Intermolecular interactions between bovine serum albumin and certain water‐soluble polymers at various temperatures

Viscometric behaviors of dextran (Dx), poly(N‐vinyl‐2‐pyrrolidone) (PVP), and poly(ethylene oxide) (PEO) with bovine serum albumin (BSA) in aqueous solutions have been studied at 25, 30, and 35°C. The reduced viscosity and intrinsic viscosity have been experimentally measured for the polymer/water and polymer/BSA/water systems by classical Huggins equation. Measurements of reduced viscosities of the Dx, PVP, and PEO in water have been calculated and all intrinsic viscosities of PEO([η]_PEO) are larger than that of Dx([η]_Dx), and PVP([η]_PVP) in aqueous solutions, at all temperatures. The intrinsic viscosities of PVP, PEO, and Dx were found to be dependent on the concentration of BSA. The presence of BSA (0.05, 0.10, and 0.30 wt %) led to a decrease in the intrinsic viscosities of polymers, at 25, 30, and 35°C. The concentration difference of BSA (Δ[BSA]) is most effective in decreasing the intrinsic viscosities of Dx at 25°C and PEO at 30 and 35°C. In other words, Δ[η] (%) order followed as Dx > PEO > PVP at 25°C and PEO > Dx > PVP at 30 and 35°C. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1554–1560, 2006     

Rheological properties of concentrated polymer solution: Polybutadiene in good and θ solvents

The zero shear viscosity, η° of three polybutadiene samples having different molecular weights over a wide range of concentration (1.0–35.0% polymer) in good and θ solvents has been studied. Superposition of viscosity data has been made to give a single composite curve for each solvent by shifting them vertically by a factor (M°/M)^3.4, where M° represents the molecular weight of the reference sample. The shift factor is found to be proportional to M^3.4 in the region of higher concentration, which indicates that the 3.4-power law is valid for the data of polybutadiene. The double-logarithmic plots of relative viscosity η°_r as a function of c⁵M^3.4 yielded a single composite curve approximating a straight line with slope of unity at the higher values of the variables. The results indicate that over a considerable range of the variables (molecular weight and concentration) at a constant temperature, the relative viscosity is a single function of c⁵M^3.4. The results for double-logarithmic plots of zero shear specific viscosity η°_csp as a function of concentration confirmed those observed in polycholoroprene samples studied earlier that the η0_sp values in θ solvents at higher concentration region are found to be higher than those found in good solvents, whereas in the moderately concentrated region the values are just opposite in θ and good solvents. The viscosity crossover in θ solvents is not as sharp as is found in case of polychloroprene samples and that crossover, too, has taken place in the range of concentration of 11.7–31.6% polymer, which is comparatively higher than that of polychloroprene samples (6.06–21.0% polymer). The results indicate some relation between viscosity crossover and polymer polarity, supporting the idea of enhanced intermolecular association in poor solvents. To correlatethe viscosity data obtained in good and poor solvents, two methods, one given by Graessley and the other given by Dreval and coworkers involving the correlating variable c[η], were considered. The plots of relative viscosity η°, versus the correlating variable c[η] in benzene (good solvent) yielded one curve, but in the case of θ solvents (dioxane and isobutyl acetate), the same plots yielded three separate curves instead of a single curve, which is rather unusual. The appropriate correction on the correlating variable for chain contraction in the concentrated region in a good solvent moved the data to a common curve, especially in lower concentration region, but at the higher concentration region a slight overestimation of data seems to have been effected. On the other hand, the plots of log η as a function of correlating variable c[η] yielded a single curve for three samples in the good solvent benzene, but in poor solvents (diozane and isobutyl acetate) the same plots yielded three separate curves for three samples instead of a single curve, the reason for which is not known at present. However, the normalization of the correlating variable c[η] with Martin constant K_M reduced all experimental data of the polymer samples to a common curve. The correlation of the viscosity data by either of the two methods seems to be possible in the case of the nonpolar flexible polymer, polybutadiene.     

