Polymer diffusion and mobility in mixtures of polystyrene and polymethylstyrenes

Tracer diffusion coefficients D* of both components were measured in mixtures of polystyrene with poly(o-methylstyrene), poly(p-methylstyrene), and a commercially available random copolymer of p- and m-methylstyrene, respectively. D* values were determined by applying the holographic grating technique where between 5 and 10% of the respective polymer component was labelled at the end group with a photoreactive dye. For molecular weights between 15 000 and 37 000 and temperatures between 175 and 200°C, the D* values differed relatively slightly when compared at equal molecular weight and equal temperature distance T–T_g from the glass transition temperature T_g. The differences were compared with those of monomeric friction coefficients obtained from dynamic mechanical experiments.     

Miscibility of poly(vinyl chloride) with ethylene/N,N-dimethylacrylamide copolymers.

The incorporation of N,N-dimethylacrylamide (DMA) as a comonomer in polyethylene yields a material possessing dramatically improved mechanical compatibility with poly(vinyl chloride) (PVC). At increased levels of DMA (25–30 wt.-%) miscibility with PVC is achieved. This behavior is believed to be due to the specific interaction of the tertiary hydrogen of poly(vinyl chloride) (weak “acid” or proton donor) with the disubstituted amide in the ethylene copolymer (weak “base” or proton acceptor). Dynamic mechanical characterization of the ethylene/DMA copolymer (EDMA)/PVC blends reveals separate glass transitions temperatures at DMA levels below 20 wt.-%; they merge into a single T_g when the DMA content reaches a value above 25 wt.-% in the ethylene copolymer. The secondary loss transition for PVC (?40°C) is lowered in temperature and greatly suppressed in magnitude. This is further evidence of molecular miscibility. Mechanical property data obtained on the EDMA/PVC blends are consistent with the foregoing considerations.     

Mechanismus der photopolymerisation des styrols, 1. Zur desaktivierung elektronisch angeregten styrols durch chemische konzentrations-löschprozesse: Photooligomere und photopolymere

Electronically excited styrene—in bulk or in concentrated solution—via intermolecular fluorescence self quenching processes undergoes a series of parallel and consecutive chemical reactions, leading to photooligomers and photopolymers. The oligomeric photoproducts, as shown by gas chromatography analysis, consist of dimers (M₂) and trimers (M₃) of styrene, whereby the quantity of M₂ exceeds M₃ by a factor of 20. The dimer fraction is built up of (a) 4 non olefinic cyclic C₁₆-hydrocarbons: cis-1,2-diphenylcyclobutane (c-CB, 45–50 wt.-%), trans-1,2-diphenylcyclobutane (tr-CB, 8–10 wt.-%), 1-phenyl-1,2,3,4-tetrahydronaphthalene (1-PhT, 7–9 wt.-%), and 2-phenyl-1,2,3,4-tetrahydronaphthalene (2-PhT, 3–5 wt.-%), (b) an open chain unsaturated compound–1-vinyl-2-(2-phenylethyl)benzene (VPEB, 5–7 wt.-%), and (c) 5 highly unsaturated mono-, bi-, and/or tricyclic C₁₆-valence isomers (19–32 wt.-%) which are considered to be the result of the participation of the aromatic benzene system in 1,2-, 1,3- or 1,4-photocycloaddition reactions, respectively. Among the numerous phototrimers, two saturated C₂₄-hydrocarbons were identified: 1-phenyl-4-(1-phenylethyl)-1,2,3,4-tetrahydronaphthalene (T₁) and 2-phenyl-4-(1-phenylethyl)-1,2,3,4-tetrahydronaphthalene (T₂). Under conditions where simultaneous thermal processes could be excluded (?20?T/°C?25), the presence of 1-PhT, 2-PhT, T₁ and T₂ gives strong evidence for the involvement of two 4π + 2π-photointermediates, viz. 1-phenyl-1,2,3,8a-tetrahydronaphthalene ( 1 ) and 2-phenyl-1,2,3,8a-tetrahydronaphthalene ( 1 ′), which undergo two consecutive reactions: (a) a unimolecular, photo-induced 1,3-sigmatropic rearrangement (1-PhT, 2-PhT) and (b) a bimolecular, photo-induced ene-reaction with styrene as enophilic component (T₁, T₂). Because of the non-concerted, stepwise nature of this photo-ene-process, the trimers have to be interpreted as the products of a cage reaction between two radical pairs |R₁…R₂| and |R₁…R₂′|. Their presence therefore gives strong evidence that the non-concerted ene-reaction is the most probable pathway for the production of the free radicals, which are responsible for the initiation of photopolymerization.     

