Foundation GPC Polymers and Molecular Weight · GPC/SEC provides critical information for the polymer chemist: Distribution of chain lengths (Relative molecular weights) Further parameters

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



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



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.



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



Molecular Weight

Universal Calibration



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



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



Typical dn/dc Values



Angular Dependence

Polymers as multi-point scatterers



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



Advanced GPC/SEC Detectors

True Molecular Weights



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




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




Mark-Houwink Plots

Clear trend in Mark-Houwink plots

Increased branching/decreased molecular size leads to a decrease in IV



Upgrading your system



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



http://www.chem.agilent.com/Library/primers/Public/5990-7196EN.pdf

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



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



Thanks for Listening

Any Questions



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



http://www.agilent.com/chem/gpc-solutions



Documents

Foundation GPC Polymers and Molecular Weight · GPC/SEC provides critical information for the polymer chemist: Distribution of chain lengths (Relative molecular weights) Further parameters