Dilute solution viscosity properties of high molar mass poly(acrylonitrile‐co‐itaconic acid)

The intrinsic viscosities [η] and viscosity constants of high molar mass poly(acrylonitrile‐co‐itaconic acid) copolymer in DMF were obtained by the methods of Huggin, Fuoss, Martin and Schulz‐Blaschke. The values of [η] by averaging procedures suggested by Sakai were close to those from Huggins method. There was an abnormal positive deviation from the rectilinearity of the reduced viscosity (η_red) versus concentration (c) plot in all the cases in the dilute regime, which was attributed to the polyelectrolytic effect. This was further confirmed by the analysis by Fuoss method. The deviation from the Huggins dependence is discussed for a good solvent (DMF) alone and in the presence of a non‐solvent, methanol. The deviation cross‐over points c′ and c″ changed with molecular weight, and the concentration range greater than c″ and less than c* was taken for a more reliable determination of intrinsic viscosity. The non‐solvent played a key role in determining the polymer–polymer interactions. The Huggins coefficient increased and the cross‐over points c′ and c″ shifted to higher concentration regime as the mixed solvent became poorer. The inter‐ and intra‐polymer interactions increased in the presence of methanol. In poor solvent, the enhanced intramolecular interactions caused the polymer to shrink in size, causing a reduction in [η] and hydrodynamic volume. Copyright © 2003 Society of Chemical Industry     

Intrinsic viscosity of polymer solutions at high shear rates

Although low-shear intrinsic viscosity is a well-accepted tool for polymer characterization, it often happens (particularly with increasing molecular weights) that it is easier to detect the high-shear (second) Newtonian viscosity η₂ rather than its low shear counterpart. It has also been predicted that because of a higher degree of order, due to disentanglement and orientation, high-shear viscosity data should simplify the prevailing correlations. The possibility of using high-shear viscometric data for polymer characterization was examined by determining intrinsic viscosities for several polyisobutylene samples through extrapolation of the high-shear ultimate viscosity numbers, UVN, to zero concentration: [η]₂ = lim UVN_{C → 0} = lim_{C → 0} (η₂–η_s)/η_sC where η_s is the viscosity of the pure solvent. Five samples of unfractionated polyisobutylene (molecular weights of 1.1 × 10⁶–6.6 × 10⁶) in toluene, kerosene, decalin, and gas oil at concentrations of 0.05–2.4 g./dl. were studied. Higher dilution was avoided because of the problem of onset of turbulence. The absence of shear degradation was ascertained by measuring low-shear intrinsic viscosity data before and after the polymer was exposed to high-shear conditions. The data show two types of behavior: for the lower molecular weight samples in the low-viscosity solvents the UVN decreases linearly with dilution, and for the higher molecular weights and higher solvent viscosities the UVN increases with high dilution, i.e., shows an upturn effect. The first type of data can be successfully correlated with appropriate molecular weights by using a typical Mark-Houwink equation. The exponents in these relationships are in the range of 0.28–0.64, increasing systematically with decrease of solvent viscosity and independent of the “goodness” of the latter. The data that show an upturn effect are not currently amenable to reliable extrapolation techniques. The upturn, however, predicts the conformation of very flexible, isolated polymer chains in viscous solvents under conditions of high shear.     

Effect of solvent,concentration, and molecular weight on the rheological properties of polymer solutions

