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Ben MacCreath, PhD
Product Manager
GPC/SEC Instrumentation
26th March 2013
Expand your
capabilities with multi-
detector GPC/SEC
Houston, 26th March '13
Polymer People Seminar Tour
• Calibrate the column with a set of
polymer standards
• Plot retention time (RT) versus peak
log molecular weight (logM)
• Calibration is used to generate
molecular weights of unknowns
• BUT Molecular Weights are only
equivalent to the Standards used
• So a Polystyrene calibration will give
Polystyrene equivalent molecular
weights for all samples analysed.
Conventional GPC
Generating molecular weights
Houston, 26th March '13
Polymer People Seminar Tour
Increasing the information from GPC/SEC
GPC/SEC provides critical information for the polymer chemist:
Distribution of chain lengths
(Relative molecular weights)
Further parameters can be determined by employing advanced
detectors
The molecular weight (accurate or absolute)
The polymer’s size
The polymer’s shape
Can be used to investigate polymer branching
Houston, 26th March '13
Polymer People Seminar Tour
Why use advanced detectors for GPC/SEC?
To understand why advanced detectors are
required, we need to first understand the
limitations of Conventional GPC.
Column separates on basis of molecular size
NOT molecular weight
Two polymers of different chemistries will interact
differently with a particular solvent
• At any molecular weight, the two polymers will
have different sizes in solution
→ Molecular weights from Conventional
GPC/SEC are relative. They depend on a
comparison in size between the standards and
the sample.
Houston, 26th March '13
Polymer People Seminar Tour
Improving the experimental information
Molecular weight sensitive detectors for GPC
Houston, 26th March '13 Polymer People Seminar Tour
• Viscometer detector
– Response proportional to the intrinsic viscosity (IV) of the polymer
– Generate accurate molecular weight for polymers using the Universal Calibration
principle
– Determination of Branching
– Conformation & size of polymer
• Dual angle light scattering (LS) detector
– Response directly proportional to molecular weight (Mw) of the polymer – ‘Absolute
Molecular Weight’
– Scattered light measured at more than one angle permits determination of Radius of
gyration (Rg)
– Determination of Branching
– No column calibration required
Introduction to the Viscometer
4 capillary bridge viscometer
T
At any given MW, a high IV means the
sample is a large diffuse molecule, a small
IV means a compact, dense molecule
Houston, 26th March '13
Polymer People Seminar Tour
Molecular Weight
Universal Calibration
Houston, 26th March '13
Polymer People Seminar Tour
Retention time / mins
Lo
g M
w
Polyethylene
Polystyrene
Lo
g IV
* M
w
Ref : Grubisic, Rempp, Benoit, J. Polym.
Sci., Part B, Polym. Lett., 5:753 (1967)
The IV of the standards is used to generate a
Universal Calibration. By measuring the viscosity
response of the samples, ‘true’ molecular weights
independent of the standards used for the column
calibration are calculated.
Conformation
Using Viscometry
Using the sample
response from our
viscometer we can
generate a Mark-
Houwink Plot. The
slope will indicate the
conformation of the
polymer.
Furthermore this can be used to
determine the size of the polymer.
Intrinsic viscosity
is related to
the radius of hydration, Rh
Linear homopolymers have linear slopes
Houston, 26th March '13
Polymer People Seminar Tour
Molecular Weights
Using Light Scattering
Excess scattered light from a sample
in solution is directly proportional to
molecular weight (Mw).
Absolute determination
No reliance on column calibration so
‘absolute’ molecular weights are
calculated
Concentration and dn/dc are critical factors when using Light Scattering
Houston, 26th March '13
Polymer People Seminar Tour
Typical dn/dc Values
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Angular Dependence
Polymers as multi-point scatterers
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Scattering Function This can only be determined by
simultaneously measuring at more than
one angle. Allows determination of Rg.
Conformation
Using Light Scattering
• A Conformation plot of log Rg versus log M should give a straight line for a
linear homopolymer
• K and slope vary between different solvents and polymers
• The slope gives an indication of the conformation of the polymer in solution
Houston, 26th March '13
Polymer People Seminar Tour
Advanced GPC/SEC Detectors
True Molecular Weights
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Polymer People Seminar Tour
HDPE in TCB at 160°C
3 x PLgel Olexis (300 x 7.5mm)
PL-GPC 220 with RI & LS
Calibrated with polystyrene
standards (for conventional GPC)
Molecular Weight Averages / g.mol-1
Conventional GPC GPC / Light Scattering
Mn 42,700 15,100
Mw 141,300 48,600
Mz 386,800 130,400
PD 3.31 3.22
3.8 log Mw 6.5
dw
/dlo
g M
0
1
Advanced GPC/SEC Detectors
Mark-Houwink plot to investigate size
Polystyrene Poly(bromo)styrene
The molecular weight distributions show that both samples were of similar modality, with the polystyrene appearing to have a lower molecular weight.
