Carbon-13 and proton magnetic resonance studies of poly(N-vinylcarbazole) in solution

Spin-lattice relaxation times T₁ of individual carbons and protons were measured by the partially relaxed Fourier transform (PRFT) method for poly(N-vinylcarbazole) in solution. The ¹³C-T₁ value of the methylene carbon is about one-half of that of the methine carbon, and the carbazolyl CH carbons have T₁ values close to that of the skeletal CH carbons. The effective correlation time for the skeletal carbon is estimated as ca. 0,95 ns on the basis of the measured T₁ and ¹³C-¹H nuclear Overhauser effect (NOE) factor. Moreover, the ¹³C normal Fourier transformation (NFT) spectrum and proton T₁ indicate strong steric interactions between the pendant carbazolyl groups in the polymer. The results demonstrate that the polymer in solution has a rigid local structure with hindered internal rotation of the bulky side-chain groups.     

13C NMR relaxation studies of poly(vinyl alcohol) and its derivatives

Spin-lattice relaxation times (T₁) have been measured by ¹³C NMR for poly(vinyl alcohol), poly(vinyl benzoate), poly(vinyl cinnamate) and poly(vinyl acetate) in dimethyl sulfoxide as a function of temperature and concentration. As expected, T₁ increases with increasing temperature and decreases with increasing polymer concentration. The influence of the microstructure (tacticity) of the polymers on the relaxation times is negligible. T₁ for the methine carbon of the polymer main chain is observed to serve as a measure of the rigidity and/or mobility of the chain. Assuming isotropic motion of the polymer chains, the activation energies for the protonated carbons were determined using the calculated correlation times.     

Polymerization of Propylene with Cs Symmetric Zirconocene/Half Titanocene System at Low Temperature

Propylene polymerization was conducted with C_s symmetric (Ph₂C)CpFluZrCl₂/B(C₆F₅)₃/Cp* TiMe₃ system using AlOct₃ as a scavenger at –50°C. The polymer produced was consisted by two kinds of fractions; i. e., hexane soluble (atactic) fraction and hexane insoluble fraction. The insoluble polymer had highly syndiotactic structure, indicating that the polymer was produced from C_s symmetric zirconocene. M̄_n's increased linearly with increasing polymer yield, although the activity was low. Thus, it could be said that syndiospecific polymerization of propylene proceeded in a living like manner with C_s symmetric zirconocene active species by using the mixed metallocene system. And by the reaction of the syndiotactic poly(propylene) chain end with carbon monoxide (CO), it could be found that CO was quantitatively incorporated into the syndioPP‐Zr chain end.     

Adsorption of polymers at the solution/solid interface, 15. Styrene-vinylferrocene copolymers

A series of styrene-vinylferrocene random copolymers is synthesised and characterised. Their adsorption from carbon tetrachloride and from chloroform is measured on to pyrogenic SiO₂, TiO₂ and Al₂O₃. The level of adsorption depends on the solvent, the adsorbent and the copolymer composition. From chloroform, very few vinylferrocene units are required to increase adsorption markedly above that of polystyrene, and further compositional change has little effect on the level of adsorption. The compositional dependence of adsorption of the copolymers from carbon tetrachloride is more complex. ¹H NMR studies show that a very high proportion of repeating units are held close to the silica surface. With polystyrenes, the fraction of units of restricted mobility decreases with polymer molecular weight and with surface coverage; at partial surface coverage virtually all the phenyl groups of low molecular weight polystyrene (mol. wt. = 4000) are immobilised. The copolymers also show large restricted fractions, which decrease along the adsorption isotherm, but which show no significant dependence on polymer composition. Higher restricted fractions seem to be associated with poorer solvent quality.     

