Conformational analysis of poly(methyl acrylate) by 1H nuclear magnetic resonance spectroscopy

The ¹H NMR spectra of poly(methyl acrylate-d₁) +CHD? CH(COOCH₃)+_n were measured in o-dichlorobenzene and CDCl₃ in the temperature range between ? 20 and 145°C. Trans and gauche coupling constant were determined from the temperature dependence of the geminal coupling constants, neglecting g' conformers. It was estimated that the proportion of trans conformer is 1,5 to 1,9 times that of the gauche conformer in this temperature range.     

Solvent effects on free-radical polymerization, 2. IR and NMR spectroscopic analysis of monomer mixtures of methyl methacrylate and N-vinyl-2-pyrrolidone in bulk and in model solvents

Binary systems of methyl methacrylate (MMA)/N-vinyl-2-pyrrolidone (NVP) and MMA/N-methyl-2-pyrrolidone (NMP) with NMP as saturated model of NVP and of NVP/methyl isobutyrate (MiB) with MiB as saturated model of MMA were investigated by means of IR and NMR spectroscopy. Investigations were carried out at room temperature or at 60°C in CHCl₃ (IR) or CDCl₃ and C₆H₁₂/C₆D₁₂ (NMR). It can be concluded from IR and NMR spectra that the polarity of MMA increases in the presence of NVP and the polarity of NVP decreases in the presence of MMA. Equilibrium constants K of complex formation were determined to: K = 0,169 ± 0,037 L · mol^?1 for MMA/NVP at 30°C, 0,112 ± 0,024 L · mol^?1 for NVP/MiB at 60°C and 0,125 ± 0,030 L · mol^?1 for MMA/NMP at 60°C.     

1H NMR and 2D NMR relaxation and wide line measurements in partially deuterated polystyrenes

Solutions of chain- (PS-d₃) and phenyl ring (PS-d₅) deuterated polystyrenes in perdeuterated PS-d₈ have been investigated with ¹H and ²D NMR relaxation and wide line methods. The intra- and intermolecular parts of the ¹H second moments at ?100°C are 3,7 G² and 2,0 G², respectively, for PS-d₃, and 14,7 G² and ca. 0 G², respectively, for PS-d₅. The intermolecular contribution to the ¹H spin lattice relaxation rate, determined at 55 MHz between 150°C and 250°C, is about one third of the total rate in PS-d₃, and negligible in PS-d₅. We suggest that this contribution is caused by rotational fluctuations of the intermolecular H ?H vectors. The intramolecular ¹H- and ²D-relaxation rates indicate that the phenyl group motion is somewhat faster than the rotational segmental motion of the polymer chain.     

Molecular structure of some model compounds for poly(aryl ether ketone)s

The molecular structure of a series of model compounds for poly(aryl ether ketone)s was investigated by means of ¹³C NMR spectroscopy, quantum chemical calculation, and wide-angle X-ray scattering. The comparison of the chemical shifts for the model compounds dissolved in 98% H₂SO₄ and CDCl₃ (or CDCl₃ + DMSO-d₆) suggested that their carbonyl groups are partially protonated by sulfuric acid and the induced positive charges are delocalized in their aromatic rings. This result was supported by the charge distribution obtained by quantum chemical calculations. The model compounds were also used to characterize the molecular structure of poly(aryl ether ketone)s. The length of the repeating unit of the polymer chain, which was calculated based on the whole chain length or fragment chain length of the model compounds obtained by semiempirical PM3 method, is compared with the c-axis of the crystal unit cell of the polymer. For poly(aryl ether ketone)s containing biphenyl moieties, the length of the c-axis of the unit cell is approximately twice that of the repeating unit of the macromolecule.     

