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     

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.     

Evaluation of a Commercial Differential Viscometer as a GPC Detector and Its Application to Polymer Characterization

Abstract

When used as a GPC detector, Viscotek's differential viscometer (DV) measures specific viscosities at each elution volume across the chromatogram. With the addition of a concentration detector, intrinsic viscosities may be calculated. As a result, true molecular weights can be calculated via the universal calibration method.

It was found that true molecular weights and branching analysis obtained using DV for acrylate polymers initiated by VAZO and benzoyl peroxide show excellent agreement with those from low angle laser light scattering (LALLS) measurement. Moreover, comparison of intrinsic viscosities for different polymers at the same molecular weights can be made from the DV technique. In general, linear polymers will have a higher IV than branches ones and the concept has been verified for acrylate polymers in this work.

A comparison between DV and LALLS in terms of capabilities, ease of use, and maintenance is also included.     

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.     

Overloading and Degradation Study in GPC Using Low Angle Laser Light Scattering Detector (LALLS)

Abstract

The unique macromolecular compression effect or delayed GPC elution of high M.W. material was observed using the GPC + LALLS technique for a polystyrene standard of M.W. 5.0 E5. Further overloading which resulted in nonlinear fractionation is also described. The degradation of a 4.2 E6 standard after elution was detected by LALLS with calculated M.W. of 1.0-1.1 E6 but not by GPC, as indicated by normal GPC retention time and the shape of the chromatogram. This degradation was further verified by reinjection of the collected fractions into the GPC which showed a bimodal distribution with calculated M.W. of ca. 1.0 E6 via GPC calibration and LALLS. The source of degradation was attributed to the 2 micron exit frit in the single Jordi mixed bed column. Similar degradation of 2.3 E6 standard to same M.W. of ca. 1.0 E6 was also observed. The use of these standards as GPC calibrants should not be affected by this “post column” degradation.     

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.     

The Errors in the Treatment of Gel Permeation Chromatography Data: Origins and Corrections

Abstract

This paper deals with the origins of errors in data interpretation when using modern GPC with dual detection (refractometer-viscometer) as a method of determination of average molecular weights of polymers. We describe here the different errors classified in two groups: typical chromatographic errors and data treatment errors and we show that they can lead to very miscalculated molecular weight values. For every case, we have tried to propose the best way to avoid or correct these errors so as to use modern GPC as a very accurate method of polymer characterization.     

Gel-permeation chromatography: X. Molecular weight detection by low-angle laser light scattering

Effluent from a gel-permeation chromatographic column has been simultaneously and continuously monitored with a differential refractometer and a low-angle laser light-scattering (LALLS) photometer. This provides a true and direct determination of molecular weight distribution rather than through a calibration method as obtained by conventional GPC techniques. Computer assisted data reduction provides a rapid determination of M?_w, M?_n, M?_z, M?_w/M?_n, as well as a plot of molecular weight distribution. Samples of very narrow molecular weight distribution (MWD) polystyrene from Pressure Chemicals Co. and relatively wide MWD samples of poly(methyl methacrylate) in chloroform have been characterized.     

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.     

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     

Size Exclusion Chromatography of Polyamides

Abstract

We report here a new chromatographic method for characterization of polyamides and polyether-block-amide copolymers by Size Exclusion Chromatography. First, it concerns absolute characterization of polyamide probes by classical light scattering and Ubbelohde viscometry measurements and the choice of narrow distribution standards to calibrate the GPC system. The GPC analysis of polyamides 6, 11, 12 and copolymers is based upon the dual detection refractometer/on-line continuous viscometer at 130°C using columns packed with cross-linked polystyrene gels, benzyl alcohol as mobile phase and polytetrahydrofuran standards for calibration. The main results are absolute average molecular weights and distribution curve, intrinsic viscosity and viscosity law. In addition, viscometric data produced evidence of long-chain branching occuring beyond a limiting molecular weight in some polyamide 12 samples.     

A pH Effect in the HPSEC Separation of Polyacrylamide-Based Copolymers

Abstract

Four polyacrylamide-based samples, having the same nominal molecular weight and molecular weight distribution, have been characterized by HPSEC using two column sets and a mobile phase of phosphate buffer. Depending upon the pH, the separations demonstrate that the systematic differences between samples are influenced by the level of anionic sites along the polymer chain. It is found that the HPSEC elution profiles of these samples are reversed when the pH is changed from 2.2 to 7.0. The anionicity of the samples ranges from less than 0.5 mole % carboxyl content (the homopolymer of acrylamide) to 33.0 mole %.

Capillary viscometry data support these findings in the two solvent media, indicating that no adsorption effects prevail in the chromatography. Static and on-line low angle laser light scattering (LALLS) data on the homopolymer of acrylamide also suggest that no adsorption or degradation is occurring in the chromatographic process.     

Size Exclusion Chromatography of Quaternized Poly(vinylpyrrolidone-co-dimethyl Amino Ethyl Methacrylate) Copolymer (PVPDMAEMA): Absolute Molecular Weights and Molecular Weight Distributions by Low Angle Laser Light Scattering and Universal Calibration

Abstract

In 0.1M tris. pH 7 buffer containing 0.5M LiNO₃, PVPDMAEMA (which exists as a cationic polyelectrolyte) was found to elute based on hydrodynamic volume on Waters Ultrahydrogel columns. Within the exclusion limit of the column set an accurate weight average molecular weight of PVPDMAEMA can be obtained by universal calibration which is in very good agreement with the SEC/LALLS result.     