13C NMR spectra of poly(alkyl α-chloroacrylate)s

¹³C NMR spectra of isotactic and syndiotactic poly(ethyl α-chloroacrylate)s and poly(isopropyl α-chloroacrylate)s were measured in toluene-d₈ at 25 MHz. The spectra were analyzed for triad, tetrad and pentad tacticities comparing the spectra with the results previously obtained by ¹H NMR spectroscopy. Tetrad tacticities of the polymers were measured from the resonance of the backbone methylene carbon and favorably compared with tetrad values obtained by ¹H NMR. The resonance of the carbonyl carbon showed the peaks corresponding to the tactic triad with a pentad splitting in mm resonance. The triad values obtained from the carbonyl carbon resonance were in good agreement with those calculated from the tetrad values as well as the triad tacticities obtained by ¹H NMR. The quaternary carbon reconances were very complicated because the chemical shift differences for the different tactic triads were of the comparable magnitude with those for the pentads, and a tentative peak assignment was made with the aid of the statistical calculation of pentad values assuming first-order Markovian statistics for the isotactic polymer and Bernoullian statistics for the syndiotactic polymer.     

Living Alternating Copolymerization of a Methylenecyclopropane Derivative with CO to Afford Polyketone with Dihydrophenanthrene‐1,10‐diyl Groups

Summary: Pd complexes prepared from [PdCl(Me)(L)] (L = N‐ligands) and NaBARF catalyze the alternating copolymerization of 7‐methylenedibenzo[a,c]bicyclo[4.1.0]heptane with CO to produce the polyketone. Pd complexes with substituted 1,10‐phenanthroline ligands produce the polymer with narrow molecular weight distribution. Addition of 4‐tert‐butylstyrene to the growing polymer after consumption of the initially charged monomer, results in polymer growth to afford an AB‐type block copolyketone. A Pd complex with an optically active bisoxazoline ligand produces the optically active polymer with narrow polydispersity. The addition of DBU to a solution of polyketone converts the cis‐fused six‐membered rings into the trans‐fused rings via epimerization of the CH carbon attached to the carbonyl group.

Addition of I to cationic Pd complexes catalyzes the ring‐opening copolymerization of the monomer with CO to produce the polyketone, ? (C(?CH₂)? C₁₄H₁₀? CO)_n? ( II ).     

Conformation and gas permeability of poly(α-amino acid) membranes

The permeability of some poly(?-amino acid) (PAA) membranes like such of poly(N,δ-carbobenzoxy-L -lysine) (PCBL), poly(N,δ-carbobenzoxy-L -ornithine) (PCBO) as well as of copolymers of L -lysine and carbobenzoxy-L -lysine to oxygen and carbon dioxide were determined at different water content especially with regard to their use for artificial lungs. The conformations of these polymer membranes were studied by means of IR-spectra and X-ray diffraction. The results on the diffusion coefficient obtained for PCBL and PCBO were analysed in terms of Eyring's theory. They suggest that the microvoids in the interstices between the α-helices, assumed on the basis of X-ray analyses, play an important role, especially below the glass transition temperature T_g of the side-chains. This seems also to contribute partly to the diffusion of gas through the membrane even above T_g and results in an abnormally high “apparent activation energy” of diffusion in the wet state below T_g. It was found that the permeability of the membrane of partially decarbobenzoxylated PCBL for oxygen in a certain temperature range is higher than that for carbon dioxide. This has never been observed for any other synthetic polymer, because usually carbon dioxide has a higher solubility in these materials than oxygen. In the case of the partially decarbobenzoxylated PCBL membranes, however, the diffusion coefficient of carbon dioxide, and therefore the permeation of this gas, decreases much more than that of oxygen with increasing decarbobenzoxylation accompanied by the formation of β-structure and concomitantly the formation of intermolecular hydrogen bonds. Obviously, this phenomenon may be responsible for the permselectivity of these membranes for oxygen compared with carbon dioxide.     

Synthesis of carboxy- and chloro-terminated poly(propylene)s using Zn(C2H5)2 as chain transfer reagent

Propene was polymerized with conventional and Solvay-type TiCl₃ combined with Al(C₂H₅)₂Cl using Zn(C₂H₅)₂ as a chain transfer reagent. The produced terminal Zn-carbon bonds of the polymer were reacted with carbon dioxide and chlorine in the presence of N-methylimidazole followed by hydrolysis to obtain terminally carboxylated and chlorinated poly(propylene) in approximately 50% yield.     