The Mark-Houwink plot highlights the differences in conformation. The polybromostyrene has a lower offset slope indicating that the material is much denser.
Rh can be calculated to support size differences.
Houston, 26th March '13 Polymer People Seminar Tour
Lo
g IV
-1.7
1.0
4.0 log Mw 6.3
Hyperbranched Polyesters
Effect of Branching on IV
Hyperbranched polyesters have been found to contribute to improved physical, chemical and mechanical properties
• Polyester AB/AB2 polymers produced by the condensation of A and B end groups
• Branching introduced by the addition of AB2 monomers into the reaction
• A Hyperbranched polymer structure is formed
• Different chain length AB2 monomers can be used to vary the ‘compactness’ of the polymer molecule in solution
S. Kunamaneni, W. Feast, IRC in Polymer Science and
Technology, Department of Chemistry, University of Durham, UK
Houston, 26th March '13
Polymer People Seminar Tour
Hyperbranched Polyesters
Molecular Weight Distributions
There is no trend in molecular
weight distributions.
Eluent : THF (stabilised with 250 ppm BHT)
Columns : 2 x PLgel 5µm MIXED-C
System : Agilent 1260 Infinity Multi-
GPC/SEC System equipped with
DRI, Viscometer & Light Scattering
Houston, 26th March '13
Polymer People Seminar Tour
Hyperbranched Polyesters
Mark-Houwink Plots
Clear trend in Mark-Houwink plots
Increased branching/decreased molecular size leads to a decrease in IV
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Polymer People Seminar Tour
Upgrading your system
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Polymer People Seminar Tour
DRI
Viscometer
Light scattering detector
Room temperature.
Agilent front end or 3rd party
vendor. High temperature.
Designed to fit inside oven
to prevent precipitation.
Introduction to Multi-Detector GPC/SEC
To learn more about
Multi-Detector GPC
please ask your local
Account Manager for the
Guide to multi-detector
GPC Primer
Houston, 26th March '13
Polymer People Seminar Tour
Expanding Conventional GPC/SEC
Viscometer and Light Scattering Detectors
Advanced detectors give a greater understanding of the analyte
as well as overcoming the limitations of Conventional GPC.
GPC/SEC
Technique Molecular Weight Molecular Size Information
Conventional
(RI or UV)
Relative to standards
used for calibration
No Molecular weight
distribution, concentration
Viscometry More accurate from
Universal Calibration
Yes,
hydrodynamic
radius (Rh).
Conformation, branching.
Works with copolymers
Light
Scattering
Absolute
determination
Yes, Radius of
Gyration (Rg)
directly.
Conformation, branching.
Triple Absolute
determination
Yes, Rg and Rh,
directly.
The ultimate configuration
for comprehensive
polymer characterisation
Houston, 26th March '13
Polymer People Seminar Tour
Summary
Increasing the power of the GPC/SEC experiment
• Molecular weight distribution is critical for the polymer chemist however, further information can be obtained from the same experiment using
– Light Scattering
– Viscometry
• Little change required to conventional experiment methodology
– Stricter lab practice for Light Scattering
– Accurate concentrations required
• Can provide information on
– Accurate molecular weights
– Size
– Shape
– Branching • Branching results often qualitative rather than quantitative
Houston, 26th March '13
Polymer People Seminar Tour
Thanks for Listening
Any Questions
Houston, 26th March '13
Polymer People Seminar Tour
GPC/SEC Resources
Download at http://www.agilent.com/chem/gpc-solutions
Brochure Agilent GPC/SEC solutions - comprehensively better polymer analysis 5990-8844EN
Application
Compendia
Engineering polymers 5990-6970EN
Polyolefin analysis 5990-6971EN
Analysis of elastomers by GPC/SEC 5990-6866EN
Biodegradable polymers 5990-6920EN
Low molecular weight resins and prepolymers 5990-6845EN
Excipient analysis 5990-7771EN
Analysis of food additives by GPC/SEC 5990-8634EN
Primers Introduction to GPC/SEC 5990-6969EN
A guide to multi-detector GPC 5990-7196EN
Product
guides
1260 Infinity GPC/SEC System 5990-9920EN
1260 Infinity Multi-GPC/SEC System 5990-9921EN
Agilent PL-GPC 50 5990-9937EN
Agilent PL-GPC 220 5990-9926EN
Agilent GPC/SEC Software 5991-0478EN
Aqueous and polar GPC/SEC columns 5990-7995EN
Organic GPC/SEC columns 5990-7994EN
GPC/SEC standards 5990-7996EN
Selection
guide Quick guide for selecting columns and standards for GPC/SEC 5990-6868EN
Houston, 26th March '13
Polymer People Seminar Tour