Beiträge zur polymerisation von 2-isopropenylnaphthalin, 3. Anionische homopolymerisation von 2-isopropenylnaphthalin

The anionic homopolymerization of 2-isoprenylnaphthalene with butyllithium in tetrahydrofuran at –78°C is described. The refractive index increment amounts to dn/dc = 0,2084 ml/g for these polymers in toluene at 25°C and wavelength λ = 436 nm. Determination of the molecular weights by light scattering yielded values between 13 000 and 270 000. The second virial coefficients also determined by light scattering measurements are comparable with the corresponding data of poly(α-methylstyrene). A calibration curve is given for gel permeation chromatography of the poly(2-isoprenylnaphthalene)s, whose polymolecularity indexes M_w/M_n lie between 1,06 and 1,2. Their intrinsic viscosity/molecular weight relationship is [η] = 1,43·10^?2 M^0,663. From ¹H NMR of the α-methyl group fractions of isotactic triads between 30 and 55% are evaluated. The glass transition temperature extrapolated to infinite molecular weight is T_g∞ = 221°C. Above 300°C fast degradation by monomer formation is observed.     

T1 and T2 temperature dependence of female human breast adipose tissue at 1.5 T: groundwork for monitoring thermal therapies in the breast

The T₁ and T₂ temperature dependence of female breast adipose tissue was investigated at 1.5 T in order to evaluate the applicability of relaxation‐based MR thermometry in fat for the monitoring of thermal therapies in the breast. Relaxation times T₁, T₂ and T_2TSE (the apparent T₂ measured using a turbo spin echo readout sequence) were measured in seven fresh adipose breast samples for temperatures from 25 to 65 °C. Spectral water suppression was used to reduce the influence of the residual water signal. The temperature dependence of the relaxation times was characterized. The expected maximum temperature measurement errors based on average calibration lines were calculated. In addition, the heating–cooling reversibility was investigated for two samples. The T₁ and T_2TSE temperature (T) dependence could be fitted well with an exponential function of 1/T. A linear relationship between T₂ and temperature was found. The temperature coefficients (mean ± inter‐sample standard deviation) of T₁ and T_2TSE increased from 25 °C (dT₁/dT = 5.35 ± 0.08 ms/°C, dT_2TSE/dT = 3.82 ± 0.06 ms/°C) to 65 °C (dT₁/dT = 9.50 ± 0.16 ms/°C, dT_2TSE/dT = 7.99 ± 0.38 ms/°C). The temperature coefficient of T₂ was 0.90 ± 0.03 ms/°C. The temperature‐induced changes in the relaxation times were found to be reversible after heating to 65 °C. Given the small inter‐sample variation of the temperature coefficients, relaxation‐based MR thermometry appears to be feasible in breast adipose tissue, and may be used as an adjunct to proton resonance frequency shift (PRFS) thermometry in aqueous tissue (glandular + tumor). Copyright © 2015 John Wiley & Sons, Ltd.     

Comparative NMR studies of diffusional water permeability of red blood cells from different species. X. Camel ( Camelus dromedarius ) and alpaca ( Lama pacos )

The diffusional water permeability (P _d) of camel and alpaca red blood cells (RBCs) was measured by a doping nuclear magnetic resonance (NMR) technique on control cells and following inhibition withp-chloromercuribenzene sulphonate (PCMBS). The values ofP _d were, in the case of alpaca RBC≈4.6×10⁻³ cm/s at 25°C, 5.4×10⁻³ cm/s at 30°C, 6.6×10⁻³ cm/s at 37°C and 7.7×10⁻³ cm/s at 42°C. In case of camel RBC the values ofP _d where ≈4.2×10⁻³ cm/s and 9.0×10⁻³ cm/s at 42°C. Systematic studies on the effects of PCMBS on water diffusion in camel RBC indicated that the maximal inhibition was reached in 45 min with 1–2 mm PCMBS. The values of maximal inhibition were around 47% at 25°C and 68% at 30°C for alpaca RBC and around 62% at 25°C and 56% at 37°C for camel RBC. The basal permeability to water of alpaca RBC was estimated at around 2.6×10⁻³ cm/s at 25°C, 1.7×10⁻³ cm/s at 30°C and of camel RBC as 1.8×10⁻³ cm/s at 25°C and 3.0×10⁻³ cm/s at 37°C. The values of the activation energy of water diffusion (E _{a, d}) were around 23 kJ/mol for camel and 34 kJ/mol for alpaca RBC. This suggests that in addition to the number of transport channels other features of the pathways might be important for defining the temperature dependence of the water permeability.     

