Cross Linkage Research Articles

An epoxy novolac emulsion system for ambient cure protective coatings

Water-borne two-pack coatings based on a novel low particle size epoxy novolac emulsion, crosslinked with polycycloaliphatic polyamine provide a good balance of several properties. Because the films cured possess a high crosslink density of cross linkage, expectations such as rapid through film drying time, high hardness development at an early stage during cure, very good film formation at 10°C and 80% R.H., and chemical resistance can be met. However, there are also adverse aspects to consider regarding the combination of a water-insoluble hydrophobic polyamine and a modified epoxy novolac emulsion. eg no visible end of pot life, relative short pot life and a brittleness of coatings associated with a tendency to peeling when exposed to salt spray and humid conditions. The study also revealed that the quality of a cured two-component epoxy binder emulsion system depends to a great extent on the quality of the emulsion, particularly on the size and distribution of the droplets. A low particle size epoxy emulsion improves the film formation, drying time, water resistance, gloss, adhesion and hardness. For this purpose epoxy emulsions with a narrow particle size distribution and relatively low particle size (mean value ca. 0.4 µm) can be developed using a proprietary mechanical emulsion process. The aqueous coating system described may be useful for applications where conventional epoxy novolacs are already used as low temperature heat cure coatings like drill pipe coatings, oil pipelines and fuel storage tanks and in fields where their chemical, water and solvent resistance can be utilised. Further ambient cure applications may be protective coatings for indoor use, eg food factories, schools, hospitals and office buildings, industrial maintenance coatings for concrete, mortar, bricks, plaster and wood.

Kinetics of expression and subset distribution of the TNF superfamily members CD40 ligand and Fas ligand on T lymphocytes in cattle

CD40 and Fas are members of the tumor necrosis factor receptor (TNFR) superfamily. CD40 and Fas play key roles in T cell–B cell interactions. Cross linkage of these molecules induces cell activation and cell death, respectively. The interaction of CD40 with its ligand (CD40L), which is expressed on activated T cells, plays a pivotal role in the generation of the T-dependent (TD) immune response, and FasL-bearing T cells, which have been shown to be predominantly of either the T H0 or T H1 type, have the potential to induce the apoptotic death of Fas expressing B cells. We investigated bovine CD40L mRNA expression in established T cell clones by RT-PCR and Southern blotting. T cells analyzed included CD4 + T H0 and T H1 cell subpopulations, CD8 +, and γ/ δ T cells stimulated with either specific antigen or Con A. All CD4 + clones but not all CD8 + or γ/ δ T cell receptor (TCR)-bearing clones expressed mRNA for CD40L. To determine the activation requirements for CD40L expression in cattle, we examined the kinetics and induction requirements for CD40L transcription in peripheral blood T cells using a phorbol ester and/or ionomycin, immobilized mouse anti-bovine CD3, or Con A. Our results demonstrate that CD40L mRNA appears relatively early after activation (1 h) and peaks at 2–4 h poststimulation. A rise in intracellular calcium concentration mediated by ionomycin treatment alone was sufficient to induce CD40L mRNA expression at relatively high levels. Ionomycin treatment in combination with other agonists (anti-CD3, PMA) did not enhance CD40L mRNA expression above levels obtained with ionomycin alone. The bovine Fas ligand gene was partially cloned and mRNA expression determined by RT-PCR in a panel of T cell clones. Our results demonstrate that T H0 and T H1 bovine T cell clones expressed Fas ligand transcripts although only one γ/ δ T cell clone did. This expression was upregulated within 3 h after mitogen stimulation and reduced by 24 h.

アクリル酸系ＳＡＰの親水性混合溶媒中に於ける膨潤，凝集挙動に関する研究

The writers have found the phenomenon that the low concentration of Microfibrillated Cellulose (MFC) has a high viscosity when evenly dispersed in a mixed solvent of water and water miscible organic solvent. In case that SAP (Super Absorbent Polymer) in a state of particles is dispersed in that dispersion solvent, it is possible to disperse SAP particles more stably in a high concentration condition due to the effect of the viscosity.Furthermore, it is possible to prevent the coagulation behavior caused by the mutual contact among SAP particles in the solvent due to the effect of dispersed MFC. Also it is possible to keep dispersed slurry having a long pot life.Consequently, in case of forming and removing the solvent from the above-mentioned slurry, it is possible to obtain the composite of SAP and MFC, whose SAP particles are combined tightly, due to the effect of strong hydrogen bonding. As the first report on the research regarding the composite of SAP and MFC, we have studied on the swelling & coagulation behaviors of acrylic acid base SAP in water, which does not contain MFC, and water miscible organic solvent mixture as a model condition. As a result of the study, we have found the following : 1. It is necessary to select an appropriate organic solvent and the most suitable mixing ratio with water that SAP does not show any swelling and coagulation behaviors to get a stable dispersion state of SAP ;2. Regarding SAP, specially the dispersion state is affected by the particle size and whether its surface has been done a surface cross linkage treatment or not : and3. Regarding the organic solvent, the dispersion state is affected by its dielectric constant, its mixture ratio with water, and its temperature.As a result, we have set to use the dispersion solvent of ethanol 60% and water 40% at 20°C as a standard condition