Glass transition temperatures in blends of poly(N-vinyl-2-pyrrolidone) with a copolymer of bisphenol A and epichlorohydrin or with poly(vinyl butyral)

Blends of poly(vinyl butyral) (PVB) and of a copolymer of bisphenol A and epichlorohydrin (Phenoxy) with poly(N-vinyl-2-pyrrolidone) (PVP) were prepared by solution casting. The glass transition temperatures T_g for different compositions of the blends were measured by differential scanning calorimetry (DSC). The T_g behaviour of PVB/PVP blends suggests the existence of a single phase for blends containing less than 50 wt.-% PVP, and of two phases in blends containing more than 50 wt.-% PVP. Phenoxy/PVP blends showed to be miscible over the entire composition range. It was found that the Gordon-Taylor equation predicts adequately the T_g-composition dependence with a K parameter equal to 0,5 and 1,25 for PVB/PVP and Phenoxy/PVP blends, respectively.     

Carbon-13 relaxation study of crosslinked gels of poly(methyl methacrylate)

The motion of covalently crosslinked gels of poly(methyl methacrylate) (PMMA) swollen by benzene-d₆ was studied by means of ¹³C NMR spectroscopy. The dependence of the segmental motion of PMMA on stereosequence was not affected by the presence of the covalently crosslinked part in the chain; isotactic sequence was more mobile than syndiotactic sequence. The spin-lattice relaxation times, T₁'s, for all the ¹³C nuclei of PMMA swollen with benzene (benzene content, 90 wt.-%, 0,01 mole-% of crosslinking) were considerably longer than those observed for the linear PMMA (benzene content, 75 wt.-%). Moreover, all the T₁ values decreased with increasing of the degree of crosslinking, regardless of the crosslinking agent and reached to the values of T₁ observed for uncrosslinked PMMA or to slightly larger values when the content of crosslinking agent was 1 mole-%. However, the nuclear Overhauser enhancement data were essentially independent of the degree of crosslinking within experimental error.     

Preclinical hyperpolarized 129Xe MRI: ventilation and T2* mapping in mouse lungs at 7 T using multi‐echo flyback UTE

Fast apparent transverse relaxation (short T₂*) is a common obstacle when attempting to perform quantitative ¹H MRI of the lungs. While T₂* times are longer for pulmonary hyperpolarized (HP) gas functional imaging (in particular for gaseous ¹²⁹Xe), T₂* can still lead to quantitative inaccuracies for sequences requiring longer echo times (such as diffusion weighted images) or longer readout duration (such as spiral sequences). This is especially true in preclinical studies, where high magnetic fields lead to shorter relaxation times than are typically seen in human studies. However, the T₂* of HP ¹²⁹Xe in the most common animal model of human disease (mice) has not been reported. Herein, we present a multi‐echo radial flyback imaging sequence and use it to measure HP ¹²⁹Xe T₂* at 7 T under a variety of respiratory conditions. This sequence mitigates the impact of T₁ relaxation outside the animal by using multiple gradient‐refocused echoes to acquire images at a number of effective echo times for each RF excitation. After validating the sequence using a phantom containing water doped with superparamagnetic iron oxide nanoparticles, we measured the ¹²⁹Xe T₂* in vivo for 10 healthy C57Bl/6 J mice and found T₂* ~ 5 ms in the lung airspaces. Interestingly, T₂* was relatively constant over all experimental conditions, and varied significantly with sex, but not age, mass, or the O₂ content of the inhaled gas mixture. These results are discussed in the context of T₂* relaxation within porous media.     