Properties of supercritical CO2 saturated poly(ethylene glycol) nonylphenyl ether

Density and viscosity of poly(ethylene glycol) nonylphenyl ether (PEG-NPE) saturated with supercritical carbon dioxide (SC CO₂), as well as the interfacial tension in the PEG-NPE-SC CO₂ system, were evaluated for the temperature range of 323 K to 343 K and pressures of 10.0 to 25.5 MPa. Remarkable polymer swelling as a result of solvent penetration was observed, and the coefficient of swelling for the above mentioned experimental conditions was evaluated. Data obtained show that the viscosity of polymer-rich phase is a decreasing function of both temperature and pressure. Moreover interfacial tension is a decreasing linear function of carbon dioxide density.     

The structure of poly(ethylene oxide)-salt complexes with 13c CPMAS NMR and relaxation studies

¹³C cross polarization and magic-angle spinning (CPMAS) NMR studies were made on poly(ethylene oxide) (PEO) complexed wit LiClO₄, NaClO₄, BaSCN, Bal₂ and Ba(ClO₄)₂. The proton and carbon spin-lattice relaxation times in a rotating frame (T_1ρH, T_1ρC) as well as the rate of cross polarization were measured at room temperature. For Ba(ClO₄)₂ the measurements were made with different polymer molar masses and salt concentrations. The changes in relaxation behaviour indicate changes in polymer chain mobility as well as strong interaction between ions and PEO chains. The T_1ρH and T_1ρC decrease with decreasing salt concentration towards the relaxation times of the pure polymer. Nonexponential relaxation behaviour was found for the samples according to the T_1ρC and T_CH measurements.     

A New Approach toward Investigation of Structure of Terminal Units of Poly(1,3‐Pentadiene) using T2‐Filtered NMR Spectroscopy

A new method for the identification of the structure of terminal units in poly(1,3‐pentadiene) synthesized by cationic mechanism is developed. The conducting of NMR experiments with a T₂ filter allows the intensities of the spectral signals of carbon and hydrogen atoms of main chain groups of poly(1,3‐pentadiene) with a short relaxation time to be decreased and significantly increases the intensities of signals of carbon and hydrogen atoms of head and end groups, which are characterized by higher mobility. Using 1D NMR spectroscopy with a T₂ filter as well as 2D heteronuclear single‐quantum correlation and heteronuclear multiple‐bond correlation NMR spectroscopy, it is found that the position of four out of five carbon atoms of the head group fully coincides with the position of spectral signals of carbon atoms of trans‐1,2‐ and trans‐1,4‐ units of a main polymer chain. This new method allows the identification of the signals of all carbon atoms in head trans‐1,4‐ group of poly(1,3‐pentadiene).     

Direct method of synthesis of polyureas by N-acylphosphoramidites

Polyureas and polythioureas were prepared under mild conditions by direct polycondensation of carbon dioxide and carbon disulfide, respectively, with diamines in the presence of diethyl N-acetyl-N-methylphosphoramidite or its analogs containing an active P? N bond. The influence of the substituents in the phosphoramidite, of the CO₂ pressure, solvent, organic base and diamine structure on the yield and inherent viscosity of the polymer was investigated. A reaction mechanism involving the intermediate formation of a mixed anhydride of dialkylphosphorous and alkyl(aryl)carbamic acid is discussed.     

Vinyl polymerization by metal complexes, 20. Initiation by vinylamine/vinyl alcohol copolymer · copper(II) systems

The polymerization of acrylonitrile (AN) and of methyl methacrylate (MMA) initiated by various copper(II) chelates was studied in the presence of carbon tetrachloride. Several vinylamine (VAm)/vinyl alcohol (VA) copolymers with different contents of NH₂ and OH bearing monomeric units were chosen as polymer ligands as well as polyvinylamine (PVAm)/poly(vinyl alcohol) (PVA) mixtures (of equal NH₂ and OH group contents as the corresponding copolymers), PVAm, and PVA. The activity of the used polymer chelates to initiate the AN and the MMA polymerization was compared at various pH values of the reaction systems. For the polymerization of MMA, the VAm/VA copolymer systems showed a higher activity than the PVAm chelate containing the same amount of NH₂ groups, contrary to the case of the polymerization of AN, where the polymerization activity showed a reverse behavior. The initiation mechanism is discussed.     

