Peculiarities of polyacrylamide analysis by aqueous GPC

Various commercially available stationary phases of gel permeation chromatography (GPC) were tested to determine their effectiveness in aqueous exclusion chromatography. It was found that controlled pore glass (GPG) is the most suitable material for the separation of polyacrylamides and poly(acry1amide-co-sodium acrylate), dextrans, and poly(sodium styrene–sulfonates) in 0.1M aqueous Na₂S0₄ solutions of ionic strength 0.3. A calibration curve was established by using broad molecular weight distribution polyacrylamide standards in a trial and error procedure. To avoid artificial oscillations on the evaluated distribution curves a cubic B-spline representation of the calibration curve was used instead of the conventional polynomials. By applying this system the solution instability of polyacrylamides was observed by GPC and is discussed because of its general importance to the applicability of indirect molecular weight determination methods for polyacrylamides. The effectiveness of aqueous GPC was demonstrated in an evaluation of thermal degradation measurements of polyacrylamides. Finally, the feasibility of universal calibration of aqueous GPC by means of poly(sodium styrene–sulfonates) was investigated. It is apparent that in spite of some problems concerning adsorption of the polymer universal calibration is a successful tool for calibrating aqueous GPC.     

Surface active azogroup-containing polymers and their use in emulsion polymerization

Polymeric azoinitiators have been obtained by the acidcatalyzed polyreaction of azobisisobutyronitrile (AIBN) with tetraethylene glycol (TEG) and 1.6-hexanediol resp. The kinetics of decomposition of these polyazoesters were investigated by differential scanning calorimetry (DSC) resulting in an activation energy of E_a=124.5 KJ/mol and a frequency factor of A= 3.6 · 10¹⁴ sec^–1.The polyazoesters were used to initiate radical polymerization of acrylamide limiting the decomposition of the initiator to 37%. The resulting polyacrylamides containing azogroups had molecular weights between 50 000 and 250 000 g/mol. They are surface active polymers having a critical micell concentration of 0.1 to 0.3 g./l. By use of these polyacrylamides as an emulsifying initiator system stable emulsions of polymers were obtained without additional use of a tenside. Polymethacrylic acid containing azogroups can be used as well as an emulsifying initiator.The latex particles are stabilized by a solvated shell of a polymer. Thus it is possible to obtain stable emulsions in organic solvents by use of an azogroup-containing prepolymer which is soluble in that solvent. An emulsion of polyacrylamide in methanol ohtained by use of an azogroup-containing polyvinylacetate is an example.Dedicated to Professor F. H. Müller.Thanks are due to Dr. R. Menhold, Bayer AG, Leverkusen for performing the electronmicroscopic investigations. Financial support by Deutsche Forschungsgemeinschaft and Fonds der Chemischen Industrie is gratefully acknowledged.     

Gel permeation chromatography of poly(styrene-co-divinylbenzene) microgels. Effect of electrolyte concentration in the solvent system dimethylformamide plus lithium bromide

Tightly crosslinked poly(styrene-co-divinylbenzene) microgels with molecular weights in the range 10⁷-10⁸gmol^?1 have been dissolved in dimethylformamide containing LiBr and investigated by gel permeation chromatography and viscometry. The effect of LiBr concentration on the elution volume in GPC can be explained in terms of a diffuse double layer. The product [η]M adequately describes the separation in GPC provided that the LiBr concentration is high and adsorption is absent.     

COMPARISON OF GPC AND THERMAL FIELDFLOW FRACTIONATION METHODS FOR LINEAR AND STAR BRANCHED POLYSTYRENE SAMPLES

The Thermal Field-Flow Fractionation (TFFF) method was used to determine the elution volumeof a series of star branched polystyrene having different number of arms but the same arm molecularweigh and polystyrene standards with narrow distribution whose molecular weight ranged from5.0×10~4 to 8.6×10~5. Results were obtained by measuring at two temperature difference (△T=30℃and △T=50℃in THF. The same star branched samples were measured by means of GPC method.Comparison of Vr-Mrelationships obtained from TFFF and GPC showed that the displacement of V_r-M curves for star and linear polystyrene is larger than that in GPC. This difference is caused by theentirely different mechanism of separation for these two methods. As the controlling factor is hy-drodynamic volume of the polymer chain in solution for GPC, it is the diffusion coefficient of polymermolecules for TFFF. The experimental results indicate that the influence of variance of chain struc-ture on diffusion coefficient is stronger than that on the hydrodynamic volume and that TFFF tech-nique may be used as a method for characterizing branching of polymer molecules. For this pur-pose a proper theoretical model and more accurate experiments are needed.     

