Synthesis and microstructural characterization of low to high molecular weight poly(vinylphosphonic acid)s: effect of molecular weight and temperature on acidity and polyelectrolyte behavior

Poly(vinylphosphonic acid) (PVPA) was synthesized by free radical polymerization of vinylphosphonic acid (VPA) in different solvents. Bromotrichloromethane as a chain transfer agent (CTA) was used in some experiments to control molecular weight of the PVPA. The effects of solvent type and initiator and CTA concentrations on the microstructure, molecular weight and stereoregularity of the resulting PVPA was extensively investigated by FTIR, ¹HNMR, ³¹PNMR and elemental analysis. Polymers with a number-average molecular weight (M_n) in the range of 1550 to 42,190 gmol^?1 were prepared. High molecular weight PVPA with M_n of 42,190 gmol^?1 was obtained from aqueous solution polymerization of VPA with initiator/monomer molar ratio of 0.16/100 at 80°C. Molecular weight decreased with increasing the concentration of initiator and CTA. ¹HNMR spectra were used to investigate tetrad sequences for the methylene protons of PVPA, from which stereochemical information of the polymer chain was obtained. Tetrad sequences were also calculated by Bernoullian probabilities. Moreover, the percent of head-to-head and tail-to-tail irregularities of the resulting PVPA were obtained to be in the range of 16.6–58% depending on the reaction conditions. The PVPA synthesized in acetic anhydride as a solvent had highest amount of the irregularities due to the high reaction rate, which does not allow controlling the structure. Furthermore, due to the importance of PVPA in the proton exchange membranes (PEMs), the effects of molecular weight and temperature on the acidity and titration behavior of PVPA polyelectrolyte were investigated. It was found that molecular weight has no significant effect on the acidity and dissociation of protons at operational conditions of degree of dissociation lower than 0.5. It was also found that by increasing the temperature, pH values were decreased, meaning that dissociation of protons and consequently the proton conductivity of PVPA membranes can be affected by temperature. Titration behavior of PVPA also showed that the PVPA has a behavior similar to a monoprotic acid.     

Evaluation of thermo‐viscosity parameters of dextran in polar and nonpolar solvent

Some thermo‐viscosity parameters like Viscosity‐molecular weight constant (K), the short‐range parameter, (A) and long‐range parameter (B) have been evaluated for the polymer “Dextran” of three different molecular weights (M?_w = 19,500, 75,000, and 250,000) in three different solvents like 6 (M) aqueous urea, 2 (M) aqueous glycine, and 50% aqueous glucose at temperatures ranging from 25 to 50°C. The study reveals that the viscosity‐molecular weight constant (K) decreases with increase in temperature for polar solvents like aqueous urea and aqueous glycine. The value of “K” increases with the rise in temperature within the range of 25 to 35°C in case of a nonpolar solvent aqueous glucose and then “K” decreases with the increase in temperature within the range of 40 to 50°C for the nonpolar solvent aqueous glucose. The short‐range parameter (A) shows the same trend as shown by “K” and the long‐range parameter “B” exhibits no definite trend with the variation of temperature. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 440–452, 2001     

Solution properties of dextran in water and in formamide

We investigate here solution properties of the common polysaccharide dextran (with various molecular weight fractions: T70, T110, T500, and T2000) in aqueous and in formamide solutions at 20°C and 40°C, as obtained from viscosity measurements. Dextran behaves as a random coil in water and formamide solutions on the basis of the Mark-Houwink-Sakurada constant being in the range 0.5< α < 0.8 and the molecular weight dependence of the hydrodynamic coil radius, R_coil ∼ M_W^1/2. Dextran segments interact more favorably with the formamide solvent molecules than with water, as attested by higher intrinsic viscosity, R_coil, and hydrodynamic expansion factor α_η values in formamide compared to aqueous solutions. This can be attributed to formamide offering more readily available sites (CO and NH₃) to form hydrogen bonds with dextran. Apparently the stronger cohesive forces (reflected in higher surface tension σ and solubility parameter δ values) between water molecules make it harder for dextran to break them, thus the dextran coils swell less in this medium. As the temperature increases from 20°C to 40°C, dextran is driven toward theta conditions in both water and formamide solutions. Upon heating, the polymer segments interact less with the solvent molecules and adopt a less expanded conformation in the solution; the solvent quality decreases, and the coils contract. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Spectrophotometric study of dissociation of p-nitroanilinium ion in urea-water solvents at 25°C—effect of solvent

