Chromatographic study of the conformational behavior of graft copolymers with a broad distribution of grafting densities in dilute solutions in selective solvents for grafts

A graft copolymer of poly(4-methylstyrene-graft-2-vinylpyridine) was prepared by the living “grafting onto” method. Its molecular weight and composition was analyzed by size-exclusion chromatography, liquid chromatography under limiting conditions of desorption, ¹H NMR, and light scattering. The results indicated a non-negligibly broad distribution of grafting density. Its conformational behavior was studied by reversed phase liquid chromatography with gradient elution. Targeted studies provided two discrete base-line separated fractions. Their compositions were estimated by pyrolysis gas chromatography. The results suggest that distinct chain conformations (differing in grafting density and interacting differently with stationary phase) exist in studied solutions and can be separated by well-tuned chromatographic techniques. Experimental data were analyzed and interpreted on the basis of theoretical and computer studies of the conformational behavior of graft copolymers in selective solvents.     

Hydrodynamic Radius Characterization of a Vinyl-Type Polynorbornene by Size-Exclusion Chromatography with a Static and Dynamic Laser Light Scattering Detector

Both absolute molecular weight and molecular sizes (radius of gyration and hydrodynamic radius) of a vinyl-type polynorbornene eluting from size-exclusion chromatography columns were determined by combined with a static and dynamic laser light scattering detector. The hydrodynamic radius of polymer fraction eluting from size-exclusion chromatography columns was obtained from dynamic laser light scattering measurements at only a single angle of 90° by introducing a correction factor. According to the scaling relationship between molecular sizes and molecular weight and the ratio between radius of gyration and hydrodynamic radius, the vinyl-type polynorbornene took a random coil conformation in 1,2,4-trichlorobenzene at 150 °C.     

Production and characterization of pullulan from beet molasses using a nonpigmented strain of Aureobasidium pullulans in batch culture

The production of pullulan from beet molasses by a pigment-free strain of Aureobasidium pullulans on shake-flask culture was investigated. Combined pretreatment of molasses with sulfuric acid and activated carbon to remove potential fermentation inhibitors present in molasses resulted in a maximum pullulan concentration of 24 g/L, a biomass dry wt of 14 g/L, a pullulan yield of 52.5%, and a sugar utilization of 92% with optimum fermentation conditions (initial sugar concentration of 50 g/L and initial pH of 7.0). The addition of other nutrients as carbon and nitrogen supplements (olive oil, ammonium sulfate, yeast extract) did not further improve the production of the exopolysaccharides. Structural characterization of the isolated polysaccharides from the fermentation broths by ¹³C-nuclear magnetic resonance spectroscopy and pullulanase digestion combined with size-exclusion chromatography confirmed the identity of pullulan and the homogeneity (>93% dry basis) of the elaborated polysaccharides by the microorganism. Using multiangle laser light scattering and refractive index detectors in conjunction with high-performance size-exclusion chromatography molecular size distributions and estimates of the molecular weight (M _w =2.1−4.1×10⁵), root mean square of the radius of gyration (R _g =30−38 nm), and polydispersity index (M _w /M _n =1.4−2.4) were obtained. The fermentation products of molasses pretreated with sulfuric acid and/or activated carbon were more homogeneous and free of contaminating proteins. In the concentration range of 2.8−10.0 (w/v), the solution’s rheologic behavior of the isolated pullulans was almost Newtonian (within 1 and 1200 s⁻¹ at 20°C); a slight shear thinning was observed at 10.0 (w/v) for the high molecular weight samples. Overall, beet molasses pretreated with sulfuric acid and activated carbon appears as an attractive fermentation medium for the production of pullulan by A. pullulans.     

Star-shaped polymers by living cationic polymerization. VIII. Size and shape of star poly(vinyl ether)s determined by dynamic light scattering and computer simulation

The sizes and shapes of star-shaped poly(vinyl ether)s, prepared by living cationic polymerization, were studied by dynamic light scattering and molecular mechanics-based computer simulation. The hydrodynamic radii (R_h) of star poly(isobutyl vinyl ether)s (4a; M?_w = 2.2 × 10⁴ ? 1.7 × 10⁵) determined by dynamic light scattering were in the range from 30 to 90 Å in tetrahydrofuran or ethyl acetate. Consistent with the expected multiarmed architecture of 4a, the radius for a given number (f) of arms per molecule increased with the degree of polymerization [DP(arm)] of the arms, and for a fixed DP(arm), the radius increased with f. The relationship between arm number f and the “shrinking” factor h [R_h(star)/R_h(linear)] was consistent with multibranched structures for the star polymers. These results are supported by those for the molecular weight itself; the apparent weight-average molecular weights by size-exclusion chromatography are less than the corresponding absolute values by static light scattering. The dependence of h on f suggests some degree of asymmetry in the star shape. Similar results were also obtained by the computer simulation of potential energy-minimized conformations of the arms, which implied almost spherical but slightly asymmetric shapes. The computer simulation also demonstrated that the star polymer (4b) with pendant hydroxyl groups in the arms is smaller in size than the corresponding alkyl (isobutyl) (4a) with the identical arm number and arm degree of polymerization. © 1995 John Wiley & Sons, Inc.     

