good agreement with experimental results.

No abstract

Absaact: Titanium complexes were prepared by the reaction of 2,2'-thiobis(6-mbutyl-4-methylphenol) (TBP) with TiC1, or Ti(OPf),.These complexes in combination with methyalumoxane as cocatalyst are highly active towards ethylene and propene, giving polymers having high molecular weights. The polymerization activities for ethylene-and propene are comparable to those of Cp2ZrC MA0 catalyst. Polypropylene obtained had extremely high molecular weigk (Mw>6 million) and low regioregularity (30% of head-to-head and tail-to-tail linkages). Highly syndiotactic polystyrene was obtained with these catalysts with activity up to 27 kg polymer per g Ti and hour. Copolymerization of styrene with ethylene gave highly alternating copolymer with isotactic styrene units. These catalysts are also active toward both conjugated and nonconjugated dienes such as butadiene and 1,5-hexadiene. Polybutadiene had mainly cis-l,4-strucm e (98%). The structure of poly(1J-hexadiene) is rather complicated, which is quite different from that prepared with heterogeneous Tic& catalysts.INTRODUCTION Titanocenes and titanium tetraalkoxides combined with an alkylaluminium compound can polymerize olefins.') However, the catalytic activities are very low compared with that of commercial catalysts, i.e., Tic4 and MgCG-supported catalyst. Kaminsky and Sinn found that titanocene and zirconocene compounds, when they are combined with methylalumoxane (MAO) instead of alkylaluminium compounds, become extremely active toward ethylene, giving polyethylene with high molecular weight.".') They also found that these catalyst systems are also active toward propene, but the polypropylene obtained had very low molecular weight!) Afterwards, Ewen?)*@ and Kaminsky') showed that racemic m-metallocene c o m p o~n d~)~~) with MA0 gives isotactic polypropylene. However, the molecular weight of the resulting polypropylenes was still low.

No abstract

Polypropylenes produced with various heterogeneous titanium-based Ziegler-Natta catalysts were fractionated by solvent extraction technique. The infrared analysis of the fractions indicates the presence of a crystalline syndiotactic sequence, soluble in xylene at 20"C, and boiling hexane soluble fractions of all samples examined. Highly syndiotactic polypropylene (proportion of rrrr pentad is 0,50), comparable in syndiotacticity to the syndiotactic polymer prepared at -78 "C with a homogeneous vanadium catalyst, was separated from the xylenesoluble fraction of the polymer prepared with the system TiC13-AI(C,H,),C1 by means of elution column fractionation. The steric irregularities are mainly rrrm and rrmr (ratio = I : I),suggesting that the propagation is controlled mainly by end-groups. Chemical inversions, i. e., head-to-head or tail-to-tail linkages of propylene units, are practically absent, though they are seen in syndiotactic polypropylenes prepared with vanadium catalysts.