Membrane Osmometry Research Articles

SEC Absolute Molar Mass Detection by Online Membrane Osmometry

A membrane osmometer with a short response time based on a previously developed concentric design with a capillary-shaped membrane has been applied as an online SEC detector for absolute molar mass detection in combination with a concentration detector. The flow cell volume is 12.2 μL, the response time approximately 15 s, and the molar mass cutoff is below 5 kg/mol. The performance has been tested with polystyrene standards in toluene under realistic SEC conditions.

Association behavior of linear ω‐functionalized polystyrenes in dilute solutions

AbstractLinear polystyrenes with dimethylamino end groups were prepared by anionic polymerization, using 3‐(dimethylamino)propyllithium as initiator and high vacuum techniques. The amino group was transformed to a sulfozwitterionic moiety by reaction with 1,3‐propanesultone. The dilute solution properties were studied by means of membrane osmometry (MO), low‐angle laser light scattering (LALLS) and viscometry in solvents with different polarity. The amine‐capped polymers, studied by LALLS in tetrahydrofuran (THF), toluene and CCI4 show no evidence of association. In contrast, the zwitterionic samples exhibited a relatively strong association in CCI4 (relative permittivity ε = 2.24), weak in THF (ε = 7.4), and intermediate in toluene (ε = 2.4). The association numbers were lower than those found for linear polyisoprenes and polybutadienes with the same end groups. Viscosity measurements supported the results drawn from LALLS. The results provide strong evidence that the micelles behave hydrodynamically as star polymers. The association behavior is best described by the linear head packing model.

Predicting the phase diagram for a gelatin-pectin system

It is a recognised phenomenon that mixtures of biopolymers in aqueous solution may result in the formation of a two-phase system. Increasingly biopolymers are being used together in food production. Therefore i t is important to understand the conditions and concentration limits that result in phase separation. Gelatin and pectin are important food polymers having the functional properties of gelling, binding and thickening agents [ I ] Hence for the gelatin-pectin system the theoretical treatment of Edmond and Ogston based on excluded volumes [2] has been explored making ube of direct measurements made on the individual biopolymers using sedimentation equilibrium, membrane osmometry and light scattering with the intention of finding the most suitable method for the prediction of the gelatin-pectin phase diagram. In previous work [3], we demonstrated that the phase diagram prediction using weight average molecular weights (MW) and virial coefficients determined from sedimentation equilibrium did not result in a good comparison with the measured binodal. Preliminary indications are that we need to measure number average MWs and virial coefficients as the binodal equation [ 2 ] for predicting the binodal is derived from osmotic pressure formulations, and in this case the MW is always a number average [4]. In this report we present data on number average molecular weights and virial coefficients using osmotic pressure measurements and light scattering. An industrial low-methoxy pectin (Hercules) and a gelatin (Extraco, 2.50 Bloom) were used. The gelatin and pectin were dissolved in 0.5M NaCl and adjusted to pH 5.5 for the osmotic measurements while for the light scattering measurements they were dissolved in O.IM NaCl and adjusted to pH 5.5. The reduced osmotic pressure for both biopolymers was measured over a range of concentrations and is shown in figure 1. The MW and virial coefficients were calculated from the data using the Fisher c-matrix method 141.

Synthesis, Characterization, and Conductivities of Poly(2-Vinylpyridine)-graft-Polyoxyethylene Using a Macromer Technique

