Average Intrinsic Viscosity Research Articles

Kinetics of Radical Polymerization at High Conversion I. GPC Measurements of Molecular Mass Distribution

A series of poly(methyl methacrylate) (PMMA) samples was prepared with different monomer concentrations and to different degree of conversion in benzene, at 50°C. Average molecular weights and intrinsic viscosity values in the eluent (THF) measured by GPC using an online viscometer are reported. At monomer concentrations up to 50 mol %, no gel effect is observed even in the case of very high conversions (∼90%); both molecular weights and kinetic parameters which determine the length of the polymer chain remain practically unchanged independent of conversion. From monomer concentrations of 75 mol %, significant increase of both of these values is observed depending on conversion. The average branching numbers of polymer chains for all samples remain close to zero. The polydispersity values are generally near 1.7. These results denote that there is no significant chain transfer to polymer and the disproportionation probability in chain termination reactions agree with earlier results described in the literature.

Screening the physical properties of novel Pseudomonas exopolysaccharides by HPSEC with multi-angle light scattering and viscosity detection

The physical properties of three novel acidic exopolysaccharides obtained from P. marginalis types A, B and C, one from P. ‘gingen’, one from P. andropogenis and one from P. fluorescens have been partially characterized. These EPSs were chromatographed on three serially placed SE Shodex OH pak columns covering a molar mass range for pullulans from about 4 × 10 7 to 1 × 10 3. The mobile phase was 0.05 M NaNO 3. Physical measurements were performed on about 30 mg of sample for each EPS. The weight average molar mass of these EPSs ranged from about 0.71 to 2.85 × 10 6, the weight average intrinsic viscosity from 7.15 to 35.3 dl/ g and the radius of gyration from 62 to 123nm. The polydispersities of these EPSs ranged from 1.01 to 1.37. The large molar mass, size and viscosities of these EPSs may indicate that they have potential for use as thickeners, stabilizers, emulsifiers, and gelling agents in the food and non-food industries.

Physicochemical studies on xylinan (acetan). I. Characterization by G permeation chromatography on sepharose Cl‐2B coupled with static light scattering and viscometry

Laboratory-made samples of the polysaccharide xylinan (acetan) were fractionated on Sepharose Cl-2B using 0.1M NaCl as eluant. The weight average molar masses and intrinsic viscosities were estimated in the fractions by multiangle laser light scattering (off-line) and capillary viscometry, respectively. The Mark-Houwink-Sakurada plot was found to be indicative of semiflexible coils (a = 0.90). The angular dependence of scattered light was interpreted by fitting with theoretically calculated "Master Curves" in terms of a wormlike chain model. The ambiguity of the interpretation of scattering curves owing to the overlapping effects of chain stiffness and polydispersity is discussed in detail. The experimental data is found to be consistent with a persistence length of Lp = 100 nm. The main proportion consists of double-stranded chains (consistent with a robust double-helix), but single- and multistranded chains also are present. Our results suggest a fractionation according to the contour length rather than the molar mass.

Influence of fermentation hydrodynamics on gellan gum physico-chemical characteristics

The physico-chemical characteristics of gellan gum polymers produced using various impeller systems and different aeration conditions were studied. The degree of esterification, average molecular weight (Mw), intrinsic viscosity ([η]), and molecular weight distribution of the highly clarified polymers were found to be greatly dependent upon the fermentor hydrodynamics. For example, the highly homogeneous conditions of fermentation obtained with a helical ribbon impeller led to a gellan exhibiting a molecular weight twice as high as that prepared from the most heterogeneous fermentations obtained with Rushton turbines. The composition of the polymer itself is also affected since the degree of esterification of gellan can vary with the fermentation conditions. Finally, a Mark-Houwink relation (i.e. [η] = KMwa) has been tentatively established for the deesterified gellan polymer.

A novel polyurethane macroinitiator for free radical polymerization

Polyurethane macroinitiator (PUMI) has been prepared from toluene diisocyanate and benzopinacol and successfully used to polymerize acrylonitrile (AN). The effects of PUMI and AN concentrations and polymerization time on the yield, number average molecular weight and intrinsic viscosity of the resulting Polyacrylonitrile have been studied.