Polymerization of vinyl chloride with organolithium compounds. V. Fractionation and solution properties of high molecular weight poly(vinyl chloride)

A sample of high molecular weight poly(vinyl chloride) (PVC) was fractionated by classical precipitation fractionation and gel-permeation chromatography (GPC) on a preparative scale. The fractions thus obtained were characterized by light scattering, viscometry, and by the GPC method. The measured weight-average molecular weights M?_w, intrinsic viscosity [η], and polydispersity index M?_w/M?_n values were used for the determination of the Mark-Houwink equation, [η] = KM^a, for PVC in cyclohexanone (CHX) at 25°C valid for molecular weights from 100,000 to 625,000.     

SIZE EXCLUSION CHROMATOGRAPHIC COLUMN PACKED WITH REGENERATED CELLULOSE GELS*

Microporous regenerated cellulose gel particles were prepared by mixing cellulose cuoxam with silk fibroin aspore former, and the mean pore size and pore volume of the pallicles were 525 nm and 7.27 mL g~(-1), respectively. Apreparative size-exclusion chromatography (SEC) column (550 mm×20 mm) packed with the cellulose gel particles wasused for the fractionation of two polysaccharides Dextran 07 (M_w = 7.14×10~4, d= 1.7) and Dextran 50(M_w = 50.5×10~4,d = 3.8) in water phase. The fractionation range of the stationary phase covered M_w from 3×10~3 to 1.1×10~6. The dailythroughput was 2.9 g for Dextran 07 (D07) and 4.3 g for Dextran 50 (D50) with a flow-rate of 1.5 mL min~(-1). The fractionsobtained by using the SEC were analyzed by an analytical SEC combined with laser light scattering (LLS), and thepolydispersity indices of fractions for Dextran 07 and Dextran 50 were determined to be 1.34-1.57 and 1.53-3.36,respectively. The preparative SEC is a simple, rapid, and suitable means not only for the fractionation of polysaccharides inwater but also for other polymers in organic solvents.     

Dynamic and electrophoretic light scattering of poly(dimethyldiallylammonium chloride) in salt-free solutions

Dynamic and electrophoretic light scattering were used to study the diffusion and electrophoretic mobility of poly(dimethyldiallylammonium chloride) as a function of polymer molecular weight in salt-free solutions. Two relaxation modes characterized as fast diffusion (D_f) and slow diffusion (D_s) were obtained from dynamic light scattering. Although the slow diffusion coefficient D_s strongly depends on molecular weight (M_w), the fast diffusion coefficient D_f was found to be independent of M_w over the range in the study. The fast diffusion was considered as the diffusion of a part of the polymer chain; the slow diffusion was interpreted by multichain diffusion. Electrophoretic light scattering results in the salt-free solution show that the electrophoretic mobility of the polymer is independent of M_w. © 1996 John Wiley & Sons, Inc.     

Speciation of nickel,copper, zinc,and manganese in different edible nuts: a comparative study of molecular size distribution by SEC–UV–ICP–MS

Molecular size distribution patterns of Cu, Mn, Ni, and Zn were determined in several nut species by size-exclusion liquid chromatography (SEC) coupled on-line to UV and inductively coupled plasma mass spectrometry (ICP–MS) for detection. The molecular weight (MW) fractionation of the different metals was performed with a Superdex Peptide column, injecting 100 L of the extracted solutions. The association of the elements with different MW fractions was observed with sequential detection by UV and ICP–MS. Various separation conditions were evaluated to obtain proper resolution and reproducible results with the size-exclusion column. Complete MW information of the elemental fractions in the nut samples was obtained within a retention time of 30 min. Fractionation of the above mentioned elements was done in nine different nut species commonly found in commercial markets. Variability of the fractionation patterns for two different extraction media, 0.05 mol L^–1 NaOH and 0.05 mol L^–1 HCl, was evaluated for every nut sample. Differences in the elemental fractionation patterns were found depending on the extraction procedure, nut species, and the type of element studied. It was also observed that the elements studied showed predominant association with high MW fractions when extracted with basic solution whereas with acidic extraction media only low MW fractions were obtained.     

