Polychloroprene. I. Etude de la microstructure par RMN 1H

The microstructure of polychloroprenes was studied by ¹H-NMR at high field (350 MHz). An examination with two solvents, CDCl₃ and C₆D₆, was necessary to show all the addition modes. The complementary information obtained made possible the quantitative determination of head-to-tail, head-to-head, tail-to-tail, trans-1–4, and cis-1–4, 1–2, and 3–4 additions.     

Influence of polar modifiers on microstructure of polybutadiene obtained by anionic polymerization. Part 4: Acid-base polar modifiers forming σ-μ complexes: Amine-alkoxide,amine-ether-alkoxide,and ether-alkoxide

The influence of acid-base polar modifiers (σ-μ complex): amine-alkoxide, amine-ether-alkoxide, and ether-alkoxide complexes on microstructure of polybutadiene obtained by anionic polymerization was studied. The content of butadiene isomeric structures was determined based on FT-IR-ATR, ¹H, and ¹³C NMR data analyses. The results obtained indicated a very similar influence of all types of polar modifiers forming σ-μ complex on polymer microstructure leading to high vinyl polybutadiene with nearly equal ratios of cis-1,4 and trans-1,4 butadiene isomeric structures.     

Structure of polypiperylene chain segments according to high-resolution 13C NMR spectra

The microstructure of stereoregular 1,4-trans-and 1,4-cis-polypiperylenes, as well as polymers prepared from the trans-and cis-piperylene isomers via cationic polymerization in the presence of TiCl₄, was studied by high-resolution ¹³C NMR spectroscopy. Polypiperylene synthesized through the cationic polymerization of the cis isomer had a more diversified morphology of the macromolecular chain, i.e., had higher relative amounts of 1,2-cis-units and combinations of irregular-addition 1,4-trans-units. It was shown that ¹³C NMR spectra give the most comprehensive and independent information on the details of structure of the piperylene macromolecular chain.     

Polymérisation anionique des diènes. VI. Microstructure des polybutadiène et polyisoprène par résonance magnétique protonique à 250 MHz et mécanismes de propagation

Analysis by 250-MHz proton magnetic resonance (PMR) allows more precise examination of the microstructure of anionic polyisoprenes and polybutadienes obtained in the presence of organo-alkali metals. Besides vinyl addition, the propagation of contact ion pairs in dioxane solvent gives a mixture of cis and trans products with isoprene, whereas only trans product is obtained with butadiene. The presence of 1,4-trans-polyisoprene appears to be inconsistent with the cis configuration of the polyisoprenyllithium living end in dioxane or tetrahydrofurane media. In taking into account the existence of complexation phenomena, it was suggested that propagation mechanisms should involve a transition state which should begin with the trans configuration before isomerization into the more stable cis configuration. For the free ions, the living end of the carbanion should be entirely trans.     

Microstructure of polyisoprene produced by cationic polymerization: NMR spectroscopic study

High-resolution ¹H and ¹³C NMR spectroscopy, including two-dimensional heteronuclear experiments, has been used to study the microstructure of polyisoprene produced by cationic polymerization. It is shown that macromolecules resulting from both regular and inverse additions are predominantly composed of trans-1,4-units, while 1,2- and 3,4-units are present in small amounts. NMR spectra demonstrate the absence of cis-1,4-units in the polymer, whereas broad signals (pedestals) are related to the presence of saturated structures. It is proposed to determine the content of trans-1,4-, 1,2-, and 3,4-units in cationic polyisoprene via the combined measurements of intensities of signals in the olefinic regions of ¹H and ¹³C NMR spectra.     

Polymérisation radicalaire du pentadiène-1,3. II. Microstructure des résidus pentadiéniques dans les homo- et copolymères des cis et trans pentadiènes-1,3 avec l'acrylonitrile