High-speed aqueous gel-permeation chromatography

High-speed gel-permeation chromatography (GPC) of water-soluble polymers has been investigated by using TSK-GEL, type-PW columns packed with small porous particles. Being semirigid, the column packing could be operated under high pressure and, therefore, it was possible to achieve high-speed GPC. A resolution higher than that of ordinary GPC in organic solvent system was attained when the measurement of one sample was completed within 40 min with a 6-ft column set. Samples with a wide range of molecular weights, from oligomers to polymers having a molecular weight greater than 10⁶, could be fractionated. Dextran, polyethylene glycol, polyacrylamide, poly(vinyl alcohol), and poly(vinyl pyrrolidone) were separated according to molecular size with no evidence of adsorption. Investigation of other water soluble polymers is now in progress.     

Analysis of Low Molecular Weight Polymers with Gel Permeation Chromatography

Intrinsic viscosities and gel permeation chromatography (GPC) elution times were determined in toluene on commercially available standards of polystyrene (PSTY) and polymethyl methacrylate (PMMA) having M_n in the range of 10³ to 10⁵ and 10⁴ to 10⁶, respectively. In addition, elution times were determined on the discrete GPC peaks of dimer, trimer, tetramer, etc. as seen in lower molecular weight PSTY and PMMA. Intrinsic viscosities of oligomers were estimated by extrapolation of the Mark-Houwind-Sakurada equations determined from our data, and the results were used to establish a universal calibration curve over a wide range of molecular weights. A similar approach was taken by using literature data for the intrinsic viscosities of PSTY and PMMA in tetra-hydrofuran. It was verified by proton NMR that the universal calibration curve so constructed is useful at M_n, values as low as 300. No correction was necessary for chain length dependence of the detector response.     

Preparation and block copolymerization of oligodihexanoylchitin having hydroxy groups at both ends

The preparation of oligodihexanoylchitin (3) having hydroxy groups at the both ends was carried out by an acid hydrolysis of a parent dihexanoylchitin in a mixed solution of acetic acid and conc. hydrochloric acid (11 : 1 in volume) at a room temperature. After 13–21 h, the products were isolated and their molecular weights were calculated as 7400–1100 by GPC analyses. The structure of the product 3 was determined by ¹H and ¹³C-NMR and IR spectra. The IR spectra of the products yielded for longer hydrolysis times than 30 h, however, indicated the occurrence of the dehexanoylation. The block copolymerization of 3 with poly (propylene glycol) (PPG) using 4,4'-methylenedi (phenyl isocyanate) (MDI) as a coupling reagent gave the block copolymer 6 . The molecular weight of 6 as obrained by GPC was 52,000. © 1994 John Wiley & Sons, Inc.     

Determination of molecular weight distributions of novolac resins by gel permeation chromatography

The number- and weight-average molecular weights of several statistical and high ortho novolac resins were determined using gel permeation chromatography (GPC). The standards used were pure compounds having between 2 and 12 phenol units bridged via methylene linkages. Three series of compounds were studied: (i) those with methylene linkages substituted in only the ortho positions relative to the phenolic hydroxyl group; (ii) those in which all para positions, together with sufficient ortho positions, were used to synthesize the compounds; and (iii) those in which the methylene linkages were substituted at a mixture of ortho and para positions. Such compounds, having known molecular architecture and units similar to the segments of industrial novolac resins, provide for a more exact measurement of the molecular weight than do the commonly used poly(styrene) standards. Using these new standards the number average molecular weights of the resins determined by GPC were in good agreement with the average molecular weight obtained by ¹H-NMR spectra of the resins, particularly for low molecular weight resins. GPC analysis of higher molecular weight resins tends to underestimate the molecular weights because of complications introduced by hydrogen bonding. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1399–1407, 1997     