The dissociation constants (K_s) of p-nitroanilinium ion have been determined at 25°C spectrophotometrically in urea-water mixtures containing 11.52, 20.31, 29.64 and 36.83 wt.% urea. Standard free enrgies of transfer, ΔG°_t(B) of the base p-nitroaniline from water to the mixed solvents have been evaluated at 25°C from the measurement of solubilities. Strength of the acid, p-nitroanilinium ion increases with the increase in proportion of urea in the solvents, the rate of increase being sharp at the begining. The solvent effect on the dissociation of the acid: δ(ΔG°) = 2.303 RT [p(K_s) ? p(K_w)] is unusually large in urea—water solvent system compared to those in aqueous mixtures containing methanol, ethylene glycol, acetone and acetic acid. Solvent effect has been discussed in terms of the standard free energies of transfer (ΔG°_t) from water to aqueous urea solvents of the uncharged base (B), the hydrochloride of the base (BHCl) and the hydrochloric acid (HCl) and also of the individual species involved in the dissociation process. The corresponding data in ethylene glycol—water solvent system obtained from literature are also compared. The difference in solvent effects on the dissociation in the two solvent systems has been shown to result from the contrasting behaviour of ΔG°_t(H⁺)?ΔG°_t(BH⁺) arising from the difference in the extent of the solute—solvent interactions.     

Urea/NaOH aqueous solution as new solvent of aeromonas gum

Aeromonas (A) gum, an acidic heteropolysaccharide, formed aggregates easily in NaCl aqueous solution. A novel solvent of the A gum, which can prevent aggregation, was found to be 0.20M urea/0.25M NaOH aqueous solution. The weight‐average molecular weight (M_w), radius of gyration (〈s²〉^1/2), and intrinsic viscosity ([η]) of the samples were determined in 0.20M urea/0.25M NaOH aqueous solution at 25°C by light scattering (M_w, 〈s²〉^1/2) and viscometry ([η]). The values of M_w, 〈s²〉^1/2, and [η] were close to those in 0.20M lithium chloride/dimethylsulfoxide, in which the A gum exists as a semiflexible single chain, implying the same conformation for the A gum in 0.20M urea/0.25M NaOH aqueous solution. The results revealed that 0.20M urea/0.25M NaOH aqueous solution is a good solvent, which effectively avoids the aggregates of the A gum in aqueous solution. Moreover, it can be used to investigate the solution properties and chain conformation of water‐insoluble polysaccharides or the polysaccharides that are easily aggregated in aqueous systems. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1710–1713, 2005     

Unperturbed molecular dimensions and the theta temperature of dextran in dimethylsulfoxide (DMSO) solutions

Summary The unperturbed molecular dimensions of dextran samples have been determined in dimethylsulfoxide (DMSO) solutions from intrinsic viscosity measurements at different temperatures. The unperturbed dimension parameter, K_o, has been calculated from extrapolation methods.The unperturbed root-mean-square end-to-end distance, <r²>_o ^1/2, found for the polymer samples in DMSO solutions, indicate that the polymer coils are contracted. This distance varies from 3.25 × 10⁻⁷ cm to 2.94 × 10⁻⁷ cm for the sample T 40 and from 8.28 × 10⁻⁷ cm to 7.48 × 10⁻⁷ cm for the sample T 500, in the chosen solvent as the temperature is raised from 25°C to 45°C. In the system of dextran/DMSO, the long-range interaction parameter, B, was also determined and a significant decrease is observed between 25°–45°C. The theta temperatures, Θ, were obtained as Θ= 327.25 K, Θ= 327.41 K and Θ= 323.38 K from the temperature dependence of the interaction parameter in Kurata-Stockmayer-Fixman, Berry and Inagaki-Suzuki-Kurata equations, respectively. Received: 19 January 1998/Revised version: 9 June 1998/Accepted: 10 June 1998     

Dissolution of starch in urea/NaOH aqueous solutions

Dissolution of starch in urea/NaOH aqueous solutions was studied by using polarizing microscope and viscometry. The experimental results revealed that starch could dissolve in urea (2–20 wt %) and NaOH (10–1 wt %) aqueous solutions at temperature ranging from ?12 to 25 °C, where the optimized dissolution condition was in the aqueous solution of mixed urea 14% and NaOH 4% at 0 °C for 30 min or above. Under the conditions, the starch solubility could be 99.0 and 92.1% as the starch weight percent was 1 and 10%, respectively. Measurements for the molecular weight and amylose content of the starch before and after the dissolution indicated that there was no serious degradation during the process. The results from determinations of X‐ray diffraction, Fourier transform infrared, and rapid visco analysis revealed that the recovered starch from the starch solutions was an amorphous solid with a part of V‐type pattern (single‐helix). The urea/NaOH aqueous solvent may have potential significance for starch processing and modification. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43390.     