The microstructure of diene units was investigated in radical homopolymers of the cis and trans isomers of 1,3-pentadiene and copolymers with acrylonitrile, synthetized in bulk and emulsion. Experiments were carried out by infrared spectroscopy, 100 MHz ¹H-NMR, and 25 MHz ¹³C-NMR studies. No difference between the bulk and emulsion samples was noted. The microstructure of poly(1,3-pentadiene) is practically independent of the cis or trans configuration of the diene monomer and is as follows: 56–59% trans-1,4, 15–17% cis-1,4, 16–20% trans-1,2 7–10% cis-1,2 and 0% 3,4. On the other hand, up to about 30% of incorporated acrylonitrile (10% in the feed), the microstructure of the pentadiene fraction in the copolymers is not affected. This finding suggests that the penultimate unit has very little influence on the polymerization process involving the terminal pentadienly unit. Beyond 10% of acrylonitrile in the feed, the proportions of the structural units were linearly dependent upon the acrylonitrile content: trans-1,4 content increased whereas the amounts of cis-1,4 trans-1,2 and cis-1,2 decreased (except the cis-1,2 fraction, constant in the copolymers from the cis-diene). These results are discussed on the assumption that the microstructure of pentadiene residues is strongly associated with the acrylonitrile comonomer in the feed.     

NMR and DSC investigations of the miscibility of blends of cis-1,4-polyisoprene with polybutadienes of different microstructures

Differential scanning calorimetry and torsional braid analysis investigations of the phase diagram of cis-1,4-polyisoprene/polybutadiene blends as a function of the polybutadiene microstructure were reported by several authors. Polybutadienes containing a high vinyl content were shown to be miscible with cis-1,4-polyisoprene on the DSC spatial scale, whereas polybutadienes containing a low vinyl content were immiscible. In this article, we used variable-temperature determinations of ¹H NMR free induction decays and low-temperature, high-resolution solid-state ¹³C NMR measurements of proton spin-lattice relaxation times in the rotating frame to probe the phase behavior of the cis-1,4-polyisoprene/polybutadiene blends at the smaller spatial scale of the NMR technique. Blends of cis-1,4-polyisoprene with a polybutadiene having a large number of vinyl 1,2 linkages appeared to be miscible on the molecular scale, in spite of small regions in which the polybutadiene component is not uniformily dispersed in the other polymer. On the contrary, blends in which the polybutadiene has a low content of vinyl 1,2 sequences were phase separated over the whole temperature range considered and no intermixed regions could be detected. The limiting case was observed with the polybutadiene containing 33 wt % vinyl 1,2 units, for which miscibility on a molecular scale is highly dependent on the blend composition. © 1995 John Wiley & Sons, Inc.     

Carbon-13 NMR analysis of cyclobutane dimers from benzocycloalkenes

¹³C NMR Spectra for a series of 11 substituted cyclobutanes derived from photodimerization of benzocycloalkenes were recorded. Comparison of the carbon chemical shifts for the head-to-head and head-to-tail cis-syn-cis and cis-anti-cis isomers reveals shielding trends which should facilitate structural and stereochemical assignments for related compounds. The head-to-head isomers show a larger separation of cyclobutane carbon resonances than the head-to-tail isomers. The cis-syn-cis isomers relative to the cis-anti-cis isomers exhibit distinctive upfield shifts of all carbon resonances, except those of aromatic carbons ortho to alkyl-substituted aromatic carbons.     

Head-to-head vinyl chloride–vinyl acetate copolymer

Addition chlorination of cis-1,4-polybutadiene in the presence of acetic acid as a cosolvent resulted in the formation of head-to-head vinyl chloride–vinyl acetate copolymer. Chlorine analysis, IR, and NMR spectra of the chlorinated polybutadiene indicated that reaction was primarily double bond addition; there was little evidence for substitutive chlorination. Acetate was incorporated by nucleophilic participation of the acetic acid cosolvent. The extent of incorporation of the acetate group in the polymer chain was a function of the acetic acid concentration. Both the glass transition temperatures and the densities of the chloroacetylated polymers decreased as the degree of acetylation increased.     

Carbon-13 NMR of polybutadiene

By using the carbon-13 NMR technique, it is shown that there are no cis-1,4–trans-1,4 linkages in a n-BuLi-catalyzed polybutadiene. The polymer consists of “blocks” of cis-1,4 units and trans-1,4 units separated by isolated vinyl units. Preliminary evidence suggests this might also be true for other types of 1,3-diene polymerization. Some of the implications of this finding on the mechanism of polymerization are discussed. Tacticity triad distributions are readily determined in polybutadienes with high 1,2 addition contents.     