Solution characterization of the novel organometallic polymer poly(ferrocenyldimethylsilane)

A series of four well‐defined poly(ferrocenyldimethylsilane) (PFS) samples spanning a molecular weight range of approximately 10,000–100,000 g mol⁻¹ was synthesized by the living anionic polymerization of dimethyl[1]silaferrocenophane initiated with n‐BuLi. The polymers possessed narrow polydispersities and were used to characterize the solution behavior of PFS in tetrahydrofuran (THF). The weight‐average molecular weights (M_w ) of the polymers were determined by low‐angle laser light scattering (LALLS), conventional gel permeation chromatography (GPC), and GPC equipped with a triple detector (refractive index, light scattering, and viscosity). The molecular weight calculated by conventional GPC, with polystyrene standards, underestimated the true value in comparison with LALLS and GPC with the triple detection system. The Mark–Houwink parameter a for PFS in THF was 0.62 (k = 2.5 × 10⁻⁴), which is indicative of fairly marginal polymer–solvent interactions. The scaling exponent between the radius of gyration and M_w was 0.54, also consistent with marginal polymer–solvent interactions for PFS in THF. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 3032–3041, 2000     

Solution properties of poly(dimethyl siloxane)

The solution properties of poly(dimethyl siloxane) (PDMS) were studied with light scattering (LS), gel permeation chromatography/light scattering (GPC/LS), and viscometry methods. PDMS samples were fractionated, and the weight‐average molecular weights, second virial coefficient, and the z‐average radius of gyration of each fraction were found according to the Zimm method with the LS technique. In this work, the molecular weight range studied was 7.5 × 10⁴ to 8.0 × 10⁵. Molecular weights and molecular weight distributions were determined by GPC/LS. The intrinsic viscosities of these fractions were studied in toluene at 30 °C, in methyl ethyl ketone (MEK) at 20 °C, and in bromocyclohexane (BCH) at 26 °C and 28 °C. The Mark–Houwink–Sakurada relationship showed that toluene was a good solvent, and MEK at 20 °C and BCH at 28 °C were θ solvents for PDMS. The unperturbed dimensions were calculated with LS and intrinsic viscosity data. The unperturbed dimensions, expressed in terms of the characteristic ratio, were found to be 6.66 with different extrapolation methods in toluene at 30 °C. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2678–2686, 2000     

Molecular characterization of branched polysaccharides from Tremella fuciformis by asymmetrical flow field‐flow fractionation and size exclusion chromatography

To accurately characterize branched polysaccharides with high molecular weights from medicinal and edible mushrooms and identify the limitations of size exclusion chromatography, molecular characteristics of polysaccharides from Tremella fuciformis were determined and compared by asymmetrical flow field‐flow fractionation coupled with multiangle laser light scattering and refractive index detection, and size exclusion chromatography coupled with multiangle laser light scattering and refractive index detection, respectively. Results showed that molecular weights of three batches of T. fuciformis polysaccharides were determined as 2.167 × 10⁶ (TF1), 2.334 × 10⁶ (TF2), and 2.435 × 10⁶ Da (TF3) by size exclusion chromatography, and 3.432 × 10⁶ (TF1), 3.739 × 10⁶ (TF2), and 3.742 × 10⁶ Da (TF3) by asymmetrical flow field‐flow fractionation, as well as 3.469 × 10⁶ Da (TF1) by off‐line multiangle laser light scattering, respectively. Results suggested that size exclusion chromatography was unable to accurately characterize T. fuciformis polysaccharides, which may be due to its limitations such as shear degradation and abnormal coelution. Compared to size exclusion chromatography, asymmetrical flow field‐flow fractionation could be a better technique for the molecular characterization of branched polysaccharides with high molecular weights from medicinal and edible mushrooms, as well as from other natural resources.     

