13C NMR Assignments of the Methine Carbons in Polypropylene Using Two-Dimensional 13C-13C INADEQUATE NMR Spectroscopy

Abstract

ABSTRACT:The methine carbon resonances for atactic polypropylene were assigned based on methyl carbon resonances by two-dimensional 13 C-13 C INADEQUATE NMR spectroscopy. In combination with the analysis of 1 H decoupled 13 C NMR spectra of isotactic, syndiotactic and atactic polypropylenes, nine peaks observed were assigned to three heptad resonances (mmmmmm, mmmmmr, and rmmmmr), and six pentad resonances (mmmr, rmmr, mmrr, rmrr, mmrm, and mrmr and rr). KEY WORDSPolypropylene / Tacticity / 13 C NMR / Two-Dimensional INADEQUATE NMR / 13 C NMR spectroscopy is a powerful tool for the study of stereochemical structure of polypropylene. Zambelli and coworkers made assignments of the methyl pentad stereosequences on the basis of the spectra of model compounds of polypropylene. 1 Subsequently, Zambelli and coworkers 2 and Schilling and Tonelli 3 analyzed the methylene hexad stereosequences on the basis of the calculation using rotational isomeric states (RIS) and ygauche parameters. Both assignments, however, showed notable disagreement. Recently, Chen and Lee indicated that the assignment by Schilling and Tonelli was correct from the examination of the 13 C NMR spectra of atactic polypropylene. 4 lation. 3 Similarly, Zhu and coworkers investigated the methine carbon signals of highly isotactic polypropylene. 5 Since only five isolated peaks were obtained, they did not make complete assignment. Thus, only limited experimental evidence for the assignment of the methine carbon resonances has been presented.In addition to the methylene hexad, Schilling and Tonelli made assignments of the methine pentad stereosequences in atactic polypropylene on the basis of a similar calcut To whom correspondence should be addressed.The objective of this work is to establish the assignment of the methine carbon resonances. For this purpose, we used the two-dimensional (2D) 13 C-13 C INADEQUATE NMR method which gives information about the methine carbon resonances through the firmly assigned methyl carbon resonances. EXPERIMENT AL MaterialsIsotactic polypropylene (IPP) was prepared 809

Full Assignment of the 13C NMR Spectra of Regioregular Polypropylenes: Methine Region

“…In substantial agreement with Miyatake's attributions, 7 from the latter figure one can immediately deduce the following sequence of methine peaks (from low to high field): mmmmmm, mmmmmr, rmmmmr, mmmr, mmrr. On the other hand, quite surprisingly, the main component of the rmmr pentad appears to be overlapped with the intense and broad multiplet which includes the remaining six mr-and rr-centered pentads.…”

“…6 Schilling and Tonelli, in particular, extended to the methine carbon the semiempirical equations based on the γ-gauche effect already adopted successfully for the methyl and methylene carbons. More recently, however, Miyatake et al 7 showed that Schilling and Tonelli's calculations disagree with experimental data obtained at a higher field (125 MHz), and proposed a partly different attribution.…”

“…However, Miyatake et al devised an intelligent strategy based on 13 C 13 C correlated (INADEQUATE) 2D NMR spectroscopy . In ref , these authors used the INADEQUATE spectrum of an atactic polypropylene sample (recorded at 125 MHz and 120 °C) for attributing several methine pentads and the three mmmm -centered heptads, by correlating the corresponding peaks with the well-assigned and highly spread methyl ones.…”

“…With this starting point, the analysis of the 1D spectra of Figure 3a is greatly simplified. Indeed, it is trivial to identify the main contributions to the most intense peaks in the spectra of the predominantly isotactic samples A and B as follows (peak numbers in parentheses): mmmmmm (1), mmmmmmrr (2), mmmmmmrm (3), mmmmrr (4), mmmmrm (7), mmmrrm (8), mmrrmm+ mmmrmm (9). In the spectrum of sample A, moreover, the mmmmmm peak (1) is split in two components, which can be assigned to the mmmmmmmm (1′) and mmmmmmmr (1′′) nonads.…”

Stereochemistry of Polymers

“…6.7) enables direct observation of neighboring 13 C-13 C correlation and has been applied to poly( vinyl alcohol) [20] and polypropylene [22]. 6.7) enables direct observation of neighboring 13 C-13 C correlation and has been applied to poly( vinyl alcohol) [20] and polypropylene [22].…”