Charged membranes prepared by SPEEK of very low degree of sulfonation

Novel charged membranes were prepared with sulfonated poly(ether ether ketone) (SPEEK). Methylsulfonic acid was used as solvent to accommodate the very low degree of sulfonation of the SPEEK. Membranes were prepared by immersion phase inversion method, using coagulation baths of different composition and temperature. Low molecular weight and negatively charged dye molecules were used as model solutes to test the nanofiltration (NF) performance of the membranes. Higher than 93% rejection of the two dye molecules, Rose Bengal and Reactive Brilliant Red, was observed at normal operating temperature. A permeate flux as high as 497 L m^?2 h^?1 and higher than 90% of solute rejection at 80°C was achieved in the NF of Reactive Brilliant Red aqueous solution, in contrast to a flux of 226 L m^?2 h^?1 and about 78% of solute rejection at the same temperature in the case of Rose Bengal solute. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Properties of aqueous salt solutions of poly(vinylpyrrolidone). II. Polymer dimensions and thermodynamic quantities

The unperturbed dimensions and thermodynamic parameters of poly(vinylpyrrolidone) (PVP) have been studied in aqueous salt solutions, e.g. phosphates, mono- and dihydrogen phosphates, carbonates, sulphates of sodium and potassium. Values of K₀ ( = [η]_ΘM^-1/2, where [η]_Θ is intrinsic viscosity at the theta temperature and M is molecular weight) with M_w = 78 000 g mol^-1 were found to range from 4·63×10^-4 to 5·56×10^-4 dl g^-1, and root-mean-square end-to-end distances, 〈r²〉₀^1/2, ranging from 1·61×10^-6 to 1·68×10^-6cm were evaluated. Values of the characteristic ratio, C_n, the steric parameter, σ, and the enthalpy and the entropy of dilution parameters, χ_H and χ_S, have also been calculated, and the interaction parameter was found to be χ-0·5<-0·001 for aqueous salt solutions of PVP. ©1997 SCI     

Hydrodynamic properties of aqueous dextran solutions

The hydrodynamic performance of aqueous dextran solutions, including the rheological and thixotropic properties, were investigated. Three kinds of dextrans with different molecular weights were employed to examine the effects of the molecular weight, concentration, temperature, and so forth on the hydrodynamic properties of aqueous dextran solutions. The results showed that an aqueous solution of a dextran with a high molecular weight of 5.223 × 10⁵ at a high concentration of 30 wt % had pseudoplastic properties, in contrast to the conclusions of other researchers finding that aqueous dextran solutions were Newtonian liquids. The viscosity of the aqueous dextran solutions decreased with temperature, and the activation energy was calculated to be 16,849.2 J/mol with a 10 wt % dextran (weight‐average molecular weight = 5.223 × 10⁵) solution. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Caffeine Molecular Imprinted Microgel Spheres by Precipitation Polymerization

Imprinted uniform microgel spheres were prepared by precipitation polymerization. Acetonitrile was used as the dilute solvent with MAA as the monomer, EDMA as the crosslinker and caffeine as the print molecule. Comparison of caffeine adsorption on molecular imprinted and blank microgel spheres was made. Langmuir model was used to fit the adsorption data. It was found that the caffeine imprinted microgel spheres show specific binding sites to the target molecules. A binding study of caffeine on imprinted microgel spheres was made by Scatchard analysis; the dissociation constants (K_D) and the maximum binding capacity were K_D= 1.84×10⁻⁴mol/L,Q _max = 16.98 μmol/g for high affinity binding site and K_D=1.33×l0⁻³ mol/L, Q_max=46.84 μmol/g for lower affinity binding site, respectively This microgel spheres can be useful affinity adsorbents in further applications.     