The zero-shear viscosity η⁰ of polychloroprene samples of different molecular weights over a wide range of concentration in good and poor solvents has been studied. Butanone and cyclohexane were used as θ solvents and benzene at two different temperatures (25 and 45.5°C) was used as two good solvents. The zero shear specific viscosity η in θ solvents, at the high concentration region is found to be higher compared to the values obtained in good solvents. whereas in a moderately concentrated region the values are just opposite in θ and good solvents. The high values of specific viscosity in poor solvent at the concentrated region have been explained as due to the fact that the efficiency of entanglements is much bigger in θ solvent than in good solvent. There are indications from our data that, at the crossover point concentration, the onset of entanglements begins, and from this concentration the entanglement begins to play a role in the viscosity. The superposition of viscosity data for each solvent was carried out by shifting vertically the curve along log η⁰ axis at constant concentration by a factor (M/M⁰)^3.4, where M⁰ is the molecular weight of the reference sample. The shift factor was found to be exactly proportional to M^3.4 in the range of higher concentration (beyond the crossover point concentration) and approximately to M in the lower concentration range (below the crossover point concentration). This showed that the relation η⁰ ∝ M^3.4 was obeyed by the present data. To correlate the viscosity data obtained at good and θ solvents, the method as given by Graessley has been employed, which has taken into account the contraction of dimensions of chains with concentration in good solvents. It has been observed that, though this approximate correction for variation of chain dimensions on correlating variable, C[η], has moved the correlations for θ and good solvents closer to a common curve, complete superposition of data has not been effected by this correction. On the other hand, the correlation of the data by the method given by Dreval and co-workers showed the plot of log{η/(C[η])} vs. C[η] produced a single curve for solutions of polychloroprene samples in two different θ solvents (butanone and cyclohexane) over the entire concentration range. But in the case of good solvents (benzene at 25°C and benzene at 45.5°C) the similar plots yielded, instead of one, two curves. However, the normalization of the correlating variable, C[η], by the Martin constant K_M, which is related to the flexibility of macromolecular chain and polymer-solvent interaction, reduced all data of the polymer samples to a common curve. This zero-shear viscosity master curve is valid for the entire range of concentration independent of molecular weight and the nature of solvents.     

Viscosity–molecular weight relationship for aminopropyl‐terminated poly(dimethylsiloxane)

Aminopropyl‐terminated poly(dimethylsiloxane) (ATPS) with different molecular weights was prepared by base‐catalyzed equilibration of octamethylcyclotetrasiloxane and 1,3‐bis(3‐aminopropyl)‐1,1,3,3‐tetramethyldisiloxane with different ratios. Their number‐average molecular weights (M_n) were determined by end–group analysis, and intrinsic viscosity ([η]) in toluene was measured with a Ubbelohde viscometer. A relationship between M_n and [η] was obtained for ATPS. For 1.0 × 10⁴ < M_n < 6.0 × 10⁴, it was in accord with [η]_{toluene,25°C} = 5.26 × 10^?2 M_n^0.587. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 975–978, 2001     

Dynamic rheological properties of polyetherimide/polyetheretherketone/liquid crystalline polymer ternary blends

The dynamic rheological properties of poly(etherimide)/poly(etheretherketone)/liquid crystalline polymer (LCP) ternary blends were measured in order to correlate these properties with the morphology obtained after extrusion. The viscosity radio, η_d/η_m, where η_d = disperse phase viscosity and η_m = matrix viscosity, had to be redefined. Below 50 wt% LCP, η_d = η_LCP, η_m = η_PEEK+PEI and η_d/η_m < 1. Above 50 wt% LCP, η_d = η_PEEK+PEI, η_m = η_LCP and η_d/η_m > 1. Fibrillar morphologies were obtained in both cases, except below a concentration of 20 wt% LCP. At low concentrations of LCP the ternary blends had lower viscosities than the component polymers, showing a flow promotion effect of the LCP on the PEI- and PEEK-rich phases.     

