Supporting info - Microstrcutreof polymyrcene by NMR

…, 1997

13 C NMR spectroscopy is the main source of information on the stereochemistry of Ziegler-Natta and related transition metal catalyzed propene polymerizations. In simple cases, like those of polypropylenes formed under pure enantiomorphic-site or chain-end control, the origin of the stereoselectivity can be easily recognized from the steric pentad distribution obtained from routine 13 C NMR spectra. On the other hand, the variety of innovative polymers that can now be prepared with "highyield" heterogeneous and metallocene-based homogeneous catalysts under hybrid, multiple, or oscillating stereocontrol represent very complex systems, which are beyond the possibilities of configurational analysis by routine 13 C NMR. In such cases, high-field 13 C NMR can be highly advantageous. Indeed, in this paper we show that from the methyl and methylene regions of 150 MHz 13 C NMR spectra of polypropylenes of various tacticities, the stereosequence distribution can be determined at a much finer level of detail, so as to obtain an adequate experimental basis for the investigation of the many complicated mechanisms of stereocontrol presently encountered in Ziegler-Natta catalysis.

Macromolecules, 2011

A thorough 13 C NMR analysis of a series of propene/4-methyl-1-pentene copolymers, prepared with the isoselective metallocene precatalyst [rac-(EBTHI)ZrCl 2 ], has paved the way to the first full description of such potentially interesting family of copolymers at the triad level. Several tetrads and even longer sequences were assigned and quantified as well. The main problem, consisting in the partial overlap of the resonances of the RR-methylenes of the chain and the R-methylenes of the branch, generally utilized for the microstructural description of propene/linear higher R-olefins copolymers, was overcome by analyzing other less informative regions of the spectra along with the application of two-dimensional heteronuclear ( 1 HÀ 13 C) correlation measurements. A computational procedure for checking the correctness of the proposed assignments was applied to the 13 C NMR observed integrals of two samples differing in comonomer compositions. In both cases, a correspondence between the observed and calculated values of the sequence molar fractions was found.

Angewandte Chemie, 2008

Polymer, 2014

The microstructural analysis of 1,4-cis-and 1,4-trans-polymyrcene was conducted by means of thorough investigations at a very high field NMR (21.1T, 900 MHz). A set of 1D and 2D experiments helped to entirely assign the resonances of the spectra for both stereoisomers. A simple method to distinguish between each stereoisomer by NMR spectroscopy is finally provided.

Angewandte Chemie International Edition, 2008

Journal of the American Chemical Society, 1992

Journal of Chemical Education, 2017

The use of 1 H NMR spectroscopy to analyze the number-average molecular weight of a methoxy poly(ethylene glycol) (MPEG) and an acetate derivative of this MPEG is described. These analyses illustrate NMR principles associated with the chemical shift differences of protons in different environments, NMR integration, and the effect of the natural abundance of 13 C carbons in a polymer and the resulting low but predictable intensity of the satellite peaks due to 13 C− 1 H spin−spin coupling. Also included in this discussion is an example of end-group analysis of the product of an acetylation reaction. In the discussion of the acetylation product, an 1 H NMR spectrum of a crude product mixture where the small peaks due to end groups can be seen along with a set of impurities due to catalyst, solvents, and byproducts is included because, in practice, chemists often first see these sorts of spectra.

Moscow University Chemistry Bulletin

23 13 C NMR spectroscopy is widely used to confirm the formation of metal-stabilized carbocations from their precursors, which usually include alcohols or, rarely, alkenes [1, 2]. It was noted earlier that the successive replacement of hydrogens by alkyl groups at a carbocation center (C +) is accompanied by a considerable increase in the chemical shift of the corresponding carbon atom [3-6]. It has been supposed many times that such an order of change in chemical shifts may reflect the degree of the shift in electron density from metal to C + [4]. However, there has been lack of structural data until recently to confirm this assumption. In spite of many structural studies of metal-stabilized carbocations [7-20], no complex structural or spectral study has been made for primary, secondary, and ter

Macromolecular Symposia, 1994

lH NMR and 13C NMR have been used to study the end groups and tacticity in PMMA macromonomers and oligomers. These macromonomers are terminated almost exclusively in one vinylidene group per chain. The end group signals from the macromonomers are identified in both the I3C and 'H NMR spectra. The spectra of the purified oligomers (n = 1-4) were used to aid in assignment. The macromonomers are predominantly syndiotactic, and the tacticity measured is consistent with Bernoullian statistics. The tetramer is a mixture of r and m isomers in a 4: 1 ratio. It is shown that Tl experiments can provide a useful method of distinguishing resonances due to low molecular weight impurities from those due to stereochemical or isomeric effects in macromonomers. The absence of internal double bonds was confirmed by isomenzing the vinylidene group of several oligomers and of the macromonomer, and verifying the absence of the isomerized signals in the NMR spectra of the original materials.

Journal of Polymer Science Part A: Polymer Chemistry, 1988

Homopolymers of myrcene and farnesene were prepared anionically in pure cyclohexane. The microstructure, determined from an analysis of the I3C-NMR spectrum and spin-lattice relaxation times, indicates the polymers are at , and under 3% trans-l,l.