Gel Permeation Chromatography of Polyethylene Terephalate

Abstract

This paper describes the development of the gel permeation chromatography (GPC) technique for the measurements of cyclic trimer content, molecular weights, and molecular weight distribution of polyethylene terephthalate (PET), utilizing a solvent system of o-chlorophenol-chloroform. Mark-Houwink constants for this solvent system are also described.

The GPC technique was applied to the study of the cyclic trimer content, molecular weights and molecular weight distribution of a variety of commercial PET resins. The results indicate that the cyclic trimer content in PET is dependent on molecular weight, polycondensation process and catalyst system. Solidstate polymerized PET contains less cyclic trimer than PET made by the melt-phase process of the same molecular weight. The cyclic trimer content in solid-stated PET appears to be dependent on the conditions of solid-state polymerization.

The polydispersity index determine for a variety of PET samples is higher than the theoretically predicted value of 2.0; however, there is no systematic dependence on molecular weight or polycondensation process.     

Application to Gel Termination Chromatography of Micro High Performance Liquid Chromatography

Abstract

The raicroscale liquid chromatographic tecnnique was applied to gel perraination chromatography. As the results, the miniaturized GPC column requires smaller amounts of sample, packing materials and carrier solvent than those required with the ordinary GPC column, and it would be applicable to preparatory experiments to select the operation conditions for fractionation by GPC.     

Gel Permeation Chromatography of Unsaturated Polyester Resins. Possibilities and Limitations

Abstract

The use of gel permeation chromatography (GPC) for the characterization of unsaturated polyester resins is demonstrated on several examples. Number-average molecular weights determined by this method are compared to data obtained by means of vapor pressure osmometry (VPO) and by end group analysis (EG). The determination of the polyester resin composition as a function of molecular weight by stop-and-go UV scanning procedure is described. A comparison of theoretical and experimental molecular distribution is applied to the estimation of branching extent.     

Molecular Weight Characterization and Structural Properties of Controlled Molecular Weight Dextrans Synthesized by Acceptor Reaction using Highly Purified Dextransucrase

ABSTRACT

Controlled molecular weight dextrans were synthesized using a highly purified dextransucrase from Leuconostoc mesenteroides NRRL B-512F in a multi-step process. Maltose was used as acceptor for the first reaction step. The purified product obtained at a given reaction step was used as acceptor for the next reaction step. Dextrans of molecular weights ranging from 1,000 to 100,000 were thus obtained with a good yield (80 %). After purification, the molecular weight distribution of the products was characterized using size exclusion chromatography coupled with low angle laser light scattering (LALLS). Polydispersity of the products was shown to be similar to that of commerical dextrans.

¹³C NMR spectra and enzymatic hydrolysis data are consistent with the fact that the enzymatically synthesized dextrans are essentially composed of α(1->6) linkages. It was observed that controlled molecular weight dextrans were less branched than commercial products obtained by acidic hydrolysis of high molecular weight dextrans.     

Characterization of Xylansulfate by Size Exclusion Chromatography

Abstract

A sulfated, low molecular weight beech xylan was fractionated preparatively on Sephadex G-50 into ten fractions with molecular weights from 17 000 to 1 800. The degree of sulfation, refractive index increment, molecular weight, and specific optical rotation of each fraction was determined. The fractions were then used to calibrate a Sephacryl S–200 gel column for the molecular weight distribution analysis of xylansulfate.

The molecular weights, M _W, obtained by SEC for samples of xylansulfate were in good agreement (within 4 ± 1%) to the values derived by low angle light scattering.     

A study of aqueous solutions of dextrans by gel permeation chromatography using a multiple detection system

We studied the elution of dextrans in gel permeation chromatography (GPC) using a low-angle laser light-scattering (LALLS) system to monitor the molecular weight and the standard refractive index (RI) detector to measure the concentration. In pure water the dextrans show bimodal chromatograms of the RI response as well as of the LALLS response. The first eluted peak reflects the macroion exclusion due to the repulsion between negatively charged macromolecules and equally charged gel. In spite of the resulting distortion of the chromatograms, correct values of the weight-average molecular weights (M?_w) are obtained from them. If instead of pure water a salt solution (0.1 M KNO₃) is used as eluant, the charge effect is completely suppressed and single-peak chromatograms are found. Again correct values of M?_w are obtained, but number-average molecular weights turn out to be too large owing to axial column dispersion in the coupling arrangement. By introducing a spreading factor, values of M?_n could be corrected. Investigations of the charge effect were also carried out by monitoring the electric conductivity of the eluted dextran zone. In this way, the phenomenon of ion inclusion, evidently provoked by charged dextran molecules, was observed.     

High-Performance Gel Permeation Chromatography of Pectins

Abstract

A high-performance gel permeation chromatographic (GPC) method was developed to determine the molecular weight distribution of pectins. The chromatographic system consisted of a hydrophilic coated silica (SynChropak) as the packing and a pH 3.7 acetate buffer as the mobile phase. By use of this system, high-methoxy, low-methoxy, and amidated pectins could be analyzed within fifteen minutes. By determining partition coefficients (K_d) of pectins as a function of mobile phase composition, K_d values were found to be independent of ionic strength from 0.055 to 0.7 M using pH 3.7 acetate buffers, which was in agreement, with intrinsic viscosity data.