NMR, Study of polymers

For NMR studies of polymer mixtures, the earliest approach proposed was the Coleman-Fox model.(5) This model assumes the coexistence of two interconverting Bemoullian propagating sites and was used extensively for poly(methyl methacrylate).(6-8)... 

NMR studies of polymers made with deuterated monomers provide additional information on the cyclic isotactic transition state. Miyazawa and Ideyuchi (97) have shown that the isotactic polymerization of propylene takes place with cis opening of the olefinic double bond. This shows that the 4-membered cyclic transition occurs with reaction of the new monomer on the front side of the propagating ion as illustrated in Fig. 12. 

Thus, in agreement with the results observed by Price, who obtained polymars with a microstructure depending exclusively on the configuration of the monomers C-NMR studies of polymers reveal that polymerizatfon of ethylene oxide almost entirely proceeds through inversion of configuration at the carbon atom attacked by a monomer molecule... 

NMR studies of polymers, and magnetic resonance imaging (MRI). In an interesting study, the solid state CPMAS NMR data sets for a pharmaceutical compound were analyzed using DECRA. In these experiments the exponential decay of the signal intensity in the data matrix D decayed as a result of H spin lattice T relaxation. The DECRA results allowed the resolution of two distinct crystalline polymorphs within the compound. DECRA has also used to analyze the C MAS NMR spectra of irradiated cross-linked polyolefin cable insulation. In this study, the two proportional data... 

Choice of Solvent. The most appropriate solvent for NMR studies of polymers would allow a range of polymer concentrations to be investigated, be free of overlap problems and hopefully provide a signal for internal lock. Not all of these conditions can usually be met as many high molecular weight polymers pose solubility problems and can be examined in only a limited number of solvents. Deuterium resonance is the typical choice for an internal lock signal on most modern NMR spectrometers. Unfortunately, the majority of available deuterated solvents are poor solvents for many addition polymers such as the polyolefins while it is generally possible to find a number of appropriate deuterated solvents for many of the condensation polymers. The... 

This book is dedicated to Frank A. Bovey, a pioneer researcher in NMR studies of polymers, on the occasion of his receipt of the American Chemical Society award in Applied Polymer Science, sponsored by the Phillips Petroleum Company, March 22, 1983. 

In the past 4-5 years, quite a number of relevant review articles and books have appeared. These included general reviews on NMR of polymers (1 10), reviews on solid state NMR (11-15), solid state multidimensional techniques (16-19), spatially resolved techniques (20), solid state NMR studies of polymer dynamics and structure (21), hydrated polymers (22), vulcanized elastomers (23), crosslinked polymers (24), and polymer networks (25), Reviews have also been written on polymer gels (26-28), polymer colloids (29), polymer-surfactant systems (30), and polymers on surfaces (31). 

Isotopic labeling is a very useful technique in NMR studies of polymers. For exanqjle, NMR studies of polymers and copolymers prepared using C-enriched initiators have been carried out to obtain information about the chemo-, regio-, and stereo-selectivity of radicals derived from such initiators (93-95), In addition, and labeling has permitted the studies of chain ends obtained from F and P-containing initiators and chain transfer agents (72,95),... 

Liquid state NMR studies of polymer dynamics and conformation... 

There is a point when the NMR characteristics of a bulk polymer have to be treated as non-liquid-like, that is below the glass transition temperature. The NMR spectrum will then be dominated by static effects, such as the orientation dependence of chemical shift and the dipolar interaction. The earliest forms of solid-state polymer NMR were developed in the knowledge that these solid-state effects would be present, and would complicate the resulting data interpretations. Proton NMR studies of polymers have an impressive pedigree, and have relied on applications of a distinct solid-state theory. But it is only relatively recently that aspects of this theory have been refined to the point where experimental observations can be understood more fully. In particular, the process of spin diffusion is much better appreciated. Proton broad-line NMR does not necessarily require the use of large magnets and despite the theoretical uncertainties it has been widely accepted within the realms of rapid analysis. In its simplest form it has been used to quantify liquid and solid ingredients, for example, in plasticised polymers. 

Shen, L., Soong, R., Wang, M. et al. 2008. Pulsed field gradient NMR studies of polymer adsorption on colloidal CdSe quantum dots. J. Phys. Chem. B 112 1626-1633. 

X. FLUORINE NMR STUDIES OF POLYMERS The table is ordered according to the monomers forming the polymer, with the lowest molecular weight monomer appearing first. 

Two-dimensional NMR studies of polymer solutions (26) can also be used to detect and assign NMR resonances from lesser chain structures in polymers (e.g., chain ends, defects, branches, and block junctions), critical in characterizing many synthetic polymers. 

Fluorine-19 is spin 1/2, 100% abundant, and has a sensitivity relative to the proton of 0.83. It is a very easy nucleus to observe, and even prior to 1970 a great deal of information was obtained. NMR has found widespread application in chemistry and biology for example, the high-resolution F NMR study of polymers in solution furnishes relevant chemical information concerning polymer structures furthermore, fluorine NMR can be useful for studying the binding of fluorinated molecules and macromolecules and membranes. 

NMR relaxation or line width measurements are sensitive to the degree of crystallinity in solid polymers, because the protons in the crystalline lattice experience strong dipole-dipole interactions which cause fast spin-spin relaxation and line broadening. As a result, line width and relaxation studies have been used to measure crystallinity in a broad range of polymers. The use of high pressure as an experimental variable in NMR studies of polymer crystallinity offers new details about polymer crystallization. The study of pressure and temperature effects on the... 

Adamic, K. J., Greenbaum, S. G., Abraham, K. M., Alamgir, M., WintersgiU, M. C., Fontanella, J. J., Lithium-7 nmr study of polymer electrolytes based on composites of poly[i>w((methoxyethoxy)ethoxy)phosphazene] and poly(ethylene oxide). Chemistry of Materials, 1991, 3, 534-538. 

This chapter will be restricted to discussing solution NMR studies of polymers. For an excellent description of solid-state NMR techniques, the reader should first consult Chapter 2.07 of this comprehensive, by Saalwachter and Spiess. In the next section, some basic principles of NMR will be presented, followed by a discussion of ID-, 2D-, and 3D-NMR principles, techniques, and the information to be gained from each technique. The last seaion will be dedicated to examples of how these techniques can be used to leam about polymer struaures, including monomer composition, stereosequence effects, monomer sequence effects, short-chain branching, chain end structure, dendrimer stracture, and polymer branching, and other polymer defect structures. 

With a few exceptions such as (I = 1), which has a small nuclear quadmpole moment, the nonspherical charge distribution of nuclei with a spin number I a 1 have a large electric quadmpole moment that affects the relaxation time, and the width of their NMR signals are broad. These broad lines usually mask the ability to measure useful NMR parameters such as chemical shifts and coupling with neighboring nuclei. As a result, they are not discussed here, as most of the solution NMR studies of polymers were performed on J = 1/2 nuclei. In the solid state, quad-rapolar interactions from measurements of NMR can yield valuable molecular stmcture and dynamics information this is discussed in Chapter 2.07. Some of the NMR characteristics of commonly observed nuclei are summarized in Table 1. 

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