The cationic polymerization of 3-chloro-2-methyl-1-propene

The polymerization of 3-chloro-2-methyl-1-propene was investigated at temperatures between 0 and ?80°C, using AlCl₃ and AlBr₃ as initiators. The molecular weights of the resulting oily products depend on the polymerization temperature and varied in the range of the number-average molecular weight M?_n = 400–620. The course of polymerization was studied and the characteristic groupings in the oligomeris were identified by means of ¹H NMR and ¹³C NMR spectroscopy. Based on the results the mechanism of partial reactions was discussed to explain the new type of propagation in the cationic polymerization.     

Study of photopolymer, 10. Cationic polymerization of vinyloxyethyl acrylate

Cationic polymerizations of vinyloxyethyl acrylate (VEA) catalyzed by boron trifluorideether complex were carried out in toluene at 10, ?10, and ?30°C. In this system, a critical catalyst concentration (C₀) exists; when the catalyst concentration is below this concentration, the polymerization of VEA cannot be initiated. The rate of polymerization is expressed as –d[M]/dt=k_p(C^*)·[M]^a, where a was found to be 0,44 (at 10°C), 0.51 (at ?10°C), and 0,63 (at ?30°C), respectively. From these results, it is concluded that the rate of polymerization of VEA is proportional to the first power of catalyst concentration and to 0,44–0,63 power of monomer concentration between 10 and ?30°C, respectively. Furthermore, it is recognized that an increasing monomer concentration tends to decrease the degree of polymerization.     

Synthesis of high-molecular-weight poly(L-lactide) initiated with tin 2-ethylhexanoate

The bulk polymerization of L ,L -dilactide was studied as a function of polymerization temperature (T_p), time and concentration of catalyst (tin 2-ethylhexanoate). Poly(L -lactide) (PLLA), with the highest value of intrinsic viscosity ([η] = 13 dl · g^?1; M?_v ≈ 1 · 10⁶) and heat of fusion (ΔH_m = 64,7 J · g^?1), was synthesized at a low catalyst concentration (0,015 wt.-%) and at the lowest T_p studied (100°C), just above the melting point of L ,L -dilactide (98°C). The ceiling temperature of PLLA was found to be 275°C, as deduced from an M?_{v max.} ? T_p curve. The M?_w/M?_n ratios of as-polymerized PLLA samples ranged from 2 to 3. Fractions of PLLA with M?_{v max.} were already present at 50% conversion. The experimental results support a proposed nonionic insertion polymerization mechanism. Polymerization at 100–140°C resulted in early crystallization of PLLA leading to a rather untangled polymer and microporous (pores up to 100 nm) sample texture.     

Macrocyclic peptides, 8. Enantiomeric differentiations of various (R)- and (S)- ammonium and (R)- and (S)-α-amino acid ester salts by macrocyclic pseudopeptides

The interactions of the hydrobromides of (R)- and (S)-alanine-N-methylanilides ( 1 ) with 24-, 27- and 36-membered ring pseudopeptides ( H-24, H-27 and H-36 , respectively) derived from glycine and (2S,3′ S)-4-methyl-2-(2′-oxo-3′-isobutyl-1′-piperazinyl)pentanoic acid were studied by means of ¹H and ¹³C NMR measurements in CDCl₃. It was found from these results that H-24 and H-27 distinguished (R)- and (S)-isomers of 1 , while H-36 did not entirely. Moreover, the enantioface-differentiating abilities of these cyclic peptides were investigated by means of ¹H NMR measurements in CDCI₃ using (R)- and (S)-1-phenylethylammonium and (R)- and (S)-p-methoxy-1-phenylethylammonium bromides as the substrates, showing that the enantio-selectivity of H-36 is superior to those of H-24 and H-27 . Also, the chiral recognition ability of H-24 for the hydrochlorides of (R)- and (S)-alanine (Ala), -leucine (Leu), -methionine (Met), -phenylalanine (Phe), -proline (Pro) and -valine (Val) methyl esters were examined by ¹H and ¹³C NMR measurements in CDCl₃. Among these hydrochlorides, HCl · Phe? OCH₃ was distinguished more effectively with H-24 .     