Structure and physical properties of methylcellulose synthesized in NaOH/urea solution

Summary A series of methylcellulose (MC) samples were successfully synthesized using dimethyl sulphate (DMS) as a methylation reagent in 7 wt% NaOH/12 wt% urea aqueous solution through controlling the reaction conditions. The MC samples were characterized with ¹H and ¹³C NMR, gas chromatography (GC), ultraviolet spectroscopy, viscometry and solubility measurement. Analysis of GC showed that there were no unsubstituted anhydroglucose units (AGU) and few completely substituted AGU along the molecular chains of the MC samples, and there was a uniform distribution of methyl substitution along the MC molecular chains. The stability of 7 wt% NaOH/12 wt% urea solution for the methylation of cellulose was investigated for the first time. The results showed 2 wt% cellulose solution in the 7 wt% NaOH/12 wt% urea solvent was almost stable at room temperature, and little decomposition of the cellulose molecular chains occurred during the methylation reaction.     

Effect of solvent on the free radical polymerization of N,N‐dimethylacrylamide

The free radical photopolymerization of N,N‐dimethylacrylamide was investigated at 25 °C and at low conversion in several solvents ranging from weak polar solvents to water. The polymerization is strongly accelerated in the aqueous medium, with the polymerization rate increasing one order of magnitude when the solvent is changed from an organic one to aqueous medium. These results were analysed in terms of macroradical conformation, effect of medium viscosity, aggregate formation, hydrogen bond formation and effect of temperature. The results suggest that the main factor that controls the polymerization rate is a kinetic effect due to the hydrogen bonding between the amide carbonyl group and water molecules. Also, we found that polymer properties, such as the thermodynamic quality of the solvent for the polymer backbone and molecular weight control using transfer agents, are influenced by the intermolecular hydrogen bonding. Copyright © 2010 Society of Chemical Industry     

Physical solubility of hydrogen sulfide in several aqueous solvents

The solubility of hydrogen sulfide in several aqueous solutions was measured over the temperature range 25°C to 60°C. The solvents investigated in this work include 0 to 50% aqueous solutions of polyethylene glycol, ethylene glycol, methyldiethanolamine and diethanolamine. The amine solutions used in this work were neutralized by the addition of hydrochloric acid in order to suppress the hydrogen sulfide reaction (H₂S → H⁺ + HS^?) so that only the physical solubility of hydrogen sulfide would be measured. The solubility data determined in this work are expressed in terms of Henry's law. The Henry's law constants found in this work were correlated well by a particularly simple empirical formula based on the molecular weight of the solvent.     

Synthesis and characterization of an amphiphilic graft copolymer with a poly(acrylic acid) backbone and n-octylphenyl polyoxyethylene side chains

A novel, well-defined, amphiphilic graft copolymer was synthesized by the free-radical copolymerization of acrylic acid and an amphiphilic macromonomer, n-octylphenyl polyoxyethylene acrylate. This acrylic copolymer was characterized by IR and ¹H-NMR. The number-average molecular weight was determined by gel permeation chromatography to be 4.37 × 10⁴ (weight-average molecular weight/number-average molecular weight = 1.23). The graft copolymer exhibited good solubility in water and high surface activity at much lower concentrations. The molecules of the AA–C₈PhEO₁₀Ac copolymer formed polymolecular micelles at 3.0 × 10⁻⁴ g/mL. The aggregation of the copolymer was examined in aqueous solution by measurement of the fluorescence of 2-p- toluidinylnaphthalene 6-sulfonate as a fluorescent probe. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Ein Beitrag zur Temperaturabhängigkeit der Viskosität wäßriger Polyethylenglykollösungen

An automatic falling ball viscosimeter of the Höppler type with pneumatic rotary actuator and electrical time measuring was used to determine the viscosity of aqueous polyethylene oxide solutions between the temperature range of 20 to 80°C. For these investigations polyethylene oxide fractions were used having molecular weights of 600 to 20 000 g/mol. The concentration of the solutions was up to 5 base mol-% of polymers. Parameters according to Eyring- and Vogel-equations were evaluated by the measured viscosity data. This evaluation led to the result, that the parameter T₀ decreased linearly with increasing molecular weight and concentration. The effect was explained by the water-structure-breaking by means of the polymer molecules. The logarithmic intrinsic viscosity in the solutions containing water and polyethylene oxide of a molecular weight of 6 000 g/mol decreased rapidly with the temperature and led to a value of ?8.6 · 10^?3 for d In [η]/dT.     

