Nuclear magnetic resonance polymer composition determined

The latexes were cleaned by ion exchange and serum replacement, and the number and type of surface groups were determined by conductometric titration. The molecular weight distributions of the polymers were determined by gel permeation chromatography. The stability of the latexes to added electrolyte was determined by spectrophotometry. The compositional distribution was determined by dynamic mechanical spectroscopy (Rheovibron) and differential scanning calorimetry, and the sequence distribution by C13 nuclear magnetic resonance. 

If you have been working your way through this epic in a more or less linear fashion, then you might have started to ask yourself some fundamental questions such as, How do you know if a vinyl polymer is isotactic, or atactic, or whatever How do you know the composition and sequence distribution of monomers in a copolymer How do you know the molecular weight distribution of a sample This last question will have to wait until we discuss solution properties, but now is a good point to discuss the determination of chain microstructure by spectroscopic methods. The techniques we will discuss, infrared and nuclear magnetic resonance spectroscopy, can do a lot more than probe microstructure, but that would be another book and here we will focus on the basics. 

Of considerable importance in the determination of polymer composition and structure is nuclear magnetic resonance (NMR) spectroscopy. A large number of literature reports are available regarding the application of this technique in the study of polymers (see e g. [5]). This technique allows the identification of various structural units in polymers based on the chemical shift and spin-spin coupling either in proton NMR spectra or... 

Copolymer Analysis. Even though the overall copolymer composition can be determined by residual monomer analysis, it still is necessary to have reliable quantitative techniques for copolymer composition measurements on the actual copolymer, mainly because concentration detectors for SEC or HPLC are sensitive to composition and because the conversion histories are not always available. Some of the techniques used to determine copolymer composition are melt viscometry (46), chemical analysis, elemental analysis, infrared spectroscopy (IR), Nuclear Magnetic Resonance (NMR), ultra-violet spectroscopy (UV), etc. Melt viscometry, chemical and elemental analysis are general techniques that can be applied to almost any polymer. The spectroscopic techniques can be applied depending on the ability of the functional groups present to absorb at specific wavelengths. 

In this way, EA can be applied to determine monomer composition in copolymers and polymer blends and any other composite material. Although results from EA are comparable to those obtained from spectroscopic techniques such as IR and NMR (nuclear magnetic resonance) spectroscopies, developments in EA are needed to improve the accuracy and precision of the method. 

Yan et al. [52] explored the use of IPN techniques to produce a composite vinyl-acrylic latex. The first-formed polymer was produced using VAc and divinyl benzene (DVB), while the second formed polymer constituted a BA/DVB copolymer. In both cases the DVB was added at 0.4 wt%. They compared this product with another product, a bidirectional interpenetrating netwodc (BIPN) in which VAc was again polymerized over the first IPN. They noted that the compatibility between the phases was more pronounced in the BIPN than in the IPN as determined using dynamic mechanical measurements and C nuclear magnetic resonance spectroscopy. The concept of polymer miscibility has also been used to produce composite latex particles and thus modify the pafamance properties of VAc latexes. Bott et al. [53] describe a process whereby they bloid VAc/ethylene (VAc/E) copolymers with copolymers of acrylic acid or maleic anhydride and determine windows of miscibility. Apparently an ethyl acrylate or BA copolymer with 10-25 wt% AA is compatible with a VAc/E copolymer of 5-30 wt% ethylene. The information obtained from this woik was then used to form blends of latex polymers by polymerizing suitable mixtures of monomers into preformed VAc/E copolymers. The products are said to be useful for coating adhesives and caulks. 

The composition of carbon-chain polymers with monomeric units having widely differing analytical composition, characteristic elements or groups, or radioactive labels can be readily determined. Chemical (microanalysis, functional group determination, etc.) and spectroscopic methods (infrared, ultraviolet, nuclear magnetic resonance, etc.), as well as the determination of radioactivity, yield the average composition of the polymer. The mean composition can also be determined from the refractive indices of solid samples. The composition can be calculated from the principle that the copolymer is considered to be a solution of one unipolymer (from one of the monomeric units) in the other. The composition can also be found by means of the refractive index increment dw/dc in solution, which gives the variation in refractive index with concentration. The mass fraction of the monomeric unit A can be calculated from... 