Solution properties of poly(octadecyl methacrylate) in butyl acetate, 2. Semidilute solution

Semidilute solutions of a fraction of poly(octadecyl methacrylate) (PODMA) obtained by radical-initiated polymerization were investigated in the theta-solvent butyl acetate (BuAc) with static and dynamic light scattering (SLS, DLS, resp.) at four different temperatures between 13°C (near theta-temperature Θ) and 70°C. The molar mass of the investigated sample (PODMA 4) was 3,2 · 10⁶ g · mol^?1. A concentration region from dilute to 8 c^* was covered, where c^* = 1/[η] was taken as the coil overlap concentration, [η] denoting intrinsic viscosity. Above c = 3c^* the DLS correlation function exhibited bimodal behaviour at all temperatures. At these concentrations one finds two “apparent” molar masses, radii of gyration and diffusion coefficients for each concentration. The smaller apparent molar masses, smaller radii of gyration and larger diffusion coefficients correspond to characteristics of the transient network. The larger apparent molar masses, larger radii of gyration and smaller diffusion coefficients may be attributed to the formation of inhomogeneities in the semidilute solution.     

The interaction between apparent diffusion coefficients and transverse relaxation rates of human brain metabolites and water studied by diffusion‐weighted spectroscopy at 7 T

The dependence of apparent diffusion coefficients (ADCs) of molecules in biological tissues on an acquisition‐specific timescale is a powerful mechanism for studying tissue microstructure. Unlike water, metabolites are confined mainly to intracellular compartments, thus providing higher specificity to tissue microstructure. Compartment‐specific structural and chemical properties may also affect molecule transverse relaxation times (T₂). Here, we investigated the correlation between diffusion and relaxation for N‐acetylaspartate, creatine and choline compounds in human brain white matter in vivo at 7 T, and compared them with those of water under the same experimental conditions. Data were acquired in a volume of interest in parietal white matter at two different diffusion times, Δ = 44 and 246 ms, using a matrix of three echo times (T_E) and five diffusion weighting values (up to 4575 s/mm²). Significant differences in the dependence of the ADCs on T_E were found between water and metabolites, as well as among the different metabolites. A significant decrease in water ADC as a function of T_E was observed only at the longest diffusion time (p < 0.001), supporting the hypothesis that at least part of the restricted water pool can be associated with longer T₂, as suggested by previous studies in vitro. Metabolite data showed an increase of creatine (p < 0.05) and N‐acetylaspartate (p < 0.05) ADCs with T_E at Δ = 44 ms, and a decrease of creatine (p < 0.05) and N‐acetylaspartate (p = 0.1) ADCs with T_E at Δ = 246 ms. No dependence of choline ADC on T_E was observed. The metabolite results suggest that diffusion and relaxation properties are dictated not only by metabolite distribution in different cell types, but also by other mechanisms, such as interactions with membranes, exchange between “free” and “bound” states or interactions with microsusceptibility gradients. Copyright © 2014 John Wiley & Sons, Ltd.     

Inversion recovery ultrashort echo time imaging of ultrashort T2 tissue components in ovine brain at 3 T: a sequential D2O exchange study

Inversion recovery ultrashort echo time (IR‐UTE) imaging holds the potential to directly characterize MR signals from ultrashort T₂ tissue components (STCs), such as collagen in cartilage and myelin in brain. The application of IR‐UTE for myelin imaging has been challenging because of the high water content in brain and the possibility that the ultrashort T₂* signals are contaminated by water protons, including those associated with myelin sheaths. This study investigated such a possibility in an ovine brain D₂O exchange model and explored the potential of IR‐UTE imaging for the quantification of ultrashort T₂* signals in both white and gray matter at 3 T. Six specimens were examined before and after sequential immersion in 99.9% D₂O. Long T₂ MR signals were measured using a clinical proton density‐weighted fast spin echo (PD‐FSE) sequence. IR‐UTE images were first acquired with different inversion times to determine the optimal inversion time to null the long T₂ signals (TI_null). Then, at this TI_null, images with echo times (TEs) of 0.01–4 ms were acquired to measure the T₂* values of STCs. The PD‐FSE signal dropped to near zero after 24 h of immersion in D₂O. A wide range of TI_null values were used at different time points (240–330 ms for white matter and 320–350 ms for gray matter at TR = 1000 ms) because the T₁ values of the long T₂ tissue components changed significantly. The T₂* values of STCs were 200–300 μs in both white and gray matter (comparable with the values obtained from myelin powder and its mixture with D₂O or H₂O), and showed minimal changes after sequential immersion. The ultrashort T₂* signals seen on IR‐UTE images are unlikely to be from water protons as they are exchangeable with deuterons in D₂O. The source is more likely to be myelin itself in white matter, and might also be associated with other membranous structures in gray matter.     

