A simple method for determining protic end-groups of synthetic polymers by 1H NMR spectroscopy (original) (raw)
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Macromolecular Chemistry and Physics, 1995
The hydroxylic end-groups in the soluble fraction of poly(pheny1 glycidyl ether) (PPGE) obtained with the aluminium isopropoxide (AIP)/ZnCl, initiator system are studied using nuclear magnetic resonance spectroscopy (NMR). To achieve complete assignment, model compounds are synthesized and their carbamate and trifluoroacetate derivatives obtained from trichloroacetyl isocyanate (TAI) and trifluoroacetic anhydride (TFAA) are prepared. These derivatizating reagents allow primary and secondary alcohols to be distinguished, since upfield or downfield shifts are produced, and at the same time they have the potential of separating overlapping peaks. Several PPGEs with different degrees of regularity are also synthesized using various initiator systems. Thus, it is possible to identify the carbon signals of both final hydroxylic groups and their adjacent units, and the presence of two types of unit linked to secondary hydroxylic end-groups is demonstrated. Likewise, in the soluble fraction prepared with AIP/ZnCl, the absence of the irregular units linked to secondary hydroxylic end-group is demonstrated, so proving the high regularity of this fraction.
Using 1H NMR Spectra of Polymers and Polymer Products To Illustrate Concepts in Organic Chemistry
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.
Configurational sequence determination of poly(isobornyl acrylate) by NMR spectroscopy
Journal of Molecular Structure, 2011
Poly(isobornyl acrylate) (PiBA) was prepared by atom transfer radical polymerization (ATRP). Complete characterization of microstructure of PiBA was carried out using one-dimensional [ 1 H, 13 C{ 1 H}] and two-dimensional (HSQC, TOCSY and HMBC) NMR spectra. The methyl, methylene, methine, quaternary and carbonyl carbon resonance signals were found to be sensitive to various configurational sequences. The methine carbon (C 12 ) was assigned up to triad configurational sequences in 13 C{ 1 H} NMR spectrum whereas b-methylene carbon resonances were assigned up to diad configurational sequences. The quaternary carbon in 13 C{ 1 H} NMR spectrum were resolved completely with the help of HMBC NMR spectrum. The stereoregularity of PiBA was found to be random with mm = 20%, mr = 53%, and rr = 27%.
Macromolecules, 1997
Recently, 31 P NMR has been introduced as a powerful tool for the elucidation of the different types of phenolic, alcoholic, and carboxylic structures that are present in lignins. 1,2 It was shown that the reaction of 1,3,2dioxaphospholanyl chloride 2,3 or 2-chloro-4,4,5,5-tetramethyldioxaphospholane 4,5 (I) with the above labile proton-containing moieties produces phosphinic esters whose 31 P NMR chemical shifts are very sensitive to the chemical structure around the 31 P nucleus. Comparison with model compounds 3 provided valuable information regarding the highly complex structure of various types of lignins, 1,2,5 and the factors affecting the 31 P chemical shifts were studied in detail. 2,6 Consequently, Chan et al. applied the above methodology and proposed a facile qualitative and quantitative route for the determination of phenolic functional groups in poly(phenylene oxide) (PPO) resins. In this communication, we further explore the use of quantitative 31 P NMR for the accurate determination of number-average molecular weights (M n ) in poly-(hydroxyalkanoate)s (PHAs). PHAs are a family of bacterially synthesized thermoplastic polyesters whose inherent biodegradability and biocompatibility have made them notorious. The most recent advances are collected in a Supplement journal issue and edited by Page. The chemical composition and M n of PHAs can be controlled by varying the fermentation and isolation conditions, 10,11 leading to homologous polymers of varying physical properties. An absolute method for the facile and accurate determination of the molecular weight of polymers produced at various fermentation times and conditions would be advantageous with respect to presently used indirect methods, such as GPC or viscometry.
