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.     

Polymer diffusion in mixtures of polystyrene and polymethylstyrene studied by forced rayleigh scattering and photon correlation spectroscopy

Tracer diffusion coefficients D^* of both components were measured in mixtures of polystyrene (PS) and polymethylstyrene (PMS), a random copolymer from 60 wt.-% of m-methylstyrene and 40 wt.-% of p-methylstyrene. The results are interpreted in terms of the free-volume theory which yields master curves even for “asymmetric” mixtures of oligomer and polymer chains, if D^* is drawn versus the distance from the glass transition temperature, T–T_g. Whereas D^* was measured by the forced Rayleigh scattering technique, we also studied photon correlation spectroscopy in these mixtures and observed “slow modes” with decay constants that correspond to diffusion coefficients 2–3 decades smaller than the interdiffusion coefficient.     

Evaluation of enzymatic proteoglycan loss and collagen degradation in human articular cartilage using ultrashort echo time-based biomarkers: A feasibility study

The objective of the current study was to investigate the feasibility of quantitative 3D ultrashort echo time (UTE)-based biomarkers in detecting proteoglycan (PG) loss and collagen degradation in human cartilage. A total of 104 cartilage samples were harvested for a trypsin digestion study (n = 44), and a sequential trypsin and collagenase digestion study (n = 60), respectively. Forty-four cartilage samples were randomly divided into a trypsin digestion group (tryp group) and a control group (phosphate-buffered saline [PBS] group) (n = 22 for each group) for the trypsin digestion experiment. The remaining 60 cartilage samples were divided equally into four groups (n = 15 for each group) for sequential trypsin and collagenase digestion, including PBS + Tris (incubated in PBS, then Tris buffer solution), PBS + 30 U col (incubated in PBS, then 30 U/ml collagenase [30 U col] with Tris buffer solution), tryp + 30 U col (incubated in trypsin solution, then 30 U/ml collagenase with Tris buffer solution), and tryp + Tris (incubated in trypsin solution, then Tris buffer solution). The 3D UTE-based MRI biomarkers included T₁, multiecho T₂*, adiabatic T_1ρ (AdiabT_1ρ), magnetization transfer ratio (MTR), and modeling of macromolecular proton fraction (MMF). For each cartilage sample, UTE-based biomarkers (T₁, T₂*, AdiabT_1ρ, MTR, and MMF) and sample weight were evaluated before and after treatment. PG and hydroxyproline assays were performed. Differences between groups and correlations were assessed. All the evaluated biomarkers were able to differentiate between healthy and degenerated cartilage in the trypsin digestion experiment, but only T₁ and AdiabT_1ρ were significantly correlated with the PG concentration in the digestion solution (p = 0.004 and p = 0.0001, respectively). In the sequential digestion experiment, no significant differences were found for T₁ and AdiabT_1ρ values between the PBS + Tris and PBS + 30 U col groups (p = 0.627 and p = 0.877, respectively), but T₁ and AdiabT_1ρ values increased significantly in the tryp + Tris (p = 0.031 and p = 0.024, respectively) and tryp + 30 U col groups (both p < 0.0001). Significant decreases in MMF and MTR were found in the tryp + 30 U col group compared with the PBS + Tris group (p = 0.002 and p = 0.001, respectively). It was concluded that AdiabT_1ρ and T₁ have the potential for detecting PG loss, while MMF and MTR are promising for the detection of collagen degradation in articular cartilage, which could facilitate earlier, noninvasive diagnosis of osteoarthritis.     

Solid Polymer Electrolytes, 9

Summary: A new hybrid polymer electrolyte system containing polysiloxane and polyether segments has been designed and prepared by epoxide crosslinking. The thermal behavior, structure and ionic conductivity of the hybrid materials were investigated and characterized by differential scanning calorimetry (DSC), ¹³C solid‐state NMR spectroscopy and alternating current (AC) impedance measurements. Two glass transition temperatures were observed, showing a dependence on the composition and LiClO₄/PC content. The miscibility of the polymer components in the hybrid was studied by examining the ¹H spin relaxation times in the laboratory frame (T₁(H)) and in the rotating frame (T_1ρ(H)) with various compositions. Multi‐relaxation T_1ρ(H) behavior has been observed, indicative of the presence of structural heterogeneity on the timescale of T_1ρ(H). These results are correlated and used to interpret the phenomenon of the conductivity of the lithium ion in the matrix of hybrid networks.