Influence of Polar Modifiers on Microstructure of Polybutadiene Obtained by Anionic Polymerization. Part 2: Lewis Base (σ) Amine-Ether and Ether-Type Polar Modifiers

The influence of Lewis base (σ complex) amine-ether and ether-type polar modifiers on the microstructure of polybutadiene obtained by anionic polymerization was studied. Analysis of FT-IR-ATR, ¹H, and ¹³C NMR spectral data for polybutadienes obtained in the presence of the complexing agents showed that increase of concentration of all tested polar modifiers very strongly promoted formation of 1,2 butadiene isomeric structures, especially increasing the content of vinyl–vinyl and vinyl–trans-1,4 diads.     

Synthesis of poly(tert-butoxycarbonyl-p-phenylene): precursor to poly(p-phenylene)

Poly[2-(tert-butoxycarbonyl)-1,4-phenylene] ( 2 ) was prepared by the Ni-catalyzed polymerization of tert-butyl 2,5-dichlorobenzoate ( 1 ). The microstructure of polymer 2 was probably alternating head-to-head and tail-to-tail. This polymer was soluble in dipolar aprotic solvents, chloroform, tetrahydrofuran, and dichloromethane. Polymer 2 was saponified easily by thermal or acid treatment to yield poly[2-carboxy-1,4-phenylene] ( 3 ). Decarboxylation of polymer 3 in quinoline in the presence of copper(II) oxide produced poly(p-phenylene) (PPP) ( 4 ).     

Recherches dans la série des cyclitols XLII. Synthèses de cyclitols tout-cis dérivés du cyclopentane; préparation des cyclopentane-tétrol et - pentol tout-cis

All-cis cyclitols derived from cyclopentane have been prepared in two ways: (i) by LiAlH₄ reduction of all-cis epoxypolyos; (ii) by dimethyl sulfoxide treatment, in the presence of sodium hydrogencarbonate, of brominated derivatives containing a neighbouring benzoyloxy group; under these conditions, the halogen is replaced by a cis-oriented hydroxyl group. Thus all-cis cyclopentane-tetrol and -pentol have been prepared; their configuration has been confirmed by NMR. spectroscopy.     

Microstructure of poly(alkylene phosphates) related to biopolymers (teichoic acids)

The microstructure of polyphosphites and polyphosphates obtained by the ring-opening polymerization of asymmetrically substituted 5-membered cyclic phosphites was studied. It has been established, using ³¹P NMR, that 4-substituted 2-hydro-2-oxo-1,3,2-dioxaphospholanes underwent polymerization giving polymers with head-to-tail dyads as well as head-to-head and tail-to-tail structures. Analyses of ³¹P NMR spectra of racemic and optically active poly(2-hydro-4-methyl-2-oxo-1,3,2-dioxaphospholane) and model compounds estimated the statistical mode of ring scission of cyclic phosphites. Similar results were obtained for the polymerization of 4-acetoxymethyl-2-hydro-2-oxo-1,3,2-dioxaphospholane, which provided the simplest model of teichoic acid, namely poly(1,2-glycerol phosphate).     

Conformation et Spectrometrie de RMN. III. Spectres 13C de Diméthylamino Cyclanols et Dérivés

The ¹³C NMR spectra of 2-dimethylaminocyclohexanols and the four trans-3-dimethylamino-2-decahydronaphtols are described. The gauche interactions allow precise estimation of chemical shifts for each carbon atom; thus, band attribution can be resolved without mistake. In the case of the cis and the trans diequatorial compounds, the conformational perturbations which we have suggested before are verified by our present measurements on the substituted carbon atoms. We also show effects on adjacent atoms, which were unobservable with the usual IR and ¹H NMR techniques.     

A new insight into the mechanism of 1,3‐dienes cationic polymerization. II. Structure of poly(1,3‐pentadiene) synthesized with tBuCl/TiCl4 initiating system

The microstructure of poly(1,3‐pentadiene) synthesized by cationic polymerization of 1,3‐pentadiene with ^tBuCl/TiCl₄ initiating system is analyzed using one‐dimensional‐ and two‐dimensional‐NMR spectroscopy. It is shown that unsaturated part of chain contains only homo and mixed dyads with trans?1,4‐, trans?1,2‐, and cis?1,2‐structures with regular and inverse (head‐to‐head or tail‐to‐tail) enchainment, whereas cis?1,4‐ and 3,4‐units are totally absent. The new quantitative method for the calculation of content of different structural units in poly(1,3‐pentadiene)s based on the comparison of methyl region of ¹³C NMR spectra of original and hydrogenated polymer is proposed. The signals of tert‐butyl head and chloromethyl end groups are identified in a structure of poly(1,3‐pentadiene) chain and the new approaches for the quantitative calculation of number‐average functionality at the α‐ and ω‐end are proposed. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3297–3307     