Evaluation of 3D NMR Experiments for the Characterization of Polymer Structure
Journal of Magnetic Resonance, 1998
A series of three-dimensional (3D) nuclear magnetic resonance ment is used, signals originating from the chain ends often (NMR) pulse sequences, utilizing pulsed-field gradient (PFG) have intensities which are comparable to those originating techniques, were developed or adapted from biological experifrom the polymer backbone. One drawback of this technique ments for applications in the characterization of polymer strucinvolves the interference from overlap with extremely inture. These experiments form the foundation of a suite of experitense signals of the polymer backbone. These signals often ments which can be used to characterize the structure of polymers interfere with detection of the weak chain end signals of and other heteroatom-containing organic materials, in much the interest. same way that the data from multiple 3D NMR experiments have To resolve this problem, utilization of a third NMR-active been used in biological structure determination. Several variations nucleus can often be useful. This can be accomplished by of an 1 H/X/Y chemical shift correlation (HXY) experiment are exhibited, and the HCX sequence (where Y Å 13 C) is combined artificial enrichment or by utilizing an X nucleus such as 31 P with 13 C homonuclear isotropic mixing to generate new pulse seor 19 F (100% natural abundance) which is already present quences which provide additional structural information. In this in the structure. In favorable cases, direct observation of this paper, the spectra of poly(a,b-13 C 2-styrene) (PS) prepared by third nucleus provides a spectrum with very large chemical diphenylphosphinyl radical (DPPR) initiated polymerization of shift dispersion and only a few resonances (when there are a,b-13 C 2-styrene are used to illustrate the application of these a limited number of X atoms in the molecule). The idea of techniques for characterization of polymer chain end structures. using isotopic labeling together with triple resonance NMR Comments on the relative advantages of the pulse sequence are techniques to selectively observe resonances from the label provided. Although polymers are used to illustrate the applications site, while filtering the remainder of the signals from the of these pulse sequences, the sequences can just as easily be used to study other organic structures containing an NMR-active X spectrum, was described in 1982 (4, 5). nucleus. Organometallic chemistry is especially suited for applica-Recently, triple resonance experiments have taken the tions of these NMR experiments. ᭧ 1998 Academic Press form of three-dimensional (3D) NMR and have been used Key Words: 3D NMR; triple resonance NMR; polystyrene; 13 Cin conjunction with isotopic labeling to study the structures labeling. of biological macromolecules. The HNCO experiment was originally developed by Bax et al. (6, 7) to help determine the structures of 13 C-and 15 N-labeled proteins. Later, Berger
Nonaqueous Capillary Electrophoresis−Mass Spectrometry of Synthetic Polymers
Analytical Chemistry, 2004
In this work, the separation and characterization of ionizable organic polymers nonsoluble in water is carried out using nonaqueous capillary electrophoresis-ion trap mass spectrometry (NACE-MS). The polymers studied are poly(N E -trifluoroacetyl-L-lysine) (poly(TFA-Lys)) obtained by ring-opening polymerization of the corresponding N-carboxyanhydride. Different parameters (i.e., liquid sheath nature and flow rate, electrospray temperature, and separation buffer composition) are optimized in order to obtain both an adequate CE separation and a high MS signal of the samples under study. The optimum NACE-MS separation conditions allow the molecular mass characterization of poly(TFA-Lys) up to a degree of polymerization of 38. NACE-MS provides interesting information on the chemical structure of (i) the polymer end groups and (ii) other final byproducts. The MS spectra obtained by using this CE-MS protocol confirm that the polymerization was initiated by the reaction of n-hexylamine (initiator) on the monomer. CE-MS-MS and CE-MS-MS-MS results demonstrate that two different termination reactions occurred during the polymerization process leading to the transformation of the reactive amine end group into a carboxylic or a formyl groups. Byproducts such as 3-hydantoinacetic acid or diketopiperazine were also detected. To our knowledge, this is the first work in which the great possibilities of NACE-MS and NACE-MS n for characterizing synthetic polymers are demonstrated.
Macromolecules, 1994
Phenolic compounds can be readily phosphitylated with 1,3,2-dioxaphospholanyl chloride (9; Scheme 1) directly in an NMR tube. Using 3lP NMRspectroacopy different phenols can be easily discriminated. Using this technique we have developed a facile qualitative and quantitative method for the determination of phenolic functional groups in PPO resin. On the basis of the developed technique, we were able to obtain the hydroxyl concentration of normal phenolic ends, hydrogen-bonded phenolic ends, and phenolic groups on the backbone, as well as the number-average molecular weight of the polymers. In addition, based on nitrogen content analyses and quantitative 3lP NMR, the Mannich type ends were also determined. The precision of the method was determined to be f15 ppm for the determination of individual hydroxyl functionalities. The results of quantitative 31P NMR when compared to those obtained by applying traditional analytical techniques were in excellent agreement. -0 4 O H 1 2 3 ---qOH B P N 4 Bu 7 4 s -0 9 a0 Abstract published in Advance ACS Abstracts, September 1, esterification reaction required was relatively cumbersome and needed to be performed on a large scale."J Earlier work" has demonstrated that a large variety of phenoliclla and carbohydratellb model compounds and 1994.