Correlation between carbon-13 NMR chemical shifts and conformation of polymers. 4. Solid-state spectra of poly(3-methyl-1-pentene)

Abstract

A semiquantitative analysis of the solid-state 13C NMR spectra of poly(3-methyl-l-pentene) is presented. The analysis is based on an empirical scheme for the computation of the chemical shifts of hydrocarbons, which takes into account conformational effects. The calculations provide a structural interpretation of the differences between the spectra of the optically active and the racemic polymers observed by Sacchi et al.1 The effects of distortions of the helical structure from perfectly staggered conformations are also discussed.

Simple Trends in the Methylene Regions of the NMR Spectrum of Poly(propylene) and Ethylene‐Propylene Copolymers

“…With such a qualitative description it is not surprising that the use of the parameters of refs. [24,29] with only a scale adjustment, leads directly to a good agreement between calculated and experimental values (s = 0.07 ppm with the correct disposition of sequences). Due to the small number of data and the strong correlation of probabilities, it is impossible to make a multiple regression to determine all the screening parameters in order to improve the fit.…”

“…To this end, conformations are labeled as t, g, and g, which correspond to T, G ± , and G ∓ , where the upper and lower signs correspond to (+) and (-) enantiotopic bonds. [14,20] Screening Parameters Grant and Paul were the first to show [21] that the chemical shift of 13 C nuclei of a hydrocarbon in solution can be approximately computed as the weighted sum of [24] although, in order to simplify the discussion focused on relative chemical shift values, if more states have the same screening contribution, they are all considered as reference states, rather than taking as reference the state with the higher number of trans dihedrals. The Newmann projection on the top refers to a (+) bond; and therefore, the t, g, and g states of Flory nomenclature correspond to IUPAC T, G + , and G − states.…”

“…[22] It is common practice to interpret the conformational dependence of the chemical shift of carbon C in terms of a negative γ parameter for each C-C α -C β -C γ gauche interaction. However, experimental works, in either indirect [23,24] or direct [25] ways, and successive computational studies [26,27] have shown that C α -C-C α -C β gauche interactions also lead to upfield shifts (the β-gauche effect). We will adopt here the β and γ parameters of Ferro et al [24] Figure 2 shows the screening parameters relevant in this paper.…”

“…[29] Apart from a fitted additive constant either four screening parameters were adopted according to ref. [24] or two additional parameters were fitted. The pedices of the parameters refer to the bond numbering of Figure 1.…”

Microstructure of Copolymers of Norbornene Based on Assignments of 13C NMR Spectra: Evolution of a Methodology

“…α-, β-, and especially the conformationally sensitive γ-effects were used to assign the NMR spectra and determine the microstructures of polymers in solutions and melts, where they are conformationally flexible [2,[6][7][8][9][10][11] .The first applications of the rotational state isomeric model for describing the conformational statistics date back to the late 70s and early 80s in the case of polypropylene (PP) [6,9]. Nowadays, PP resonances in high-resolution solution 13 C NMR spectra exhibit a sensitivity to stereosequences at the undecad level.…”