Schematic structure of polysiloxane/polyether networks.     

Pressure Effects on the Thermodynamics of trans‐Decahydronaphthalene/Polystyrene Polymer Solutions: Application of the Sanchez‐Lacombe Lattice Fluid Theory

The cloud‐point temperatures (T_cl's) of trans‐decahydronaphthalene(TD)/polystyrene (PS, M _w = 270 000) solutions were determined by light scattering measurements over a range of temperatures (1–16 °C), pressures (100–900 bar), and compositions (4.2–21.6 vol.‐% polymer). The system phase separates upon cooling and T_cl was found to increase with rising pressure for constant composition. In the absence of special effects, this finding indicates positive excess volume for the mixing. Special attention was paid to the demixing temperatures as a function of pressure for different polymer solutions and the plots in the T‐? plane (where ? signifies volume fractions). The cloud‐point curves of polymer solutions under different pressures were observed for different compositions, which demonstrated that pressure has a greater effect on the TD/PS solutions when far from the critical point as opposed to near the critical point. The Sanchez‐Lacombe lattice fluid theory (SLLFT) was used to calculate the spinodals, the binodals, the Flory‐Huggins (FH) interaction parameter, the enthalpy of mixing, and the volume changes of mixing. The calculated results show that modified PS scaling parameters can describe the thermodynamics of the TD/PS system well. Moreover the SLLFT describes the experimental results well.

Pressure dependence of the phase transition temperature for the TD/PS polymer solutions at the indicated compositions (In SI units: 1 bar = 10⁵ N · m^?2).     

Shear‐Induced Crystallization and Shear‐Induced Dissolution of Poly(ethylene oxide) in Mixtures with Tetrahydronaphthalene and Oligo(dimethyl siloxane‐b‐ethylene oxide)

Cloud point temperatures (T_cp) and crystallization temperatures (T_l/s) were measured at different constant shear rates for the ternary system tetrahydronaphthalene/poly(ethylene oxide)/oligo(dimethyl siloxane‐b‐ethylene oxide) using a rheo‐optical device and in the case of T_l/s additionally a viscometer. This system enables for the first time a joint investigation of both transitions with a given mixture. Shear favors the homogeneous liquid state and the formation of crystals. T_cp (liquid/liquid demixing, UCST) shifts to lower and T_l/s (liquid/solid, segregation of PEO) to higher temperatures by several degrees as the shear rate, , is increased up to 500 s^?1. The normalized shift in T_cp fits well into previous results for high molecular weight blends, oligomer mixtures, polymer solutions in single solvents and low molecular weight mixtures. A phase separated near critical blend was examined 1 K below its T_cp by means of a shear cell (Linkam) in the quiescent state and under shear with respect to its morphology. Upon an increase in one observes a transition from the co‐continuous structures existing in the quiescent state via deformed and oriented particles to string like morphologies. Finally, at sufficiently high shear rates the mixture becomes homogeneous and structures can no longer be seen under the microscope. The morphologies developing after the secession of shear are pointing to pronounced influences of the flow history of the system on the final structure of two phase blends.

Equilibrium phase diagram of the system THN/COP/PEO at the indicated temperatures as obtained from turbidimetric titration. The curve for 42 °C indicates the compositions under which the mixtures segregate the first solid PEO particles upon cooling. The curves for the higher temperatures denote the demixing of the homogeneous system into two liquid phases.     

Molecular dynamics in polystyrene from electron spin resonance (ESR) measurements: comparison between spinprobes and -labels attached to the chain ends

The commercially available ¹⁵N-Tempone

1 N-Tempone: 4-oxo-2,2,6,6-tetramethylpiperidine-¹⁵N-oxyl; Tempol: 4-hydroxy-2,2,6,6-tetramethylpiperidine -¹⁵N-oxyl.

nitroxide radical has been used for the endfunctionalization of anionically polymerized polystyrene. The temperature dependence of molecular motions of the nitroxide radicals in this chain end labeled polystyrene (PS) and a PS/Tempol mixture has been studied using cw-ESR. Furthermore, these two samples were compared with a mixture of PS with a biradical which has a large molecular volume and is used in its unoxidized form as a polymer additive in commercial products. The temperature dependent spectra were evaluated to give T_50G. This allows the volume for reorientation of the radicals and that of a polymer unit to be compared. The temperature dependent spectra were simulated in order to yield the rotational correlation time τ_R. In contrast to the Tempol probe radical which is highly mobile even at temperatures well below the glass transition temperature (T_g) the spin-label strongly couples to the α-process of polystyrene. The biradical exhibits an intermediate mobility and seems to be weakly coupled to the glass transition dynamics. Line shape analysis shows that the motional behavior of the PS/Tempol mixture can adequately be described by the model of isotropic rotational diffusion, whereas for the chain end label significant deviations from this model are observed indicating anisotropic motion due to restrictions imposed by the polymer chain.     

