Effects of the thermal history and concentration on the aggregation of Erwinia gum in an aqueous solution

The aggregation of Erwinia (E) gum in a 0.2 M NaCl aqueous solution was investigated by multi‐angle laser light scattering and gel permeation chromatography (GPC) combined with light scattering. The GPC chromatograms of five fractions contained two peaks; the fractions had the same elution volume but different peak areas, suggesting that aggregates and single chains coexisted in the solution at 25 °C. The apparent weight‐average molecular weights (M_w) of the aggregates and single chains for each fraction were all about 2.1 × 10⁶ and 7.8 × 10⁴, respectively. This indicates that the aggregates were composed of about 27 molecules of E gum in the concentration range used (1.0 × 10⁻⁶ to 5.0 × 10⁻⁴ g/mL). The weight fraction of the aggregates (w_ag) increased with increasing concentration, but the aggregates still existed even in an extremely dilute solution. The fractionation process and polymer concentration hardly affected the apparent aggregation number but significantly changed w_ag. The E‐gum M_w decreased sharply with an increase in temperature. When the E‐gum solution was kept at 100 °C, w_ag decreased sharply for 20 h and leveled off after 100 h. Once the aggregates were decomposed at a higher temperature, no aggregation was observed in the solution at 25 °C, indicating that the aggregation was irreversible. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1352–1358, 2000     

Aggregation and disaggregation of Aeromonas gum in an aqueous solution under different conditions

The aggregation and disaggregation of Aeromonas (A) gum, an acidic heteropolysaccharide, were investigated by viscometry, a fluorescent probe, and gel permeation chromatography combined with laser light scattering techniques in aqueous solutions containing desired NaCl at different temperatures. The A gum had a strong tendency of aggregation and high viscosity in the aqueous solutions. The weight‐average molecular weight, z‐average radius of gyration, weight‐average molar number (w_ag), and apparent aggregation number (N_ap) of the aggregates were investigated and discussed. The results indicated that there were three regions that corresponded to three kinds of aggregates and two transition temperatures at about 35 and 75 °C in the disaggregation course. When the temperature was higher than 75 °C, the w_ag hardly changed, and there was still a certain amount of aggregates even at 100 °C, indicating that the aggregates were difficult to disrupt completely. Moreover, the aggregation was thermally irreversible. Decreasing polysaccharide concentration reduced the content of the aggregate. However, N_ap remained constant around 20, independent of the polysaccharide concentration in a 0.5 M NaCl aqueous solution at 25 °C. At a salt concentration greater than or equal to 0.05 M, the aggregation was almost independent of the salt concentration used here. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2644–2651, 2000     

RHEOLOGICAL BEHAVIOR OF ERWINIA GUM IN AQUEOUS SOLUTION*

Erwinia (E) gum, an extracellular polysaccharide, is composed of fucose, galatose, glucose andglucuronic acid. Its viscosity behavior was investigated by a low-shear-rate multiball viscometer and arotational viscometer. Its weight-average molecular weight M_w and intrinsic viscosity [η] in 0.2 mol/L NaClaqueous solution were measured by light scattering method at 35℃and viscometry at 25℃and found to be1.06×10~6 g/mol and 1050 mL/g, respectively, and its aggregates in aqueous solution were proved by gelpermeation chromatography (GPC). These results indicated that E gum in water has exceedingly highviscosity and exhibits Binham fluid behavior, owing to its aggregation. The viscosity of E gum decreasedwith increasing temperature, and the turning point appeared at 38℃for dilute solution and 80℃forconcentrated solution suggesting that the aggregates of E gum in water started to disaggregate under thesetemperatures. In addition, the aggregates can be disrupted by adding either acid or base. The experimentalresults indicated that the E gum is a good thickening agent, and its fluid behavior is similar to xanthan.     

