Data Treatment in Aqueous GPC with On-Line Viscometer and Light Scattering Detectors

Abstract

Gel Permeation Chromatography (GPC) is becoming a very powerful tool for polymer characterization with the coupling of mass detectors using viscometry and light scattering techniques. The triple coupling seems to be the best way since the light scattering detector gives absolute molecular weights and viscometric detection provides intrinsic viscosity, leading to absolute molecular weights through universal calibration and information on long-chain branching. However, instrumentation becomes more sophisticated, expensive and, simultaneously, very sensitive to several parameters which are not critical in classical GPC. Moreover, an on-line computer is required for data acquisition and appropriate software for reliable interpretation of chromatograms.

Our experiments were performed with a Waters Associates room temperature instrument in which a home-made continuous viscometer, using pressure transducers, and a light scattering detector (LALLS Chromatix-CMX 100) were inserted on-line between the column set and the refractometer. Data were interpreted through personal software written on HP9836 and PC-AT computers.

We describe, here, the behavior of some polymers in aqueous solutions, mainly those that are commonly used as calibration standards (polyethylene oxides, pullulans). Experiments were run using two different sets of columns (‘Ultrahydrogel’ from Waters Associates and ‘Shodex OH-Pak’ from Showa Denko K.K.) in several aqueous solvents, pure water or water with various salts (LiNO₃, NaNO₃, LiCl, NaCl, Na₂SO₄) at different concentrations. Intrinsic viscosities were determined through viscometric detection and weight average molecular weights through the LALLS detector, leading to a plot of universal calibration curves Log([ηl.M) versus elution volumes.     

Size Exclusion Chromatography of Poly(vinylpyrrolidone)

Abstract

Poly(vinylpyrrolidone) and poly(ethylene oxide) separate by hydrodynamic volume on Toyo Soda TSK-PW columns in a mixed solvent mobile phase of 50:50 (v/v) MeOH/H₂O containing 0.1M LiNO₃. From this separation a single universal calibration curve based on hydrodynamic volume [η]M can be obtained. Accurate weight average molecular weights of PVP were obtained by both SEC/LALLS and universal calibration showing good agreement between the two methods. SEC/LALLS overestimates the number average molecular weight for broad distribution polymers due largely to the lack of sensitivity of the LALLS detector to the low molecular weight portion of the polymers, while the universal calibration method slightly underestimates the number average molecular weight as compared to osmometric values.     

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     

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     

An Eluent Pressure Detector for Aqueous Size Exclusion Chrohatography

Abstract

An on-line viscometer which measures the eluent pressure drop across a long capillary was developed for use in aqueous size exclusion chromatography (SEC). Intrinsic viscosities of several polymer standards were calculated from data collected by the viscometer. These viscosities agree well with the measurements made with a Ubbelohde four-bulb shear dilution viscometer. The on-line viscometer becomes more sensitive as polymer hydro-dynamic volume increases. Therefore, it can be more effective than a refractive index detector for SEC analysis of high molecular weight, water soluble polymers.     

Copolymers of p-Nitrobenzyl Acrylate with Methyl Acrylate: Synthesis,Characterization, and Monomer Reactivity Ratios

Abstract

Copolymers of p-nitrobenzyl acrylate and methyl acrylate with different feed ratios are synthesized in ethyl methyl ketone using benzoyl peroxide as a free radical initiator at 70 ± 1°C. The copolymers were characterized by IR and ¹H-NMR spectroscopic techniques. Copolymer compositions were determined by ¹H-NMR analysis of the polymers. The monomer reactivity ratios were determined by the application of conventional linearization methods such as Fineman–Ross and Kelen–Tüdös. Gel permeation chromatography was used for determining the molecular weights M _n and M _w, and the polydispersity index. The intrinsic viscosities and the thermal properties of the homo- and copolymers are also discussed.     