Photochemical isomerization of azobenzene incorporated in poly(N,N-dimethyl-4-vinylphenethylamine-block-styrene) diblock copolymer by cross linkage

Photochemical isomerization of p,p′-bis(chloromethyl) azobenzene (CAB) was investigated in poly-(N,N-dimethyl-4-vinylphenethylamine-block-styrene) block copolymer [P(PTA-b-St)]. The P(PTA-b-St) was prepared by anionic living polymerization. Both ends of CAB were attached to amino groups of the PPTA in the P(PTA-b-St) by quaternization in order to permit cross-linked films. When the films were irradiated with u.v. light (300 nm < λ1 < 380 nm), CAB underwent photoisomerization from the trans to the cis form. The photoisomerization did not proceed in a first-order kinetics. Hence, irradiation time-dependence of the results was analysed by the Kohlraush-Williams-Watts equation. The resultant values of parameter α, trans fraction at equilibrium (Ce) and a half-life period (Γ1/2), remained constant from 15°C to 30°C, but discontinuously changed at approximately 30°C which is close to the glass transition temperature (Tg) of PPTA. Therefore, the films were first irradiated with u.v. light at 60°C for 2h, resulting in a 28% content of cis form in CAB. Subsequently, when the films were irradiated with visible light (420nm< λ2) at 20°C for 2 h and 90°C for 2 h, the cis content of CAB changed to 21% and 0%, respectively. The retention and deletion of the cis form was controlled by an alternation of the thermal motion of PPTA above and below the Tg of PPTA in the P(PTA-b-St) block copolymer.

The cellular and mediator basis of asthma in relation to natural history

The cellular and mediator basis of asthma in relation to natural history

Chelator effect on ion diffusion in ferrous‐sulfate‐doped gelatin gel dosimeters as analyzed by MRI

Ferrous-sulfate-doped gelatin gel dosimeters are useful tools for the measurement of three-dimensional absorbed radiation dose distributions. The diffusion of ferric ions through these gels causes degradation with time of the dose distribution image. It would be useful to reduce ferric ion diffusion without decreasing gel sensitivity. The amount of ferric ion diffusion is a function of the time delay after radiation, the gel temperature, and the gel concentration. These effects can be quantified by measuring the ferric ion diffusion coefficient. Determination of the diffusion coefficient by irradiating the lower section of a cylinder of gel, which was then imaged repeatedly over time with a clinical magnetic resonance imager, is described. Analysis of the edge spread function formed at each of several times after irradiation by drawing a profile over the imaged junction between the irradiated and unirradiated halves of the cylinder, gave estimates of the variance of the edge spread function. These variances were used to obtain an estimate of the ferric ion diffusion coefficient for the gel. A method of reducing ferric ion diffusion by adding a chelator and the cross linkage agent formaldehyde is suggested. The chelators investigated were 1,10 phenanthroline, xylenol orange, and bathophenanthroline disulfonic acid. These reduced diffusion to varying extents, and influenced the gel sensitivity. The diffusion coefficient in gels containing xylenol orange was found to be 0.44 mm2h-1. The gel sensitivity was 0.0093 s-1Gy-1. This compared with a diffusion coefficient of 0.82 mm2h-1 for the base line gel that did not contain formaldehyde or chelators. The sensitivity of this base line gel was 0.0129 s-1Gy-1. The addition of xylenol orange produced the most improved gel dosimeter of the gels studied. This gel had a decreased ferric ion diffusion coefficient and a decreased sensitivity. It was still sensitive enough to be useful.

Cross linking of collagen is increased in colonic diverticulosis.