Synthesis of nitropyridine‐based π‐conjugated polymers and their chemical properties

π‐Conjugated poly(3‐nitropyridine‐2,5‐diyl) ( PPy‐3‐NO₂ ), poly(3,3′‐dinitro‐2,2′‐bipyridine‐5,5′‐diyl) ( PBpy‐3,3′‐diNO₂ ), and a poly(arylene ethynylene) type polymer consisting of a 3,3′‐dinitro‐2,2′‐bipyridine unit ( PAE‐1 ) were synthesized by Cu‐promoted Ullmann coupling reaction and Pd‐catalyzed coupling reaction. PPy‐3‐NO₂ and PAE‐1 were soluble in organic solvents such as DMSO, DMF, and chloroform, and gel permeation chromatography analysis showed a number average molecular weight (M_n) of 9,300 and 12,300, respectively. PPy‐3‐NO₂ gave intrinsic viscosity, [η], of 0.53 dL g^?1 in DMF. PBpy‐3,3′‐diNO₂ had somewhat lower solubility. The polymers exhibited a UV–vis peak at about 430 nm. PPy‐NO₂ received electrochemical reduction at ?1.5 V versus Ag⁺/Ag in acetonitrile, and gave an electrochemical redox cycle in a range from 0 to ?1.1 V versus Ag⁺/Ag in an aqueous solution. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1763–1767, 2006     

Comparison of various solvents for determination of intrinsic viscosity and viscometric constants for cellulose

Different solvents used to determine the intrinsic viscosity and the viscometic constants, a and K, published in the literature for cellulose, were compared. The various parameters affecting the viscometric constants were also evaluated. The main conclusions obtained from the experimental data available in the literature are that (1) the intrinsic viscosities in various solvents are ordered as follows: [η]_LiCl/DMAc > [η]_NH3/NH4SCN ≥ [η]_FeTNa > [η]_CED > [η]_Cadoxen > [η]_Cuoxam; (2) the reported intrinsic viscosities and molecular weights for cellulose are lower than the true value due to degradation of cellulose in the solvents; (3) the rate of degradation was the smallest in LiCl/DMAc and NH₃/NH₄SCN, moderate in cadoexn and FeTNa, and the highest in CED and cuoxam; (4) the plot of log K versus exponent a was linear and inversely related; (5) the curve was used for estimation of the constant K for cellulose in a solvent (NH3/NH4SCN) with a known exponent a; and (6) among various reported solvents, LiCl/DMAc and NH₃/NH₄SCN are advantageous over other solvents because of a complete dissolution of the polymer with a negligible reduction in its intrinsic viscosity. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2189–2193, 2002     

A single-mode rheological model for steady flows of polymer melts

The steady shear viscosity (η_s), the steady first normal stress coefficient (Ψ₁), the steady second normal stress coefficient (Ψ₂), and extensional viscosity (η_e) are four important parameters for polymer melts during polymer processing. In this article, we propose a stress and rate-dependent function to describe creation and destruction of polymer junctions. Moreover, we also introduce a movement expression to describe nonaffine movement of network junctions. Based on network theory, a nonaffine single-mode rheological model is presented for the steady flow of polymeric melts, and the equations of η_s, Ψ₁, Ψ₂, and η_e are derived from the model accordingly. Furthermore the dependences of η_s and η_e on model parameters are discussed for the model. Without a complex statistical simulation, the single-mode model with four parameters yields good quantitative predictions of the steady shear and extensional flows for two low density polyethylene melts reported from previous literature in very wide range of deformation rates. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Random orientation of in situ composites based on liquid‐crystalline polymers by compression moulding

In this study, randomly oriented in situ composites based on liquid‐crystalline polymers (LCPs) were prepared by thermal compression moulding. The LCP employed was a semi‐flexible liquid‐crystalline copolyesteramide with 30 mol% of p‐aminobenzoic acid (ABA) and 70 mol% of poly(ethylene terephthalate) (PET). The matrices were poly(butylene terephthalate) (PBT) and polyamide 66 (PA66). The rheological properties, compatibility and morphological structures of these in situ composites were investigated. The results showed that PA66‐LCP and PBT–LCP component pairs of the composites are miscible in the molten state, but partially compatible in the solid state. The ratios of viscosity, λ₁ = η_LCP/η_PA66 and λ₂ = η_LCP/η_PBT, are all greater than 1.0. However, the melt viscosity of the LCP/PBT and LCP/PA66 blend is much lower than that of PBT and PA66, and it decreases markedly with increasing LCP content. When the LCP/PA66 or LCP/PBT blends are compression moulded, the LCP/PA66 or LCP/PBT melts and flows easily due to their low viscosity, and the LCP phases in the melts deform easily along the flow directions, which are random. It leads to uniformly dispersed LCP micro‐fibres randomly orientation in the thermoplastic matrix due to the compatibility between the blending components. © 2003 Society of Chemical Industry     