Swelling of poly(methyl methacrylate) thin films in low molecular weight alcohols

The effects of solvent size, temperature, and polymer molecular weight on the swelling of poly(methyl methacrylate) (PMMA) thin films in low molecular weight alcohols were investigated using an in situ ellipsometer. Apparent activation energies were indicative of non-Fickian diffusion, although optical data showed substantial Fickian character for swelling in methanol and moderate Fickian character in ethanol. Penetration rates were strongly dependent on the solvent molar volume for methanol, ethanol, and isopropanol, but 1-butanol and 2-pentanol had rates similar to isopropanol. The effective cross sections of these longer molecules are similar to isopropanol, and this apparently explains the similar penetration rates. The effect of polymer molecular weight (MW) on methanol penetration rates (21–27°C) was investigated with monodisperse PMMA (M_n = 6.4–40.0 × 10⁴ g/mol). A minimum at intermediate MW was observed. Isopropanol swelling rates (45–52°C) were insensitive to MW. The swelling data were also used to determine parameters for transport models that describe the swelling of thin polymer films.     

The unperturbed molecular dimensions of poly(ethylene oxide) in aqueous solutions from intrinsic viscosity measurements and the evaluation of the theta temperature

Intrinsic viscosity measurements were carried out on five well characterized fractions of poly(ethylene oxide) in aqueous solutions at 24.9°, 34.9°, and 45.5°C. The Stockmayer-Fixman extrapolation was applied to the data: it yields the unperturbed dimensions K₀ of the chain. The unperturbed root-mean-square end-to-end distance $\text{〈}\text{R}\text{?}{}^2\text{〉}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}{}_0$ calculated for the polymer fractions in water indicate that the polymer molecules are expanded in this solvent as the temperature is raised. The temperature coefficient of unperturbed dimension, $\text{d In}\text{〈}\text{R}\text{?}{}^2\text{〉}{}_0\text{d}\text{t}\text{= 0.024}\text{K}{}^{\mathrm{?1}}$, calculated for poly(ethylene oxide) in water using the present data is about 100 times higher than the literature values of 0.23 (±0.02) × 10^?3 K^?1 and 0.2 (±0.2) × 10^?3 K^?1, respectively, obtained from force-temperature (‘thermoelastic’) measurements on elongated networks of the polymer in the amorphouse state and form viscosity measurements on this polymer in benzene. A value of θ=108.3°C was obtained from the temperature dependence of the interaction parameter B in the Stockmayer-Fixman equation.     

Conformation of poly(ethylene oxide) in the solid state,melt and solution measured by Raman scattering

The Raman spectrum of poly(ethylene oxide) (PEO) $\text{M}\text{?}{}_{\mathrm{w}}\text{= 3 × 10}{}^6$ and 6 × 10³ has been measured in bulk as a function of temperature and in aqueous and chloroform solution as a function of solvent concentration. The spectral features are assigned to particular isomeric configurations and the changes on melting are found to be consistent with a helix-coil transition. In both solvents the ordered nature of the polymer is largely lost at a critical concentration, approximately 50% by weight; residual ordering in dilute aqueous solution is lost and the random coil configuration attained only above the melting temperature. The wavenumber change of the 862 cm^?1 mode as a function of water concentration showed formation of a complex involving three water molecules and was consistent with a simple H-bonding model. The differences between the spectra in the two solvents are explained by this H-bonding. The results are in general agreement with n.m.r. work.     

Molecular size and aggregation behavior of Erwinia gum in aqueous solution

Erwinia (E) gum, a stabilizer and thickening agent of food, is composed of glucose, fucose, galactose, and glucuronic acid (1 : 0.1 : 0.05 : 0.3 by molar ratio). The apparent weight‐average molecular weight M_w and intrinsic viscosity [η] in 0.2 M NaCl aqueous solution were measured to be 7.83 × 10⁵ and 268 mL g⁻¹, respectively, by light scattering and viscometry. The aggregation behavior of E gum in aqueous solution was investigated by gel permeation chromatography (GPC) and dynamic light scattering. The results showed that 7.5% E gum exists as an aggregate, whose diameter is 12 times greater than single‐stranded chain, in aqueous solution at 25°C, and the aggregates' content decreased with increasing temperature or decreasing polymer concentration. The aggregates at higher temperature were more readily broken than in exceeding dilute solution. GPC analysis proved that a significant shoulder, corresponding to a fraction of higher molecular weight due to chain aggregation, appeared in the chromatogram of E gum in 0.05 M KH₂PO₄/5.7 × 10⁻³ M NaOH aqueous solution (pH 6.0) at 35°C, and decreased with increasing temperature, finally disappeared at 90°C. The disaggregation process of E gum in aqueous solution can be described as follows: with increasing temperature, large aggregates first were changed into the middle, then disrupted step by step into single‐stranded chains. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1083–1088, 2000