Continuous fractionation and solution properties of PVC, 6. Pressure dependence of the viscosity — influence of molecular weight and composition

Viscosities were measured as a function of pressure and temperature with solutions of PVC 75 000 in cyclohexanone (CHO) and polymer contents ranging from 0,6 to 12 wt.-%, by means of a Searle-type (≥3 wt.-%) and a rolling-ball viscometer (<3 wt.-%). Furthermore, the influence of molecular weight was determined with solutions of 8 wt.-% of PVC 20 000, PVC 37 000 and PVC 100 000. (The numbers in the codes of the PVC specimens are their approximate molecular weights.) For all concentrations and molecular weights, the viscosity increases in a more or less exponential manner with increasing pressure. The ratio f₁₀₀₀ of the viscosity of the solution at 1 000 and 1 bar can be varied by the change of the polymer content from 2,5 (the value of the pure solvent, index s) to 3,5 (12 wt.-% PVC 75 000) at t = 25°C and from 2,23 to 2,94 at t = 80°C. An increase of the molecular weight of the polymer raises f₁₀₀₀ in a similar manner as the polymer concentration. Using the reduced variables V^≠/V^≠ (ratio of the volumes of activation of the solution and the pure solvent) and c? (product of the polymer concentration and the intrinsic viscosity), all results obtained by variation of T, c and M_w can be represented by a master curve. This means that it is possible to calculate the pressure dependence of a given polymer solution of arbitrary polymer concentration from a mere measurement of the intrinsic viscosity at normal pressure. Criteria are presented which allow a forecast concerning the occurrence of minima in the concentration dependence of the energy of activation of the viscous flow E^≠ and V^≠.     

Modeling of T2* decay in vertebral bone marrow fat quantification

Bone marrow fat fraction mapping using chemical shift encoding‐based water–fat separation is becoming a useful tool in investigating the association between bone marrow adiposity and bone health and in assessing cancer treatment‐induced bone marrow damage. Vertebral bone marrow is characterized by short T₂* relaxation times, which are in general different for the water and fat components and can confound fat quantification. The purpose of the present study is to compare different approaches to T₂* correction in chemical shift encoding‐based water–fat imaging of vertebral bone marrow using single‐voxel MRS as reference. Eight‐echo gradient‐echo imaging and single‐voxel MRS measurements were made on the spine (L3–L5) of 25 healthy volunteers. Different approaches were evaluated for correction of T₂* effects: (a) single‐T₂* correction, (b) dual‐T₂* correction, (c) T₂' correction using the a priori‐known T₂ from the MRS at each vertebral body and (d) T₂' correction using the a priori‐known T₂ equal to previously measured average values. Dual‐T₂* correction resulted in noisier imaging fat fraction maps than single‐T₂* correction or T₂' correction using a priori‐known T₂. Linear regression analysis between imaging and MRS fat fraction showed a slope significantly different from 1 when using single‐T₂* correction (R² = 0.96) or dual‐T₂* correction (R² = 0.87). T₂' correction using the a priori‐known T₂ resulted in a slope not significantly different from 1, an intercept significantly different from 0 (between 2.4% and 3%) and R² = 0.96. Therefore, a T₂' correction using a priori‐known T₂ can remove the fat fraction bias induced by the difference in T₂* between water and fat components without degrading noise performance in fat fraction mapping of vertebral bone marrow. Copyright © 2015 John Wiley & Sons, Ltd.     

A Method to Calculate the Volume of Palatine Tonsils

The purpose of this study was to obtain a mathematical formula to calculate the tonsillar volume out of its measurements assessed on surgical specimens. Thirty consecutive surgical specimens of pediatric tonsils were studied. The maximum lengths (“a”), widths (“b”), and depths (“c”) of the dissected specimens were measured in millimeters, and the volume of each tonsil was measured in milliliters. One‐sample Kolmogorov–Smirnov test was used to check the normality of the sample. To calculate the reproducibility of the quantitative variables, intraclass correlation coefficients were used. Two formulas with high reproducibility (coefficient R between 0.75 and 1) were obtained: 1) [a*b*c* 0.5236] with R = 0.8688; and 2) [a*b*b* 0.3428] with R = 0.9073. It is possible to calculate the volume of the palatine tonsils in surgical specimens precisely enough based on their three measures, or their two main measures (length and width). Anat Rec, 2010. © 2010 Wiley‐Liss, Inc.     