Investigation of the interpolymer association between poly(vinyl alcohol) and poly(sodium styrene sulfonate) in aqueous solution

A viscosimetric method has been used to study the interpolymer association between poly(vinyl alcohol) (PVA) and poly(sodium styrene sulfonate) (PSSNa) in aqueous solution. At constant molecular weight of PSSNa, it was found that, the PVA and PSSNa associations were improved with the decrease of molecular weight of PVA and the decrease of its hydrolysis degree. The measurement of intrinsic viscosity [η] and the determination of Huggins associative coefficient K_H of different PVA samples were used to select the most appropriate PVA sample, which leads to homogeneous polymer–polymer mixtures (PVA with hydrolysis degree 87–89%, molecular weight 124,000–186,000 g/mol, intrinsic viscosity [η] = 1.02 dL/g, and Huggins associative coefficient K_h.ass = 0.76). The obtained results show that the interpolymer association between PVA and PSSNa, in aqueous solution, is mainly due to intermolecular hydrogen bonds between hydroxyl groups of PVA and sulfonate groups of PSSNa. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis of star‐shaped poly(ϵ‐caprolactone) by samarium‐based tetrafunctional initiator and its dilute‐solution properties

An in situ–generated tetrafunctional samarium enolate from the reduction of 1,1,1,1‐tetra(2‐bromoisobutyryloxymethyl)methane with divalent samarium complexes [Sm(PPh₂)₂ and SmI₂] in tetrahydrofuran has proven to initiate the ring‐opening polymerization of ?‐caprolactone (CL) giving star‐shaped aliphatic polyesters. The polymerization proceeded with quantitative conversions at room temperature in 2 h and exhibited good controllability of the molecular weight of polymer. The resulting four‐armed poly(?‐caprolactone) (PCL) was fractionated, and the dilute‐solution properties of the fractions were studied in tetrahydrofuran and toluene at 30°C. The Mark–Houwink relations for these solvents were [η] = 2.73 × 10^?2M_w^0.74 and [η] = 1.97 × 10^?2M_w^0.75, respectively. In addition, the unperturbed dimensions of the star‐shaped PCL systems were also evaluated, and a significant solvent effect was observed. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 175–182, 2006     

Concentration dependence on viscosity of oligourethane diols

To obtain viscosity suitable for application, relatively low molecular weight polymers, i.e., oligomers, are used in the formulation of high solids coatings. To support this requirement, the concentration dependence of the viscosity of synthesized oligourethane diols in different solvents was analyzed using Erickson's models. By regression analysis, it was found that the correlation coefficients are fairly good and the plots of the residuals are more random. The weight intrinsic viscosity, [η_o], composed of the oligomer component, O_5[η]o, and the oligomer-solvent interaction component, I_[η]o, was calculated from the intercept of the plot of 1/ln η_r vs. 1/o₀. The parameter I_[η]o, related to the solvent molar volume and the distance between the oligomer and solvent partial cohesion parameter coordinates, indicates the degree of interaction between the oligomer and solvent. The partial cohesion parameters of the oligomers obtained by the group-contribution method were used for calculating the interaction component of oligourethane diols. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1343–1351, 1997     