LIGHT SCATTERING OF POLYSACCHARIDE FROM LACQUER IN AQUEOUS SOLUTION

The polysaccharide having weight-average molecular weight M_w=1. 09×10~5, isolated from the sap of lac trees (Vietnam), was separated into 12 fractions by aqueous-phase preparative gel permeation chromatography. The molecular weights and molecular weight distributions of the fractions were measured in aqueous 0.08M KCl/0.01 M NaAc and 0.4M KCl/0.05M NaAc at pH =7. 6 by light scattering, viscometry and gel permeation chromatography. The Mark-Houwink equation in aqueous 0.08M KCl/0.01M NaAc at 30℃was found to be [η]= 2.28×10~(-2) M_w~(0.52) (cm~3/g), which indicated the polysaccharide chain in the aqueous solution to be a spherical random coil.     

Structure of gum arabic and its configuration in solution

Gum arabic was found to have an osmotic molecular weight of 250,000, in agreement with earlier determinations. A molecular weight of 365,000 was found by light scattering, somewhat higher than obtained earlier by sedimentation equilibrium analysis but lower than light-scattering values reported by other investigators. The M?_w/M _n ratio, 1.46, is quite low in gum arabic. The angular dependence of light scattering exhibited the upward curvature to be expected of a spherical molecule and a radius of gyration of about 100 A. or less, as estimated from a Zimm plot. Fractionation of the original gum arabic was done by precipitation of a 0.5% solution in aqueous 0.5% NaCl with acetone. Comparison of the curves of viscosity versus molecular weight and the estimated radius of gyration shows that the hydrodynamic volume is less than that of branched dextran of similar molecular weight. The electroviscous effects for gum arabic in aqueous solution were shown by reduced viscosity curves at various acidities and in salt. The degree of dissociation was calculated for each pH level. The minimum intrinsic viscosity was found in 0.04N HCl where the degree of dissociation at pH 1.5 was found to be 0.049. When the acidity was increased, further reduction in viscosity was found to be negligible. Routine determination of the viscosity and molecular weight of the fractions was done in 0.35M NaCl at pH 10 to which 0.25% of the sodium salt of ethylenediaminetetraacetic acid was added as a sequestrant. The intrinsic viscosity in this solvent was nearly as low as in 0.04N HCl. Light-scattering dissymmetries in water and in 0.35M NaCl plus EDTA at pH 10 were similar, 1.13 and 1.09, respectively, which showed that actual expansion of the macroion is not the cause of the large increase in viscosity of gum arabic when the ionic strength of the solvent is reduced. Periodate oxidation of the polymer confirmed the existence of a 1–3-linked backbone of galactose. Subsequent treatment of the oxidized polymer with alkali reduced the osmotic molecular weight to 45,000 but failed to remove oxidized side branches. The oxidized polymer was fractionated by gel permeation chromatography and the intrinsie viscosity–molecular weight relation compared with relations for fractions of the unoxidized polymer and for other branched and crosslinked polymers.     

CHARACTERIZATION OF MOLECULAR MASS OF SIX WATER-SOLUBLE POLYSACCHARIDE -PROTEIN COMPLEXES FROM GANODERMA TSUGAE MYCELIUM

Six water-soluble polysaccharide-protein complexes coded as GM1, GM2, GM3, GM4, GM5 and GM6 wereisolated from the mycelium of Ganoderma tsugae by extracting with 0.2 mol/L phosphate buffer solution at 25, 40 and80℃, water at 120℃, 0.5 mol/L aqueous NaOH solution at 25 and 65℃, consecutively. Their chemical components wereanalyzed by using IR, GC, HPLC and ~(13)C-NMR, and some new results were obtained. The four samples GM1, GM2, GM3and GM4 are heteropolysaccharide-prote in complexes, in which, α- (1→3) linked D-glucose is the major monosaccharidewhile galactose, mannose and ribose are the secondary ones. GM5 and GM6 are β-(1→3)-D-glucan-protein complexes. Theprotein content increased from 32% to 69% with the progress of isolation. Weight-average molecu1ar mass M_w and theintrinsic viscosity [η] of the GM samples in 0.5 mol/L aqueous NaCl solution at 25℃ were measured systematically by laserlight scartering (LLS), size exclusion chromatography (SEC) combined with LLS, and viscometry. The M_w of GM1 to GM6are 35.5, 46.8, 58.9, 41.6, 3.3 and 22.0×10~4, respectively. The conformation and molecular mass of the two fractions of sample GM5 were characterized satisfactorily by SEC-LLS without further fractionation.     