On the mechanism of olefin polymerization by titanocene/MAO catalysts: Relationships between metathesis and addition polymerization

Ethylene polymerizations and norbornene oligomerizations catalysed by Cp₂Ti¹³CH₃Cl/MAO (Cp: cyclopentadienyl; MAO: methylaluminoxane) mixtures have been carried out at different temperatures (from -20°C to 20°C), in order to test the validity of carbene mechanisms in α-olefin polymerizations. Depending on the temperature, different ratios of the cationic species [Cp₂Ti¹³CH₃]⁺[Cl · MAO]^? and precursors of the alkylidene Cp₂Ti = ¹³CH₂ exist. The in situ polymerization of ¹³C enriched ethylene was monitored by ¹³C NMR spectroscopy. Moreover, catalytic activity was determined and polyethylene samples were analyzed by ¹³C NMR and gel permeation chromatography (GPC). The following evidence has been provided against the carbene mechanism in the α-olefin polymerization with titanocene based catalysts: (a) in the in situ ethylene polymerization experiments the appearance of polyethylene signals is concurrent with the decrease of cationic [Cp₂Ti¹³CH₃]⁺[Cl · MAO]^? signals and is not related to the intensity of the alkylidene Cp₂Ti = ¹³CH₂ signals; (b) from the ¹³C NMR analysis of polyethylene chain-end groups the ¹³C enrichment of Cp₂Ti¹³CH₃Cl has only been found in the methyl chain-end group and not in the methylene of the propyl chain-end group, as should have been the case if the carbene mechanism had been valid; (c) from norbornene oligomerization (at 0°C) the addition product 2-¹³C enriched methyl-norbornane has been identified. Moreover, the identification of a ¹³C enriched methylidene-norbornane dimer at higher temperatures has revealed the possibility of norbornene addition to titanium carbenes through the formation of titanacyclobutane without the opening of the norbornene ring. However, this process requires higher energies with respect to the Cossee type insertion.     

Low-temperature 1H and 13C NMR investigation of trimethylaluminium contained in methylaluminoxane cocatalyst for metallocene-based catalysts in olefin polymerization

Toluene-d₈ solutions of methylaluminoxane (MAO) after the addition of different amounts of trimethylaluminium (TMA) have been studied by means of ¹H and ¹³C NMR at a temperature as low as ?78°C to freeze out some of the fluxional equilibria of the molecule. A comparison of the half height width of the NMR signal W_1/2 and of the mole ratio of the methyl signals before and after addition of known amounts of TMA allowed us to reach the following conclusions about the TMA contained in MAO solutions: (a) TMA is mainly bound to MAO; (b) TMA participates in disproportionation reactions.     

Unvernetzte epoxid-amin-additionspolymere, 27. Hybridnetzwerke — Möglichkeiten der carbonsäureanhydridmodifizierung und nachvernetzung von epoxid-amin-prepolymeren

The reaction of cyclic dicarboxylic anhydrides ( 3 ) with prepolymers 2 (from aniline and 2,2-bis[4-(2,3-epoxypropoxy)phenyl]propane ( 1 )) results in new modified prepolymers 4–6 containing carboxylic groups and reactive glycidyl end groups. The structure of 4–6 was determined by IR, ¹H NMR, ¹³C NMR spectroscopy, elemental analyses and M?_n (by v. p.o.) values. By simple heating to 100–140°C prepolymers 4–6 were crosslinked to hybrid networks ( 7 ). Their structure was studied by IR and solid-state ¹³C NMR spectroscopy.     

