Studies on comblike polymers. 7. Carbon-13 NMR characterization of poly(oxiranes) containing long hydrocarbon side chains

Abstract

13C NMR spectra have been measured for some comblike polymers obtained by coordination polymerization of higher epoxides such as octadecyloxirane and decyloxirane. Backbone methine and methylene resonances of the high-melting polymer fractions appear as single unsplit peaks, thus indicating a high degree of stereoregularity (isotactic structure). In contrast, strong tacticity effects have been generally observed for the backbone resonances of the low-melting polymer fractions. These effects have been interpreted in terms of different stereosequences. The complete assignment to the triads mm, mr (rm), and rr and comparison with the spectra of poly(methyloxirane) and anionically prepared poly(octadecyloxirane) allowed us to conclude that the low-melting polymers are atactic and contain substantial amounts of abnormal (head-to-head and tail-to-tail) linkages. Measurement of Tx of the main-chain carbons and NOE showed their independence of the tacticity. Moreover, the length of the hydrocarbon side chain does not substantially affect the backbone relaxation. As for the side chains, only the T! values of the interior atoms showed a marked tacticity effect. Experimental dynamic parameters have been interpreted either on the basis of a single correlation time or with a model based on restricted motion on a diamond lattice.

Ring-opening polymerization of glycidylic compounds: influence of the glycidylic oxygen in the coordinative mechanism

“…In the case of PPEB (P6) (Fig. 4), this carbon is highly sensitive to the possible triads (mm, mr, rm and rr), with noticeable chemical shift differences, as has been previously reported for poly(oxiranes) with long hydrocarbon side-chains 29) . In case of the PPGTE (P5) spectrum (Fig.…”

Synthesis of New Reactive Polyethers: Poly(ω-bromoalkyl-1-glycidylether)s

“…These signals, according to previous studies, [18] are assignable to irregular linkages and point to an outstanding difference in the microstructure of both kinds of polymers. It must be pointed out that these signals can also be observed in the spectra described by other authors, [46] in which, however, no assignment was made. The relative intensities of these signals were determined using the spectra recorded in CDCl 3 and TCE-d 2 to settle their overlapping with solvent peaks.…”

“…This higher stereosequence sensitivity of the methylene main chain carbon is characteristic of polyoxiranes with no b-heteroatoms relative to the oxiranic ring such as poly(1,2-epoxybutane), [44,45] poly(1,2-epoxyoctane), [46] poly(4-phenyl-1,2-epoxybutane) [18] and poly(4phenoxy-1,2-epoxybutane). [18] The degree of tacticity calculated from the relative intensities of the different triads was very close to the one calculated for the poly(x-bromoalkyl-1-glycidylether)s (Table 6 and 7).…”

Recent Advances in the NMR Description of Polypropylene

“…Experimental data show that each 13 C nucleus is characterized not only by a different T! value depending on the number of directly bond hydrogen nuclei (dipolar relaxation mechanism) but that stereochemical environment plays also a role (5). As a consequence, for any quantitative analysis, the choice of the proper delay time is fundamental (>5 Tj ).…”