Behavior of cellulose in NaOH/Urea aqueous solution characterized by light scattering and viscometry

Cellulose was dissolved in 6 wt % NaOH/4 wt % urea aqueous solution, which was proven by a ¹³C NMR spectrum to be a direct solvent of cellulose rather than a derivative aqueous solution system. Dilute solution behavior of cellulose in a NaOH/urea aqueous solution system was examined by laser light scattering and viscometry. The Mark–Houwink equation for cellulose in 6 wt % NaOH/4 wt % urea aqueous solution at 25 °C was [η] = 2.45 × 10^?2 weight‐average molecular weight (M_w)^0.815 (mL g^?1) in the M_w region from 3.2 × 10⁴ to 12.9 × 10⁴. The persistence length (q), molar mass per unit contour length (M_L), and characteristic ratio (C_∞) of cellulose in the dilute solution were 6.0 nm, 350 nm^?1, and 20.9, respectively, which agreed with the Yamakawa–Fujii theory of the wormlike chain. The results indicated that the cellulose molecules exist as semiflexible chains in the aqueous solution and were more extended than in cadoxen. This work provided a novel, simple, and nonpollution solvent system that can be used to investigate the dilute solution properties and molecular weight of cellulose. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 347–353, 2004     

Coagulation and flocculation measurements by photon correlation spectroscopy — colloidal SiO2 bare and covered by polyethylene oxide

With photon correlation spectrometry (PCS) the diffusion coefficients, average diameters and polydispersities of colloidal particles can be determined in dilute aqueous suspensions. In this study PCS is used to follow the coagulation and flocculation of silica particles. Electrolyte solution added to suspensions of bare particles and of particles covered with adsorbed polyethylene oxide layers induces aggregation. The rate constants of aggregation are evaluated by the second-order Smoluchowski theory with the assumptions of spherical aggregated particles and volume proportional light-scattering amplitude. Adsorbed PEO layers of molar mass lower thanM _w=160000 decrease the critical flocculation concentration and the flocculation states and rate constants for bare and covered particles are the same at high electrolyte concentrations. Polymer layers of high molar mass (M _w=325000, 900000) reducved at full coverage the rate constants and stabilize the suspensions even at high electrolyte concentrations. At low coverage adsorption of high molar mass polymers results in the same values as of low molar mass PEO. The correlation between rate constants and hydrodynamic PEO layer thicknesses demonstrates the steric influence of the tails of the adsorbed macromolecules on stability and flocculation.Dedicated to Prof. Dr. Joachim Klein on the occasion of his 60th birthday     

Solvent Role on Cobalt(II) Dioxygen Carriers Based on Simple Polyamine Ligands

The kinetics and thermodynamics of O₂ addition to Co^II complexes containing the simple triamine ligand (L) diethylenetriamine (=N‐(2‐aminoethyl)ethane‐1,2‐diamine; dien) or N,N″‐dimethyldiethylenetriamine (=N‐methyl‐N′‐[2‐(methylamino)ethyl]ethane‐1,2‐diamine; dmdien) in the aprotic solvent dimethyl sulfoxide (DMSO) were studied by UV/VIS spectrophotometry, potentiometry, and O₂ absorption measurements. A parallel investigation on the anaerobic formation of Co^II complexes with dmdien, as well as on their reactivity towards O₂, was carried out in aqueous 0.1M NaClO₄ solution. [CoL]²⁺ and [CoL₂]²⁺ were the common species formed under anaerobic conditions in both aqueous and DMSO solutions. Under aerobic conditions, O₂ adducts of different stoichiometry were formed: a superoxo complex [CoL₂O₂]²⁺ in DMSO and dimeric species in H₂O. The role of the reaction medium as well as effects of N‐alkylation of the triamine ligand in the formation and reactivity of the [Co^II(triamine)] complexes are discussed.     