Miscibility studies of polymer blends by viscometry methods

AbstractThe intrinsic viscosities of blends of poly(vinyl chloride)/poly(ethylene‐co‐vinyl acetate) (PVC/EVA), poly(vinyl chloride)/poly(styrene‐co‐acrylonitrile) (PVC/SAN), and poly(ethylene‐co‐vinyl acetate)/poly(styrene‐co‐acrylonitrile) (EVA/SAN) have been studied in cyclohexanone as a function of blend composition. In order to predict the compatibility of polymer pairs in solution, the interaction parameter term, Δb, obtained from the modified Krigbaum and Wall theory, and the difference in the intrinsic viscosities of the polymer mixtures and the weight average intrinsic viscosities of the two polymer solutions taken separately are used. © 1994 John Wiley & Sons, Inc.

Investigations into the Effects of an Enzyme Preparation for Baking on Wheat Flour Dough Pentosans

The modification of pentosans in doughs by a fungal enzyme preparation, used as flour improver, is reported. In the absence of added enzyme, 15-20% of water-unextractable anhydro-arabinose plus anhydro-xylose (ara + xyl) were solubilized during dough processing, depending on the starting flour used. At the optimal dosage for best technological effects, the enzyme preparation brought about a further (ara + xyl) solubilization of 9-29%. This liberation of arabinoxylans modified the viscosity of water extracts from the doughs. The specific viscosities of extracts from enzyme-treated doughs were much enhanced (≈ 40-65%), as compared to the control, because the average apparent intrinsic viscosity of extracted arabinoxylans (both water-extractable and enzyme-released) remained high. The effect of a pure endo-xylanase, isolated from this enzyme preparation, was essentially the same as the crude preparation on dough pentosans. Some hypotheses about mechanisms by which a depolymerizing enzyme can release high Mr arabinoxylans and increase the viscosity were investigated: an alkaline treatment, intended to split ester bonds, did not reduce the viscosity significantly; on the other hand, when a flour from which the water-extractable material had been removed was used as starting material, the intrinsic viscosity of enzyme-released arabinoxylans was much lower. The improving action of the enzyme preparation on doughs may be partly attributed to solubilized arabinoxylans.

Adsorption of Polymer Mixtures from Dilute and Semidilute Solutions

The adsorption of mixtures of thermodynamically compatible and incompatible polymer pairs from a common solvent has been studied in the concentration range of dilute and semidilute solutions. The critical concentration of overlap (crossover region) was dependent on the component ratio estimated from the relationship [η] AB = [η] AϕA + [η] BϕB, where [η] i is the intrinsic viscosity of pure components in common solvent, ϕ A and ϕ B are their volume fractions in the mixture, and [ϕ] AB is the average intrinsic viscosity of the mixture. It was found that the processes of macromolecular aggregation proceed by transition from the dilute to the semidilute regime and that during adsorption macromolecular aggregates pass onto the adsorbent surface. This transition diminishes in the crossover region. Considering the solution of polymer mixture A + B as a solution of A in mixed solvent (solvent + B) and vice versa, the peculiarities of adsorption are discussed, which are connected with the changing thermodynamic quality of mixed solvent.

Synthesis and characterization of a new biodegradable semi-solid poly(ortho ester) for drug delivery systems

Since the late 1970s, three families of poly(ortho esters) (POE) were synthesized to provide bioerodible carriers for drug delivery devices. The most recent POE is a semi-solid polymer with a viscous behavior at room temperature. Polymer synthesis by a transesterification reaction between a triol and a trialkyl ortho ester is described. The structure of the polymer was confirmed by conventional methods such as 1H-NMR, 13C-NMR and FT-IR. Information concerning average molecular weight and intrinsic viscosity was obtained respectively by GPC and viscosimetry. Residual solvents in the polymer were determined using gas chromatography. The chromatographic conditions were optimized to enable the quantification of the solvents in concentrations of a few percent. The mechanical behavior of the semi-solid POE was determined by rheometric measurements. Hydrolysis of the polymer leads to the formation of the original triol and the carboxylic acid derived from the trialkyl ortho ester used in the transesterification step. No toxicological problems associated with these compounds are anticipated.