Evaluation of unperturbed polymer dimensions from intrinsic viscosity in non-ideal solvents

For solutions of polystyrene (PS) samples of different relative molecular mass (molecular weight) M and intrinsic viscosities [n] have been measured at 298,15 K in pure toluene (T) and toluene/methanol (MeOH) mixtures. Upon mixing toluene (good solvent (1)) and methanol (nonsolvent (2)), a systematic decrease in the solvation power was obtained. A critical examination of the Stockmayer-Fixman method for obtaining unperturbed dimensions from intrinsic viscosity measurements has been made. It was found that the unperturbed dimensions were not constant and different from those measured in a theta solvent (T/MeOH mixture having volume fraction of methanol (?_MeOH) = 0,23). The derived values of unperturbed dimensions were found to increase with increasing Kuhn-Mark-Houwink-Sakurada exponent a. A modified form of the Stockmayer-Fixman equation is presented. It is suggested that the volume effect be taken into account in a complementary fashion to obtain accurate estimates of unperturbed dimensions from data in active solvents where the mean-square end-to-end distance 〈r²〉 increases at these conditions more rapidly than M. Different viscosity measurements of polystyrene (PS) and poly(N-vinyl-2-pyrrolidone) solutions containing non-ideal solvents were taken from the literature and found that the newly proposed, though purely empirical equation is valid.     

In vivo T2 relaxation time measurement with echo‐time averaging

The accuracy of metabolite concentrations measured using in vivo proton (¹H) MRS is enhanced following correction for spin–spin (T₂) relaxation effects. In addition, metabolite proton T₂ relaxation times provide unique information regarding cellular environment and molecular mobility. Echo‐time (TE) averaging ¹H MRS involves the collection and averaging of multiple TE steps, which greatly simplifies resulting spectra due to the attenuation of spin‐coupled and macromolecule resonances. Given the simplified spectral appearance and inherent metabolite T₂ relaxation information, the aim of the present proof‐of‐concept study was to develop a novel data processing scheme to estimate metabolite T₂ relaxation times from TE‐averaged ¹H MRS data. Spectral simulations are used to validate the proposed TE‐averaging methods for estimating methyl proton T₂ relaxation times for N‐acetyl aspartate, total creatine, and choline‐containing compounds. The utility of the technique and its reproducibility are demonstrated using data obtained in vivo from the posterior‐occipital cortex of 10 healthy control subjects. Compared with standard methods, distinct advantages of this approach include built‐in macromolecule resonance attenuation, in vivo T₂ estimates closer to reported values when maximum TE ≈ T₂, and the potential for T₂ calculation of metabolite resonances otherwise inseparable in standard ¹H MRS spectra recorded in vivo. Copyright © 2014 John Wiley & Sons, Ltd.     

Polybutadiene-poly(methyl methacrylate) core-shell latexes studied by high-resolution solid-state 13C NMR and DSC: Influence of the surface coverage of the polybutadiene seed latex and the latex composition on the interphase formation

High-resolution solid-state ¹³C NMR and differential scanning calorimetry (DSC) were used to examine the effect of the surface coverage of the polybutadiene seed latex by the surfactant and the latex composition on the interphase of PBut-PMMA core-shell latexes. On the basis of the determination of the relaxation time (T_1ρ(H)), glass transition temperature (T_g) and transition zone (ΔT_g), information on the interphase was obtained, such as the fraction of the PMMA in the interphase and the interphase thickness. An optimum surface coverage of the PBut seed latex particles was found to lead to the largest amount of interphase.     

