Polymers methyl resonance

Statistical analysis is important and relatively easy. Suppose we have a fully atactic polymer which we analyse for the triad content for isotactic polymer. Only three methyl resonances due to triads are observed, and the statistical ratio of mm, rr, and mr is 1 1 2. Thus even in the atactic polymer our isotactic content is 25% Pentad analysis, however, would give only 8% mmmm isotactic content Especially for catalysts with low enantiospecificity it is worthwhile keeping this in mind. 

There are only three unique triad combinations, mm, mr and rr thus a methyl configurational sensitivity to just nearest neighbor configurations would produce only three resonance in the methyl region of the C-13 spectrum. From an earlier spectrum of the amorphous polymer, we noted at least ten methyl resonances. We must therefore consider the situation where the next-nearest as well as nearest neighbor configurations are affecting the chemical shift, that is. 

Inomata 211) studied the H-NMR spectra of poly(penta-1,3-diene) and concluded that with hexane as polymerization medium the polymers were about 49% cis-1,4 and 40% trans-1,4 enchained. The polymer derived from the cis monomer had 12% of 1,2-units which were exclusively trans that from the trans monomer had some 10 % of 1,2-units, two thirds of which were trans. Aubert et al.2I6) made a more extensive study of pentadiene polymers using both1H and 13C-NMR spectroscopy and modified the cis and trans-1,4 methyl resonance assignments made by Inomata 2U). 

As was the case for polymer "E", a small amount of ethyl branching was detected in MBS 1483 as indicated in Figure 10 by the resonances observed for the appropriate methine, a2 6 and 2B carbons. (The methyl resonance is not shown.) The concentration of ethyl branches is 3 per 10,000 carbons as determined using a modified version of Equation 4. NBS 1483 was probably prepared using a Ziegler type catalyst system, as suggested by the rela-... 

The spectra of the methyl methacrylate-a-methylstyrene copolymers are similar to those of the methyl methacrylate-styrene copolymers and are not shown. The backbone methylene regions (8.1—8.6t) of the two comonomer units cannot be distinguished from each other. On the other hand, the methyl methacrylate a-methyl resonances are clearly multiple except at the two lowest values of f . In the spectrum of the 46 54 methyl methacrylate-a-methylstyrene copolymer, the shape of the methyl methacrylate a-methyl resonance is markedly altered from that observed at higher f , the peak at lower field (8.83r), which corresponds to isotactic triads in the homopolymers and is normally very small in free radical polymers, appears to be the most prominent. The a-methyl protons of the a-methylstyrene units appear at highest field, 9.6r—9.8t. Peak positions for the a-methylstyrene copolymers are... 

It should be noted that the resonances observed at 0.95 and 1.25 6 In the spectrum of the catalytlcally-prepared polymer (14) are virtually absent In the present case. These peaks coincide closely with the strong methyl resonances In the B-plnene oxide monomer (Figure 3(a)), and so It Is conceivable that they arise from contamination by monomer. In a study of the polymerization of B-plnene... 

The a-methyl resonance in poly(o -methyl styrene) is found to be split into three peaks which are assigned to isotactic, heterotactic and syndiotactic triads. Fractions of the polymers in the three configurations determined by the area of these peaks are given below for poly(o -methyl styrene) prepared with two different catalysts [S. Brownstein, S. Bywater, and D. J. Worsfold, Makromol. Chem., 48, 127 (1961)] ... 

This metathesis provides an opportunity, complementary to that provided by the metathesis of 1-methylcyclobutene, to determine the stereochemistry of trisubstituted olefin metathesis. The stereochemistry of the polymer s double bonds could be measured as 76% E, 27% Z by the intensities of two methyl resonances (at 1.57 and 1.67 S) in the proton NMR spectrum. 

The low-k films are prepared by solution casting the methyl silsesquioxane and the triblock copolymers mixtures from butanol. The size and distribution of polymer domains in the film will depend on the degree to which the polymer self-associates. Figure 4 shows the solution proton NMR spectra of the P103 triblock copolymer (EOirPOgo-EOn) mixed with methyl silsesquioxane in butanol-dio. The important feature to note is the narrow line widths for the polymer methyl and main chain resonances. Both sets of peaks are narrower than the broad peaks shown in Figure 3 for the triblock... 

Figure 3.1 Parts of the 25 MHz CNMR spectra of polymers made using [) , jS- C]AIBN showing the methyl signals from Me2C(CN)- end-groups, (a) Poly MM A (b) polySTY (c) poly(vinyl chloride). Peaks marked x in spectra (a) and (b) are due to residual hexane, used as precipitant for the polymers. The two sets of methyl resonances, referred to in the text, are well separated in spectra (a) and (c) in spectrum (b), the dotted line shows the division between...

For a given sample, the tacticity was found to be identical in the two solvents. For PMMA, the chemical shifts of the a-methyl protons are most sensitive to poljnner configuration. Therefore, triad tacticity information was obtained by integration of the a-methyl resonances. All polymer configurations are expressed in terms of triad tacticities. 

Figure 31 shows the H NMR spectrum of polymer 56c. The methyl protons appear at 1.66 ppm, and the methylene protons in the polymer backbone resonate at 1.34, 1.56, and 3.34ppm as broad singlets. The methylene protons in the polymer sidechain appear as broad singlets at 2.06 and 2.40 ppm. The cyclopentadienyl protons appear as a singlet at 5.12ppm, indicating that the polymerization reaction was successful. The complexed aromatic protons of this polymer appear as two sets of doublets at 6.31 and 6.41 ppm. Finally, the uncomplexed aromatic protons appear as two broad doublets at 7.25 and 7.37 ppm. 

The C NMR spectrum of polymer 22a is also shown in Figure 14. There are two methyl resonances at 26.94 and 30.63 ppm, and two corresponding quaternary ahphatic carbon peaks at 42.16 and 44.99 ppm. The tiuee ahphatic metiiylene peaks appear at 29.71, 35.89, and 65.34ppm, while the olefinic methylene and methtne resonances appear at 114.64 and 136.14ppm, respectively. The cyclopentadienyl carbons can be found at 77.83 ppm, and the complexed aromatic (CH) carbons... 

As can be seen in Fig. 4, the a-methyl resonance of styrene-MMA copolymers in deuteriobenzene consists of two general areas which change in relative intensity as the styrene content of the polymers changes. It seems that the higher field area is due to a-methyl protons in (SMM -h MMS) and SMS environments, as can be seen from the correlation shown in Table 2. 

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