There were also attempts to calibrate the SEC columns with help of broad molar mass dispersity poplymers but this is less lehable. The most common and well credible SEC cahbration standards are linear polystyrenes, PS, which are prepared by the anionic polymerizatioa As indicated in section 11.7, according to lUPAC, the molar mass values determined by means of SEC based on PS calibration standards are to be designated polystyrene equivalent molar masses . Other common SEC calibrants are poly(methyl methaciylate)s, which are important for eluents that do not dissolve polystyrenes, such as hexafluoroisopropanol, further poly(ethylene oxide)s, poly(vinyl acetate)s, polyolefins, dextrans, pullulans, some proteins and few others. The situation is much more complicated with complex polymers such as copolymers. For example, block copolymers often contain their parent homopolymers (see sections 11.8.3, 11.8.6 and 11.9). The latter are hardly detectable by SEC, which is often apphed for copolymer characterization by the suppliers (compare Figure 16). Therefore, it is hardly appropriate to consider them standards. Molecules of statistical copolymers of the same both molar mass and overall chemical composition may well differ in their blockiness and therefore their coils may assume distinct size in solution. In the case of complex polymers and complex polymer systems, the researchers often seek support in other characterization methods such as nuclear magnetic resonance, matrix assisted desorption ionization mass spectrometry and like. 

McCormick, C. L., Chen, G. S. and Hutchinson, B. H., Water-Soluble Copol3rmers. V. Compositional Determination of Random Copolymers of Acrylamide with Sulfonated Comonomers by Infrared Spectroscopy and C13 Nuclear Magnetic Resonance, J. Appl. Polym. Sci., 27 3103 (1982). 

Hevea family, Hevea Euphorbiaceae and HeveaMoraceae, was compared with that from Hevea Brasihaisis to examine the gel content. Composition of latex and presence of soft (soluble) gel depended on the botanical family. Hard gel, caused by chemical crosslinking between the polymer chains, appears dependent on extended storage. Molecular weight of samples was determined by size exclusion chromatography, and structural information on the polymer chain by nuclear magnetic resonance spectroscopy. 17 refs. BRAZIL JAPAN... 

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... 

Nuclear magnetic resonance (NMR) spectrometers offer spectral capabilities to elucidate polymeric structures. This approach can be used to perform experiments to determine comonomer sequence distributions of polymer products. Furthermore, the NMR can be equipped with pulsed-liied gradient technology (PFG-NMR), which not only allows one to determine self-diffusion coefficients of molecules to better understand complexation mechanisms between a chemical and certain polymers, but also can reduce experimental time for acquiring NMR data. Some NMR instruments can be equipped with a microprobe to be able to detect microgram quantities of samples for analysis. This probe has proven quite useful in GPC/NMR studies on polymers. Examples include both comonomer concentration and sequence distribution for copolymers across their respective molecular-weight distributions and chemical compositions. The GPC interface can also be used on an HPLC, permitting LC-NMR analysis to be performed too. Solid-state accessories also make it possible to study cross-linked polymers by NMR. 

Nuclear Magnetic Resonance (NMR) spectroscopy is a powerful technique to identify and determine the structure of a pure organic compound or the repeat unit of a polymer. For polymer materials and composites, infrared (IR) and Raman spectroscopy are commonly used for identification of different functionalities. IR [49, 58-63], Raman [64, 65] and NMR [40, 43, 66, 67] spectroscopy have been carried out on PBIs and their composites to identify and/or confirm the chemical structure of the polymers. As an example of the wPBI, the IR spectrum in the region from 2000 to 4000 cm is of particular interest since most of the informative N-H stretching modes occur in this range, with typically three distinguishable bands at around 3415, 3145, and 3063 cm ... 

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