Potato leafroll virus contains a double-stranded DNA

The nucleic acid of potato leafroll virus (PLRV) has been isolated from highly purified virus preparations by two methods: (1) From a treatment with 0.5 N perchloric acid at 70° and quantitative estimation of the products, the DNA:protein ratio has been found to be nearly 40:60 (w/w). (2) The nucleic acid extracted under more protective conditions, namely, with a mixture of phenol and sodium dodecyl sulfate, is resistant to RNase, sensitive to DNase, possesses a sharp melting profile with a T_m of 87.4° in 1 × SSC, a buoyant density of 1.698 in cesium chloride solution, and a molecular weight of 0.56 × 10⁶. The buoyant density and T_m values are slightly higher than those of DNA preparations from the uninfected host plant, Physalis floridana Rydb. The results show that the nucleic acid of PLRV is a double-stranded DNA.     

Three‐dimensional ultrashort echo time cones T1ρ (3D UTE‐cones‐T1ρ) imaging

We report a novel three‐dimensional (3D) ultrashort echo time (UTE) sequence employing Cones trajectory and T_1ρ preparation (UTE‐Cones‐T_1ρ) for quantitative T_1ρ assessment of short T₂ tissues in the musculoskeletal system. A basic 3D UTE‐Cones sequence was combined with a spin‐locking preparation pulse for T_1ρ contrast. A relatively short TR was used to decrease the scan time, which required T₁ measurement and compensation using 3D UTE‐Cones data acquisitions with variable TRs. Another strategy to reduce the total scan time was to acquire multiple Cones spokes (N_sp) after each T_1ρ preparation and fat saturation. Four spin‐locking times (TSL = 0–20 ms) were acquired over 12 min, plus another 7 min for T₁ measurement. The 3D UTE‐Cones‐T_1ρ sequence was compared with a two‐dimensional (2D) spiral‐T_1ρ sequence for the imaging of a spherical CuSO₄ phantom and ex vivo meniscus and tendon specimens, as well as the knee and ankle joints of healthy volunteers, using a clinical 3‐T scanner. The CuSO₄ phantom showed a T_1ρ value of 76.5 ± 1.6 ms with the 2D spiral‐T_1ρ sequence, as well as 85.7 ± 3.6 and 89.2 ± 1.4 ms for the 3D UTE‐Cones‐T_1ρ sequences with N_sp of 1 and 5, respectively. The 3D UTE‐Cones‐T_1ρ sequence provided shorter T_1ρ values for the bovine meniscus sample relative to the 2D spiral‐T_1ρ sequence (10–12 ms versus 16 ms, respectively). The cadaveric human Achilles tendon sample could only be imaged with the 3D UTE‐Cones‐T_1ρ sequence (T_1ρ = 4.0 ± 0.9 ms), with the 2D spiral‐T_1ρ sequence demonstrating near‐zero signal intensity. Human studies yielded T_1ρ values of 36.1 ± 2.9, 18.3 ± 3.9 and 3.1 ± 0.4 ms for articular cartilage, meniscus and the Achilles tendon, respectively. The 3D UTE‐Cones‐T_1ρ sequence allows volumetric T_1ρ measurement of short T₂ tissues in vivo.     

The solid state 13C NMR studies of intermolecular hydrogen bonding formation in a blend of phenolic resin and poly(hydroxyl ether) of bisphenol A

The formation of intermolecular hydrogen bonds in blends of novolac type phenolic and poly(hydroxyl ether) of bisphenol A was investigated by studying its T_g behavior, excess volume, and solid state ¹³C NMR spectra. The T_g and parameters of solid state ¹³C NMR, such as the T_CH and spin‐lattice relaxation time in the rotating frame T^H_1ρ, indicate that the London dispersion force (entropically favored) significantly affects the intermolecular hydrogen bonding of the blend. The phenoxy chain forces opening of the intra‐association of phenolic and thus creates more free OHs. This strong entropic effect reduces the total hydrogen bonding of the system, especially when one of the polymer is the minor component. This also results in the reduction of T_g and free volume expansion, reflecting in the increase of cross‐polarization (C—H) time and molecular mobility within the phenolic/phenoxy blend.     

Heterofunctionalized Multiarm Star Polymers via Sequential Thiol‐para‐Fluoro and Thiol‐Ene Double “Click” Reactions