Cationic addition polymerization of 1,4‐dioxene using gacl3 as lewis acid catalyst: Long‐lived species‐mediated polymerization

Effective cationic addition polymerization of 1,4‐dioxene, a six‐membered cyclic olefin with two oxygen atoms adjacent to the double bond, was performed using a simple metal halide catalyst system in dichloromethane. The polymerization was controlled when the reaction was conducted using GaCl₃ in conjunction with an isobutyl vinyl ether–HCl adduct as a cationogen at –78°C to give polymers with predetermined molecular weights and relatively narrow molecular weight distributions. The long‐lived properties of the propagating species were further confirmed by a monomer addition experiment and the analyses of the product polymers by ¹H NMR and MALDI–TOF–MS. Although highly clean propagation proceeded, the apparent rate constant changed during the controlled cationic polymerization of 1,4‐dioxene. The reason for the change was discussed based on polymerization results under various conditions. The obtained poly(1,4‐dioxene) exhibited a very high glass transition temperature (T_g) of 217°C and unique solubility. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Polymerization of 1,3‐dienes with functional groups. III. Free‐radical polymerization of N,N‐diethyl‐2‐methylene‐3‐butenamide

Free‐radical homo‐ and copolymerization behavior of N,N‐diethyl‐2‐methylene‐3‐butenamide (DEA) was investigated. When the monomer was heated in bulk at 60 °C for 25 h without initiator, rubbery, solid gel was formed by the thermal polymerization. No such reaction was observed when the polymerization was carried out in 2 mol/L of benzene solution with with 1 mol % of azobisisobutyronitrile (AIBN) as an initiator. The polymerization rate (R_p) equation was R_p ∝ [DEA]^1.1[AIBN]^0.51, and the overall activation energy of polymerization was calculated 84.1 kJ/mol. The microstructure of the resulting polymer was exclusively a 1,4‐structure where both 1,4‐E and 1,4‐Z structures were included. From the product analysis of the telomerization with tert‐butylmercaptan as a telogen, the modes of monomer addition were estimated to be both 1,4‐ and 4,1‐addition. The copolymerizations of this monomer with styrene and/or chloroprene as comonomers were also carried out in benzene solution at 60 °C. In the copolymerization with styrene, the monomer reactivity ratios obtained were r₁ = 5.83 and r₂ = 0.05, and the Q and e values were Q = 8.4 and e = 0.33, respectively. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 999–1007, 2004     

Réactions d'élimination présentées par des acides polyhydroxyadipiques

The tetrahydroxyadipic acids and one trihydroxyadipic acid have been methylated, using methyl iodide and silver oxide in the presence of dimethylformamide. In addition to Δ²-di- or tri-methoxyadipic esters and the products expected for a double E2 elimination, cis-trans α, α'-dimethoxymuconic ester was frequently the principal product. The proposed theoretical interpretations involve as intermediates either a silver complex or a lactonic compound. A few preferential conformations, based on NMR. data, are proposed.     

Interactions intramoléculaires. XXVI—Constantes de couplage et hétérogénéités conformationnelles dans une série de R-3 et R-5 cyano-4 cyclohexènes deutériés (R=méthyl ou t-butyl)

For trans-3-R- and 5-R-1-acetoxy-4-cyanocyclohexene-6,6-d₂ the molar fractions of diequatorial conformers are 0.83 (3-methyl), 0.68 (5-methyl), 0.57 (3-tert-butyl) and 0.55–0.69 (5-tert-butyl). For the last two compounds the values of the coupling constants are in agreement with the hypothesis of an ee?aa equilibrium. For the cis isomers, the molar fractions of equatorial alkyl conformers are 0.76 (3-methyl and 5-methyl) and 1.0 (3-tert-butyl and 5-tert-butyl). The cis-1-acetoxy-3-tert-butyl-4-methoxycarbonyl-cyclohexene presents a conformational heterogeneity. The conformational free energy of the methyl group in position 4 has been evaluated as ?0.6 kcal mol^?1 (2.5 kJ mol^?1).