Dipolar polymeric compounds and their properties in the aqueous medium

Reactions between poly(4-vinylpyridine) and acrylic acid as well as poly(vinylimidazole) and the same acid led to polymers containing carboxybetaine repeating units with a percentage higher than 90%. Chemical structures and compositions of chemically modified polymers were established from their ¹H NMR and IR spectra. The solution properties of the two poly(carboxybetaines) were analyzed by potentiometric titrations and viscometric measurements. Deionized water as well as CaCl₂ and NaCl aqueous solutions of different concentrations were used as solvents. From potentiometric titrations with 0.5 M HCl, the apparent pK_a values were determined using Henderson–Hasselbach equation. These values are strongly depended of the solvent nature. Thus, both poly(carboxybetaines) have the lowest pK_a values when deionized water was used as solvent. Therefore, the lowest binding ability of the H⁺ by COO⁻ groups occurs in this solvent.The viscometric measurements revealed that reduced viscosity values are non-responsive towards the polymer solution concentrations irrespective of the used solvent (i.e., deionized water or NaCl and CaCl₂ aqueous solutions). Therefore, the behaviour of these carboxybetaine macromolecules in the above-mentioned solvents is that of hung up hard spheres. Consequently, the intrinsic viscosity values were calculated according to the Einstein–Simha equation applicable for such systems. The [η] versus salt solution concentration plots show a decreasing part in the concentration range from 0 to 0.05 M that is followed by a slow [η] increasing.In 0.5 M HCl both poly(carboxybetaines) exhibit the viscometric polyelectrolyte behaviours because of their shift to the corresponding cationic polyelectrolytes.     

Viscosity of polypropylene oxide solutions over the entire concentration range

An empirical equation is presented which describes polymer solution viscosity, η, over the entire concentration range from a knowledge of intrinsic viscosity, [η], Huggins constant, k′, and bulk flow viscosity of polymer, η₀. The equation is: \documentclass{article}\pagestyle{empty}\begin{document}$ \frac{{\eta _{sp}}}{{C[\eta]}} = \exp \left\{{\frac{{{\rm k'[}\eta {\rm]C}}}{{1 - bC}}} \right\} $\end{document} where solution viscosity, η, is contained in η_sp. No arbitrary parameters are invoked since b can be evaluated at bulk polymer (C = polymer density) where everything else is known. The equation accurately portrays the viscosity of polypropylene oxide (PPG 2025) from infinite dilution to bulk polymer in a very good solvent (benzene) and in a somewhat poorer (～ θ) solvent (methylcyclohexane). The hydrodynamic consequences of the thermodynamic interactions between polymer and solvent are reflected in the constants. This equation should be applicable to other polymer/solvent systems, and thus be immediately useful to those working with concentrated polymer solutions.     

Water-soluble copolymers. VI. Dilute solution viscosity studies of random copolymers of acrylamide with sulfonated comonomers

Dilute solution viscosity of a series of random copolymers of acrylamide (AM) with sodium-2-acrylamido-2-methylpropane sulfonate (NaAMPS) and with sodium-2-sulfoethylmethacrylate (NaSEM) has been studied using a four-bulb shear dilution capillary viscometer. The hydrodynamic volume of the copolymers in aqueous media was determined as a function of salt concentration, temperature, shear rate, and time. A linear relationship was observed between the intrinsic viscosity [η]₀ and the reciprocal of the square root of ionic strength in sodium chloride solutions, with salt concentrations varying from 0.043M to 0.257M. Negative temperature coefficients for [η]₀ indicate a decrease in the hydrodynamic volume of the ionic polymer molecules with increasing temperature. The relative zero-shear-intrinsic-viscosity change in distilled water to 0.257M sodium chloride aqueous media is used to elucidate viscosity–structure relationships. A maximum value is reached for this parameter at a composition of about 30 mol % of ionic comonomers for AM–NaAMPS and AM–NaSEM copolymer series.     

