"% '99- GPC-Viscometry Study in TI-IF,DMF and DMAC C. Kuo, T. Provder, and M. E. Koehler, The Glidden Company, Member of ICI Paints 16651 Sprague Rd., Strongsville, Ohio 44136 The characterization of molecular weight distribution, intrinsic viscosity and polymer chain branching as a function of molecular weight for polymer standards andpolymers of commercial interest are reportedfor tetrahydrofuran (THF), dimethylformamide (DMF) and dimethylacetamide (DMAC) mobile phases. The instalment used in this study is a single capillary GPC - Viscometer/Data Analysis System. In this chapter additional studies on operational variables, particularly dead volume, is reported. The validity of universal calibration in DMF and DMAC is discussed for a range of polymer types, and column packings. Recent developments in gel permeation chromatography (GPC).have been focused on molecular size sensitive detectors in the form of light scattering detectors and viscometer detectors for the determination of absolute molecular weight distribution and polymer chain branching. Commercially available GPC viscometers were introduced by Viscotek in 1984 (!) and by Millipore Waters Chromatography Division in 1989 2(2). In a previous publication (_) the principle ofoperaUon, instrumentation, operational variable considerations and data analysis methodology and its application to polymer systems in THF were described and discussed for a commercial single capillary GPC-Viscometer System. In this chapter the effect of dead volume on viscosity law parameters is further elaborated and comparative molecular weight results in THF are presented for linear and randomly branched polystyrene polymers. The practice of GPC in highly polar solvents such as DMF and DMAC is not fully understood with respect to polymer-solvent-columns packing interactions. These interactions often prevent validated universal calibration curves from being generated which in turn, subsequently, prevent accurate molecular weight distribution information from being attained from viscometer detector data for a variety of polymer types. Another related effect which hinders accurate quantitation of GPC data in highly polar solvent systems is the presence of solvent trash peaks in the molecular weight range of interest. In this chapter experimental conditions for 147
Transcript
"%
'99-
GPC-Viscometry Study in TI-IF,DMF and DMAC
C. Kuo, T. Provder, and M. E. Koehler,The Glidden Company, Member of ICI Paints16651 Sprague Rd., Strongsville, Ohio 44136
The characterization of molecular weight distribution, intrinsicviscosity and polymer chain branching as a function of molecularweight for polymer standards and polymers of commercial interest arereported for tetrahydrofuran (THF), dimethylformamide (DMF) anddimethylacetamide (DMAC) mobile phases. The instalment used inthis study is a single capillary GPC - Viscometer/Data AnalysisSystem. In this chapter additional studies on operational variables,particularly dead volume, is reported. The validity of universalcalibration in DMF and DMAC is discussed for a range of polymertypes, and column packings.
Recent developments in gel permeation chromatography (GPC).have been focusedon molecular size sensitive detectors in the form of light scattering detectors andviscometer detectors for the determination of absolute molecular weight distributionand polymer chain branching. Commercially available GPC viscometers wereintroduced by Viscotek in 1984 (!) and by Millipore Waters ChromatographyDivision in 1989 2(2). In a previous publication (_) the principle ofoperaUon,instrumentation, operational variable considerations and data analysis methodologyand its application to polymer systems in THF were described and discussed for acommercial single capillary GPC-Viscometer System. In this chapter the effect ofdead volume on viscosity law parameters is further elaborated and comparativemolecular weight results in THF are presented for linear and randomly branchedpolystyrene polymers.
The practice of GPC in highly polar solvents such as DMF and DMAC is notfully understood with respect to polymer-solvent-columns packing interactions.These interactions often prevent validated universal calibration curves from beinggenerated which in turn, subsequently, prevent accurate molecular weightdistribution information from being attained from viscometer detector data for avariety of polymer types. Another related effect which hinders accurate quantitationof GPC data in highly polar solvent systems is the presence of solvent trash peaks inthe molecular weight range of interest. In this chapter experimental conditions for
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minimizing the effect of solvent trash peaks are explored. The validity of universalcalibration in conjunction with viscometer detection is examined for various columnpacking types in DMF and DMAC based solvent systems for a variety of polymertypes.
Experimental
(A) Instruments: (1) Millipore Waters Single Capillary GPC-Viscometer/DataAnalysis System (GPCV) 2(2);(2) Glidden GPC Viscometer/Data AnalysisSystem (GPC/VIS(,3))
(/3) Columns: (1) Millipore Waters Ultrastyragel Column_ with 103, 104, 105,10° A porosity; (2) MiUipore Waters pstyragel HT Lijaear columns (10 #m);(3)Polymer Laboratories PLgel column_ (5 pro) with 103, 103, and 50porosity;(4) MiUipore Waters Ultrahydrogel linear column (6-13pro);(5) Shodex KD-802.5 (7/an), (6) Shodex KB-802.5(7pm)(hydroxyl functionalpacking) (7) Millipore Waters Prototype td-IT.
