Catalytic Olefin Polymerization

Ethylene, Styrene, and α-Methylstyrene Polymerization by Mono(pentamethylcyclopentadienyl) (Cp*) Complexes of Titanium, Zirconium, and Hafnium: Roles of Cationic Complexes of the Type [Cp*MR2]+ (R = Alkyl) as both Coordination Polymerization Catalysts and Carbocationic Polymerization Initiators

“…The a-PS formed at −78 °C exhibited a lower weight average molecular weight, ∼5.3 × 10 3 , presumably because of the freezing out of the monomer before polymerization was complete, but a significantly narrower molecular weight distribution, 2.1. The a-PS samples were readily soluble in many organic solvents, including methyl ethyl ketone, and were identified by 1 H NMR spectroscopy 4a. No s-PS was formed in any of the toluene polymerizations carried out at temperatures <0 °C 5c…”

“…The tacticities were in all cases assessed by 13 C{ 1 H} NMR spectroscopy on solutions in 1,1,2,2-tetrachloroethane- d 2 at 120 °C, the resonances of the ipso -carbon atoms being well-resolved singlets at δ 145.36, characteristic of the rrrr pentad of s-PS. 4a,d,e In general, values of M w increased from ∼1 × 10 5 at 70 °C to ∼2 × 10 6 at 0 °C, while M w / M n was essentially constant at ∼2.3. Glass transition temperatures and melting points were generally ∼104 and ∼272 °C, respectively, comparable with data from the literature, , but the yields obtained here and our observations of rapid solidification of the product are not reported previously for this and similar initiators. 2b,c,i,k-o, However, we find that rigorous exclusion of moisture is necessary for rapid and reproducible polymerization to solid s-PS to occur. The overall percentage conversion of styrene to s-PS appears to be significantly higher than those reported elsewhere for this and similar initiators. , …”

“…In contrast, although it might be anticipated that electronically less saturated, sterically less hindered monocyclopentadienyl complexes of the general stoichiometries [Cp‘MRL 2 ] 2+ or [Cp‘MR 2 L] + might behave as even more reactive catalysts, in fact until recently relatively few publications have described the utilization of monocyclopentadienyl compounds of titanium, zirconium, and hafnium as olefin polymerization initiators are concerned largely with polymerization of styrene to syndiotactic polystyrene (s-PS), a material which is currently receiving considerable attention because of its high melting point and low solubility in organic solvents 4f…”

Surface Chemistry and Spectroscopy of Chromium in Inorganic Oxides

“…Typical Cr loadings in Phillips catalysts are 1 wt % for slurry type and 0.2 wt % for gas-phase polymerization. 187 Lower polymer weights are obtained by increasing the catalyst activation temperature and by using silicas having larger pore diameters. Furthermore, industrial Cr/SiO 2 catalysts are sometimes promoted by the addition of surface titania to the catalyst.…”

An EPR Study of the V(IV) Species Formed Upon Activation of a Vanadyl Phenoxyimine Polymerization Catalyst with AlR3 and AlR2Cl (R = Me, Et)

“…Systems based on [V(acac) 3 ] and alkylaluminums are used commercially in the production of ethylene-propylene-diene elastomers. [1][2][3][4][5][6][7][8][9][10] Despite the ongoing interest in synthesis of new vanadium polymerization catalysts [11][12][13][14][15][16][17][18] little is known about the reaction mechanism. The main problem is the paramagnetism of alkylvanadium compounds, which precludes their characterization by NMR spectro- scopy.…”