Influence of small uncharged but amphiphilic molecules on the lower critical solution temperature of highly homogeneous N‐alkylacrylamide oligomers

The influence of small alkylamines with increasing carbon chain length (≤5) on the temperature‐induced precipitation of two N‐alkylacrylamide oligomers, poly‐N‐isopropylacrylamide [PNIPAAm; weight‐average molecular weight (M_w ) = 1600 g/mol] and poly‐N,N‐diethylacrylamide (PDEAAm; M_w = 4000 g/mol), from an aqueous solution was investigated. The alkylamines in question were too small to form micelles in the classical sense but were capable of premicellar aggregation. PNIPAAm was prepared by radical polymerization in the presence of a chain‐transfer agent and, therefore, carried a carboxylic acid end group. The structure was heterotactic. PDEAAm was prepared by anionic polymerization and, therefore, carried a butyl end group. The structure was predominately isotactic. The solubility of the oligomers was investigated by cloud‐point measurements and differential scanning calorimetry. In addition, pyrene was used as a fluorescent polarity probe. Alkylamines up to C₂ depressed the lower critical solution temperature (LCST) of PNIPAAm, whereas higher alkylamines first depressed the LCST and at higher concentrations elevated it. The LCST minimum showed a clear dependence on the alkyl chain length and structure. For PDEAAm, only pentylamine addition resulted in an LCST minimum. Otherwise, the LCST was raised. When the critical self‐association concentration (CSAC) of the alkylamines in water was compared to the critical association concentration (CAC) in aqueous oligomer solutions, PDEAAm, but not PNIPAAm, stabilized mixed aggregates (CAC < CSAC). The transition enthalpy of PNIPAAm decreased with an increasing alkylamine concentration and became 0 above the CAC. For PDEAAm, no transition endotherm could be recorded above an alkylamine concentration of 0.1 M. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4218–4229, 2000     

Effect of the degree of deacetylation and the substitution of carboxymethyl chitosan on its aggregation behavior

The aggregation behavior of carboxymethyl chitosan (CM‐chitosan) with various degrees of deacetylation (DD) and substitution (DS) was characterized with viscometry, gel permeation chromatography (GPC), and GPC coupled with laser light scattering (GPC‐LLS). The results indicate that CM‐chitosan has a strong tendency to form aggregates in aqueous solution and the aggregation behavior depends on DD and DS values. The apparent aggregation number (N_ap), the gyration radius (R_g), and the weight fraction of the aggregates (F_a) reached maximum at a DD value of 50%, then decreased, with the DD value deviating from 50%. A higher DS value helped to form aggregates; when the DS value increased from 0.65 to above 1.0, N_ap and R_g increased sharply. The dependence of the refractive index increment (dn/dc) on the DD and DS values was related to variation of the charge density and the hydrophobic interaction along the molecular chains. The conformations of CM‐chitosan aggregates were studied by the LLS method. The aggregates showed a spherical shape, and the chain stiffness increased with introduction of the acetyl groups. The DS value had no clear influence on the chain conformation that was observed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 296–305, 2005     

Potentiometric and spectrometric study: Copper(II), nickel(II) and zinc(II) complexes with potentially tridentate and monodentate ligands