Abstract Poly(2-vinylpyridine) (P2-VP) with uniform polyoxyethylene (PEO) grafts was synthesized using a macromer technique. 2-Vinylpyridine was copolymerized with PEO macromer in solution by using azobisisobutyronitrile (AIBN) as the initiator. The effects of the amount of AIBN, the concentrations of 2-vinylpyridine and macromer, the number average molecular weight of macromer, and the charging ratio of macromer to 2-vinylpyridine in the copolymerization were studied. The copolymerization rate of the PEO macromer with 2-vinylpyridine was also investigated. The grafting efficiency reached about 56%. The crude graft copolymer was purified by extraction and precipitation, and it was characterized by IR, 1H-NMR, and Bruss membrane osmometry. The PEO grafts were doped with LiClO4 and showed ionic conductivity around 4.10 × 10−6S°Cm−1 at 25°C whereas the P2-VP main chains were complexed with TCNQ to obtain electronic conductivity around 5.50 × 10−6 S°Cm−1 at 25°C The mixed (ionic and electronic) conductivity of the doped copolymer could reach about 5.40 × 10−5 S°Cm−1 at 25°C and showed a synergistic effect.

Model Mono-, Di-, and Tri-.omega.-Functionalized Three-Arm Star Polybutadienes. Synthesis and Association in Dilute Solutions by Membrane Osmometry and Static Light Scattering

Three-arm polybutadienes with one, two, and three functional end groups were prepared by anionic polymerization using [3-(dimethylamino)propyl]lithium and sec-butyllithium as initiators and methyltrichlorosilane as linking agent. Characterization carried out on the dimethylamine-capped polymers by SEC, in THF, low-angle laser light scattering (LALLS) in THF, and membrane osmometry (MO) in toluene indicates a high degree of molecular and structural homogeneity. The 1,2 content, determined by NMR spectroscopy, of the arms having the functional groups was higher (12-32%) than that of the arms without the functional groups (7-10%), owing to the tertiary amine group of the initiator. The dimethylamine end groups were transformed to the highly polar sulfozwitterionic ones by reaction with cyclopropanesultone. Association of the different ω-functionalized star polybutadienes was studied in dilute solutions of cyclohexane by MO and LALLS. It was found that although the dimethylamine-capped polybutadienes do not associate, the corresponding zwitterionic species associate strongly in this solvent. At fixed molecular weight of the arms, the degree of association increases with decreasing number of functional groups and, for the same number of functional groups, with decreasing molecular weight of the arms. The trifunctional species form gels at concentrations needed for MO experiments. Comparison with linear ω-zwitterionic polybutadienes in cyclohexane shows that the stars associate less strongly, maybe due to the sterically hindered star structure (monofunctional species) and to intramolecular interactions (di- and trifunctional species)

Characterization of Low-Molecular-Weight Polymers: Failure of Universal Calibration in Size Exclusion Chromatography

Abstract Accurate measurement of molecular weights for polymers in the 500–5000 molecular weight range requires considerable care. Absolute methods such as membrane osmometry or light scattering are generally imprecise because of membrane permeation or low scattering intensity. Many polymers are too fragile to be studied by mass spectrometry. Other techniques, such as vapor phase osmometry, cryoscopy, and ebulliometry require calibration and data replication if accurate molecular weights are to be obtained. Size exclusion chromatography (SEC) also requires calibration but can be a very rapid and accurate method if proper calibration can be achieved. SEC calibration is now often achieved via “universal calibration” (UC). which is based on the premise that polymers with the same hydrodynamic volume will have the same SEC retention time, At very low molecular weights, the UC approach is clearly invalid since intrinsic viscosities can become negative for certain polymers. We demonstrate here that the invalidi...

Studies on molecular weights of polysaccharides of Auricularia auricula-judae

Three d-glucans (A, C, and E) and two acidic heteropolysaccharides (D and B), isolated from the fruit bodies of Auricularia auricula-judae (which grows in Fangshan, Hubei, China) were analysed by paper chromatography, gas chromatography, and IR and 13 C NMR. Glucans A, C, and E consist mainly of a backbone chain of β-(1 → 3)- d- glucose residues, with various branched groups. Polysaccharides D and B contain residues of d-xylose, d-mannose, d-galactose, d-glucose, and d-glucuronic acid. The weight-average molecular weights M w , number-average molecular weights M w , intrinsic viscosities [ν], and Huggins constants k′ of these polysaccharides were studied by light scattering, membrane osmometry, and viscometry. The values of M w for samples of A, C, E, D, and B are 117 × 10 4, 144 × 10 4, 200 × 10 4, 30 × 10 4, and 50 × 10 4, respectively. Analysis of the M w , M n , [ ν], and k′ data indicates polysaccharides A and E to have stiff chains, and C, D, and B flexible chains in aqueous solutions.

