Nuclear magnetic resonance polymer extracts

Structural information at the molecular level can be extracted using a number of experimental techniques which include, but are not restricted to, optical rotation, infra-red and ultra-violet spectroscopy, nuclear magnetic resonance in the solid state and in solution, diffraction using electrons, neutrons or x-rays. Not all of them, however, are capable of yielding structural details to the same desirable extent. By far, experience shows that x-ray fiber diffraction (2), in conjunction with computer model building, is the most powerful tool which enables to establish the spatial arrangement of atoms in polymer molecules. 

It is possible to use techniques in which the additives can be determined by direct analysis of the sample, such as nuclear magnetic resonance (NMR) spectrometry, ultraviolet (UV) spectrometry, and UV desorption-mass spectrometry. These techniques are very useful when the concentrations of additives in the polymer are high. However, when additives are present in trace levels, it is necessary to carry out a preliminary extraction/concentration step before analysis. Some of the most common additives used in plastics materials are presented in Table 1. 

Schaefer et al. (19) studied the interphase microstructure of ternary polymer composites consisting of polypropylene, ethylene-propylene-diene-terpolymer (EPDM), and different types of inorganic fillers (e.g., kaolin clay and barium sulfate). They used extraction and dynamic mechanical methods to relate the thickness of absorbed polymer coatings on filler particles to mechanical properties. The extraction of composite samples with xylene solvent for prolonged periods of time indicated that the bound polymer around filler particles increased from 3 to 12 nm thick between kaolin to barium sulfate filler types. Solid-state Nuclear Magnetic Resonance (NMR) analyses of the bound polymer layers indicated that EPDM was the main constituent adsorbed to the filler particles. Without doubt, the existence of an interphase microstructure was shown to exist and have a rather sizable thickness. They proceeded to use this interphase model to fit a modified van der Poel equation to compute the storage modulus G (T) and loss modulus G"(T) properties. 

Nuclear magnetic resonance (NMR) is a physical process in which nuclei in a magnetic field absorb and reemit electromagnetic radiation. Analysis of NMR spectra allows the determination of polymer composition, and the distribution of monomer units can be deduced from the diad and triad sequences by NMR spectral analysis. For characterization of polymer, the extracted polymer wiU be dissolved in CDCI3 followed by NMR analysis. The NMR spectrum for PHB shows three characteristic signals. A doublet at 1.53 ppm represented the methyl group (CH3) coupled to one proton while a doublet of... 

The difficulty results, in part, from the fact that only a small fraction of the chemical bonds, generally less than one in a thousand, are involved in me-chanochemical processes. The concentration of connecting units is therefore at the detection limit and below for traditional analytical methods such as conventional nuclear magnetic resonance and infrared spectroscopy. The sensitivity can, of course, be enhanced by techniques such as cumulative, multiple scans, Fourier transform analysis, and difference techniques for detection to one part in ten thousand and better. It may yet be difficult to determine whether polymers are linked by chemical bonds or whether they are simply intimate mixtures. For this distinction, other tests can be of value. For example, the difference between blocks and blends for ethylene-propylene polymer systems has been distinguished by thermal analysis [5]. In many cases, simple extraction tests can distinguish between copolymers and blends. For example, for rubber milled into polystyrene, the fraction of extractable rubber is a measure of mechanochemistry. Conversely, only the rubber in this system is readily cross-linked by benzoyl peroxide after which free polystyrene may be conveniently extracted [6]. In another case, homopolymers of styrene and methyl methacrylate can be separated cleanly from each other and from their copolymers by fractional precipitation [7]. The success of such processes, of course, depends on both the compositions and molecular weights involved. 

Starch and its blends have attracted much attention as environmentally biodegradable polymers (29-31). However they suffer fi-om disadvantages as compared with conventional polymers and blends such as brittleness and a narrow processability window (32). The thermal behavior and phase morphology of starch-blend systems have been studied by differential scanning calorimetry (DSC), Fourier Transform Infrared (FTIR) spectroscopy, scanning electron microscopy solvent extraction. X-ray diffraction, optical rotation, nuclear magnetic resonance (NMR) and polarizing optical microscopy (33-36). Like polymer blends wide applications starch-based blends have the potential to be... 

A technique for the determination of HALS in polypropylene was developed. The HALS, based on a polysiloxane backbone with tetramethyl piperidine side chains, was melt blended with the polypropylene which was then spun into fibres. The chopped fibres were dissolved in toluene, the polymer precipitated using methanol, and the filtrate dried. A solution of the filtrate was then prepared and analysed by proton nuclear magnetic resonance spectroscopy. The peak at 0.1 ppm was attributed to the methyl group on the silicon atom of the HALS, and was used for quantitative purposes. Polypropylene pellets were also prepared containing a lower concentration of HALS, which was subsequently subjected to direct extraction to prevent the loss which may occur during polymer reprecipitation. 3 refs. 

To determine the polymer(s) that are present in a rubber it is usual to use either Fourier-transform infrared spectroscopy or nuclear magnetic resonance (NMR) spectroscopy. These techniques are normally applied to a sample that has undergone some preliminary preparation. For example, a solvent extraction can be carried out to remove process oils and other low-Mw organic compounds and then the extracted sample is often pyrolysed to remove any interferences from the fillers present. As solid-state NMR techniques become more advanced and sensitive, however, it may become easier to obtain this information directly on samples in the future. 

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