fourier transform infrared spectroscopy size exclusion chromatogwhy

99 Pages·2000·4.28 MB·English

FOURIER TRANSFORM INFRARED SPECTROSCOPY
IN
SIZE EXCLUSION CHROMATOGWHY
Keivan Torabi
A thesis submitted in conformïty with the requirements
for the Degree of Master of Applied Science
Graduate Department of Chernical Engineering and Applied Chemistry
University of Toronto
O Copyright by Keivan Torabi, 1999
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Size Exclusion Chromatography (SEC) is now a cornmon method for analyzing the
molecular weight distribution of polyrners. SEC separates the molecules accordhg to
their size in soiution to permit each size to be exarnined by a "detector". A
differential rehctive index (DRI) detector is most fiequently used to obtain
concentration of each size. Howeve. this detector provides ambiguous data if the
polymer molecules Vary in composition as well as size (e-g. are fiom a copolymer or
a polymer blend). If a Fourier Transform Infiared (FTIR) spectrometer could be used
instead of the DRI it could more than overcome this disadvantage by providing a
great deal of information on rhe concentration of individual functional groups. FTIR
has begun to be used for SEC. However, there are d l la rge uncertainties associated
with this application particuiarly when it is used for quantitative d y s i s .
Quantitative analysis using FTIR detection for is the topic of this work. Polystyrene,
poly(methy1 methacrylate) and their blends as well as a sytrene methyl methacrylate
copolymer were analyzed. The first objective was to assess a SEC flow ceil
approach. It was rapidly demonstrated that absorbance interference of the carrier
solvent was intoierdbie. The dilute polymer concentrations used in SEC, combined
with the very limited wavelength windows present in SEC mobile phases, greatly
reduced FTIR utility. The second objective was to develop experimental methods for
obtaining FTIR calibration data applicable to the solvent evaporation interface by
using conventional solvent cast films. This involved determining how best to solvent
cast polymer films and successfully devising a method for effectively measuring film
quality. Use of a mask to detennine localized spectra at different points on the nIm
provided the latter. The third objective dominated the work. It was to develop
quantitative interpretation methods for FTIR data obtained using a solvent
evaporation interfixe with SEC. The solvent evaporation interface allows the
chromatograph to produce each molecular sue as a dried polymer f i h on a
germanium pellet. Accomplishing this objective required the development of both
intemal and extemal calibration methods. Internai calibration refers to the use of a
DR1 detector with the FTIR detector to obtain concentration versus mass data based
on pure linear homopolymers. Extemai calibration refers to the use of solvent cast
films to obtain such information. Linear regression and partial least squares were
used for calibration and then for prediction to determine quantitative estimates of
composition. The mass variation with retention tirne in the size exclusion
chromatopph was integïated to provide total mass of polymer recovered in the
solvent evaporation interface. it was found that partial least squares and the use of
annestled sampies provided the best precision and accuracy in estirnates of both
composition and total mass recovered.
ACKNOWLEDGEMENT
I would like to thank Professor S.T. Balke for aii his advice, guidance,
encouragement. and patience during this work. His dedicated supervision and
continuai support have contributed greatly to my research accomplishmen~
1 am also indebted to Dr. Timothy C. Schunk of Eastman Kodak (Rochester, New
York) for his invaluable guidance and involvement in my project In particuiar 1 am
gratehl for his helpfid suggestions in the use of the analytical software and the
experimental techniques.
This project would not have been possible without the financial support of the
Eastman Kodak Company (Rochester New York).
1 wouid also like to acknowledge my fnends in the Department of Chemicai
Engineering and Applied Chemistry: Lianue hg, Chistopher Gilmor, and Audrey
Yakimov.
Finally, the great support of my parents has been instrumental in the completion of
this thesis.
