Poly proton spectrum

The spectra of stereoregular polymers show a single sharp line for each chemically distinct carbon because within each type of chain, each monomer residue is identical. However, the chemical shifts for isotactic and syndiotactic chains are not the same. For example, in isotactic poly(propylene), the CH3, CH and CH2 carbons occur at 20.0, 27.1 and 44.4 ppm, respectively, whereas in syndiotactic poly (propylene), the corresponding shifts are 18.7, 27.0 and 45.4 ppm [53]. NMR does not yield an unequivocal identification of the tacticity as does the CH2 proton spectrum, but it does permit different tacticities to be distinguished. 

This is a simulation of the CH2 proton spectrum of PVC as a composite lineshape from overlap of six tetrads [59]. The chemical shifts of each tetrad were obtained from an analysis of the spectrum of poly(vinyl chloride-a-di)... 

Figure 3.42 (a) H and (b) NMR spectra of poly(1,4-phenylene ether sulfone) in deuterated dimethyl-sulfoxide, DMSO-de. Spectrum (b) shows the NOE that occurs on proton decoupling of the 0 spectmm. The peaks for the protonated carbon atoms 2 and 3 ate enhanced by the NOE over the signals from the unprotonated carbon atoms 1 and 4. The peak in the proton spectrum at 3.3 ppm is due to water in the solvent the peak at 40 ppm in the C spectrum is due to natural C in the solvent. (From Williams, E.A. Characterization of Materials, Part I., 1992. Copyright Wiley-VCH Verlag GmbH Co. KGaA. Used with permission.)... 

Since there is no J coupling between the CH2 and a-CHs protons, the NMR phenomenon for poly(methyl methacrylate) is relatively simple. In the proton NMR spectrum, the ester methyl protons appear near 6.5r, the p-methylene protons appear near 8.0r, and the p-methyl protons appear between 8.5 and 9.0r. Figure 19.9 shows the p-methylene proton spectrum Figure 19.10 shows the p-methyl proton spectrum. Both were observed at 220 MHz. In both spectra, the ester methyl protons appear near 6.5r, but, in order to show the details of p-methylene protons and p-methyl protons, they were not shown in the two figures. In both cases, the sample was prepared by dissolving poly(methyl methacrylate) in 10-15% chlorobenzene, with the temperature of the NMR measurement at 135°C. 

As with many other polymers, the use of the superconducting NMR spectrometer seems to have removed nearly all of the interpretive ambiguities. Fig. 9 shows the 220 MHz proton spectrum of poly-a-rf -vinyr chloride in chlorobenzene solution at 140° [77], together with the tetrad chemical shift assignments. 

Fig. 9. 220 MHz proton spectrum of poly-a- /j-vinyl chloride (15% w/v in chlorobenzene at 140°) (ref 17)...

Poly(methyl methacrylate) (PMMA) was the first polymer studied in this manner and the interpretation of the corresponding H-NMR spectra illuminated the nature of the tacticity. The methylene proton spectrum of the anionically initiated polymer exhibits an AB quartet (/gem = 14.9 Hz) centered 1.86 ppm and therefore this polymer is predominately isotactic. In the spectrum of the free-radieal polymer, the methylene-proton resonance is a broad singlet, and so this polymer is predominately syndiotactic. This interpretation of the stereoregularity of these two polymers is a direct result of the expectations illustrated in Fig. 7.9. 

Figure 7.11 Methylene proton portion of the 220-MHz NMR spectrum of poly(methyl methacrylate) (a) predominately syndiotactic and (b) predominately isotactic. [From F. A. Bovey, High Resolution NMR of Macro molecules, Academic, New York, 1972, used with permission.]...

NMR Spectra - The proton NMR spectrum of poly(N-pheny1-3,4-dimethy-lenepyrroline) (VII) had three singlet absorptions at 6 2.56, 4.81 and 7.60 respectively (Figure 10). The integration of these peaks showed a ratio of 4 4 5. The presence of exocyclic olefinic protons was not observed, indicating that 1,4- addition was predominant in the polymerization with little or no 1,2 addition taking place. 

Figure 6. 50 MHz NMR spectrum of the masked poly(oxyethylene)-t -polyfpivalolactone) copoiymeric salt, 4, using attached proton test sequence (CH, CH3, Pos. CH2, C, neg.) in CDCI3 at 25°C.

Examination of the mass spectrum of P2VPY taken during the maximum decomposition rate reveals the major decomposition products as methylpyridine (93 a.m.u.), protonated vinyl pyridine (106 a.m.u.), and protonated dimer (211 a.m.u.) with ion ratios 74 100 59 respectively. Trimeric and tetrameric protonated species (316 and 421 a.m.u.) are also observed but in relatively small amounts. Protonated ions, rather than the simple monomers and dimers observed for the decomposition of poly(styrene) by MS11, may be created by a mechanism similar to that reported for the decomposition of 2-(4-heptyl)pyridine12 in the mass spectrometer. 