The successful postfunctionalization of multiarm star polystyrene (PS) with pentafluorophenyl and allyl moieties at the periphery is demonstrated employing modular thiol‐para‐fluoro and photoinduced radical thiol‐ene double “click” reactions, respectively. α‐Fluoro and α‐allyl functionalized PS (α‐fluoro‐PS and α‐allyl‐PS) are in situ prepared by atom transfer radical polymerization of styrene and their mixture is used as macroinitiator in a crosslinking reaction with divinyl benzene (DVB) yielding (fluoro‐PS)_m–polyDVB–(allyl‐PS)_m multiarm star polymer. It is found that the multiarm star polymer includes nearly identical number of arms possessing pentafluorophenyl and allyl moieties at the periphery. The obtained multiarm star polymer is then reacted with 1‐propanethiol through thiol‐para‐fluoro “click” reaction to give (propyl‐PS)_m–polyDVB–(allyl‐PS)_m multiarm star polymer, which is subsequently reacted with N‐acetyl‐l ‐cysteine methyl ester via radical thiol‐ene “click” reaction in order to give well‐defined heterofunctionalized (propyl‐PS)_m–polyDVB–(cysteine‐PS)_m multiarm star polymer, with higher molecular weight and narrow molecular weight distribution. Multiarm star polymers are characterized by using viscotek triple detection gel permeation chromatography, ¹H, and ¹⁹F NMR.

     

Thermodynamics of Phase Behavior in PEO/P(EO‐b‐DMS) Homopolymer and Block Co‐Oligomer Mixtures under Pressure

The cloud‐point temperatures (T_cl's) of poly(ethylene oxide) (PEO) and poly(ethylene oxide)‐block‐polydimethylsiloxane (P(EO‐b‐DMS)) homopolymer and block‐oligomer mixtures were determined by turbidity measurements over a range of temperatures (105 to 130 °C), pressures (1 to 800 bar), and compositions (10–40 wt.‐% PEO). The system phase separates upon cooling and T_cl was found to decrease with an increase in pressure for a constant composition. In the absence of special effects, this finding indicates negative excess volumes. Special attention was paid to the demixing temperatures as a function of the pressure for the different polymer mixtures and the plots in the T‐? plane (where ? signifies volume fractions). The cloud‐point curves of the polymer mixture under pressures were observed for different compositions. The Sanchez‐Lacombe (SL) lattice fluid theory was used to calculate the spinodals, the binodals, the Flory‐Huggins (FH) interaction parameter, the enthalpy of mixing, and the volume changes of mixing. The calculated results show that modified P(EO‐b‐DMS) scaling parameters with the new combining rules can describe the thermodynamics of the PEO/P(EO‐b‐DMS) system well with the SL theory.

Cloud point curves for various PEO/P(EO‐b‐DMS) polymer mixtures at various pressures on the T‐?_PEO plane.     

Spinodal decomposition induced by cross-linking reaction in a binary polymer mixture

Phase separation of a binary polymer mixture of poly{styrene-co-[p-2,2,2-trifluoro-1-hydroxy-1-trifluoromethylethyl-α-methylstyrene]} (PS(OH)) and poly[(methyl methacrylate)-co-(glycidyl methacrylate)] (PMMA(G)) upon cross-linking reaction was studied using time-resolved light scattering (TRLS) and optical microscopy. The blends of PS(OH)/PMMA(G), in which PMMA(G) containing 1.4 mol-% epoxy groups can be selectively cross-linked with the multifunctional agent 4,4′-methylenebis(o-chloroaniline) (MOCA) and PS(OH) contains 1.8 mol-% of the strongly proton-donating group  C(CF₃)₂OH, exhibit a lower critical solution temperature (LCST). The cross-linking reaction was carried out for two compositions of PS(OH)/PMMA(G)/MOCA, 50/50/0.7 and 40/60/0.8 (w/w/w), at various temperatures located in the one-phase region between the coexistence curve and the glass transition temperature of the blends. TRLS investigation shows that the phase separation takes place via spinodal decomposition (SD) induced by the increase in the molecular weight of PMMA(G) during the cross-linking reaction. A modulated phase structure with the characteristic features of periodicity and dual connectivity of the phases was developed in this case. The dynamics of SD were investigated in terms of changes of the peak scattering vector q_m(t) as a function of time. They are dependent on the reaction temperature and composition. A scaling relation q_m(t) ∝︁ t^−af(x) describing the behavior of the evolution of phase separation upon reaction was supported by the experiments.     