Reaction between carbon monoxide and a Ti-polyethylene bond with a MgCl2-supported TiCl4 catalyst system

The reaction between carbon monoxide and the Ti-polyethylene bond was investigated by using a stopped-flow polymerization method which can provide quasi-living polymers with very low molecular weights. Ethylene polymerization was conducted with a typical MgCl₂-supported TiCl₄ catalyst combined with triisobutylaluminium (Al(i-C₄H₉)₃) or Al(CH₃)₃. The quasi-living polymers were introduced into either the heptane solution saturated with carbon monoxide or the heptane solution containing ¹³C-enriched carbon monoxide at ?78°C. The mixture was gradually heated up to room temperature. During this procedure, a small portion of the reaction mixture was taken out at ?78°C, 0°C and at room temperature. The polymers produced were analyzed by means of Fourier-transform infrared spectroscopy, gel-permeation chromatography, proton nuclear magnetic resonance (¹H NMR) and ¹³C NMR spectroscopy. The analytical data show that carbon monoxide is predominantly incorporated into the polymers as a ketonic carbonyl.     

Comparative Cell Shape and Diffusional Water Permeability of Red Blood Cells from Indian Elephant (Elephas maximus) and Man (Homo sapiens)

Red blood cells (RBC) from an Indian elephant (Elephas maximus) were studied by light microscopy (LM), scanning electron microscopy (SEM) and a new nuclear magnetic resonance (NMR) ‘imaging’ method based on the translational diffusion of water, NMR q-space analysis. Also, the transmembrane diffusional permeability, P _d of water in RBC was measured by using a Mn²⁺-doping NMR technique, taking human RBC as a reference. The main diameter of the elephant RBC was measured as 9.3 ± 0.7 μm by LM, 9.3 ± 0.7 μm by ‘shrinkage-corrected’ SEM, and 9.3 ± 0.4 μm by q-space anlaysis. The value is ∼1.4 μm larger than that for the human RBC. The values of P _d were, in the case of elephant RBC, 3.2 × 10⁻³ cm/s at 25 °C, 3.9 × 10⁻³ cm/s at 30 °C, 5.2 × 10⁻³ cm/s at 37 °C and 6.5 × 10⁻³ cm/s at 42 °C; all values were significantly lower than the corresponding values of P _d for human RBC, namely 4.3 × 10⁻³ cm/s at 25 °C, 5.2 × 10⁻³ cm/s at 30 °C, 6.1 × 10⁻³ cm/s at 37 °C, 7.8 × 10⁻³ cm/s at 42°C. The maximal inhibition of P _d (56%) was reached in 30 min at 37 °C with 2 mm p-chloromercuribenzene sulphonate (PCMBS) for both species of RBC. The basal permeability to water at 37 °C was estimated to be 2.3 × 10⁻³ cm/s for elephant and 2.6 × 10⁻³ cm/s for human RBC. The values of the activation energy for water permeability (E _a,d ) was significantly higher for elephant RBC (31.9 kJ/mol) than for human RBC (25.9 kJ/mol). This indicated that features other than the number of transporters per cell are likely to be important in defining the differences in water permeability in the RBC from the two species.     

Comparative Cell Shape and Diffusional Water Permeability of Red Blood Cells from Indian Elephant ( Elephas maximus ) and Man ( Homo sapiens )