(C) Mobile Phases: (1) TI-IF; (2) DMF; (3) DMF/0.1M LiBr; (4) DMAC.(D) Calibrants: (1) Narrow molecular weight distribution (MWD) polystyrene
(E) Materials: (1) Broad MWD PS: Dow 1683, NBS 706, ASTM PS4; (2) BroadMWD PMMA: Polymer Bank 6041, Aldrich 18226-5; (3) PVC: PressureChemical PV-4; (4) Polyvinyl acetate (PVAe): Cellomer 024 CO1 and 024CO3; (5) Branched PS: Branch B (The University of Akron).
Results and Discussion
Ultrastyragel GPCVfrHF. Dead Volume (Viscometer Delay Time): As shown inthe previous paper 3(2)the dead volume difference between the viscometer and theDRI detectors must be accounted for. Otherwise, systematic errors in the Mark-Houwink parameters K and c_can occur. Table I shows the effect of dead volumeon the molecular weight averages, the intrinsic viscosity and the Mark-Houwinkparameters. As we reported previously (4,5) K and a are very sensitive to the valueof the dead volume between detectors. However, the molecular weight averagesand the bulk intrinsic viscosity are barely affected. The viscometer delay time wasestimated to be 1.5 seconds (24.6 pl) by matching K and cevalues to those obtained
from the viscosity law plot from narrow molecular _eight distribution polystyrenestandards by on line GPC-viscometry CK= 1.5 x 10 and ce= 0.702). Themeasured delay time between detectors using toluene was 4.8 seconds (79/xl) whichis close to the value calculatable from the physical dimensions of the tubing. Thecause of the discrepancy, known as the "LeSec Effect", and the remedy to correct itwas the subject of a recent study 6(6)reported in the First InternationalGPC/Viscometry Symposium held at Del Lago Resort, TX, April 24-26, 1991. This"Lesec Effect" also was investigated in this laboratory through a modifiedrefractometer where the original connecting tubing was replaced with larger IDtubing resulting in a larger dead volume (300 #1). In the process of calibrating thismodified refractometer with narrow MWD polystyrene standards, a set ofreasonable K and a values (0.00019 and 0.69) is obtained. However, the results
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obtained for the broad MWD polystyrenes 0VBS 706 and Dow 1683) indicated theat values are highly overestimated. Even with zero dead volume, the at value is stillas high as 1.00. Apparently, negative dead volume values had to be used to obtain areasonable at value. This confirms our earlier observation that the GPCV softwareis treating the dead volume different from Glidden GPCNIS 3(_, and indicates aninadvertent minus sign error in the Millipore-Waters GPCV software.
Linear and Branched Polymers. The results of a series of commercially availablepolymers analyzed with this system have been reported in the previous paper (3_). Inthis chapter, attention will be focused on a randomly branched polystyrene samplewhich was obtained from the University of Akron. The results are listed in Table IIalong with those of the linear NBS 706. It is seen that although the molecularweight of this branched sample is equivalent to that of the linear NBS 706, viscosityis lower. Upon comparing the log [_/]vs. log M (viscosity law) plot in Figure 1 theindication of branching is evidenced by the deviation of the viscosity from the linearNBS 706 polystyrene polymer in the higher MW regions. The branching index canbe obtained as a function of molecular weight by ratioing the viscosity of thebranched polystyrene sample to that of the linear polystyrene sample at the samemolecular weight.
GPCV/DMF and GPCV/DMF (0.1M LiBr)
To provide MWD information for polymers which are not TI-IF soluble, DMF wasinvestigated as a GPC eluant. Various combinations of columns were explored.One major problem in using DMF with the crosslinked polystyrene gel packing isthe interference of the solvent trash peaks with the low molecular weighl i (M_polystyrene standards as shown in Figure 2 for three PLgel columns (10 J, 10_,50 A). It is seen that the polystyrene 500 MW standard eluted after the solvent peakwhich also interferes with the polystyrene 2100 MW standard. The apparentretardation of elution of low MW polystyrene molecules was explained by earlierworkers (7.,8_)in terms of adsorption of the polystyrene on the apolar polystyrene gelpackings. Addition of LiBr modifier did not improve but further retarded theelution time. Similar limitations in the low MW region were observed for a columnset consisting of 3 gI-IT linear columns pills a Shodex KD-802.5 column,
By using a Ultrahydrogel column (PMMA-type gel packing) with the 3 ttHTlinear columng, the solvent trash peak elutes much later in time as shown in Figure 3for the polystyrene 1350 standard. With the addition of the Ultrahydrogel column,the low MW region can be extended to resolving the polystyrene 800 MW standard.This will provide for improved quantification of molecular weight distributionstatistics in the low molecular weight region. This column set Was calibrated withthe narrow MWD polystyrene standards with the GPCV data system.
