Nuclear magnetic resonance copolymers composition

The objective of this study is to characterize tin-containing polymers on a molecular level by means of high field, high resolution, multinuclear Fourier Transform Nuclear Magnetic Resonance (FT-NMR) (4 ). This study is generally an applied approach dealing with composition and configuration of specific formulations of the copolymer. 

Spectroscopic analyses are widely used to identify the components of copolymers. Infrared (IR) spectroscopy is often sufficient to identify the comonomers present and their general concentration. Nuclear magnetic resonance (NMR) spectrometry is a much more sensitive tool for analysis of copolymers that can be used to accurately quantify copolymer compositions and provide some information regarding monomer placement. 

Carbon-13 nuclear magnetic resonance was used to determine the molecular structure of four copolymers of vinyl chloride and vinylidene chloride. The spectra were used to determine both monomer composition and sequence distribution. Good agreement was found between the chlorine analysis determined from wet analysis and the chlorine analysis determined by the C nmr method. The number average sequence length for vinylidene chloride measured from the spectra fit first order Markovian statistics rather than Bernoullian. The chemical shifts in these copolymers as well as their changes in areas as a function of monomer composition enable these copolymers to serve as model... 

Table 6.2 Copolymer composition Xt versus monomer feed composition x° of bulk radical copolymerization of glycidyl methacrylate M, and styrene M2 (T = 60 °C, p < 0.1). In three columns the experimental data obtained [217] by means of chemical analysis of epoxy group content (EA), Infra Red (IR) and Proton Nuclear Magnetic Resonance (NMR) spectra are presented...

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. 

Copolymer composition was determined frc n I%iR spectra obtained on a Varian T-60 Nuclear Magnetic Resonance Spectrcmeter using CCI4 solutions and TMS as internal reference. Hie followup equation was derived to calculate the relative amounts of isdiutylene and inene in the copcdymer ... 

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. 

The application of UV spectrophotometers to the analysis of styrene containing copolymers has been extensively reported in the literature. However, hypochromic effects and band shifts which result in deviations from Beer s Law have limited the use of UV detectors as mass or composition detectors in size exclusion chromatography applications. Deviations from Beer s Law for low conversion styrene-acrylonitrile copolymers in tetrahydrofuran have been experimentally investigated and compared with results previously reported in the literature. The behaviour of the extinction coefficient as a function of the copolymer composition is discussed in view of the information obtained from infrared and nuclear magnetic resonance measurements on the same polymers. As a result of this investigation, a quantitative correlation of the extinction coefficients of styrene-acrylonitrile copolymers with the length of the styrene sequences has been obtained which, in turn, allows for the use of UV spectrophotometers as sequence length detectors. 

Copolymer compositions were determined by a high resolution nuclear magnetic resonance spectrometer (180 HMz). Copolymers of methyl methacrylate and styrene were dissolved in deuterated chloroform for the analysis. Deuterated pyridine was the solvent for the methyl methacrylate - methacrylic acid copolymers. Elemental analysis was also used in copolymer composition analysis to complement the NMR data. 

The first organometallic miktoarm star copolymer, PFS(PI)3, with PDI of 1.04 was synthesized through an anionic polymerization by using SiCl4 as a coupling agent, as shown in Scheme 3.11.32 The well-defined structure was confirmed by the characterizations of GPC and H nuclear magnetic resonance (NMR) spectroscopy. The PFS(PI)3 miktoarm star copolymer was obtained in a moderate yield after size-exclusion column purification (Mn = 21,300 PDI = 1.05) and with a composition ratio of PFS PI = 1 9.5. 

These generalizations may be illustrated by example (61). Consider the experiments outlined in Table 1. PHEMA, PMMA and copolymers of the two were prepared by dilute solution polymerization. Copolymer compositions (Table 1A [parentheses] ), obtained by application of proton Nuclear Magnetic Resonance spectroscopy (as detailed later in the discussion), are almost identical to the monomer feed ratios, despite high conversions. The latter increase through series 3 to 1, due to the square root relationship between initiator concentration and instantaneous rate of polymerization (63). Close to random co-polymerizations have been observed also in monomer mixtures containing... 

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. 

Copolymer composition can be obtained using nuclear magnetic resonance spectroscopy (NMR), IR spectroscopy, high-performance liquid chromatography (HPLC), elemental analysis or in some cases by titration of specific groups (see Section 11.2.3). 

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... 

The study of ethylene and propylene copolymerisation, on vanadium and titanium catalysts of various compositions [70], led to the conclusion that studied catalytic systems contain two or three types of AC. This conclusion has been made as a result of the analysis of the MWD curves, carbon nuclear magnetic resonance spectroscopy analysis, and copolymers composition fractionation data. The analysis of a large number of copolymer fractions, produced by their dissolution in several solvents at various temperatures, has indicated the existence of several types of AC different both in stereospecificity and in reactivity. According to the authors of [70], a combination of copolymer fractionation results with gel chromatography data indicates the presence of two or three types of AC. 

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. 

All spectroscopic methods allowing the identification of chemical structures and the quantitative determination of identified chemical functions can be used to determine the composition of a copolymer. Nuclear magnetic resonance is by far the most used method for this purpose, but infrared and Raman spectroscopy can also be used. 

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). 

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