Methylene region, sequence assignments

Figure 5.9 shows the C-NMR spectrum of a stereoregular 1-hutene-propylene copolymer. On the basis of previous assignments [55], complicated peaks arising from different comonomers sequences longer than pentad are observed in the resonance regions of the methyl carbon of propylene (A), the central methylene carbon of a PP diad (B), and the side-chain methylene carbons of 1-butene (C) among propylene units. 

In the region of the methyl carbon in the propylene unit (21.4 ppm to 22.0 ppm), the side-chain methylene carbon in the 1-butene unit (27.5 ppm to 28.5 ppm), and the central methylene carbon of the PP diad (46.5 ppm to 47.5 ppm), the peaks arising from different comonomers sequences longer than pentad are observed. To provide assignments of these peaks, chemical shift differences among pentad and hexad comonomers sequences were calculated by the y-effect method. Table 5.6 shows the calculated chemical shift differences in the resonance regions of methyl and methylene carbons in 1-butene-propylene copolymer ... 

Figure 5.1 shows typical NMR spectra (methylene and methine regions) of the copolymers (THF-soluble fraction) prepared by [Me2Si(C5Mc4)(N Bu)] TiCL, (l,2,3-Me3C5H2)TiCl2(0-2,6- Pr2C6H3) catalysts in the presence of a MAO cocatalyst [13b]. Table 5.1 also summarizes the assignments of resonances for poly(ethylene-co-styrene) in the NMR spectrum based on the distortionless enhancement by polarization transfer (DEPT) spectrum and data reported previously [12-18], and monomer sequences in the copolymer are shown in Scheme 5.1. As described below, the naicrostructures for the resultant poly(ethylene-co-styrene)s depend on the catalysts used. As shown in Figure 5.2, the glass transition temperature (Tg) as measured by DSC increased with an increase in the styrene content (-8.1 to 58.3 °C). This is because, as...

The determination of the sequence distribution of (PVA-Ac) copolymers using H and C-NMR techniques have been reported by a number of researchers. - Figure 2 shows C-NMR spectra in the region of CH2 carbons in (PVA-Ac) copolymers with various degree of saponification. Resonances (X) at 41-43 ppm were assigned to the methylene carbons of poly(vinyl acetate)... 

The infrared absorption of ethylene copolymers in the 14.28-11.76 pm region can provide information about their sequence distributions. Studies on model hydrocarbons by workers various [1-4] have shown that the absorption of methylene groups in this region is dependent on the size of methylene sequences in the compounds. Methylene absorptions observed in this region, and their relation to structures occurring in ethylene copolymers, are shown in Table 7.1. The absorptions at 13.81 and 13.68 pm of several ethylene-propylene copolymers have been assigned [5] to... 

The T resonances in the 73-74 ppm region have multiple-bond correlations in the HSQC-TOCSY spectmm to proton resonances of S and/or S , methylenes. Therefore, they are attributed to Xm groups such as those found in stmcture 20. Analysis of these data provided resonance assignments for all the S and T type carbons for the stmctures in Scheme 1. Detailed analysis of expansions of the peak-containing regions of the 2D-NMR data provided complete resonance assignments for all monomer sequences up to the tetrad level in poly(EV). 

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