The use of 13 carbon nuclear magnetic resonance (NMR) spectroscopy in the molecular characterization of macromolecules has advanced our knowledge into structural areas that have been nearly impossible to measure by other spectroscopic techniques. Innovative applications have led to determinations of polymer configurational distributions, comonomer sequence distributions, average sequence lengths, structure and distribution of short chain branches, and analyses of nonreactive end groups. As a result, the importance of 13C NMR to the field of polymer science cannot be overemphasized. The key to the success of 13C-NMR studies in defining polymer molecular structure has been a structural sensitivity which encompasses more than just a few functional groups or carbon atoms. A sensitivity to polymer repeat unit sequences of lengths from two to as many as five, seven, and even nine contiguous repeat units [1,2] has been observed. Of course, any structural technique that senses a unique response from as f...

A review of high resolution liquid 13carbon nuclear magnetic resonance characterizations of ethylene-based polymers

(1980). Reverse Turns in Peptides and Protein. Critical Reviews in Biochemistry: Vol. 8, No. 4, pp. 315-399.

Reverse turns in peptides and proteins.

Recent developments that increase the time and distance scales accessible in the simulations of specific polymers are reviewed. Several different techniques are similar in that they replace a model expressed in fully atomistic detail with a coarse-grained model of the same polymer, atomistic → coarse-grained (and beyond!), thereby increasing the time and distance scales accessible within the expenditure of reasonable computational resources. The bridge represented by the right-pointing arrow can be constructed via different procedures, which are reviewed here. The review also considers the status of methods which reverse this arrow, atomistic ← coarse-grained. This “reverse-mapping” recovers a model expressed in fully atomistic detail from an arbitrarily chosen replica generated during the simulation of the coarse-grained system. Taken in conjunction with the efficiency of the simulation when the system is in its coarse-grained representation, the overall process Open image in new window permits a much more complete equilibration of the system (larger effective size of Δt) when that equilibration is performed with the coarse-grained replicas (II → III) than if it were attempted with the fully atomistic replicas (I → IV).

Bridging the Gap Between Atomistic and Coarse-Grained Models of Polymers: Status and Perspectives

Catalyst components for the(co)polymerization of ethylene comprising Ti, Mg, halogen, ORI groups, where RI is a C1-C12 hydrocarbon group optionally containing heteroatoms, having ORI/Ti molar ratio in the range 0.1-1.5, a Mg/Ti molar ratio of less than 8, an amount of titanium, with respect to the total weight of said solid catalyst component, higher than 4% by weight characterized by a specific SS-NMR pattern are particularly useful for preparing narrow MWD crystalline ethylene polymers.

Catalyst components for the polymerization of olefins

A highly regioselective secondary enchainment of propylene in a group IV catalyst system is reported. End-group analysis of polypropylene formed using the phenoxyimine-based titanium catalysts revealed a reversal in the regioselectivity of insertion for this class of catalysts. To the best of our knowledge, bis(phenoxyimine)-based titanium complexes are the only known group IV catalysts that insert propylene with exclusive 2,1-regiochemistry. Insertion of propylene into the initiating titanium hydride occurs with high 1,2-regiochemistry. Subsequent insertions into primary titanium alkyls are regiorandom, while insertions into secondary titanium alkyls proceed with high 2,1-regioselectivity. Cyclopolymerization and ethylene/propylene copolymerization strategies are employed to support this proposal.

Mechanism of propylene insertion using bis(phenoxyimine)-based titanium catalysts: an unusual secondary insertion of propylene in a group IV catalyst system.

Monomer Sequence Distribution in Ethylene-Propylene Rubber Measured by13C NMR. 3. Use of Reaction Probability Model

Crystal Structure of Poly(vinyl chloride) Single Crystals

One can measure r1r2 for an ethylene—propylene rubber by determining composition and χ, the ratio of contiguous to isolated propylene units. Our previous determination of χ depended on measuring methine carbon resonances in a 13C NMR spectrum. The χ method based solely on methine peak area measurements is inaccurate. This is not because the χ method is theoretically unsound, but because it is impossible to accurately extract the methine areas, necessary to calculate χ from the complex 13C NMR spectra of ethylene—propylene rubbers. The presence of inverted propylene produces ambiguity in a portion of the methine region. This means the methine areas can be used only to calculate a maximum and minimum boundary for r1r2. Another difficulty in using only methine areas to determine χ arises at propylene levels less than 35 wt%, because the methine areas for contiguous propylene triads become very small and are overlapped by strong resonances from long methylene sequences. We have developed a reaction p...

Monomer Sequence Distribution in Ethylene-Propylene Rubber Measured by 13C NMR. 3. Use of Reaction Probability Model

Influence of Polymer Association on the Interpretation of Nuclear Magnetic Resonance Measured Tacticity of Poly(vinyl chloride) in Solution

Considerable progress has been made in the analysis of monomer sequence distribution in ethylene-propylene copolymers and terpolymers. Fourier transform Carbon-13 nuclear magnetic resonance spectra provide a significant increase in signal-to-noise over our previously published continuous wave (CW) spectra. Most of the methylene, methyl, and methine carbon resonances have been assigned and verified. A few uncertainties remain in the deconvolution of overlapping peaks or the prorating of coincident peaks for some of the minor constituent structures. For a series of four terpolymers containing approximately 1% ethylidenenorbornene as the third monomer, r1 r2 was determined to be 1.0. The precision is estimated to be better than ±0.2. The spectra contain enough data to ultimately provide several internal checks. When the methyl assignments are further refined, comparison may be made between the propylene sequence distributions calculated from methyl and from methine resonances. Devising a system for treating the effects of propylene inversion on the methylene resonances will allow description of the ethylene sequence distribution. The net result should be very reliable r1 r2 products for ethylene-propylene copolymers and terpolymers of low third monomer content.

Monomer sequence distribution in ethylene‐propylene terpolymers measured by 13C nuclear magnetic resonance

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