An unusual bacterial polyester with a phenyl pendant group

The microorganism Pseudomonas oleovorans is known to produce polyesters containing 3-hydroxyalkanoate units when grown on n-alkanes and n-alkanoic acids under nutrient limiting conditions, but when 5-phenylvaleric acid was supplied as the only carbon source, poly[3-hydroxy-5-phenylpentanoate], a polyester with a phenyl pendant group, was produced. The optimum substrate concentrations and harvesting times were determined by measuring the change of cell growth and polymer yield during the growth. A 12-L cell culture yielded 222,5 mg polymer/L and 25% polymer per cellular dry weight. This bacterial polymer showed an optical rotation of [α] = ?24,5° ± 0,2°. The structure was corroborated by ¹H NMR and ¹³C NMR spectroscopy. The composition of the polymer was also determined by methanolysis to the methyl ester of the repeating unit, which was subsequently analyzed by GC. By this procedure the polyester was found to be a homopolymer to the extent of at least 99%. The polyester has a glass transition at 13°C, a melting range from 54 to 69°C, and a weight-average molecular weight of M?_w = 350000 with a polydispersity M?_w/M?_n of 3,5, as determined by GPC relative to polystyrene standards.     

Preparation of Self‐Assembled Carbon Network Structures with Magnetic Nanoparticles

Nanosized particles of different metals in a polymer matrix have attracted considerable interest in various research fields of chemistry, because of their physical and chemical catalytic properties and their application potential in nanoelectronics. In this paper, we present an experimental method for the preparation of self‐assembled honeycomb carbon network patterns with Co and Ni particles. Starting from a 2% carboxylated nitrocellulose solution in amyl acetate submerged in cooled distilled water, we already observe the above self‐organized uniform‐size net structure at the top of the water surface. The submergence of the carboxylated nitrocellulose network in 0.25‐M water solution of cobalt acetate Co(CH₃COO)₂ (or nickel acetate Ni(CH₃COO)₂) for 1 h leads to the ion‐exchange introduction of inorganic cations Co²⁺ (or Ni²⁺) to a polymer matrix. In order to obtain samples with a large content of Co (or Ni) cations, we have carried out the sedimentation of the ion‐connected Co (or Ni) with the oxalic acid H₂C₂O₄ and, next, repeated the sorption of carboxylated nitrocellulose with the cations Co²⁺ (or Ni²⁺). For the fabrication of the Co (or Ni) nanoparticles, the carboxylated nitrocellulose networks, received after a first, second, and third sorption cycle, were heated under vacuum conditions (10^–5 mbar) at T ≥ 500°C for 2 h. The process of implementing the Co and Ni nanoparticles in the carbon network was systematically characterized with the help of measuring the specific resistivity in the temperature range from 4.2 to 295 K.     

A polymer model of lignin (D.H.P.) 13C selectively labelled at the benzylic positions: Synthesis and NMR study

D.H.P. polymer model of Lignin was synthesized by enzymatic dehydrogenation of coniferyl alcohol enriched to 90% in ¹³C-γ, on the benzylic position. On the ¹H NMR spectrum recorded at 250 MHz, of the ¹³C labelled D.H.P., the study of the J_CH-γ couplings, made possible a precise assignment of proton signals. The ¹³C NMR spectra showed that the ¹³C-γ carbon atom previously labelled in coniferyl alcohol was found in several sites in the polymer. Special NMR techniques like gate decoupling and selective proton irradiation were used together with the study of the chemical shifts, to make an assignment for the different ¹³C-γ signals. C-γ in carbonyl compounds like vanillin and vanillic acid, C-γ vinylic atom like in coniferyl alcohol and cinnamaldehyde. C-γ atom like in β? 5, β? β, β? O? 4 dilignol units, and C-γ atom involved in C-γ benzyl ether bond in β? O? 4 dimer were identified; the corresponding J_CH–γ couplings of these C-γ carbon atoms were determined.     