Stimuli‐responsive ampholytic terpolymers of N‐acryloyl‐valine,acrylamide, and (3‐acrylamidopropyl)trimethylammonium chloride: Synthesis,characterization, and solution properties

Low‐charge density ampholytic terpolymers composed of acrylamide (AM), (3‐acrylamidopropyl)trimethyl ammonium chloride (APTAC), and N‐acryloyl‐valine were prepared via free‐radical polymerization in 0.5 M NaCl to yield terpolymers with random charge distributions. Sodium formate (NaOOCH) was employed as a chain transfer agent during the polymerization to suppress gel effects and broadening of the molecular weight distribution (MWD). Terpolymer compositions were determined by ¹³C NMR spectroscopy. Terpolymer molecular weights (MWs) and polydispersity indices (PDIs) were obtained via size exclusion chromatography/multi‐angle laser light scattering (SEC‐MALLS). Intrinsic viscosity values determined from SEC‐MALLS data using the Flory–Fox relationship were compared with those determined by low‐shear dilute solution viscometry and found to be in good agreement. SEC‐MALLS experiments allowed examination of radius of gyration‐MW (R_g‐M) relationships and the Mark‐Houwink‐Sakurada intrinsic viscosity‐MW ([η]‐M) relationships for terpolymers. The R_g‐M and [η]‐M relationships indicated little or no excluded volume effects under SEC conditions indicating that the terpolymers were in near theta conditions in an aqueous buffer solution. Potentiometric titration experiments were performed in deionized (DI) water. These studies revealed that the apparent pK_a of the AMVALTAC terpolymers increases with increasing VAL content. The solution properties of low‐charge density ampholytic terpolymers have been studied as functions of solution pH, ionic strength, and polymer concentration. The charge‐balanced terpolymers exhibit polyampholyte behavior at pH values ≥ 6.5. As solution pH is decreased, these charge‐balanced terpolymers become increasingly cationic due to the protonation of the VAL repeat units. Charge‐imbalanced terpolymers generally exhibit polyelectrolyte behavior, although the effects of intramolecular electrostatic interactions (e.g., polyampholyte effects) on the hydrodynamic volume are evident at certain values of solution pH and salt concentration. The solution behavior of the terpolymers in the dilute regime correlates well with that predicted by various polyampholyte solution theories. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3125–3139, 2006     

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.     

Electrical conductivity of poly(vinyl chloride) obtained by photodehydrochlorination from laminated poly(vinyl chloride)/polypyrrole films

Poly(vinyl chloride) (PVC) has been converted to an electrically conductive structure by combined electrochemical and photochemical methods. PVC was cast on a polypyrrole (PPy) film electrode which had been electrochemically prepared. The PVC layer in the laminated PVC/PPy films was first dehydrochlorinated under the illumination of UV light, and the generated polyenes were subsequently doped with I₂ and FeCl₃. The maximum electrical conductivity achieved for such PVC film was 2.51 X 10^?2 and 8.63 10^?2 S cm^?1 after I₂ and FeCl₃ doping, respectively. The temperature dependence of the electrical conductivity showed different behavior in higher and lower temperature ranges. In the former (T > 243 K), the T^?1 law held, and the activation energy and bandgap were estimated as 0.25 and 0.49 eV, respectively. In the latter (T < 243 K), the conductivity mechanism followed the variable range hopping model (T^?1/4 law) in which the radius of the localized state wave function and the density of the localized states at the Fermi level were 1.25 × 10³ Å and 1.03 X 10¹⁵ eV^?1 cm^?3, respectively. © 1995 John Wiley & Sons, Inc.     

Depolymerization study of sodium hyaluronate by flow field-flow fractionation/multiangle light scattering

Thermal depolymerization of ultrahigh-molecular-weight (UHMW) sodium hyaluronate (NaHA) was studied systematically by using frit-inlet asymmetrical flow field-flow fractionation/multiangle light scattering/differential refractive index (FI-AFlFFF/MALS/DRI). FI-AFlFFF was utilized for the size separation of NaHA samples which had been thermally degraded for varied treatment times, followed by light-scattering detection to determine MW and structural information of degraded NaHA products. Analysis of NaHA products showed time-dependent depolymerization of raw molecules into smaller-MW components, as well as unfolding of compact structures of UHMW NaHA. To determine whether the observed decrease in MW of sodium hyaluronate originated from the chain degradation of UHMW molecules or from dissociation of entangled complex particles that may have been formed by intermolecular association, narrow size fractions (1 × 10⁷–6 × 10⁷ and >6 × 10⁷ MW) of NaHA molecules were collected during FlFFF separation and followed by thermal treatment. Subsequent FI-AFlFFF/MALS analysis of collected fractions after thermal treatment suggested that the ultrahigh-MW region (>10⁷ Da) of NaHA is likely to result from supermolecular structures formed by aggregation of large molecules.     