Synthesis and properties of oxymethylene-linked oxyethylene-oxypropylene-styrene multiblock copolymers

Oxymethylene-linked multiblock copolymers with two or three components (oxyethylene-oxypropylene-styrene) (EO-PO-St) were synthesized by coupling polyethylene glycol with polypropylene glycol and/or telechelic dihydroxyl polystyrene, using dichloromethane as coupling agent and KOH as catalyst. The copolymers were purified, characterized by i.r., 1H n.m.r., g.p.c. and membrane osmometry, and were shown to be multiblock copolymers. D.s.c. and wide angle X-ray diffraction indicated the crystallinity of the copolymer, which depended on the molecular weight and content of polyoxyethylene (PEO) blocks. The multiblock copolymers exhibit good emulsifying properties and good phase transfer catalyst properties in Williamson reactions. The tensile strength of the copolymer increases with polystyrene and PEO content as well as with the molecular weight of PEO blocks. The LiClO 4 complex of the multiblock copolymer ( EO PO = 95 5 ) shows very good room temperature conductivity, which reaches 5.8 × 10 −4 S cm −1 at 25°C and 1.2 × 10 −3 S cm −1 at 30°C.

Polymer conformation and viscometric behavior. VIII. solution properties and chain flexibility of cyclic side chain containing poly(monoitaconates)

Abstract Monocyclopentyl and monocyclohexyl itaconates and the corresponding polymers, poly(monocyclopentyl itaconate) (PMCPI) and poly(mono-cyclohexyl itaconate) (PMCHI), were synthesized and characterized. Polymers were fractionated, by fractional precipitation, using methanol-water as solvent-precipitant pair. Fractions were characterized by membrane osmometry in 2-propanol at 298 K, vapor pressure osmometry in methanol at 318 K, size exclusion chromatography in THF, and by viscometry in THF and methanol. The Kuhn-Mark-Houwink-Sakurada equations were established to determine the viscometric parameters. By using the Stockmayer-Fixman equation, the conformational parameter K θ was determined in both solvents. The rigidity index, σ, and the characteristic ratio, C∞, were calculated. These polymers show high rigidity values but they are comparable with those reported for other poly (itaconates).

Optimized calibration curve for size exclusion chromatography applied to poly(vinyl chloride)

The problem of using a polystyrene-standard-based calibration curve for other polymers has been overcome by developing an algorithm based on the concept of parameter estimation and optimization. The algorithm modifies the regression coefficients of the polystyrene-standard-based calibration curve by interactively using the chromatographic output and the absolute number-average molecular weight of the experimental polymer. Analytical expressions have been derived for calculating the directional derivatives, which ensure rapid convergence of the objective function. The algorithm, applied to commercial poly(vinyl chloride), offered a number-average molecular weight of 32037 whereas that measured by membrane osmometry is 32 000. The polymer characterization parameters calculated from the optimized calibration curve closely matched those obtained from the universal calibration curve and Q-factor values. The algorithm needs no narrow standard of the experimental polymer, and holds for homopolymers, copolymers and polymer blends. It can be easily incorporated into commercial size exclusion chromatography data-reduction software packages.