A first generation poly(amido amine) dendrimer has been functionalized with three calyx[4]arenes, each carrying a pyrene fluorophore (4) [30]. In acetonitrile solution the emission spectrum shows both the monomer and the excimer emission band, typical of the pyrene chromophore. Upon addition of Al3+ as perchlorate salt, a decrease in the excimer emission and a consequent revival of the monomer emission is observed. This can be interpreted as a change in the dendrimer structure and flexibility upon metal ion complexation that inhibits close proximity of pyrenyl units, thus decreasing the excimer formation probability. 1H NMR studies of dendrimer 4 revealed marked differences upon Al3+ addition only in the chemical shifts of the CH2 protons linked to the central amine group, demonstrating that the metal ion is coordinated by the dendrimer core. MALDI-TOF experiments gave evidence of a 1 1 complex. Similar results have been obtained for In3+, while other cations such as Ag+, Cd2+, and Zn2+ do not affect the luminescence properties of... 

Fig. 13.4 Proton-decoupled, 75.4-MHz carbon-13 NMR spectrum of Chevron HDPE LX-1159, a high-density poly(ethylene).

Figures 13.7 and 13.8 are two examples of two-dimensional NMR spectroscopy applied to polymers. Figure 13.7 is the proton homonuclear correlated spectroscopy (COSY) contour plot of Allied 8207A poly(amide) 6 [29]. In this experiment, the normal NMR spectrum is along the diagonal. Whenever a cross peak occurs, it is indicative of protons that are three bonds apart. Consequently, the backbone methylenes of this particular polymer can be traced through their J-coupling. Figure 13.8 is the proton-carbon correlated (HETCOR) contour plot of Nylon 6 [29]. This experiment permits the mapping of the proton resonances into the carbon-13 resonances.

It has also been possible to confirm the presence of the reduction product of a Schiff base on the polymer by proton magnetic resonance. For this purpose we have used unmodified poly(ethylenimine), since it too catalyzes the decarboxylation of oxalacetate to its product, pyruvate. Unmodified polyethylenimine was mixed with oxalacetate-4-ethyl ester. One-half of this solution was treated with NaBH4 the second half was exposed to a similar environment but no NaBH4 was added. The borohydride-treated polymer exhibited a strong triplet in the nmr spectrum centered at 3.4 ppm upfield from the HOD resonance. This new feature would be expected from the terminal methyl protons of the oxalacetate ester attached to the polymer. Only a very weak triplet was found in the control sample not treated with borohydride. These observations are strong evidence for the formation of Schiff bases with the polymer primary amine groups. Evidently the mechanistic pathway for decarboxylation by the polymer catalyst is similar to that used enzymatically. 

The angle dependence of the spin soliton in randomly oriented ladder poly-diactylene has also been investigated79 by pulsed HFEPR at 94 GHz. The shape of the 0-anisotropy-resolved nutation spectrum was discussed on the basis of the EPR transition moments and the differences between spin relaxation times. Reliable assignments of hyperfine couplings to the p-protons (P-H) of the alkyl side chains were achieved with the support of W-band ENDOR measurements. No significant orientational dependence of the 7i and Ti processes was found in terms of the isotropy of the p-H-hyperfine interaction. 

The 300 MHz H NMR and 20 MHz 13C NMR spectra of poly(4-methyl-l-pentene) have been found to be more complex than the corresponding spectra of poly(3-methyl-l-butene) due to the presence of an additional isomer structure in the polymer. Investigation of the 20 MHz 13C NMR spectrum of the polymer has indicated that placement of units in different triad sequences is die cause of multiple methyl proton resonances which have been observed in the H NMR spectra of poly(3-methyl-l-butene) and poly(4-methyl-l-pentene). The use of a computer program for simulating and plotting spectra has enabled measurements of polymer composition to be made of poly(4-methyl-l-pentene) s prepared under a variety of synthesis conditions. 

Morton et al.135,141) were the first to study the poly(butadienyl)lithium anionic chain end using (b). They found no evidence of 1,2-chain ends and concluded that only 1,4-structures having the lithium cr-bonded to the terminal carbon were present. A later study by Bywater et al.196), employing 1,1,3,4-tetradeuterobutadiene to minimize the complexity of the spectrum that arises from proton-proton coupling, found that the 1 1 adduct with d-9 fert-butyllithium in benzene exists as a mixture of the cis and trans conformers in the ratio 2.6 1. Glaze et al. 36) obtained a highly resolved spectrum of neopentylallyllithium in toluene and found a cis trans ratio of about 3 1. 

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