Adsorption of Polymer Mixtures from Diluted and Semidiluted Solutions

The adsorption of mixtures of thermodynamically compatibile and incompatibile polymer pairs from common solvent has been studied in the concentration regime of dilute and semidilute solutions. The critical concentration of overlapping(crossover region) was being dependent on the component ratio estimated from the relationship [η]AV=[η]AφA+[η]BφB Where [η]i is intrinsic viscosity of pure components in common solvent, φA and φB are their volume fractions in the mixture and [η]AV average intrinsic viscosity of the mixture. It was found that by transition from dilute to semidilute regime the processes of macromolecular aggregation proceed and during adsorption macromolecular aggregares pass onto the adsorbent surface. This transition diminishes in the crossover region. Considering solution of polymer mixture A+B as a solution of A in mixed solvent(solvent + B) and vice versa, the peculiarities of adsorption are discussed, which are connented with changing thermodynamic qusllity of mixed solvent.

Weighted intrinsic viscosity relationships for polysaccharide mixtures in dilute aqueous solutions

The weighted intrinsic viscosities of polysaccharide mixtures in dilute aqueous solutions have been studied. The purpose of this investigation is to demonstrate that average intrinsic viscosities would scale with the weight fraction of the individual components for polysaccharide mixtures in 0.5N NaOH(aq). The polysaccharides examined in this study were composed of polymers differing in their molecular weights, degree of branching, and bond linkages. Excellent agreement between theory and experiment was observed for the three different mixed polymer systems examined. This observation validates certain aspects of proposed theoretical treatments which employ this fundamental assumption and allows for further advances in experimental analytical developments of water-soluble polymer systems.

Simple methods of gel permeation chromatography calibration developed from one or two polydisperse polymer standards

Applying the formalism of averaged elution volumes corresponding to average molecular weights or intrinsic viscosities of polydisperse polymer standards simple, single-valued equations were developed for iterative evaluation of calibration parameters of both direct and universal GPC calibration relationships. The developed evaluation procedures are simpler and converge faster than corresponding methods described in the literature.

The effect of shear rate on the molecular weight determination of acrylamide polymers from intrinsic viscosity measurements

The rheological response of dilute solutions of high molecular weight polyacrylamides at low shear rates has been measured using a capillary viscometer that provided for a fivefold variation in shear rate at each concentration. The non-Newtonian effects were found to be significant for polyacrylamides with number-average molecular weights exceeding 106. The molecular weight average–intrinsic viscosity relationship most widely used in the literature, [η] = 6.80 × 10−4M, was found to be valid when [η] was measured at high shear rates where the polymer solutions approached Newtonian behavior. A new relationship was developed relating Mn to the intrinsic viscosity extrapolated to zero shear rate.

Effect of Tension Level on Texturizing of Nylon 6 Multifilament Yarn

Nylon 6 multifilament yarn was textured using various tension levels at the twisting zone. It was found that the breaking-stress and breaking-elongation values of the textured yarns are more dependent on the nature of change in the distribution of the intrinsic viscosities than on average intrinsic viscosity values of the samples. With increase in the tension level, the degradation on the molecular level increases, which in turn leads to an increase in the reformative processes. The final shape of the distribution curve (and as a consequence, the mechanical properties of the yarn) is dependent on the net effect of these two opposing processes.