Size Exclusion Chromatography Calibration Assessment Utilizing Coupled Molecular Weight Detectors

Abstract

This paper shows that the usual method of representing an SEC calibration curve by a single polynomial curve may often be inadequate with new high resolution columns. Data points wind about the fitted line. The significant magnitude and systematic nature of these deviations clearly appear when a plot of residuals is derived from the conventional calibration curve and expressed in terms of the percent error in molecular weight. The deviation of the calibration data from the fitted line was approximately 10% for the conventional molecular weight and intrinsic viscosity calibration curves. It became 20% for the universal calibration curve. LALLS and DV detectors were used together with the DRI detector to provide evidence that the calibration curve deviations were due to the column packings and not due to some other cause (e.g., vendor values of molecular weight). Use of a polynomial fit to a portion of the curve corresponding to the retention volume range of an unknown was used to show the significant improvement in results which occurred when the calibration variations were taken into account. At present, use of many individual narrow standards is necessary to elucidate the effect.     

Copolymers of 3-Methoxy-4-Acryloyloxy-Benzal Phenylimine with Methyl Methacrylate: Synthesis,Characterization and Monomer Reactivity Ratios

Abstract

Copolymers of 3-methoxy-4-acryloyloxybenzal phenylimine and methyl methacrylate with different feed ratios are synthesized in ethyl methyl ketone using benzoyl peroxide as a free radical initiator at 70 ± 1°CC. The polymers were characterized by IR and ¹H-NMR spectroscopic techniques. Copolymer compositions were determined by ^lH-NMR analysis of the polymers. The monomer reactivity ratios were determined by the application of conventional linearization methods such as Fineman-Rose and Kelen-Tüdös. The molecular weights M_n and M_w of the polymers and the poly-dispersity index were determined by gel permeation chroma-tography. The intrinsic viscosities and the thermal properties of the homo-and copolymers are also discussed.     

Characterization of Nylons by Gel Permeation Chromatography and Low Angle Laser Light Scattering in 2,2,2-Trifluoroethanol

Abstract

A GPC method was developed for the analysis of several commercial nylons in trifluoroethanol + 0.05M LiBr using a styrene-divinylbenzene column custom-packed by Jordi Associates.

A broad molecular weight standard method was developed by interfacing GPC with LALLS to give the absolute molecular weight for each data point or elution volume along the chromatographic peak from a nylon sample of known molecular weight. The integrity of the interface was verified by static LALLS measurements; no loss or adsorption of solute was found in the chromatographic system.

A strong ionic effect was observed for nylon samples and the method to alleviate it was described. The molecular weights and distribution of the following nylons were determined by this method: nylon 6, nylon 4,6, and nylon 6,6. Much higher than quoted molecular weights were obtained for nylons when polymethyl methacrylates and ethylene glycols were used as standards; this necessitated the use of this broad molecular weight method for column calibration. The ambient operating conditions offered several advantages over the conventional m-cresol solvent which required operation at higher than 100 C in order to reduce the viscosity, possessed a strong odor, and occasionally resulted in degradation of polyamides.     

Continuous Viscometric Detection in Size Exclusion Chromatography

Abstract

Continuous viscometric detection is based on the measurement of pressure drop in an on-line small capillary tube in which chromatographic eluents flow at constant flow rate. This detector is always coupled with a concentration detector (usually refractometer) and located before it to avoid back pressure in the refractometer. In order to obtain reliable information for polymer samples, it is generally necessary to connect these two detectors to a computer which performs data acquisition and treatment.

First, we discuss the problem of shape, geometry and dimensions of the viscometer. The typical characteristics are the result of a compromise between contradictory targets, mainly small internal volume, low shear rate and low pressure drop. It is shown that Poiseuille's laminar flow is only obtained when coiling radius of the measurement tube is greater than 6 cm, which is not the case inside the refractometer. Accordingly, two pressure transducers are necessary to eliminate pressure drop data coming from refractometer.

In a second part, we show how to extract information from pressure variation data. By using concentration data, pure solvent pressure and sample pressure it is possible to calculate intrinsic viscosity extrapolated to zero concentration at each point of the chromatogram. By comparison with intrinsic viscosity of the polymer used for calibration, a correction of hydrodynamic volume according to Benoit's universal calibration leads to absolute molecular weights.