Characterization of Branched Poly (vinyl Acetate) by GPC and Low Angle Laser Light Scattering Photometry

Abstract

Poly (vinyl acetate), PVAC, synthesized by bulk polymerization over a range of initiator concentrations ([AIBN] = 10^?5 to 4 × 10^?3 g-mole/1), temperatures (50°C, 60°C, 70°C, and 80°C) and conversion levels (3 to > 90%) were characterized using low angle laser light scattering (LALLS) photometry to measure M_w of the whole polymers. A number of these samples were characterized using GPC with a differential refractive index (DRI) and LALLS detector to measure the molecular weight distribution (weight fraction versus M_w). M_w for PVAC samples synthesized at suitably low initiator levels at various conversions were found to agree with classical light scattering measurements after Graessley.

An electronic device and a technique which optimizes the sensitivity and the signal-to-noise ratio of the LALLS photometer throughout the molecular weight distribution (MWD) of the GPC chromatogram were devised. These considerably simplify the operation of the LALLS for both offline and online operation with GPC.

Most importantly it was unambiguously shown that the commonly used universal calibration parameter (UCP) with GPC, [n]M_w, is incorrect for polymers with molecules having the same hydrodynamic volume but different molecular weights, i. e., those with only chain branching (LCB), copolymers with compositional drift, and polymer blends. The correct UCP was found to     

Water‐soluble acrylamide copolymers. VII. Preparation and characterization of poly(methacrylamide‐co‐acrylamide)

This article carries the objectives of our current acrylamide copolymer project further by examining the synthesis, characterization, and testing of a series of poly(methacrylamide‐co‐acrylamide)s and some homopolymer control products. These are characterized by traditional Fourier transform photoacoustic infrared, ¹³C NMR, and elemental analysis. A composite picture of the hydrodynamic volumes of the high molecular weight products was then obtained by a series of viscometric, gel permeation chromatographic, and multiangle laser light scattering methods. These give a good quantitative picture of the effect of the introduction of the backbone methyl group on the hydrodynamic volumes of the copolymer products. Yields were generally greater than 60%. The copolymer products generally had lower molecular weights than those obtained from the control polyacrylamide preparations. Copolymer samples with comparable molecular weights did have larger radii of gyration and intrinsic viscosities than samples of control polyacrylamides. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3146–3160, 2000     

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     

Gel permeation chromatography – Atmospheric pressure chemical ionization – Mass spectrometry for oligomer characterization

The study presents the possibility to use gel permeation chromatography (GPC) with atmospheric pressure chemical ionization (APCI)–mass spectrometry (MS) for the analysis of oligomeric structures having molecular weights up to 2000?g?mol^?1. Polymethylmethacrylate and polystyrene oligomers were analyzed in chloroform using 2.1-mm-internal diameter GPC columns. The low flow rate of 50?µL?min^?1 and the ionization with chlorine allow a fast optimization of the method parameters. Excellent correlation with the expected isotope distributions and linear calibration curves were obtained for both types of oligomers.     

Studies on the copolymerisation of N-isopropyl-acrylamide with glycidyl methacrylate

The paper describes the homopolymerisation and copolymerisation of N-isopropyl acrylamide (NIPAM) with glycidyl methacrylate (GMA) in solution at 60°C using azobisisobutyronitrile (AIBN) as an initiator and dioxan as solvent. Copolymers were synthesized by varying the mol fraction of GMA in the initial feed from 0.025-0.125. All the polymerization reactions were terminated at low % conversion (10-15%) and the copolymer composition was determined by measuring the epoxy content. Percent epoxy content was determined by titration method using pyridine-HCl mixture. The reactivity ratios determined using Fineman-Ross method were found to be 0.94±0.05 (r₁, NIPAM) and 1.05±0.08 (r₂, GMA). All the polymers have high molecular weights with wide molecular weight distribution as determined by gel permeation chromatography (GPC) i.e. M_n in the range of 3.7 x 10⁴ - 7.8 x 10⁴ and M_w in the range of 1.2 x 10⁵ - 4.1 x 10⁵ with a polydispersity index in the range of 2.3-5.3. Lower critical solution temperature (LCST) of NIPAM homopolymer and copolymers was determined by recording DSC scans of polymers in aqueous solution. Incorporation of GMA in the poly(NIPAM) backbone resulted in a decrease in the LCST.     