Separation of dextrans by gel permeation chromatography

AbstractThe role of the intrinsic viscosity [η] as separation parameter in gel permeation chromatography (GPC) was studied for dextrans (from Leuconostoc mesenteroids B512) dissolved in water with deactivated silicagel (Porasil) as the column‐filling material. For that purpose specific viscosities of dextran fractions eluted by GPC were measured as a function of the elution volume v. Provided that the elution volumes are corrected for zonal spreading, they are related to the intrinsic viscosities in an unambiguous way, probably reflecting a unique relationship between degree of branching and molecular weights. This was further investigated by developing an iteration method to prepare two calibration curves γ(v) and g(v), respectively, relating ln[\documentclass{article}\pagestyle{empty}\begin{document}$\left[ {\bar \eta } \right]$\end {document}] and InM (M is the molecular weight) to v. It required that the weight‐average molecular weight Mw, the number‐average molecular weight Mn, and the average intrinsic viscosity [\documentclass{article}\pagestyle{empty}\begin{document}$\left[ {\bar \eta } \right]$\end {document}] for a number of dextran samples (broad distributions) be previously known. The calibration curves found lead to consistent values of the above‐mentioned averages. Moreover, they allow‐establishment of the [\documentclass{article}\pagestyle{empty}\begin{document}$\left[ {\bar \eta } \right]$\end {document}]‐M relationship over the range 5000 < M < 500,000.

Changes in Molecular Size and Size Distribution and Their Effects on Mechanical Properties of Nylon-6 Yarns During Texturizing

The changes in average intrinsic viscosity and its distribution and their effect on mechanical properties of nylon-6 (poly caprolactam) multifilament yarn during texturizing were studied. It was found that change in average intrinsic viscosity is not the only indicator of the changes taking place in the, mechanical properties of the yarn. The changes in the molecular size distribution, on the other hand, can be regarded as a better indicator in this regard. The reduction in the breaking stress of the textured yarn is dependent on texturizing variables— e.g. : heater temperature, contact time twist, inherent moisture content of the feed yarn, yarn tension in the texturizing zone, etc. The elongation percentage at break, on the other hand, may either decrease or increase. The changes have been found to be dependent on the changes in the low molecular weight, high molecular weight species and broadness of the distribution curve.

Preparation d'homopolymeres du thietanne de masses moléculaires determinees

A study has been made of the polymerization of thietane by thiolates such as thia-3-pentane thiolate with sodium, potassium or tetraethylammonium as cation. The following solvents have been used: tetrahydrofurane, acetonitrile, hexamethylphosphorotriamide and dimethylsulphoxide. Such thiolates permit the preparation of homopolymers of thietane with specified molecular weights but it has not been possible to explain, in these reactions, the activity of sodium naphthalene at −78°. The relationship between number average molecular weight and intrinsic viscosity is given.

The Overload Effect in Gel Permeation Chromatography

Abstract Overload phenomena in GPC are investigated with samples of narrow polystyrenes and short but efficient columns packed with Styragel. Viscous fingering is shown to be a leading cause of peak skewing and broadening. A correlation is proposed to define a safe operating range in terms of sample concentration, volume, and the average intrinsic viscosity of the solute polymer.

Peck Substances of Sweet Cherries and Their Alteration during SO2 Brining

SUMMARY— During ripening the proportion of protopectin in the cherries decreased as did the average intrinsic viscosity of the pectic material. Brining of the cherries resulted in a further decrease in the intrinsic viscosity and a conversion of protopectin and pectinic acid to the pectic acid form. The texture of the brined cherries softened with increasing maturity of the starting material. On prolonged storage in SO2 brine the texture of the cherries softened, and the intrinsic viscosity of the pectic materials decreased. The use of brines with pH levels above and below pH 3.1‐3.5 caused a decrease in the intrinsic viscosity. A slight increase in pectic breakdown was seen when the SO2 was raised to the 2% level. The overall effect of brining on the pectic materials of the cherries was to cause extensive de‐esterification and a decrease in the viscosity average molecular weight.

Viscosity of 25% solutions of cellulose acetate versus intrinsic viscosity distribution

AbstractThe 25% w/w solutions of blends of cellulose acetate fractions have higher viscosities than solutions of single fractions of the same average intrinsic viscosity. It was found that the viscosity of a blend can be related to its composition by the relationship: where \documentclass{article}\pagestyle{empty}\begin{document}$[\bar \eta ]_{25\%}$\end{document} is the apparent intrinsic viscosity of the cellulose acetate blend in solution at 25% concentration, and [η]i are the intrinsic viscosities of the components. By application of this equation it was determined that only a portion of the high anomalous viscosity of solutions of cellulose acetate prepared from viscose grade wood pulp could be attributed to intrinsic viscosity distribution.