Copolymer-monomer miscibility during copolymerization

Significant drift in the compositions of copolymer and of unreacted monomer mixture is predicted to occur during the bulk copolymerization of N-vinyl-2-pyrrolidone (VP) with butyl acrylate (BA), when the inital feed mixture contains 75 wt.-% VP. The drift in copolymer composition has been confirmed by 1 the optical appearance and glass transition (T_g) behaviour of the products of the γ-ray initiated copolymerization at various fractional conversions (C) and 2 the T_g behaviour of low-conversion samples of poly(VP-co-BA) blended in propertions so as to simulate the overall composition of material that would be present cumulatively at selected values of C during an actual copolymerization. The compositions of unreacted monomer mixtures co-existing with copolymer at selected conversions have been calculated and intrinsic viscosities [η] of blends dissolved in these VP/BA mixtures have been measured. Theta conditions for the blends have been established turbidimetrically in chloroform/heptane and the corresponding values of [η]_Θ measured. The chain expansion factors thereby derived from [η] and [η]_Θ show a decreasing affinity of copolymer for residual monomer during the course of copolymerization.     

Diffusion of TiO2 probe particles through a poly(ethylene oxide) melt

Quasi-elastic light scattering (QELS) spectroscopy was for the first time used to measure the mutual diffusion coefficient D_m of titanium dioxide (TiO₂) particles of 0,37 μm and 0,31 μm diameters in a poly(ethylene oxide) melt (weight-average mol. wt. 7 500) between 85 °C and 160 °C. D_m exhibits a strong dependence on the temperature. The effective shear imposed by diffusing particles on the polymer melt was estimated through a comparison of the viscosity obtained by a cone-and-plate viscometer with the microviscosity calculated from the diffusion coefficients and hydrodynamic radii of the particles through the Stokes-Einstein equation. The rate of shear found was ≥ 10⁴ · s^?1.     

Longitudinal assessment of tissue properties and cardiac diffusion metrics of the ex vivo porcine heart at 7 T: Impact of continuous tissue fixation using formalin

In this study we aimed to assess the effects of continuous formalin fixation on diffusion and relaxation metrics of the ex vivo porcine heart at 7 T. Magnetic resonance imaging was performed on eight piglet hearts using a 7 T whole body system. Hearts were measured fresh within 3 hours of cardiac arrest followed by immersion in 10% neutral buffered formalin. T₂^* and T₂ were assessed using a gradient multi‐echo and multi‐echo spin echo sequence, respectively. A spin echo and a custom stimulated echo sequence were employed to assess diffusion time‐dependent changes in metrics of cardiac diffusion tensor imaging. SNR was determined for b = 0 images. Scans were performed for 5 mm thick apical, midcavity and basal slices (in‐plane resolution: 1 mm) and repeated 7, 15, 50, 100 and 200 days postfixation. Eigenvalues of the apparent diffusion coefficient (ADC) and fractional anisotropy (FA) decreased significantly (P < 0.05) following fixation. Relative to fresh hearts, FA values 7 and 200 days postfixation were 90% and 80%, while respective relative ADC values at those fixation stages were 78% and 92%. Statistical helix and sheetlet angle distributions as well as respective mean and median values showed no systematic influence of continuous formalin fixation. Similar to changes in the ADC, values for T₂, T₂^* and SNR dropped initially postfixation. Respective relative values compared with fresh hearts at day 7 were 64%, 79% and 68%, whereas continuous fixation restored T₂, T₂^* and SNR leading to relative values of 74%, 100%, and 81% at day 200, respectively. Relaxation parameters and diffusion metrics are significantly altered by continuous formalin fixation. The preservation of microstructure metrics following prolonged fixation is a key finding that may enable future studies of ventricular remodeling in cardiac pathologies.     