Equilibrium and solution structural study of mixed-metal-mixed-ligand complexes of Cu(II), Ni(II) and Zn(II) with L-cysteine, L-threonine and imidazole are conducted in aqueous solution by potentiometry and spectrophotometry. Stability constants of the binary, ternary and quaternary complexes are determined at 25 ±1°C and in I= 0.1 M NaClO₄. The results of these two methods are made selfconsistent, then rationalized assuming an equilibrium model including the species H₃A, H₂A, A, BH, B, M(OH), M(OH)₂, M(A), MA(OH), M(B), M(A)(B), M₂(A)₂(B), M₂(A)₂(B-H), M¹M²(A)₂(B) and M¹M²(A)₂(B-H) (where the charges of the species have been ignored for the sake of simplicity) (A = L-cysteine, L-threonine, salicylglycine, salicylvaline and BH = imidazole). Evidence of the deprotonation of BH ligand is available at alkalinepH. N₁H deprotonation of the bidentate coordinated imidazole ligand in the binuclear species atpH > 70 is evident from spectral measurements. Stability constants of binary M(A), M(B) and ternary M(A)(B) complexes follow the Irving-Williams order.     

Kinetic study of the radical polymerization behavior of N‐(1‐phenylethylaminocarbonyl)methacrylamide

Polymerization of N‐(1‐phenylethylaminocarbonyl)methacrylamide (PEACMA) with dimethyl 2,2′‐azobisisobutyrate (MAIB) was kinetically studied in dimethyl sulfoxide (DMSO). The overall activation energy of the polymerization was estimated to be 84 kJ/mol. The initial polymerization rate (R_p) is given by R_p = k[MAIB]^0.6[PEACMA]^0.9 at 60 °C, being similar to that of the conventional radical polymerization. The polymerization system involved electron spin resonance (ESR) spectroscopically observable propagating poly(PEACMA) radical under the actual polymerization conditions. ESR‐determined rate constants of propagation and termination were 140 L/mol s and 3.4 × 10⁴ L/mol s at 60 °C, respectively. The addition of LiCl accelerated the polymerization in N,N‐dimethylformamide but did not in DMSO. The copolymerization of PEACMA(M₁) and styrene(M₂) with MAIB in DMSO at 60 °C gave the following copolymerization parameters; r₁ = 0.20, r₂ = 0.51, Q₁ = 0.59, and e₁ = +0.70. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2013–2020, 2005     

A 13C-NMR spectral study of cellulose and glucopyranose dissolved in the NH3/NH4SCN solvent system

The ¹³C-NMR chemical shifts of a cellulose with a DP_w of 23 dissolved in the NH₃/NH₄SCN solvent system were found to be very similar to those of cellulose dissolved in DMSO (cellulose oligomers), in the LiCl/DMAC system and in the N-methylmorpholine N-oxide/DMSO system. It was concluded from this that cellulose does not react with the NH₃/NH₄SCN solvent. It was found, however, that glucose reacts with the solvent at C-1 to form β-D -glucopyranosy-lamine. Separation of this compound from the solvent resulted in another compound which was determined to be β,β-di-D -glucopyranosylamine. The compounds β-D -glucopyranosylamine, N-acetyl-2,3,4,6-tetra-O-acetyl-β-D -glucopyranosylamine, β,β-di-D -glucopyranosylamine, α,β-di-D -glucopyranosylamine, 2,3,4,6,2′,3′,4′,6′-octa-O-acetyl-α,β-di-D -glucopyranosylamine were all synthesized and the ¹³C-NMR chemical shifts of these compounds are reported. It was also found that for the low-DP cellulose sample which was used the reducing end group existed and had reacted with the solvent to form an amine at C-1.     

Study of Phase Separation of Poly(N-isopropylacrylamide-co-styrene) Aqueous Solutions with Rayleigh Scattering Technique

A thermally sensitive copolymer, poly(N‐isopropylacrylamide‐co‐styrene) [P(NIPAM‐co‐St)] (M_n?9.5×10⁵ g/mol and M_w/M_n?1.51) was synthesized by soap‐free emulsion polymerization. The phase separation of the copolymer in water was investigated by Rayleigh scattering (RS) technique. The RS spectra revealed the transition of molecular conformation and the aggregation of molecular chains in the course of phase separation. The coil‐to‐globule and globule‐to‐coil transitions of P(NIPAM‐co‐St) chains were found in one heating‐and‐cooling cycle. By means of Avrami formula, apparent activation energy of phase separation of P(NIPAM‐co‐St) aqueous solutions was estimated. Moreover, a model was proposed to describe the phase separation process.     

