Chemical shift ethylene-propylene copolymer

From Mark s RIS model for ethylene-propylene copolymers (J. Chem. Phys. 1972, 57, 2541) it is determined that P(t) = 0.380, P g+) = 0.014, and Pig") = 0.606 in 2,4-dimethylhexane (2,4-DMH). Using this RIS model, furthermore, for all the branched alkanes considered whose isopropyl groups are separated by at least one methylene carbon from the next substituted carbon and the RIS model developed by Asakura et at. (Makromol. Chem, 1976, 177, 1493) for head-to-head polypropylene to treat 2,3-dimethyl pentane, AS s are calculated for a large number of branched alkanes. The agreement between the observed and the calculated nonequivalent 13C NMR chemical shifts is quite good, including the prediction that separation of the isopropyl group from the next substituted carbon by four or more methylene carbons removes the nonequivalence. 

NOESY has also been used to elucidate the chain conformation of poly(styrene-a/ -MMA).220,221 2D INADEQUATE has been applied to studies of monomer sequence distribution in ethylene-propylene copolymer.223 Additivity rules for the 13C chemical shifts of ethylene-propylene copolymer were devised for configurational sequences as well as substituent effects.226... 

Table II. Chemical Shift Values and Peak Height Intensities of the Ethylene-Propylene Copolymer...

Figure 4.2 C-NMR spectrum of ethylene-propylene copolymer showing chemical shift assignments. Reproduced with permission from H.N. Cheng and M. Kakngo, Macromolecules, 1991, 24,1724. 1991, ACS...

Table 4.5 Observed and reference C-NMR chemical shifts in ppm for ethylene-propylene copolymers and reference polypropylenes as measured with respect to an internal trimethylsilane standard...

The C-NMR spectrum of an ethylene-propylene copolymer, containing approximately 97% propylene in primarily isotactic sequences, is shown in Figure 10.3. Major resonances are numbered consecutively from low to high field. Chemical shift data and assignments are listed in Table 10.1. Greek letters are used to distinguish the various methylene carbons and designate the location of the nearest methine carbons. 

Paxson and Randall [38] in their method use the reference chemical shift data obtained on a predominantly isotactic polypropylene and on an ethylene-propylene copolymer (97% ethylene). They concluded that the three ethylene-propylene copolymers used in their study (97-99% propylene) contained principally isolated ethylene-ethylene linkages. Knowing the structure of their three ethylene-propylene copolymers, they used the C-NMR relative intensities to determine ethylene-propylene contents and thereby establish reference copolymers for the faster IR method involving measurements at 732 cm (13.66 pm). After a detailed analysis of resonances Paxson and Randall [38] concluded that methine resonances 4 and 5 (Table 10.1) gave the best quantitative results to determine the comonomers composition. The composition of the ethylene-propylene copolymers was determined by peak heights using the methine resonances only. In no instance was there any evidence for an inclusion of consecutive ethylene units. Thus, composition data from C-NMR could now be used to establish an IR method based on a correlation with the 732 (13.66 pm) band which is attributed to a rocking mode, r, of the methylene... 

Table 7.46 - Observed and Reference NMR Chemical Shifts in ppm for Ethylene-Propylene Copolymers and Reference Polypropylenes as Measured with Respect to an Internal IMS Standard... 

Resonance assignments are often made by empirical relationships or rules that relate structural differences to chemical shift differences. These can be based on extensive studies on model compounds as in the case of the Grant-Paul or Lindeman-Adams relationships [1-3] for predicting the chemical shifts of carbon atoms in hydrocarbons and polyhydrocarbons. These have been very valuable for assigning the resonances observed in the spectra of ethylene-propylene copolymers [4,5], propylene-butene-1 copolymers [6,7], hydrogenated polydienes [8-18], and hydrogenated... 

Olefin chain ends of ethylene/propylene copolymers and their chemical shifts ... 

The chemical shift calculation (y-effect method) based on the y-effect of the chemical shift and the rotational isomeric state model (RIS model) has been developed as a reliable method for predicting chemical shift differences among pentad, hexad, and heptad sequences in various polyolefins [47-49, 14, 50, 51]. chemical shift assignments of tactic pentad and heptad sequences in polypropylene have been provided by this method [47-49]. Hayashi and co-workers [45,46] confirmed that the chemical shift due to the y-effect is also sensitive to different comonomer sequences in ethylene-propylene copolymers. Asakura and co-workers [52] have demonstrated that... 

Figure 12.7 The 129Xe NMR spectra of (a) high density PE, (b) iPP and (c) of a blend consisting of 80% iPP and 20% EP copolymer with the composition 33% propylene and 67% ethylene. The line positions show that the Xe absorbed in the iPP matrix is identical to Xe in iPP (Figure 12.7b), but that the Xe in the EP domains have a chemical shift in between that of Xe in PE (Figure 12.7a) and of Xe in iPP...

Several other propylene-based copolymers and blends have been analyzed by vibrational spectroscopy. The EPDM (ethylene-propylene-diene-monomer) content in PP/EPDM (low temperature impact) blends is a linear function of the ratio A(2850cm" )/A(2920cm" ) up to 80% EPDM. Functionalized PP (compatibilizer) for use in PP blends is often characterized by IR spectroscopy. These compatibilizers typically consist of PP grafted with anhydrides or acids, and may be analyzed in terms of chemical details and graft content. Intermolecular interaction between groups on the grafted side chain and the non-PP component in the blend has been characterized by band shifts and band broadening. 

Figures 4.2 to 4.6 show NMR spectra of ethylene copolymers with propylene, butene-1, hexane-1, octane-1 and 4-methyl pentene-1. These spectra show chemical shift assignment of T values of the resonances of the copolymers. The molar composition of these copolymers could be determined with a relative precision at about 6% and pm value measurements at 10 ppm and 50 ppm.

Carbon-13 spectroscopy has been used very effectively by Corno and coworkers [115-117] to characterize the distributions of monomer sequences in copolymers derived from episulfides using anionic catalysts. Although chiral monomers were not employed in these studies, it is worth noting that tacticity effects had a relatively small effect on the resonance patterns observed, but that the chemical shifts of in-chain carbon atoms in different sequences were s ibstantially different. On the basis of assignments and empirical shift parameters developed by Corno, et al., the spectra of stereoregular ethylene sulfide-propylene sulfide copolymers and propylene sulfide-isobutylene sulfide copolymers should be readily analyzed. Studies on copolymers derived from racemic monomers indicate them to have random structures a similar result can be e3q>ected for copolymers derived from optically active monomers. 

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