Synthesis and nonlinear optical properties of end-group modified aromatic esters as chained chromophores

We synthesized aromatic ester derivatives with some electron accepting groups at molecular ends as new class of nonlinear optical (NLO) active chromophores (ArESn-X , n = 2, 3, X = CN, CF₃, NO₂, DCV). Some second-order NLO properties for poled polymer films consisting of poly(methyl methacrylate) (PMMA) doped with 10 wt.-% ArESn-X (ArESn-X/PMMA) were investigated. UV/vis spectra of these polymer films have cutoff wavelengths (λ_co) of about 300∼380 nm, which are much shorter than in the case of p-nitroaniline (pNA) (λ_co = ca. 450 nm) as a typical strong donor-acceptor (D-A) molecule. In addition, some of these polymer films exhibited larger second-order nonlinear coefficient (d₃₃) values than PMMA film doped with 10 wt.-% pNA (pNA/PMMA) (2.8 × 10⁻⁹ esu). Namely, ArES3-CN (d₃₃ = 3.1 × 10⁻⁹ esu, 10 wt.-% in PMMA), ArES3-NO₂ (3.0 × 10⁻⁹ esu, 10 wt.-% in PMMA) and ArES2-DCV (4.0 × 10⁻⁹ esu, 10 wt.-% in PMMA) showed not only excellent second-order NLO activity but also excellent transparency in the visible region (λ_co = 304 nm (ArES3-CN) , 340 nm (ArES3-NO₂) and 370 nm (ArES2-DCV) , respectively). Consequently, these compounds are believed to be promising chromophores for second-order nonlinear optics.     

Cationic polymerization of α-pinene with aluminium-based binary catalysts, 3. Effects of added base

In the presence of nucleophilic additives such as esters (ethyl benzoate, acetate, and chloroacetate), ethers (diethyl ether and 1,4-dioxane), and ammonium salts (nBu₄NCl), oligomers of α-pinene with relatively high molecular weights (M?_n ≥ 1000) were obtained with the AlCl₃/SbCl₃ binary catalyst in toluene at 0°C ([AlCl₃]₀ = 42,5 mmol · L^?1, Sb/Al = 0,50, [additive]₀ = 10,6 mmol · L^?1). The yield was 80–90 wt.-%, and the dimer content was as low as 6 wt.-%. Also in the polymerization at 25°C, the addition of ethyl benzoate increased the oligomer's average molecular weight (M?_n = 850) and decreased the dimer content (10 wt.-%), in contrast to the low M?_n (350) and the high dimer content (40 wt.-%) in the absence of the additive. The oligomers obtained in the presence of ethyl benzoate contained the repeating unit 1 which has an endo-olefin group, at higher ratio than in the absence of the additive. Phenomenologically, the role of the additives is to retard the polymerization so as to proceed at a moderate rate even at high temperature above 0°C and thereby to suppress the dimer formation.     

Synthesis and characterization of new siloxane-modified addition polyimides

A new series of polyimides was synthesized by addition polymerization of 4,4′-(bismaleimido)-diphenylmethane, 1,4-piperazine and an amino-terminated polydimethylsiloxane. The synthesis was carried out in m-cresol solution following a two-step procedure. Copolymers containing 15 and 20 wt.-% of the polydimethylsiloxane elastomer were prepared, together with the unmodified base copolymer. Infrared spectroscopy, ¹³C and ¹H NMR, thermal and thermogravimetric analyses were used to characterize the copolymers. The DSC curves of all the samples showed an exotherm in the temperature range 230–280°C, attributable to curing and addition reactions involving the chain-end groups. Different glass transition temperatures (T_g) were observed, depending on the elastomer content. Thermogravimetric analysis indicated that no significant changes occur in the thermal stability of rubber-modified copolymers.     

Lateral diffusion of manganese in the rat brain determined by T<Subscript>1</Subscript> relaxation time measured by <Superscript>1</Superscript>H MRI

In order to optimize manganese ion-enhanced MRI in thalamic and hypothalamic nuclei, we analyzed the diffusion of manganese in the brain followed by the intra-cerebroventricular application of manganese-bicine (Mn-bicine). T₁-weighted MRI intensities, with 9-pixel ROIs in the hypothalamus perpendicular to the third ventricle, were measured during continuous infusion of Mn-bicine solution in the lateral cerebroventricle. Using a relationship between the image intensity of T₁-weighted MRI and T₁ relaxation time, the image intensity was converted into the concentration of manganese. Assuming a simple diffusion process, the apparent diffusion coefficient (D _ap) of manganese (4.2 × 10⁻⁵ mm² s⁻¹) is much lower than that of water (6 × 10⁻⁴ mm² s⁻¹), and the D _ap tended to decrease when the distance from the third ventricle increased. These results suggest (1) the Mn²⁺ ion is trapped by neural cells during diffusion and (2) the manganese efflux is discharged from the brain via veins.