In addition, for a linear polymer, the knowledge of log [η] versus log M leads to the determination of Mark-Houwink relationship coefficients. For branched polymers, viscosity laws are curved and the comparison between the linear law corresponding to the linear equivalent polymer and the experimental law allows the determination of the g' branching parameter distribution.     

Synthesis of linseed oil based biodegradable homo and copolymers: role as multifunctional greener additives in lube oil

Abstract

Homopolymer of linseed oil and its four copolymers with styrene, 1-decene, isodecyl acrylate and octyl acrylate, respectively, have been synthesized in this present context. The prepared polymers are characterized by NMR and FTIR spectroscopy. The molecular weights have been measured by gel permeation chromatography. Their effectiveness as pour point depressant (PPD), viscosity index improver (VII) and their shear stability in terms of permanent shear stability index have been evaluated in lube oil. The copolymers acted as better PPDs than the homopolymer whereas the homopolymer of linseed oil excelled as VII. Further it was observed that all the prepared polymers were stable enough under severe mechanical shear.     

Straw lignins: Hydrodynamic and conformational properties of the macromolecules

The hydrodynamic and conformational properties of the macromolecules of lignins derived from Secale sp. rye straw and Hordeum sp. barley straw were examined in dimethylformamide solutions. The molecular weights, centrifugal sedimentation coefficients, translational diffusion coefficients, and intrinsic viscosities of the polymers were determined. The fractal dimensions and Mark-Kuhn-Houwink scaling indices were calculated.     

Characterization of polysaccharide solutions by means of chromatography-multidetection

Size exclusion chromatography (SEC) combined with double detection, utilizing a differential refractive index (DRI)- and a low angle laser light scattering (LALLS) - detector represents a powerful experimental set-up in the field of chromatography-multidetection (C-MD). By means of these techniques high-quality information for profound polymer characterization is provided in a fast and semi-automatical (autosampler/PC-controlled) way. Molecular characteristics such as molecular weight distributions, molecular weight averages, tendencies for intermolecular interactions, can be obtained by these techniques. Successful handling of data from C-MD-techniques within reasonable time ranges requires adequate hardware and software. This is especially true if advanced data processing is applied, e.g. to yield polymer particle size/shape characteristics in terms of Staudinger/Mark/Houwink constants (K,a), distributions of sphere equivalent particle radii (R_cD)-, sphere equivalent mass density of solved polymer coils (ρ_cD)- and intrinsic viscosity ([η]D). For aqueous solutions of polysaccharide samples (waxy maize starch hydrolyzate, hydroxyethyl-amylopectin from waxy maize hydrolyzate, dextran) data from SEC-DRI/LALLS and universal calibration experiments are utilized for a comprehensive physico-chemical characterization of these polymers.     

Synthesis and Characterization of Monodisperse α,ω-Divinylpolydimethylsiloxane and ω-Vinylpolydimethylsiloxane

Abstract

ω-Vinylpolydimethylsiloxanes (ω-PDMS) and α,ω-divynilpolydimethylsiloxanes (α,ω-PDMS) have been synthesized by anionic polymerization of hexamethylcyclotrisiloxane (D3). The reactions were carried out in n-hexane and tetrahydrofuran (THF), respectively. The initiator was n-butyl-lithium (n-BuLi); tetrahydrofuran was used as an electron donor compound to promote the polymerization of D3. The synthesized polymers have been characterized by infrared (FTIR), proton nuclear magnetic resonance spectroscopy (NMR), light scattering (LALLS), and gel permeation chromatography (GPC). Molecular weights ranging from 20,000 to 100,000 were obtained with relatively narrow molecular weight distributions; Mw/Mn < 1.25.     