Molecular Weight Determination of Comb-Like Polymers

The molecular weight determination of the comb-like polymer poly(octadecyl methacrylate) was carried out by GPC and by membrane osmometry. It was found that the MW by GPC is smaller than by osmometry. The universal calibration curve in GPC and tha Mark-Houvink-Sakurada equation were also drawn

Poly(p‐phenylene)s with polar side groups, 1. Pd‐catalyzed synthesis, characterization and modification of poly(p‐phenylene)s bearing butoxymethyl side chains

AbstractThis is a description of the Pd‐catalyzed synthesis of two poly(p‐phenylene) (PPP) derivatives which have butoxymethyl side groups on each, or every alternate, phenylene moiety. For the latter, details are given of the quantitative transformation of the ether functionalities into bromomethyl pendant groups. Subsequent reaction of these bromo functionalities with sodium 4‐cyanophenolate or sodium acetate produced structurally homogeneous PPP's which had 4‐cyanophenoxymethyl and acetoxymethyl side groups, respectively. The PPP derivatives described here are soluble in common organic solvents and were characterized in detail by NMR spectroscopy, membrane osmometry and size exclusion chromatography (SEC). The degrees of polycondensation of the butoxymethyl‐substituted polymers were found to be in the order of 30–65. No evidence for chain degradation during the following conversions was found on the basis of the NMR and SEC measurements.

Method to improve the accuracy of membrane osmometry measures of protein molecular weight

Membrane osmometry provides a simple method to determine protein molecular weight but accuracy is limited behavior. Recent studies (Fullerton et al., Biochem. Cell. Biol., in press) show that non-ideal osmotic response of protein solutions is described by the empirical equation, M sv/ M s = RT ϱ / A s × 1 / π + I , where M s = mass of solute, M sv = mass of solvent, R = The Universal gas constant, T= absulute temperature, ϱ = solvent density, A s = solute molecular mass, π = osmotic presute and I = the nonideality parameter. This linear relation is used in this paper to demonstrate that measurement of molecular weight from the slope simplifies such measures and improves the accuracy relative to classical methods. The molecular weight of bovine serum albumin is measured with error less than 0.9%. The single dimensionless nonideality parameter, I = 4.05 + 0.07, describes non-ideal curvature in the typical πV = nRT diagram better than the customary second power virial expansion requiring 3 fitting constant. Analysis of eight data sets on four proteins from the literature shows that molecular weight calculated from the slope of the new equation agress with chemical molecular weight within an RMS error of only 1.9%.

Relationships among protein and albumin concentrations and oncotic pressure in nephrotic plasma.

We determined oncotic pressure (pi) by membrane osmometry and assayed total protein (TP) and albumin (Alb) concentrations in plasma of 102 nephrotic subjects and 27 healthy controls. All three quantities were markedly depressed in the nephrotic group. When plasma was serially diluted and concentrated, nephrotic but not control plasma also exhibited a highly variable change point in the nonlinear relationship between TP or Alb and pi. Absent a unique change point, we developed quadratic models which incorporated TP, Alb, and (TP x Alb) to prospectively predict pi in unperturbed plasma. The ability of the most successful quadratic model to predict pi in afferent or efferent arteriolar plasma was limited; the prediction errors reached 10 mmHg in nephrotic and 6 mmHg in control subjects. The nephrotic model coefficients also differed significantly from control and pointed to an important influence of nonalbumin proteins on pi in nephrotic plasma. Investigation of the intrinsic membrane properties of diseased glomerular capillary walls requires precise knowledge of pi. For this purpose we recommend that pi be directly determined by membrane osmometry rather than calculated from protein concentration(s).

Vapor-liquid equilibrium in binary and ternary aqueous solutions of poly(ethylene glycol) and dextran

Activities of water for various binary and, in particural, ternary aqueous solutions of poly(ethylene glycol) (PEG) and dextran were measured over the entire homogeneous mixing range up to a polymer weight fraction of 0.3 at 293.15, 313.15, and 333.15 K. The water activities were determined by vapor-pressure osmometry and, additionally, for dilute dextran solutions using membrane osmometry. The experimental data were evaluated using the osmotic virial equation

Polymer Molecular Weight from Loss Modulus

The method for the determination of polymer molecular weight and molecular weight distribution from transient and dynamic viscoelastic properties of a narrow molecular weight distribution linear amorphous polymer with Mw>Mc has been discussed in our previous work. In the present work, we discussed the method to calculate the polymer molecular weight and molecular weight distribution from terminal zone of loss modulus G″(ω). The terminal zone of loss modulus G″(ω) is separated from the plateau modulus Gn0 and the normalized relaxation time spectrum H(τ) is then calculated by using the first approximation formulas of Tschoegl. The polymer molecular weight and molecular weight distribution are then obtained from H(τ) by using the same numerical method as was developed in the previous work. The results calculated by this method are in good agreement with those measured from membrane osmometry, light scattering and GPC experiments etc.