Stereoregularity of polystyrene derivatives, 1. Poly(methylstyrene)s and poly(methoxystyrene)s obtained with ziegler catalyst,cationic catalyst,or radical initiators

The ¹³C NMR spectra of methylstyrenes and methoxystyrenes and their polymers prepared with radical initiators, a Ziegler catalyst, or a cationic catalyst were measured. The spectra of the polymers were assigned by the chemical shifts of the monomers and gated-decoupling method. The absorption of the aromatic C¹ carbon of each polymer, which varied by the polymerization conditions, was assigned in terms of a pentad sequence assuming that the Bernoullian statistics holds for the polymerization of ring substituted styrenes. The stereoregularities calculated from C¹ carbon absorptions were compared with those of polystyrenes obtained unter the same polymerization conditions. In the radical polymerization of ortho-derivatives, where the substituent locates near the polymer backbone, high syndiotactic polymers (P_r = 0,80 ? 0,83) were prepared. The effect of the substituent in para-derivatives did not appear. On the other hand, random polymers were generally fromed by cationic polymerization regardless of the position and the type of the substituent.     

Determination of branching of polyvinylchloride

The degree of branching of some samples of polyvinylchloride (PVC) was determined by hydrogenation of the polymer with LiAlH₄ followed by infrared measurements on the product so obtained. It is verified that during the hydrogenation process there does not occur any degradation of the polymer. The branching degrees are given as ratios of 100(CH₃/CH-₂) which are determined from the ratios of the absorbances at 1378 and 1368 cm^?1 by means of a calibration curve. The influence of some polymerization conditions on the degree of branching such as temperature, degree of conversion, and presence of the two diluents tetrahydrofurane and n-butyraldehyde were examined. Only the polymerization temperature is found to influence the degree of branching. The PVC samples prepared at 50°C have approximately one side chain for every sixty carbon atoms, whereas the samples prepared at temperatures below ?60°C are practically linear.     

Composite fibrous biomaterials for tissue engineering obtained using a supercritical CO2 antisolvent process

Several techniques have been proposed for producing porous structures or scaffolds for tissue engineering but, as yet, with no optimal solution. With regard to this topic, this paper focuses on the preparation of biocompatible nanometric filler–polymer composites organized in a network of fibers. Titanium dioxide (TiO₂) or hydroxyapatite (HAP) nanopowders as the guest particles and poly(lactic acid) (L-PLA) or the blend poly(methylmethacrylate)/poly(ε-caprolactone) (PMMA/PCL) as the polymer carrier were selected as model systems for this purpose. A supercritical antisolvent technique was used to produce the composites. In the process developed, the non-soluble particulate filler was suspended in a polymer solution, and both components were sprayed simultaneously into supercritical carbon dioxide (scCO₂). Using this technique, polymeric matrices were loaded with ～10–20 wt.% of inorganic phase distributed throughout the composite. Two different hybrid materials were prepared: a PMMA/PCL + TiO₂ system where either fibers or microparticles were prepared by varying the molecular weight of the used PMMA; and fibers in the case of L-PLA + HAP system. After further post-processing in a three-dimensional network, these nanofibers can potentially be used as scaffolds for tissue engineering.     

Exceptionally High CO2 Adsorption at 273 K by Microporous Carbons from Phenolic Aerogels: The Role of Heteroatoms in Comparison with Carbons from Polybenzoxazine and Other Organic Aerogels

Phenolic aerogels containing oxygen and other polymeric aerogels containing both oxygen and nitrogen (polybenzoxazine and a polyamide‐polyimide‐polyurea co‐polymer) are converted to carbon aerogels (800 °C/Ar), and are etched with CO₂ (1000 °C). Etching opens closed pores and increases micropore volumes and size. Heteroatoms are retained in the etched samples. All carbon aerogels are evaluated as CO₂ absorbers in terms of their capacity and selectivity toward CH₄, H₂, and N₂. CO₂ adsorption capacity is linked to microporosity. In most cases, monolayer coverage of micropore walls is enough to explain CO₂ uptake quantitatively. The interaction of CO₂ with micropore walls is evaluated via isosteric heats of adsorption, and is stronger with carbons containing only oxygen heteroatoms. The adsorption capacity of those carbons (5–6 mmol g^?1) is on par with the best carbon and polymeric CO₂ adsorbers known in the literature, with one exception however: etched carbon aerogels from low‐density resorcinol‐formaldehyde aerogels show a very high CO₂ uptake (14.8 ± 3.9 mmol g^?1 at 273 K, 1 bar) attributed to a pore‐filling process that proceeds beyond monolayer coverage, whereas surface phenoxides engage in a thermally neutral carbonate forming reaction (surface‐O^– + CO₂ → surface‐O–(CO)–O^–) that continues until micropores are filled.