Solutions of cellulose in DMAc + LiCl: migration of the solute in an electrical field

For solutions of cellulose (Solucell, M_w=230 kg mol^–1) in the mixed solvent DMAc (N,N-dimethylacetamide) + LiCl, it is demonstrated by means of an electrolysis cell, subdivided into six compartments, that cellulose migrates to the anode. This observation is interpreted in terms of a field-induced opening of associations between the [DMAc]_xLi⁺ complex and the [cellulose]Cl^– complex. This understanding is corroborated by the observed changes in the positions of the menisci in the electrode compartments of the electrolysis cell. Contrary to expectations, the rate of cellulose transport does not depend on its molar mass, at least under the present conditions.     

ESI-MS analyses of lake dissolved organic matter in light of supramolecular assembly

A high-performance size-exclusion chromatography (SEC) system was coupled on-line to an electrospray ionization (ESI) interface to detect gas-phase ions by an API 365 LC/MS/MS triple quadrupole analyzer. The SEC fractions of a strongly coloured freshwater solution containing dissolved organic matter-humic substances (DOM-HS) were screened both by UV₂₅₄ and by ESI mass spectrometry (ESI-MS) in the full-scan mode within the m/z range of 100–2,900 amu in negative and positive polarities. The ESI-MS spectra were also collected by direct infusion of the DOM-HS solution in both polarities. ESI-MS spectra did not primarily favour low mass compounds, and negative and positive total ion chromatograms were parallel to the SEC elution profile obtained by UV₂₅₄ detection from DOM-HS solution. The UV₂₅₄ detection overestimated the SEC portion of higher size/mass solutes and underestimated that of solutes of smaller sizes/masses as compared with the total ion chromatogram intensities in negative or positive polarities. The change of mass-weighted and number-weighted average sizes/masses (M _w and M _n) of different SEC fractions was fairly small, in contrast to UV₂₅₄ detection, with increasing elution volume. A reasonable explanation for the great differences between M _w and M _n values, obtained by UV₂₅₄ and ESI-MS detections for eight different SEC fractions, seems to be a supramolecular-type association of relatively small components through weak dispersive forces. M _n values obtained by vapour-pressure osmometry for different SEC fractions were to some extent analogous with those of negative and positive ESI-MS. The shapes obtained by either negative or positive polarities and calculated M _w and M _n values indicated a close structural similarity between each SEC fraction. Positive ion and negative ion spectra of different humic fractions represented quite similar components, and there was no evidence for noteworthy occurrence of multiply charged ions being able to lower mass distributions of negative ion spectra. The effect of nitrogen on the mass spectra seemed to be unimportant, and the weak ions observed at even m/z values correspond most likely to the ¹³C counterparts of the more abundant ¹²C odd ions. No uncontrolled ESI fragmentation was observable and humic solutes seemed to be quite heat-resistant. Direct infusion of the untreated DOM-HS solution and statistical calculation verified that the SEC-separated different fractions really represent distinct entities of the original DOM-HS mixture. ESI-MS results support the opinion that the structural composition of humic solutes in their original combined mixture resembles supramolecular-type associations of smaller molecular size entities possessing similar structural functionalities.     

Novel,biodegradable, functional poly(ester‐carbonate)s by copolymerization of trans‐4‐hydroxy‐L‐proline with cyclic carbonate bearing a pendent carboxylic group

