Chapter 1
An Overview of Size Exclusion Chromatography for Polymers and Coatings Cheng-Yih Kuo and Theodore Provder
Downloaded by 92.63.110.177 on January 30, 2017 | http://pubs.acs.org Publication Date: October 2, 1987 | doi: 10.1021/bk-1987-0352.ch001
The Glidden Company, Research Center, 16651 Sprague Road, Strongsville, OH 44136
Recent technological advances have sparked a new level of activity in the field of Size Exclusion Chromatography (SEC). These include: 1) high performance/high speed column technology, 2) the development and increased use of simultaneous multiple in-line detectors such as differential refractometer, ultraviolet and infrared spectrophotometric detectors, viscometers, low angle laser light scattering, and mass detection, and 3) the application of minicomputer and microcomputer technology for instrument control and data analysis. These developments in turn have led to new improved applications of SEC as well as higher quality information. In this paper, the SEC separation mechanism, molecular weight calibration methods including the use of hydrodynamic volume, instrument spreading corrections and polymer chain branching calculations will be discussed. Quantitative and qualitative examples of the application of multiple detectors will be given. Finally, there will be some discusison of the requirements necessary for high resolution SEC analysis of oligomers and examples will be shown. Polymer chemists and c o a t i n g s f o r m u l a t o r s a r e c o n t i n u a l l y b e i n g c a l l e d upon t o t a i l o r - m a k e c o a t i n g s systems which r e q u i r e polymers having s p e c i f i c a l l y designed m o l e c u l a r a r c h i t e c t u r e s and p h y s i c a l p r o p e r t i e s . Knowledge of t h e m o l e c u l a r weight and m o l e c u l a r weight d i s t r i b u t i o n (MWD) o f the polymer components i n a c o a t i n g s system i s e s s e n t i a l f o r the o p t i m i z a t i o n o f polymer d e s i g n f o r s p e c i f i c end-use p r o p e r t i e s . S i n c e i t s i n t r o d u c t i o n over two decades a g o , ( J J g e l permeation chromatography (GPC) o r s i z e e x c l u s i o n chromatography (SEC) has become an important and p r a c t i c a l t o o l f o r the d e t e r m i n a t i o n o f the MWD o f polymers. A l a r g e number of s t u d i e s has been p u b l i s h e d on the use o f SEC i n p l a s t i c s , e L a s t o m e r i c and c o a t i n g s systems. W i t h t h e advent o f h i g h e f f i c i e n c y columns, the r e s o l u t i o n i n t h e lower m o l e c u l a r 0097-6156/87/0352-0002$07.75/0 © 1987 American Chemical Society
Provder; Detection and Data Analysis in Size Exclusion Chromatography ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
1.
KUO AND PROVDER
3
SEC for Polymers and Coatings
weight r e g i o n ( m o l e c u l a r w e i g h t s i n the range of 200 t o 10,000) has been g r e a t l y improved and the speed of a n a l y s i s i n c r e a s e d . These f e a t u r e s make h i g h performance SEC (HPSEC) an i n d i s p e n s a b l e c h a r a c t e r i z a t i o n t o o l f o r the a n a l y s i s of o l i g o m e r s and polymers i n e n v i r o n m e n t a l l y a c c e p t a b l e c o a t i n g s systems.
Downloaded by 92.63.110.177 on January 30, 2017 | http://pubs.acs.org Publication Date: October 2, 1987 | doi: 10.1021/bk-1987-0352.ch001
SEC. S^J^J^ÀPJL-
e
il Ahani sm
S i z e e x c l u s i o n chromatography i s a l i q u i d chromatography method, whereby, the polymer m o l e c u l e s are s e p a r a t e d by t h e i r m o l e c u l a r s i z e or "hydrodynamic volume" i n s o l u t i o n as s o l v e n t e l u t e s through a column(s) packed w i t h a porous s u p p o r t . The degree of r e t e n t i o n of the polymer m o l e c u l e s i n the pores i s the phenomenon which a f f e c t s the s e p a r a t i o n . S m a l l e r m o l e c u l e s a r e r e t a i n e d i n the pores t o a g r e a t e r degree than the l a r g e r m o l e c u l e s . As a r e s u l t the l a r g e s t s i z e m o l e c u l e ( o r the m o l e c u l e h a v i n g the g r e a t e s t hydrodynamic volume) e l u t e s from the column f i r s t f o l l o w e d by the s m a l l e r m o l e c u l e s . The volume of l i q u i d at which a s o l u t e e l u t e s from a column or the volume of l i q u i d c o r r e s p o n d i n g t o the r e t e n t i o n of a s o l u t e on a column i s known as the r e t e n t i o n volume ( V ) and can be r e l a t e d to the p h y s i c a l parameters of the column as f o l l o w s : R
v where
= ν
R
ο
+
κν.
(1)
V = r e t e n t i o n volume of the s o l u t e V = i n t e r s t i t i a l volume (dead volume) of the column V\ = i n t e r n a l s o l v e n t volume i n the pores Κ = the d i s t r i b u t i o n c o e f f i c i e n t , based upon the r e l a t i v e c o n c e n t r a t i o n s between phases. R
q
The t o t a l column volume V
=
T
V
o
i s g i v e n by
+ V.
(2)
T h e r e f o r e , the r e t e n t i o n volume i s e x p r e s s i b l e i n terms of the two measurable q u a n t i t i e s V and V as Q
V
K
= V (1-K) + KV^
O
1
T
0 10 ) a r e needed. A l s o needed a r e v e r y h i g h r e s o l u t i o n columns f o r o l i g o m e r s (50
