Author(s)Ansunman Mahato & Alan Brookes
Agilent Technologies India & EMEA
ACCURATE MOLECULAR WEIGHT DETERMINATION OF POLYETHER POLYOLS BY TRIPLE DETECTION GPC
MATERIALS MARKET
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Polyether polyols are polymerized products produced by the catalyzed addition of monomers of propylene oxide (PO) and/or ethylene oxide (EO) to an initiator. Typical initiators are glycerin, mono-propylene glycol, sucrose, sorbitol, water and amines. They are organic materials with two or more alcohol (hydroxyl) groups (OH) at the end of the polyether chains. Polyols of varying molecular weight, functionality, viscosity and reactivity can be produced. They are liquid at room temperature, sometimes with micrometer polymer particles present in suspension. Accurate molecular weight determination for these polymers is essential as the ambiguity in molecular weights changes the physical property of the end product. GPC with Triple Detection is an excellent technique for the analysis of polymers.
ABSTRACT
Mobile Phase THF
Columns
2x PLgel 5 μm MiniMIX-D, 250 x 4.6 mm (PL1510-5504)1x PLgel 5 μm MiniMIX-D Guard, 50 x 4.6 mm (PL1510-1504)
Standards Polystyrene Low EasiVials (4ml), PL2010-0400, Batch: 0006184914
Temperature 40 ˚C (column and detectors)Injection volume 100 μLFlow Rate 0.4 ml/minSoftware Agilent GPC/SEC software
INTRODUCTIONPolyether polyols, when combined with di-isocyanates, are used in urethane applications, such as flexible foam, coatings, adhesives, sealants and elastomers. As a result, we see them in a wide variety of goods including furniture, car seating, coatings, artificial sports tracks, playground surfaces, and waterproof leisure wear. Polyether polyols are also used in non-urethane applications such as surfactants and oil demulsifiers.
EXPERIMENTALInstrumentation
Agilent 1260 Infinity II Isocratic pump (G7110B)Agilent 1260 Infinity II Vial sampler (G7129A)Agilent 1260 Infinity II MCT (G7116A)Agilent 1260 Infinity GPC/SEC Multi-Detector Suite (G7800A) Equipped withMDS Viscometer Detector MDS Light Scattering Detector MDS Refractive Index Detector
Figure 1. Formation of polyther polyols
Method for Analysis
Instrument/Detector/Column CalibrationInstrument and column calibration is performed using EasiVial polystyrene standards. Standards chromatograms are shown overlaid in Figure 2. Calibration data points are shown in Figure 3
Figure 2: Easivial Polystyrene Calibration
RT PS Mp10.2 5115010.6 2915011.0 1954011.6 997011.9 677012.2 443012.6 293013.0 193013.5 102013.9 57514.2 38015.0 162
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SAMPLE ANALYSIS
Figure 4: Polyol Sample 1
Figure 3: Calibration Curve
Three different molecular weight Polyether polyols were analyzed by GPC. Chromatograms are shown in Figures 4-6. System precision and reproducibility were evaluated by replicate injections of a Broad Polystyrene Standard shown in Figure 7.
Figure 5: Polyol Sample 2
Figure 6: Polyol sample 3
Figure 7: Broad Polystyrene
Sample Name Mp Mn Mw PD Bulk IV
Polyols sample _1 814 811 812 1.001 0.03
Polyols sample _2 4508 4393 4460 1.015 0.08
Polyols sample _3 6146 6181 6182 1.0 0.21
RESULTSMolecular weight results by Triple Detection
The column set comprising Two MiniMIX-D, 250 x 4.6 mm columns provides excellent resolution over a linear operating range from 200 to 400,000 g/mol (PS equivalent). Choosing these columns with an ID of 4.6mm allows us to use a much lower flow rate than conventional GPC columns. At 0.3ml/min we benefit from a 60% reduction in solvent consumption whilst retaining manageable run times.
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In Figure 8 we see the overlaid chromatogram plots of the three Polyester Polyols
The Agilent 1260 Infinity II GPC system equipped with the Infinity MDS allows a user to study the molecular weights of these polyols.
A well characterized broad distribution polymer sample can be used to periodically check the system performance. Calculated molecular weight by triple detection for the Broad polystyrene standard is shown in the table below.
Figure 8: Overlaid Chromatograms of 3 Polyols
SYSTEM REPRODUCIBILITY:
Instrument/Detector/Column Calibration
Sample Name
Theo-retical,
Mw
Experimental Mw calculated through triple
detector
Asym-metry
Agilent Broad
PS standard
291000 296179 1.9
Reproducibility of the Polyol sample analysis is shown by the replicate chromatograms from the 4 detector channels in Figures 9-12.
Precision of 1260 MDS System
Figure 9: Overlay of 5 replicate runs, Rl, five replicates
Figure 10: Overlay of 5 replicate runs, LS 90, five replicates
Figure 11: Overlay of 5 replicate runs, VS, five replicates
Figure 12: Overlay of 5 replicate runs, LS 15, five replicates
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Samples Mp Mn Mw PD Bulk IVPolyols sample replicate 1 4430 4279 4364 1.02 0.08Polyols sample replicate 2 4402 4284 4338 1.013 0.08Polyols sample replicate 3 4447 4318 4396 1.018 0.08Polyols sample replicate 4 4511 4357 4426 1.016 0.08Polyols sample replicate 5 4508 4393 4460 1.015 0.08
Results of repeat runs for a typical Polyols sample
1260 MDS triple detector is well suited for analysis of polyols samples even at relatively low molecular weight. System molecular weight accuracy can be monitored using a broad polystyrene polymer with known molecular weight. System reproducibility is shown by analysis of replicate injections of one of the Polyol samples.
CONCLUSIONS
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This information is subject to change without notice.© Agilent Technologies, Inc. 2017
Printed in EU, 2017-05-85991-8195EN