Anita J. Brandolini

NMR Spectra of Polymers and Polymer Additives

Aliphatic backbones - aliphatic pendant groups aliphatic backbones - aromatic pendant groups aliphatic backbones - carbolic acid, ester and amide pendant groups aliphatic backbones - miscellaneous pendant groups unsaturated backbones ester backbones ester and amide backbones miscellaneous backbones polymer additives. Appendices: major end-use applications for some commercially significant polymers graphic summary of C chemical shifts for common polymers some suppliers of ploymers and polymer additives.

Kinetics and mechanism of ethylene homopolymerization and copolymerization reactions with heterogeneous Ti-based Ziegler–Natta catalysts

A detailed kinetic analysis of ethylene homopolymerization reactions and its copolymerization reactions with 1-hexene with a supported Ti-based Ziegler–Natta catalyst (reactions in the absence and the presence of hydrogen) shows a number of distinct kinetic features which are interpreted as a manifestation of multi-site catalysis; the catalyst contains several types of polymerization centers which differ in stability and formation rates, the molecular weight of polymers they produce, and in their response to the presence of α-olefins and hydrogen. All these effects require introduction of a special kinetic mechanism which postulates an unusually low activity of growing polymer chains containing one ethylene unit, the Ti–C2H5 group, in the ethylene insertion reaction into the Ti–C bond. This peculiarity of the Ti–C2H5 group, which is probably caused by its β-agostic stabilization, predicts two kinetic/chemical features of ethylene polymerization reactions which have not been described yet, the deuterium effect on the homopolymer structure and the activation effect of α-olefins on chain initiation. Both effects were confirmed experimentally.

Ethylene polymerization reactions with Ziegler–Natta catalysts. III. Chain‐end structures and polymerization mechanism

Ethylene polymerization reactions with many Ziegler–Natta catalysts exhibit a number of features that differentiate them from polymerization reactions of α olefins: (1) a relatively low ethylene reactivity, (2) markedly higher polymerization rates in the presence of α olefins, (3) a high reaction order with respect to ethylene concentration, and (4) a strong reversible rate depression in the presence of hydrogen. A detailed kinetic analysis of ethylene polymerization reactions1 provided the basis for a new kinetic scheme that postulates the equilibrium formation of TiC2H5 species with the H atom in the methyl group β-agostically coordinated to the Ti atom in an active center. This mechanism predicts several new features of ethylene polymerization reactions, one being that chain initiation via insertion of any α-olefin molecule into the TiH bond should proceed with an increased probability compared to that via ethylene insertion into the same bond. As a result, a significant fraction of ethylene/α-olefin copolymer chains should contain α-olefin units as the starting units. This article provides experimental data supporting this prediction on the basis of both a detailed structural analysis of co-oligomers formed in ethylene/1-pentene and ethylene/4-methyl-1-pentene copolymerization reactions and a spectroscopic analysis of chain ends in the copolymers.

NMR spectroscopy of solid polymer systems

Over time, nuclear magnetic resonance (NMR) spectroscopy has proven to be a remarkably versatile tool for the description of molecular structure and dynamics. This versatility arises from the wide range of nuclear interactions affecting the NMR signal. Because these interactions depend on different nuclear and molecular parameters, one can manipulate them to extract very specific information. Since the development, in the mid-1970s, of solid-state pulse techniques, it has been possible to tailor an NMR experiment to highlight the specific interaction of interest [1–4], leading to a finer description of chemical structure, morphology, orientation, and chain dynamics [5–7].