Development of colonic diverticulosis is a function of age and declining colonic wall mechanical strength. The latter is partly a consequence of changes in the collagen structure. Collagen from unaffected human colons (n = 20, age range 20-80 years) and those with colonic diverticulosis (n = 5, age range 67-80 years) were obtained at necropsy. The total collagen content was measured as the hydroxyproline content and cross linkage by collagen solubility in weak acid was studied. The colonic total collagen content was constant with age (mean (SD) 15.8 (0.3) mg/100 mg wet weight of tissue). The acid solubility of the collagen, however, increased after the age of 40 years: at over 60 years, colonic diverticulosis was associated with an increased acid solubility ratio compared with values in unaffected colons (15.3 (0.2); compared with 9.2 (0.2), p < 0.001). The cross linking of colonic collagen increases with age. These changes seem to be a factor in the aetiology of colonic diverticulosis.

An Improved SDS–Polyacrylamide Gel Electrophoresis for Resolution of Peptides in the Range Of 3.5-200kDa

Resolution of a wide range of polypeptides, 3.5-200kDa, on a single low acrylamide and cross linkage gel of 7.7% T, 2.6% C is described here. Laemmli's (4) original discontinuous SDS polyacrylamide gel electrophoresis (SDS-PAGE) system is modified by increasing the ionic strength of both stacking and resolving gels, and replacing the usual glycine buffer with a tricine cathode buffer as described by Schagger and von Jagow (7). This system offers the advantage of a wide range of protein fractionation, with sufficient band resolution, on a single, low acrylamide concentration and cross linkage gel. Moreover, increased gel ionic concentration allows higher protein and salt load, and renders this system suitable for preparative work.

Immunologic rebound.

Evidence for accelerated specific antibody (Ab) rebound or overshoot after single or multiple therapeutic plasmapheresis (TP) is fragmentary but suggested by both clinical and experimental evidence. In vitro studies showing increased peripheral blood lymphocyte turnover and total immunoglobulin production after a series of TP without immunosuppression may signify a generalized immunostimulation through removal of regulatory molecules by TP. It is known that IgG class Ab can down regulate B cells by cross linkage of their Ag and Fc receptors. Cyclophosphamide and other cytotoxic immunosuppressive agents effectively delete proliferating lymphocytes. TP could particularly foster deletion of lymphocytes actively mediating autoimmunity, since they would be more readily stimulated to proliferation by removal of Ab or other inhibitory factors than the generally resting normal immune system. This is supported by a relatively greater reduction of autoantibody levels than total immunoglobulin after treatment with TP and cytotoxic immunosuppressives.

Synthesis of New Linear Polymers Containing Thiocarbonyl Groups: Polyaddition of Dicarbothioic Acid to Diolefins

The polyaddition of 1,4-benzenedicarbothioic acid to 1,4-divinylbenzene or 1,4-diisopropenylbenzene was carried out at 70°C in toluene under a nitrogen atmosphere by radical mode such as by addition of AIBN or UV irradiation. Both diolefin compounds gave polymers in a 90% yield. The polymer obtained from 1,4-diisopropenylbenzene was soluble in chloroform, and the molecular weight of the polymer (M̅w) was 40000. On the other hand, the polymer obtained from 1,4-divinylbenzene was partly soluble in conventional organic solvents, possibly due to a cross linkage formation by a pendant vinyl group. The model addition reaction of thiobenzoic acid to styrene gave a by-product ca. 8% being the 1:2 adduct with respect to thiobenzoic acid and styrene. Alkali hydrolysis of both polymers was investigated to confirm the cross linkage structures in the polymers.

Effect of additional calcium hydroxyapatite on sodium borophosphate glasses: physical and chemical characterizations

A narrow vitreous domain along the NaPO 3-Na 2B 4O 7 pseudo-binary system has been found in the NaPO 3-Na 2B 4O 7-Ca 5(PO 4) 3OH pseudo-ternary system. The addition of Ca 5(PO 4) 3OH in the sodium borophosphate glasses induces an improvement of most of the properties of the corresponded glasses, such as glass transition temperature, microhardness and water resistance with retention of the unexpected behavior observed in the phosphate-rich domain of the glasses which belong to the NaPO 3-Na 2B 4O 7 system. This improvement might be due to the “cross linkage” of phosphate and/or borophosphate groups by the Ca 2+ cations.