Zum Verhalten von Polyamidcarbonsäuren aus Pyromellithsäuredianhydrid und Benzidin in Lösung. II. Einfluß von Triäthylamin auf die Viskosität der Lösungen von Polyamidcarbonsäure in Dimethylacetamid

By addition of triethylamin (TEA) to a dilute solution of poly(amic acid) in dimethylacetamide (DMA) a strong increase of the reduced specific viscosity (η_sp/c) was observed. This can be explained by coil-widening caused by electrostatic forces between -COO^?-groups on the polymer chains. The ions are formed by the following proton transfer reaction: The dependence of the η_sp/c-values on the polymer concentration and the slope of the (η_sp/c)/c-curves (measured in DMA) are principially similar to those observed with polyelectrolytes in aqueous solutions. In contrast to the aqueous systems the η_sp/c-values in DMA do not pass through a maximum with increasing addition of base, but move asymptotically toward certain limiting values. The characteristic run of the viscosity-titration-curves is due to the fact, that in this case the neutralisation of the poly(amic acid) is carried out in an aprotic solvent with a base (TEA) which is incapable to dissociate itself. Therefore an excess of TEA favours the formation of ions according to the above equilibrium but does not increase the ionic strength of the solution. The ionic character of the discussed mechanisms is confirmed by corresponding electrolytic conductivity measurements. A comparison of the viscosity-titration-curves of poly(amic acid) and polymethacrylic acid shows the strong effect of the primary chain structure (stiffness of the chain) on the degree of coil widening.     

A novel determination technique of polymer viscosity-average molecular weights with flow piezoelectric quartz crystal viscosity sensing

A new method for the determination of polymer viscosity-average molecular weights was developed with flow piezoelectric quartz crystal (PQC) viscosity sensing. The experimental setup with a 9 MHz AT-cut quartz crystal and a flow detection cell was constructed and shown to be able to give highly reproducible data under the temperature of 25 ± 0.1°C and the fluid flow rate of 1.3–1.6 mL/min. A response model for PQC in contact with dilute polymer solutions (concentration <0.01 g/mL) was proposed in which the frequency change from the pure solvent, Δf_s, follows Δf_s = −k₆η_l^1/2 + k₇, where η_l is the absolute viscosity of dilute polymer solution and k₆ and k₇ are the proportionality constants. This model was examined with poly(ethylene glycol) samples (PEG-20000 and PEG-10000) under the aforementioned experimental conditions using water as solvent. The result was Δf_s = −1587η_l^1/2 + 1443. Based on this model, the method for the determination of polymer viscosity-average molecular weights, M_η, by flow PQC viscosity sensing was described and examined with an unknown poly(vinyl alcohol) (PVAL) sample. The new method proved to be an attractive and promising alternative for the determination of polymer molecular weights based on the good agreement between the molecular weight determined by the new method (M_η = 58600) for the unknown PVAL sample with that determined by the conventional capillary viscosity method. The new method has some advantages over the conventional viscosity method; for examples, operation is simpler and more rapid; the instruments required are cheaper and portable; the needed sample quantity is smaller; and the experimental setup constructed can be used in continuous measurement. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 63–69, 2001     

Spectrophotometric behavior of polyvinylpyrrolidone in aqueous solutions. II. The effects of denaturing agents

Electronic spectral behavior of aqueous polyvinylpyrrolidone solutions have been investigated by UV-vis spectrophotometry. n → * electronic excitations of the polymer were observed to shift longer wavelengths with a variety of denaturing agents. The shifting effect of denaturing agents on the λ_max increased in the order guanidinium carbonate ≡ guanidinium sulfate > guanidinium chloride > urea. Intrinsic viscosities of different concentrations of aqueous solutions of polyvinylpyrrolidone with the same denaturing agents have also been determined. Intrinsic viscosity number, [η], of polymer solutions decreased with the addition of denaturing agents. The slope, k_H[η]², of the polymer was also observed to decrease in the presence of denaturing agents. Shift to the longer wavelengths and decrease in the viscosity characteristics can be explained by the break of the molecular association between the polymer and the water molecules. © 1997 John Wiley & Sons, Inc. J Appl Polm Sci 65:1307–1311, 1997