Red blood cells (RBC) from an Indian elephant (Elephas maximus) were studied by light microscopy (LM), scanning electron microscopy (SEM) and a new nuclear magnetic resonance (NMR) ‘imaging’ method based on the translational diffusion of water, NMR q-space analysis. Also, the transmembrane diffusional permeability, P _d of water in RBC was measured by using a Mn²⁺-doping NMR technique, taking human RBC as a reference. The main diameter of the elephant RBC was measured as 9.3 ± 0.7 μm by LM, 9.3 ± 0.7 μm by ‘shrinkage-corrected’ SEM, and 9.3 ± 0.4 μm by q-space anlaysis. The value is ∼1.4 μm larger than that for the human RBC. The values of P _d were, in the case of elephant RBC, 3.2 × 10⁻³ cm/s at 25 °C, 3.9 × 10⁻³ cm/s at 30 °C, 5.2 × 10⁻³ cm/s at 37 °C and 6.5 × 10⁻³ cm/s at 42 °C; all values were significantly lower than the corresponding values of P _d for human RBC, namely 4.3 × 10⁻³ cm/s at 25 °C, 5.2 × 10⁻³ cm/s at 30 °C, 6.1 × 10⁻³ cm/s at 37 °C, 7.8 × 10⁻³ cm/s at 42°C. The maximal inhibition of P _d (56%) was reached in 30 min at 37 °C with 2 mm p-chloromercuribenzene sulphonate (PCMBS) for both species of RBC. The basal permeability to water at 37 °C was estimated to be 2.3 × 10⁻³ cm/s for elephant and 2.6 × 10⁻³ cm/s for human RBC. The values of the activation energy for water permeability (E _a,d ) was significantly higher for elephant RBC (31.9 kJ/mol) than for human RBC (25.9 kJ/mol). This indicated that features other than the number of transporters per cell are likely to be important in defining the differences in water permeability in the RBC from the two species.     

Unit cell dimensions of poly(ethylene terephthalate)

The density of crystals of poly(ethylene terephthalate), (PETP), Q_c is checked by X-ray diffraction assuming a triclinic unit cell and the indices of reflections as found by Bunn. The following unit cell dimensions are found: a = 4,48Å, b = 5,85Å, c = 10,75 Å, α = 99,5°, β = 118,4°, and γ = 111,2°. This gives the density Q_c as 1,515g/cm³ which is about 4% higher than that reported by Bunn. Negligible differences in spacings for samples annealed at different temperatures (120°C–260°C) have been found. Only for an annealing temperature of 100°C the higher d-values lead to Q_c = 1,484g/cm³. For undrawn PETP films annealed at 250°C the same value of Q_c as for drawn PETP was obtained on the basis of Guinier X-ray patterns. No systematic variation of crystal plane spacings was found for drawn PETP fibers annealed at 220°C and containing mole fractions of 1,7 to 4,2% diethylene glycol, (2,2′-oxydiethanol), as comonomer.     

Configurational double bond selectivity in the epoxidation of hydroxy-terminated polybutadiene with m-chloroperbenzoic acid

The selectivity of the three different double bonds (CIS, TRANS and VINYL) of hydroxyterminated polybutadiene regarding epoxidation was evaluated, using m-chloroperbenzoic acid in toluene below room temperature (?10°C, ?5°C, 0°C and 5°C). To determine the kinetic constants for the three configuratons (k_1,cis = (2,59–0,6) × 10^?2 L · mol^?1 · min^?1; k_{2, trans} = (5,35–0,82) × 10^?2 L · mol^?1 · min^?1; k_{3, vinyl} = (0,97–0,01) × 10^?2 L · mol^?1 min^?1), ¹H and ¹³C NMR was used along with a system of three parallel equations. The activation energy values were also evaluated (E_{a, cis} = 53,9 kJ · mol^?1; E_{a, trans} = 70,7 kJ · mol^?1 and E_a, vinyl = 261,1 kJ · mol^?1) for the three double bond types.     

Viscosity/temperature relationships for dilute solutions of poly(2,4,5-trichlorophenyl methacrylate)

The actual viscosity η of six fractions of poly(2,4,5-trichlorophenyl methacrylate) (PTCPh) with weight-average molecular weight M?_w, ranging from 9,11 · 10⁴ to 94,8 · 10⁴, was determined in benzene at a number of temperatures from 22 to 60°C. The variation of the pre-exponential term A and the apparent activation energy of viscous flow Q, with molecular weight and concentration was studied. Moore's equations are valid for PTCPh. The temperature coefficient of the unperturbed dimensions dln 〈r²₀〉/dT estimated from the intrinsic viscosity data by using the Burchard-Stockmayer-Fixman relation, is ?3 . 10^-3 (from 22 to 40°C) and ?0,87 . 10^-3 (from 40 to 60°C). These negative values indicate that extended configurations of PTCPh in benzene must be associated with lower energies.