On-line measurement of the RMS radius of gyration and molecular weight of polyimide precursor fractions eluting from a size-exclusion chromatograph

The recent introduction of multiangle light-scattering detectors for size-exclusion chromatography has made possible the measurement of the root mean square radius of gyration (R_g) and molecular weight (M) of polymer fractions eluting from a size-exclusion chromatography column. The characterization of the dimensions of a polymer may be accomplished with only a few milligrams. The dimensions of a polyimide precursor prepared by the condensation of the meta-diethyl ester of pyromellitic dianhydride with para-phenylene diamine have been measured with this technique. The dependence of R_g on M across the distribution is compared with that predicted for a freely rotating chain, and with other similar polymers measured with hydrodynamic techniques.     

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     

Molecular weight and aggregation of Aeromonas gum treated with dimethyl sulfoxide in aqueous solution

Aeromonas (A) gum, an acidic hetero polysaccharide, in 0.2 M LiCl/dimethyl sulfoxide (DMSO) was fractionated satisfactorily according to the nonsolvent addition method. Eight fractions were chosen to examine their aggregation behavior in aqueous solution. The weight‐average molecular weight (M_w), radius of gyration 〈S²〉^1/2, and intrinsic viscosities [η] of the fractions in 0.2 M LiCl/DMSO and 0.5 M NaCl aqueous solution at 25 °C were measured by static light scattering and viscometry. The results indicated that the A gum was aggregated in 0.5 M NaCl aqueous solution at 25 °C, and the aggregates were broken in 0.2 M LiCl/DMSO. The apparent weight‐average aggregation number (N_ap) of the fractions increased with the process of fractionation, that is, N_ap increased from 1.1 to 15 with decreasing M_w of the single chain. The fractions obtained by treating with DMSO were more easily dissociated in the aqueous solution, and its N_ap was lower than that of the A gum fractions that were not treated with DMSO. Moreover, the A gum molecules with relatively low M_w aggregated easily to form a compact spherelike structure in the aqueous solution. Elemental analysis and ¹³C NMR spectroscopy indicated that DMSO was adsorbed on the A gum molecules caused by the fractionation program; DMSO not only prevented the polysaccharide aggregation but also increased the solubility. A model has been proposed to describe the aggregation behavior of the A gum chains with DMSO overcoat in the aqueous solution. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2269–2276, 2002     

Speciation of essential and toxic elements in edible mushrooms: size‐exclusion chromatography separation with on‐line UV–inductively coupled plasma mass spectrometry detection

Size‐exclusion liquid chromatography was coupled to UV and inductively coupled plasma mass spectrometry (ICP‐MS) for detection to perform elemental speciation studies on different edible mushrooms. Molecular weight (MW) distribution patterns of several elements among different fractions present in various edible mushrooms are presented. The association of the elements with the high and low MW fractions was observed using sequential detection by UV and ICP‐MS. Separation was performed using a Superdex 75 column. Variability of the fractionation patterns with three different extraction media (0.05 mol l^?1 NaOH; 0.05 mol l^?1 HCl; hot water at 60°C) was evaluated for mushroom species. A comparative elemental speciation study was performed in order to determine the differences in the fractionation patterns of silver, arsenic, cadmium, mercury, lead, and tin in Boletus edulis, Agaricus bisporus, and Lentinus edodes. Differences in the fractionation patterns of the elements were found to depend on the mushroom species and the extraction medium. Most of the elements were associated with high mw fractions. It was not possible to assess the trace metal contributions from the mushroom growth media. Copyright © 2004 John Wiley & Sons, Ltd.     

Dilute solution characterization of a POLA polyester

Samples of poly(4,4′-isopropylidenediphenylene 1,1,3-trimethyl-3-phenylindan-4′,5- dicarboxylate) were fractionated by the column-elution, temperature-gradient technique. Selected fractions, covering a 10-fold range of molecular weight, were shown to have narrow molecular weight distributions by gel-permeation chromatography (GPC), i.e., M?_w/M?_n = 1.15 ± 0.10. The fractions were further characterized by viscometry, light scattering, and membrane osmometry. Characterization of the small samples (ca. 0.3 g) was facilitated by use of a low-volume light scattering cell. This allows measurements of refractive increment, light scattering, and viscosity to be performed on as little as 50 mg of sample. Molecular weights estimated by the GPC-viscometry technique were in good agreement with the values obtained by light scattering. Estimates of the perturbed coil dimensions (150–200 Å) were in satisfactory agreement with those observed experimentally. The polydispersities of the fractions, determined by osmometry and light scattering, were in fair agreement with GPC data; the latter are considered subject to less experimental uncertainty.