Water‐soluble poly(ester‐carbonate) having pendent amino and carboxylic groups on the main‐chain carbon is reported for the first time. This article describes the melt ring‐opening/condensation reaction of trans‐4‐hydroxy‐N‐benzyloxycarbonyl‐L ‐proline (N‐CBz‐Hpr) with 5‐methyl‐5‐benzyloxycarbonyl‐1,3‐dioxan‐2‐one (MBC) at a wide range of molar fractions. The influence of reaction conditions such as catalyst concentration, polymerization time, and temperature on the number average molecular weight (M_n) and molecular weight distribution (M_w/M_n) of the copolymers was investigated. The polymerizations were carried out in bulk at 110 °C with 3 wt % stannous octoate as a catalyst for 16 h. The poly(ester‐carbonate)s obtained were characterized by Fourier transform infrared spectroscopy, ¹H NMR, differential scanning calorimetry, and gel permeation chromatography. The copolymers synthesized exhibited moderate molecular weights (M_n = 6000–14,700 g mol^?1) with reasonable molecular weight distributions (M_w/M_n = 1.11–2.23). The values of the glass‐transition temperature (T_g) of the copolymers depended on the molar fractions of cyclic carbonate. When the MBC content decreased from 76 to 12 mol %, the T_g increased from 16 to 48 °C. The relationship between the poly(N‐CBz‐Hpr‐co‐MBC) T_g and the compositions was in approximation with the Fox equation. In vitro degradation of these poly(N‐CBz‐Hpr‐co‐MBC)s was evaluated from weight‐loss measurements and the change of M_n and M_w/M_n. Debenzylation of 3 by catalytic hydrogenation led to the corresponding linear poly(ester‐carbonate), 4 , with pendent amino and carboxylic groups. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2303–2312, 2004     

Excluded volume study of a sulfonate-containing polyelectrolyte in salt solutions

Chain characteristics of a linear sulfonate-containing homopolymer, sodium poly(3-methacryloyloxypropane-1-sulfonate), in aqueous salt solutions (ionic strength, C_s = 0.01N to 5N NaCl) have been investigated by light scattering and intrinsic viscosity. The molecular weight (M?_w)–viscosity relation can be well described by the Mark–Houwink and the Stockmayer–Fixman equations. The coil is highly expanded even in the most concentrated NaCl solution (6N), and no 1:1 electrolyte was found to precipitate this polymer. A linear relation was observed between the viscosity expansion factor, α^3η, and (M?_w/C_s)^1/2. Examination of the data in terms of theories for excluded volume and hydrodynamic interaction suggests that the coil experiences dominant hydrodynamic interaction, corresponding to a nondraining coil, and the second virial coefficient and coil expansion at high C^s can be correlated by the Flory–Krigbaum–Orofino equation. Results for this polymer are compared with those for other polyelectrolytes, and are discussed in terms of chain structure, flexibility, and hydrophobicity.     

RAFT polymerization of tertiary sulfonium zwitterionic monomer in aqueous media for synthesis of protein stabilizing double hydrophilic block copolymers

The reversible addition-fragmentation chain-transfer (RAFT) polymerization of a tertiary sulfonium-containing zwitterionic monomer (N-acryloyl-L-methionine methyl sulfonium salt: A-Met[S⁺]-OH) was performed in aqueous media in the presence of a water-soluble chain-transfer agent (CTA). Several parameters, such as the radical initiator, nature of the salt used as an additive, polymerization temperature, and solvent (water, buffer solution, and mixed solvents), were studied. The polymerization of A-Met(S⁺)-OH in acetate buffer using a trithiocarbonate-type CTA having two carboxylic acid moieties proceeded in a controlled fashion at 45°C, as confirmed by the low polydispersity of the products (M _w/M _n < 1.1) and pre-determined molecular weights. Poly(ethylene glycol)-based macro-CTA was also employed for the polymerization of A-Met(S⁺)-OH in mixed solvents (H₂O/EtOH and H₂O/DMF = 70/30 vol%) to afford novel nonionic-zwitterionic double hydrophilic block copolymers. The chain extension of the hydrophilic poly(N,N-dimethylacrylamide) macro-CTA with A-Met(S⁺)-OH was well controlled in pure water under the appropriate conditions, resulting in the formation of block copolymers with “as-designed” chain structures and relatively low dispersities (M _w/M _n < 1.3). The resulting sulfonium-containing double hydrophilic block copolymers having optimal nonionic/zwitterionic balance were efficient protein-stabilizing agents.