Figure 4a shows the hydrodynamic volume calibration curve and Figure 4bshows the viscosity law plot for the generation of the Mark-Houwink parameters Kand or. These values are in good agreement with the literature data (.9,1_.0)A seriesof broad MWD polymers were run on this system. The results are shown in Tablem. In general, the molecular weight averages and bulk intrinsic viscosity are inreasonable agreement with the nominal values I(].L),although the number averagemolecular weight seems to be higher than those obtained with the Ultrastyragel/THFsystem. This could be explained by the lack of resolution at the low MW regions.
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The system also can detect the branching of a polyvinyl acetate sample as shown inFigure 5 by the branching index plot.
We also examined the PLgel column set with DMF/0.1 M LiBr as the eluant.Using narrow MWD PMMA standards as calibrants, all the MW informationobtained for the broad MWD samples seem to be underestimated. The exact causeof the problem is unclear at this time, although we did observe higher systempressure. In a recent paper (1_2)in a similar study, it was mentioned that smallerparticle size (5 tan) PLgel colurnnx might not be suitable for viscous eluants such asDMF due to high operation pressure and shear degradation of high MW polymers.
GPCV/DMAC
Since the validity of universal calibration in DMF may be questionable for a widevariety of polymers due to the adsorption of polymers on the apolar polystyrene gel,dimethyl acetamide (DMAC) was explored as an alternative solvent. The resultsindicate that with 3 pJ-IT linear columns and a Shodex KD-802.5 column set, theuniversal calibration concept was applicable. Figure 6 shows the primary molecularweight calibration curves for PS, PMMA and PEO/PPG standards. As expected,POE/PPG did not fall into the same curve as those of PS and PMMA. However,when the data are plotted onto a universal calibration curve, it all fails onto acommon line as shown in Figure 7. The K and a values obtained from the narrowMWD polystyrene standards are 0.000129 and 0.696, respectively. These valuescompared favorably with the literature data 1(!2). The results obtained for the twobroad MWD polystyrenes are listed in Table IV.
Conclusions
The single capillary viscometer hardware functions well and exhibits good baselinestability. For broad MWD samples, accurate absolute molecular weight averages,bulk intrinsic viscosity values, and Mark-Houwink K and _ parameters can beobtained from a single GPC experiment. In addition, the software providesbranching information as a function of MW for the branched polymers. GPC-viscometry studies in DMF or DMF/LiBr solvent indicate that partitioning oradsorption of polymers may be occurring on apolar polystyrene gel, causingretardation of elution. The 3/J-IT and ultrahydrogel column._/DMF solvent systemappear to give normal results for MW averages while the 5 _un PLgel coblmn._greatly underestimate the MW. Further work is required to def'me the observedphenomena in terms of interactions involving solvent, polymer sample type and thetype of column packing used. The dimethyl acetamide results indicate that theuniversal calibration concept is applicable to a variety of types of polymerstandards. The trash peaks interfere less with the sample peaks when 3 pJ-tT linearcolumn._ are coupled to a Shodex KB 802.5 column.
Literature Cited
1., Haney, M. A. J. Appl. Polym. Sci., 1985, 30, 3037.2. Ekmanis, J. Proceedings of International GPC Symposium '89, p.1.3. Kuo, C.; Provder, T.; Koehler, M. E. J. Liquid Chromatogr., 1990, 13 (16),
3177.
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4. Malihi, F. B.;Kuo, C.; Koehler, M. E.; Provder, T.; Kah, A. F. In ACSSymposium Series No. 245; Provder, T. Ed., 1984, 281.
5. Kuo, C.; Provder, T.; Koehler, M. E.; Kah, A. F. In ACS Symposium SeriesNo. 352, Provder, T. Ed., 1987, 130.
6. Dark, B., Ekmanis, J. L., Harvard, T. J., Huard, T., Lesec, J.; Neilson, R."The Use of the 150CV GPC/Viscometry System for the Determination ofMark-Houwink Constants K and a", presented at the First InternationalGPC/Viscometry Symposium, Del Lago Resort, Texas, April 24-26, 1991.
7. Dubin, P. L.; Koontz, S.; Wright, K. L. L Polvm. Sci., Polym. Chem. Ed.,1977, 15, 2047.
8. Matsuzaki, T.; Inoue, Y.; Ookubo, T.; Mole, S. J. Liq. Chromatogr., 1980, 3,353.
9. Tsimpris, C. W.; Suryanarayanan, B.; Maghan, K. G. I. Polym Sci., Part A-2, 1972, 10, 1837.
10. Ogana, T. J. Liq. Chromatogr., 1990, 13, 51.11. Harm, N. D. J. Polym. Sci., Polymer Chem. Ed., 1977, 15, 1337.12. Mourey, T. H.; Bryan, T. G. J. Liq. Chromatogr., 1991, 14, 719.13. Dawkins, J. V.; Hemming, M. Polymer, 1975, 16, 554.
TABLE I. EFFECT OF DEAD VOLUME BETWEEN DETECTORS(TEST SAMPLE: DOW 1683 POLYSTYRENE)
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