Polymerization by Phase-Transfer Catalysis. Part 20. Synthesis of Polycarbonates and Polythiocarbonates with an Ester Group in the Side Chain

Abstract

Poly(ester-carbonate)s and poly(ester-thiocarbonate)s were synthesized from diphenols containing an ester group in the side chain and phosgene or thiophosgene under phase-transfer conditions. The polymers were characterized by elemental analysis and IR spectroscopy, and the molecular weights were estimated by inherent viscosity measurements. The influence of the nature of the catalysts and the structure of the diphenols on the yields and inherent viscosities was studied. We found that the catalysts were effective for all monomers, although the inherent viscosity values were low due to the insolubility of the polymers in the reaction media. Without catalyst, the polymers were not obtained.     

Rare Earth Metal-Initiated Polymerizations of Polar and Nonpolar Monomers

Abstract

Organolanthanide(III) initiated polymerization of methyl methacryate gave both syndiotactic and isotactic living polymers of high molecular weight. Organolanthanide(III) initiated polymerization of alkyl acrylates also gave high molecular weight poly(alkyl acrylate)s with very narrow molecular weight distribuion in high yield. Molecular weights of the resulting polymers increased linearly with the conversion. Random and block copolymerizations of alkyl acrylates with methyl methacrylate were realized successfully. For the sake of development of the olefin polymerization catalyst, bulky substituents were introduced into Me₂Si bridged Cp rings and they were used as ligands for the lanthanide complexes. Tri- and divalent lanthanide complexes with such ligands showed high activity for olefin polymerization and gave high molecular weight polyolefins.     

Synthesis and characterization of well-defined poly(tert-butyl acrylate) star polymers

Star polymers with different numbers and lengths of poly(tert-butyl acrylate) (PTBA) arms were obtained via atom transfer radical polymerization. Aliphatic alcohols with different number of hydroxyl groups varying from 3 to 6 and calix[4]arenes based on pyrogallol with 12 and 16 phenol groups were transformed to bromoester derivatives to prepare multifunctional ATRP initiators used as the cores of the stars. The star polymers were characterized by GPC with refractive index, multiangle laser light scattering and viscosimetric detectors. The molar masses of the stars reached 70,000 g/mol and the molar mass dispersities did not exceed 1.2. To elucidate the compact structure of the stars, their true molar masses were determined by GPC with triple detection (RI-MALLS-Visco) and compared with the apparent molar masses obtained from the calibration with linear poly(tert-butyl acrylate) standards. The intrinsic viscosities of the PTBA stars of the same molar mass decreased with the number of star arms but were always lower than the intrinsic viscosities of the analogue linear PTBA polymers. The values of the branching ratio g′ decreased with increasing number of arms indicating more compact structure of stars. The branching ratio g′ was correlated to the empirical predictions.     

A new procedure for simultaneous calibration of separation and axial dispersion in SEC

Summary A new computational procedure for the simultaneous calibration of separation and axial dispersion by using SEC coupled with a LALLS detector is presented. Its performance is tested by SEC/LALLS experiments with commercially available samples of broad and narrow polystyrene standards. The peakbroadening parameters were calculated by a novel method which utilizes the different effects of axial dispersion on polymers with narrow and broad molecular weight distribution. The dispersion function was assumed to be gaussian. The variation of the dispersion parameter with molecular weight is in good agreement with reports in the literature. Experimental chromatograms have been corrected for the axial dispersion effect.     

Rotational viscosity of ferroelectric liquid-crystalline polysiloxanes

Abstract

Some physical parameters of comb-shaped ferroelectric liquid-crystalline polymers were measured. Their rotational viscosities are two or three orders of magnitude larger than that of low molecular weight ferroelectric liquid crystals. Furthermore, they are found generally to be proportional to the second power of the weight-average molecular weight. Spontaneous polarization of the ferroelectric liquid-crystalline polymers has little dependence on molecular weight.     

Size Exclusion Chromatography with Low Angle Laser Light Scattering Detection

Abstract

A review is given of the use of low angle laser light scattering (LALLS) detection in conjunction with size exclusion chromatography (SEC) to measure polymer molecular weight distributions without conventional SEC column calibration methods. A summary of light scattering theory is presented, and instrument configurations and principles of operation are described for two LALLS photometers. Also discussed are the overall performance of the SEC/LALLS technique and data from selected applications.