Fractionation of polyethylene by gel permeation chromatography

The performance of the gel permeation chromatography (GPC) technique was studied with several commercial samples of linear high density polyethylene. A comparison of these data was made with those obtained from the elution column technique based on fractional dissolution. GPC gave reproducible fractionation data in the molecular weight range of 10³–10⁶. These data were obtained from two columns in series with nominal capacity of 1–10⁴ and 1–10⁶A. Polyethylene fractions of known molecular weights are required as calibration standards and for many commercial polyethylenes it is necessary to increase sensitivity at molecular weight higher than 10⁶.     

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     

Preparation and characterization of polydimethylsiloxanes with narrow molecular weight distribution

The preparation of polydimethylsiloxanes (PDMS) of narrow molecular weight distribution (MWD) by anionic polymerization of hexamethylcyclotrisiloxane (D₃) in an improved polymerization apparatus is described. Using (CH₃)₂Si(OLi)₂ as initiator and (CH₃)₃SiCl (TMCS) as terminating agent, polymers with only methyl groups were obtained with molecular weights ranging from 2 × 10³ to 2 × 10⁶. Kinetic investigations were performed only so far as necessary for controlling the polymerization under the chosen experimental conditions (solvent: n-hexane, solvating agent: hexamethylphosphortriamide (HMPT), polymerization temperature: 25°). The molecular weights of the polymers were determined by light-scattering and, after calibration, by viscometry and GPC. The non-uniformities of the samples with symmetrical MWD were estimated using the 4σ-method. The GPC apparatus had been calibrated with polystyrene and poly-α-methylstyrene samples of extremely small non-uniformity.     

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     

Determination of molecular weight distribution of cellulose by conversion into tricarbanilate and fractionation

Two samples of cellulose (molecular weight 2.97 × 10⁵ and 1.25 × 10⁵) were transformed into carbanilates (CTC) which were then fractionated by the elution method at a constant composition of the acetone-water elution mixture with the column temperature gradually increasing from ?30°C to 30°C, and by the GPC method in acetone and tetrahydrofuran. Tetrahydrofuran appeared to be a more suitable solvent. The molecular weights of fractions obtained by the elution fractionation were determined by the light-scattering method in tetrahydrofuran. The width of fractions was determined by the GPC method (average M _w/M _n = 1.37); the [η] values and the Mark-Houwink constants (K = 5.3 × 10^-3, a = 0.84) for tetrahydrofuran at 25°C were determined. The calibration curve for the GP method was constructed by means of the fractions thus obtained; it was demonstrated that the universal calibration curve according to Benoit can also be used. It was demonstrated that the molecular weight distribution of cellulose can be conveniently determined by conversion into CTC followed either by the elution fractionation (for preparative purposes) or by fractionation by the GPC method (for analytical purposes).     

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.     

Hyperbranched epoxy resins prepared by proton transfer polymerization from an A<Subscript>2</Subscript> + B<Subscript>3</Subscript> system

Epoxy-terminated hyperbranched polymers(EHBPs)were prepared by proton transfer polymerization and characterized by FT-IR,~1H-NMR and GPC.The solution and thermal properties of the uncured samples and mechanical properties of cured samples were examined.The thermo-stable products had good solubility in polar solvents,low solution viscosity and T_gs ranging from 15℃to 33℃depending on their molecular weights.The mechanical properties of cured films were studied and compared with those of a bisphenol-A type epoxy resin.The films of EHBPs had good impact resistance and high gloss values without sacrificing hardness and adhesion.