Determination of Fractal Dimensions of Xerogels via Förster Energy Transfer

AbstractThe fluorescence decay of anthracene and 9,10‐diphenylanthracene in xerogels with various alkyltrimethoxysilane (alkyl = methyl, n‐propyl, n‐octyl) and tetramethoxysilane content is biexponential over a large parameter range. Decreasing degrees of cross linkage as well as lengthening of the alkyl chain lead to an increase of the value and amplitude of the short decay time and finally to a monoexponential decay. The “fractal dimension” of the doped xerogels with monoexponential 9,10‐diphenylanthracene fluorescence is determined via “Förster energy transfer” using rhodamine‐6G as the acceptor. Xerogels of low cross linkage (high content of n‐propyltrimethoxysilane or n‐octyltrimethoxysilane) are characterized by the dimension 3. Further aggregation of the primary silicate clusters leads to a “fractal‐like” network with the dimension of about 2.4.

An evaluation of the physicochemical degradation of gold ion-exchange resins in hypochlorite solutions

The long-term operating characteristics of ion-exchange resins suitable for the hydrometallurgical recovery of precious metals remain largely unknown. This study examines some physicochemical properties of two promising ion-exchange resins for gold, SR-3 and PAZ-8, when subjected to experimental conditions similar to those of a typical alkaline-chlorination gold recovery process. It is shown that the degradation behavior may be related to both the micro- and macrostructural properties of the resins. Severe resin degradation occurs on pro-longed, agitated contact of the SR-3 resin beads with hypochlorite solutions at ambient tem-perature; the low cross linkage of the resin facilitates mechanical damage, while chemical degradation occurs by dehydration, oxidative scission of the functional groups, and breakdown of the polymer matrix. The PAZ-8 resin is highly cross linked and is more resistant to both mechanical and chemical attack under similar conditions.

Turned gel electrophoresis of mouse liver ribosomes in polyacrylamide agarose composite gel.

Mouse liver ribosomes were analyzed by 1.8% polyacrylamide 0.5% agarose composite gel electrophoresis (7.5% cross linkage gel). When the ribosomal suspension mixed with agarose was applied to the gel slot, ribosomes were resolved in the composite gel. When turned gel electrophoresis in which gel concentration was the same for the second run, was carride out, ribosome bands from 40S subunits to the maximum hexamers were observed. This high resolution electrophoresis may be one of the most powerful tools available to analyze the non-denatured ribonucleoprotein particles and membrane components and to study the conformational change of ribosomes.

Photochemical isomerization of p, p′-bis(chloromethyl)azobenzene incorporated in poly(tertiary aminostyrene)s by cross linkage

A photochromic p, p′-bis(chloromethyl)azobenzene (CAB) was prepared as a crosslinking agent. Three poly(tertiary aminostyrene)s prepared via living anionic polymerization were used as reactive polymers: poly( N, N-dimethyl-4-vinylphenylamine) (PPA), poly( N, N-dimethyl-4-vinylbenzylamine) (PBA) and poly( N, N-dimethyl-4-vinylphenethylamine) (PPTA). Films were cast from tetrahydrofuran solution of CAB and the polymers. The crosslinking reaction proceeded during the evaporation of solvent and the annealing of the films at 90°C for > 10 h. The result of the swelling test led us to conclude that all the CAB added to the polymer was consumed in the crosslinking reaction. Photochemical isomerization was studied for CAB incorporated in three polymers by cross linkage. The conversions for photochemical isomerization of CAB in three crosslinked films were 35–10% in the stationary state under u.v. irradiation below the glass transition temperature. This indicated that the thermal freedom of CAB was depressed by crosslinking in the glassy state.

Hydrophilic Polymers—Their Response to Soil Amendments and Effect on Properties of a Soilless Potting Mix

The levels of hydration of several hydrophilic polymers (hydrogels) varied greatly. Starch-based polymers had the fastest rate of hydration (&lt;2 hours), followed by a propenoate-propenamide copolymer. Polyacrylamide materials required 4 to 8 hours to become fully hydrated. Maximum water retention in distilled water varied from 400 to 57 g of water per gram of dry material. All hydrogels retained less water in the presence of metal ions or fertilizers in the soaking solution, with substances releasing Fe+2 being the most detrimental. After exposure to fertilizers and ions, the water-holding capacity of a polyacrylamide with a high degree of cross linkage, but not that of hydrogels of the other structures, was fully recovered by subsequently soaking in distilled water. Pots amended with a polyacrylamide polymer but without Micromax (a micronutrient source) reached maximum water retention after six irrigations, while those with Micromax required 10 irrigations to reach peak water retention. The amounts of water being held in pots decreased after repeated fertilization. Medium volume increased with increasing levels of the polyacrylamide Supersorb C (0, 2, 4, or 6 g/pot). Micromax incorporated in medium amended with Supersorb C caused a depression in volume. Medium bulk density, total water retention, and water retention per unit volume of medium were increased by the incorporation of the hydrogel, regardless of the presence of Micromax. Noncapillary porosity measured at container capacity in medium amended with Micromax progressively decreased as the amount of hydrogel increased, but remained unchanged in medium without Micromax. Repeated drying and dehydration of the medium resulted in reduced water retention and increased noncapillary pore space.

