EinleitungDurch Vermischen von Bis(cyclopentadieny1)zirkoniumdimethyl oder -dichlorid mit Aluminoxanen der Strukturen A und B entstehen auBerordentlich aktive, ltisliche Ziegler-Katalysatoren 1,2, 3). Als Ubergangsmetalle ktinnen auch analoge Titan-oder Hafniumverbindungen eingesetzt werden, die jedoch eine etwas geringere Polymerisationsaktivitiit aufweisen.

EPDM terpolymers with ethylidene norbornene as diene monomer could be prepared by means of a soluble Ziegler catalyst formed from biscyclopentadienyl zirconium dimethyl and methylaluminoxane. The overall activities lie between 100 and 1000 kg EPDM/(molZr h bar), obtainable at zirconium concentrations as low as 5 × 10−7 mol/L. After an induction period (0.5–5 h) the polymerization rates increased and then leveled to a value which was constant for several days. From copolymerization kinetics reactivity ratios r12 = 31.5, r21 = 5 × 10−3, and r13 = 3.1 could be derived, and by 13C‐NMR spectroscopy r12 · r21 = 0.3 was found (1: ethylene, 2: propylene and 3: ethylidene norbornene). The regiospecifity of the catalyst toward propylene leads exclusively to the formation of head‐to‐tail enchainments. The diene polymerizes via vinyl polymerization of the cyclic double bond, and the tendency to branching is low. Molecular weights were estimated between 40,000 and 160,000. The average molecular weight distribution of 1.7 is remarkably narrow. Glass transition temperatures of −60 to −50°C could be observed. The cure behavior and the physical properties of cured samples were also tested.

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Aniline is oxidized to nitrosobenzene as the initial product, which undergoes further oxidation to nitrobenzene. The nitrosobenzene formation is catalyzed by functionalized multiwalled carbon nanotubes (CNT) followed by a coupling reaction between nitrosobenzene and aniline to produce azobenzene. This coupling requires close proximity of the reactants. It proceeds rapidly resulting in the UV-VIS absorption spectrum showing maxima at 327 nm and 425 nm. The nitrosobenzene yield in the presence of CNTs is controlled by the amount present in the medium. As the reaction is not catalyzed by unfunctionalized CNTs or graphitic particles, the uniqueness of the functionalized multiwalled CNTs in this catalysis suggests a nanodimensional reaction pathway.

We are introducing a versatile computerized approach to model and simulate polymer tacticities using seven single-stage statistical models. The theory behind the models, e.g., Bovey's versus Price's, Bernoullian, 1st or 2nd order Markovian, enantiomeric types, and combinations thereof is explained. One of the models, "E-B gen", which can be used to produce four types of enantiomorphically controlled tacticities, and the pentad distribution for the model "E-M1" are reported here for the first time. The relations of chain-end controlled models to binary copolymerizations are discussed in detail, and equations for the conversion of tacticity based probabilities to reactivity ratios to obtain related n-ad distributions are presented. The models were applied to 20 polymers with exemplary tacticities found in the literature. A related software program ("Polytact") based on Microsoft's Excel has been designed to calculate all relevant characteristics of the polymer tacticity and to present them in graphical form in a user-friendly manner. The program can be used to produce graphs of the triad, pentad and sequence length distributions and a simulation of 50 monomer repeat units in the polymer for each of the seven models. One of the main intended uses of the program is to compare the computed n-ad distributions to those of experimental polymers obtained from NMR spectroscopy and to gain insight into the polymerization mechanisms.