A novel synthetic route to rigid‐rod polyimides

AbstractA new synthetic approach to soluble, rigid‐rod, aromatic polymides is described. The polycondensation is done by a Pd‐catalyzed aryl‐aryl coupling of N,N′‐bis(4‐bromo‐2,5‐didodecyl‐phenyl)‐1,2:4,5‐pyromellitic diimide (2) and 2,5‐didodecyl‐1,4‐benzenediboronic acid (3). Here, the imide structure is already preformed in monomer 2. A structurally identical polymer is synthesized by the classical procedure condensing 1,2:4,5‐pyromellitic dianhydride (PMDA) (4) and 4,4″‐diamino‐2,5,2′,5′,2″,5″‐hexadodecyl‐p‐terphenyl (5). Both polymers are characterized in detail by 1H and 13C NMR spectroscopy, membrane osmometry and size exclusion chromatography. The average degree of polycondensation is of the order of 15. The thermal behaviour of the polymers is studied by differential scanning calorimetry and thermogravimetrical analysis.

Molecular weight of linear polymer from storage modulus

Abstract In a previous work [1], using a binary blending rule, we had developed a numerical method to calculate the polymer molecular weight from the relaxation time spectrum of the terminal zone of stress relaxation modulus G(t). In this work, we separated the terminal zone of storage modulus G'(ω) from plateau modulus Gno and calculated the relaxation time spectrum H by using the second approximation formulas of Tschoegl [2]. The polymer molecular weight and molecular weight distribution was then obtained from H by using the same numerical method as was developed in the previous work [1]. The results calculated by this method are in good agreement with those measured from membrane osmometry, light scattering, GPC, etc.

Osmotic pressure measurements of dissociating bovine hemoglobin

While the dissociation of hemoglobin, in general, has been studied extensively using various techniques under both alkaline and acidic conditions, the dissociation under alkaline conditions using membrane osmometry has not been previously reported. An equilibrium mathematical model describing the two-stage dissociation is presented in this paper and agrees with the experimental osmotic pressure measurements of bovine hemoglobin at pH's above 7.4. Results of this study show that the pH dependency under alkaline conditions at 37°C can be regressed to give approximate values of the dissociation constants for both the dissociation of the tetramer to the dimer and the dimer to the monomer as a function of pH. The data also indicate that, in the presence of the borate buffer used in these experiments, the liberation of approximately one proton occurs for the dissociation of the tetramer into the dimers; approximately two protons are liberated for the dissociation of the dimer into the monomer. The dissociation constants reported here for bovine hemoglobin are in reasonable agreement with those obtained under similar conditions using other techniques.

Functionalized polymers I. Poly(dichloroalkyl itaconates), synthesis and solution properties

The synthesis of poly(di-2-chloroethyl itaconate) (PD2CEI) and poly(di-3-chloropropyl itaconate) (PD3CPI) was carried out. The dilute solution behaviour of these polymers in tetrahydrofuran and chloroform at 298 K has been studied, by viscometry, membrane osmometry, and size-exclusion chromatography (SEC) measurements. The Kuhn-Mark-Houwink-Sakurada relationships were established. The flexibility factors σ and C∞ and the thermodynamic parameters B were calculated using the Stockmayer-Fixman equation. The results obtained are compared with those found for the corresponding poly(methacrylates) and the poly(dialkyl itaconates), and discussed in terms of specific influence of the chlorine incorporated in the side chain.