Time Resolved Fluorescence in Doped Aerogels and Organosilicate Glasses

AbstractThe fluorescence decays of anthracene, 9,10‐dichloroanthracene and 6‐(methoxy)‐1‐(3‐sulfopropyl)‐quinolinium in sintered aerogels and of anthracene in organosilicate glasses were determined employing a precise single photon counting technique. For aerogels and organosilicate glasses, synthesized from methyltrimethoxysilane and tetramethoxysilane a biexponential decay was found. The dependence of the fluorescence behaviour on the cross linkage of the network and the adsorbed solvent indicates that the short decay is due to an efficient quenching by the network, whereas the slow component is influenced by adsorbed solvent. For aerogels the effect of aging was also investigated. For organosilicate glasses with a reactive organic sidegroup (γ‐glycidyloxypropyl) the short decay is interpreted by a decay law containing a broad distribution of life times (Kohlrausch‐Williams‐Watts). In this case the measurement of the fluorescence decay shows evidence of a heterogeneous microstructure which contains inorganic and organic network components.

A modular spinal rod linkage system to provide rotational stability.

The effect of cross linkage on the in vitro stability of paired Harrington distraction rods was studied in an unstable fracture model using calf spine segments. Cross linkage used in conjunction with sublaminar wires significantly improved torsional stability, improved lateral bending stability, and had no adverse affect on stability for axial, forward flexion, or extension loading compared to rods alone, rods with bridges, and wired rods.

Analyses of Bright and Burley Tobacco Laminae and Stems

Abstract One sample each of aged uncased, cured bright lamina, bright stems, Burley lamina and Burley stems were examined by a variety of general analytical methods and then characterized by our standard fractionation procedure. These tobacco samples were chosen to be reasonably representative of the tobaccos used in current commercial cigarette products. Although for a given variety of tobacco the concentrations of chemical constituents may vary as a function of stalk position, cultural management, geographic origin or crop year, we believe that the following conclusions based on these samples are generally valid: [1] levels of ethanol solubles, total reducing sugars and starch are much higher in bright than in Burley, [2] concentrations of soluble ammonia and nitrate are greater in Burley than in bright, [3] total alkaloid and protein concentrations are higher in lamina than in stems, [4] cellulose, potassium and chloride concentrations are much greater in stems than in lamina, [5] concentrations of pectin, lignin and soluble hemicellulose do not vary greatly from one type of tobacco to another, [6] Burley lamina has greater concentrations of protein and acid detergent solubles than do the other types of tobaccos, and [7] bright lamina has a much lower level of total ash than do the other types of tobaccos. An examination of some of the components in ash led to the following conclusions: [1] total ash values are reasonable relative indicators of the level of non-nitrate inorganics, [2] a good estimate of the total contents of potassium, calcium, chloride, sulfate, phosphorus, silicon and magnesium may be obtained by multiplying the total ash value by 0.612, and [3] it is likely that most of the potassium and calcium in total ash is actually present as carbonates rather than oxides. The significantly higher levels of both protein and acid detergent solubles found in Burley lamina are thought to indicate that this protein may be unique in terms of its carbohydrate content or in terms of the nature or extent of its cross linkage.

Living with lymphocytes.

One of the most important topics in contemporary research on specific immune responses is the delineation of the mechanisms regulating the excitation, proliferation, and differentiation of lymphocytes whose specific receptors have bound antigen. Specific B cell activation may proceed through two major pathways. One of these, referred to as factor-dependent B cell activation, involves the excitation of the cell through the cross linkage of its membrane immunoglobulin (Ig) and the stepwise action on these cells of a number of stimulatory factors which leads to their proliferation and subsequent differentiation into high-rate IgM secreting cells. The properties of one of these soluble factors, B cell stimulatory factor (BSF-1; formerly designated B cell growth factor) is described in detail. The means through which it acts, together with differentiation factors, to cause the cell to enter an IgM secretory state is also discussed.