Eight‐channel transceiver RF coil array tailored for 1H/19F MR of the human knee and fluorinated drugs at 7.0 T

The purpose of this study was to evaluate the feasibility of an eight‐channel dual‐tuned transceiver surface RF coil array for combined ¹H/¹⁹F MR of the human knee at 7.0 T following application of ¹⁹F‐containing drugs. The ¹H/¹⁹F RF coil array includes a posterior module with two ¹H loop elements and two anterior modules, each consisting of one ¹H and two ¹⁹F elements. The decoupling of neighbor elements is achieved by a shared capacitor. Electromagnetic field simulations were performed to afford uniform transmission fields and to be in accordance with RF safety guidelines. Localized ¹⁹F MRS was conducted with 47 and 101 mmol/L of flufenamic acid (FA) – a ¹⁹F‐containing non‐steroidal anti‐inflammatory drug – to determine T₁ and T₂ and to study the ¹⁹F signal‐to‐dose relationship. The suitability of the proposed approach for ¹H/¹⁹F MR was examined in healthy subjects. Reflection coefficients of each channel were less than ?17 dB and coupling between channels was less than ?11 dB. Q_L/Q_U was less than 0.5 for all elements. MRS results demonstrated signal stability with 1% variation. T₁ and T₂ relaxation times changed with concentration of FA: T₁/T₂ = 673/31 ms at 101 mmol/L and T₁/T₂ = 616/26 ms at 47 mmol/L. A uniform signal and contrast across the patella could be observed in proton imaging. The sensitivity of the RF coil enabled localization of FA ointment administrated to the knee with an in‐plane spatial resolution of (1.5 × 1.5) mm² achieved in a total scan time of approximately three minutes, which is well suited for translational human studies. This study shows the feasibility of combined ¹H/¹⁹F MRI of the knee at 7.0 T and proposes T₁ and T₂ mapping methods for quantifying fluorinated drugs in vivo. Further technological developments are necessary to promote real‐time bioavailability studies and quantification of ¹⁹F‐containing medicinal compounds in vivo. Copyright © 2015 John Wiley & Sons, Ltd.     

Cationic copolymerization of norbornadiene with styrene by AlEtCl2/tert-butyl chloride catalyst system, 1. Effect of norbornadiene/styrene feed ratio

The cationic copolymerization of norbornadiene (NBD) and styrene (St) was carried out with the AlEtCl₂/tert-butyl chloride catalyst system in CH₂Cl₂ at ?50°C, and the effect of NBD/St feed ratio on the solubility, the glass trtansition temperature (T_g) and the molecular weight of the copolymers was investigated. A soluble copolymer was prepared at 40 mol-% (or above) of St in the feed, although the NBD homopolymer comprised an insoluble fraction which might have been formed by a crosslinking reaction between the double bonds in the NBD units of the polymer. The copolymer has a statistically random sequence distribution of the two monomeric units not only in the polymer chain but also over the whole molecular weight range (from 10³ to 10⁶). The T_g of the amorphous copolymer is controlled by the NBD/St composition in the range from 100°C through 290°C. A soluble copolymer with highest T_g (ca. 170°C) could be prepared at a NBD/St feed ratio of 60/40 mol-%.     

Capturing fast relaxing spins with SWIFT adiabatic rotating frame spin–lattice relaxation (T1ρ) mapping

Rotating frame spin–lattice relaxation, with the characteristic time constant T_1ρ, provides a means to access motion‐restricted (slow) spin dynamics in MRI. As a result of their restricted motion, these spins are sometimes characterized by a short transverse relaxation time constant T₂ and thus can be difficult to detect directly with conventional image acquisition techniques. Here, we introduce an approach for three‐dimensional adiabatic T_1ρ mapping based on a magnetization‐prepared sweep imaging with Fourier transformation (MP‐SWIFT) sequence, which captures signal from almost all water spin populations, including the extremely fast relaxing pool. A semi‐analytical procedure for T_1ρ mapping is described. Experiments on phantoms and musculoskeletal tissue specimens (tendon, articular and epiphyseal cartilages) were performed at 9.4 T for both the MP‐SWIFT and fast spin echo (FSE) read outs. In the phantom with liquids having fast molecular tumbling and a single‐valued T_1ρ time constant, the measured T_1ρ values obtained with MP‐SWIFT and FSE were similar. Conversely, in normal musculoskeletal tissues, T_1ρ values measured with MP‐SWIFT were much shorter than the values obtained with FSE. Studies of biological tissue specimens demonstrated that T_1ρ‐weighted SWIFT provides higher contrast between normal and diseased tissues relative to conventional acquisitions. Adiabatic T_1ρ mapping with SWIFT readout captures contributions from the otherwise undetected fast relaxing spins, allowing more informative T_1ρ measurements of normal and diseased states. Copyright © 2016 John Wiley & Sons, Ltd.     

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.