Table of Contents
ABSTRACT
AC K N O m E D G m T S
TABLE OF C O N m T S
LIST OF FIGURES
LIST OF TABLES
LIST OF APPENDICES
NOMENCLATURE
1. rNTRODUCTION 1
2. THEORY
2.1. Fundamentals of FTIR
2.1.1. FTIR Instrument
2.1 2. Beer-Lambert's Law
2.1.3. Resolution
2.1 -4. The Spectral Manipulation
2.1.5. The Advantages and Limitations of FTZR Spectroscopy
2.2. Fundamentals of SEC
2.2.1. SEC Instrument
2 - 2 2 Calibration for Molecular Prediction
2.2.3. DR1 Ch romatogran hterpretation
2.3. Data lnterfacing Techniques in SECETIR
2.3.l Flow Ceil
2.3.2 Solvent Evaporative Interface (SEI)
2.4. Data Andysis Techniques
2.4.1. Linear Regression (LR)
2.4.2. Partial Least Squares (PLS)
2.4.3. Data lnterpretation
2.5. Calibration
2.5.1. Internai Calibration based on DR1
2 - 5 2 Externai Caiibratioa by Hand Casting
2.5.3. Cornparison of Calibration Methods
3. EXPERIMENTAL
3.1. Materials
3 -2. Size-Exclusion C hromatography (SEC)
3.3. Flow Ce11
3- 4. Solvent Evaporative Interface (SEI)
3 S. Sample Preparation and FTIR Analysis
3.6. Data halysis
4. RESULTS AND DISCUSSION
FTIR Analysis of Solutions
Solid Films for FTlR Analysis
4.2.1 Film quality from the Solvent Evaporation Interface
4.2.2. Film quality from Film Casting
Use of the Solvent Evaporation Interface with Extemal Calibration 51
4.3.1. Spectral Deconvolution 51
4.3 -2. Linear Regression Calibrarion 52
4.3.3. The Effect of Molecuiar Weight 54
4.3 -4. Assessrnent of Beer's Law Deviations 55
4.3 -5. The Composition of Polymer Blends and Total Mass Collected
57
Use of the Solvent Evaporative Interface with Internal Calibration 60
4.4.1. Internal calibration for the Compositional Analysis of
Annealed Films Using Linear Regression 61
4.4.2. Intemal calibration for the Analysis of Annealed and As
Collected Polyrner Blend Films Using PLS
4.5. Quantitative Analysis of the Composition of Copolymers
4.6. Quantitative Anaiysis of Total Mass
4.6.1. PS and PMMABIends
4.6.2. SMM Copolymer
5. CONCLUSIONS
6 . RECOMMENDATIONS
7. REFERENCES
8. APPENDICES
LIST OF FIGURES
Figure
FTIR Spectrum of PMMA
FTIR Spectrometer components
resolution Cornparison in FTIR spectnim
Second Denvative Spectnun of PMMA
SEC components
A dernountable infrared liquid ce11
Evaporative Interface designed by Dekmezian in 1990
The Collection Stage of the Solvent Evaporative interface
Diagram of the solvent evaporative interface developed by
Eastman Kodaknf
Experimental system configuration with altemate DR1 or
solvent evaporation interface connection
Detectability of Liquid Ce1 in High Concentrations
Detectabili~o f Liquid Ce11 in a broad range of concentrations
FTIR Spectra for 10 mgml PMMA in THF (0.3 mm Spacer)
FTIR Spectra for 1 -5 m g h l PMMA solution in TEE
(0.1 mm Spacer)
FTIR Spectra for 0.0 15 m g h i PMMA solution in THF
(0.1 mm Spacer)
The effect of increasing the resolution and the nurnber of
scans to improve detectability for PMMA in SEC concentration
-g=
Calibration for PMMA with large volume liquid ce11
Calibration for fS in THF with large volume liquid ce11
PMMA detectabi lity in C H s l z
detection window for PS and PMMA with dichloromethane
vii
Lack of detectability for PS in CHzClz within the SEC
concentration range
Impact of solvent annealing on the IR scattering background for
50-50 PS - PMMA blend fraction collected fiom SEC with
the solvent evaporation interface [15]
impact on 1730 c d ba nd absorbance of casting conditions
observed for manuaily cast reference films of PMMA on polished
Ge disks
Determination of film unifonnity of mandly cast PMMA f i h
using masked areas as shown in the inset
Example resdt of PeakFit software baseline and Gaussian band
fitang for a narrow region of a PS film spectnun
Calibration plots of absorbance band area determined with
PeakFit sohvare for manually cast polymer films
Online Calibration for PS and PMMA
The Effect of the ~MoleculaWr eight on the Performance of SEI
The band ratio cornparison of PS infr-ared peaks for 75% blend
and pure sarnples
The band ratio cornparison of PS ùifiared peaks for 50% blend
and pure samples
Caiculated 5050 PSPMMA blend composition using LR
external calibration expressed as weight percent PMMA of
anneded SE C fractions Ob tained fiom the solvent-evaporation
interface
LR extemal caiibration relative error in wt.% PMMA prediction
Cornparison of W.% PMMA across the SEC chromatograms
determined by FTIR LR external calibration and DIU
Nomalized DR1 chromatogram of pure PS and PMMA used in
blend SEC experiments
Calibration alternative for PMMA
Internai Calibration for PMMA
viii