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Unlike GPC, GPEC enables separation of polymers independent of their molecular weight, supporting multifaceted polymer analysis.
The Nexera Method Scouting System can realize significant labor savings and high efficiency in method development when
investigating the separation conditions for GPEC, in which selection of the mobile phase composition to be used and adjustment of
the gradient conditions are particularly important.
High Efficiency in Investigation of Polymer
Separation Based on Composition Using Gradient
Polymer Elution Chromatography (GPEC)
Kana Matsuoka, Hidetoshi Terada
Nexera Method Scouting System High Performance Liquid Chromatograph
In polymer materials, analysis and confirmation of the polymer
composition in the processes from research and development
to quality control are extremely important because the
composition has a large influence on the physical properties of
the material. Among these polymers, copolymers are polymers
which are composed of multiple types of monomers, and the
properties of copolymer materials are also known to differ due
to differences in the composition and arrangement of their
constituent monomers. Therefore, identification and isolation of
those components in copolymers are important.
Size exclusion chromatography (SEC)/gel permeation
chromatography (GPC), in which separation is conducted based
on polymer size, is generally used as a polymer separation
technique. Because the constituent polymers can be separated
by molecular weight, it is possible to obtain information such as
the molecular weight distribution, but when the sample
contains a mixture of polymers with similar molecular weights
and different compositions, separation is not possible. The
technique called gradient polymer elution chromatography
(GPEC) is useful in such cases, as the polymers are separated
according to differences in their composition, independent of
the size of the polymer. In the GPEC separation technique, the
sample material is injected in a mobile phase with a
composition (poor solvent) in which the target polymer is
insoluble, intentionally precipitated in the flow path, for
example, at the end of the column, and then redissolved and
eluted in the flow path by applying a gradient to the mobile
phase composition to a composition (good solvent) that easily
dissolves the target polymers. Since applying a gradient to the
mobile phase composition makes it possible to separate
polymers based on differences in their solubility in the solvent,
the polymers can be separated according to their compositions.
However, because investigation of the GPEC analytical
conditions is frequently based on experience, the analytical
conditions must be investigated individually for each sample.
Thus, the time and trouble required in investigating the
separation conditions for GPEC has been a drawback of this
technique.
The Nexera Method Scouting System can achieve high
efficiency in method development work, because the analytical
conditions can be screened by automatically changing the type
and composition of solvents for the mobile phase, the column
to be used, and other analytical conditions. This article
introduces an example in which the conditions for a GPEC
analysis were investigated efficiently by using the Nexera
Method Scouting System and dedicated software Method
Scouting Solution, and an analysis of a copolymer and its
constituent homopolymers (polymers consisting of only one
monomer) was carried out by the GPEC separation technique.
Introduction
Table 1 shows the copolymer used in the analysis and its
constituent homopolymers. The weight-average molecular
weights (Mw) of all of the polymers were around 1.0 x 10
4
. The
samples were all dissolved in THF and adjusted to a
concentration of 0.2 %.
Polymer Name Name
Polystyrene Homopolymer-A
Poly(tert-Butyl Acrylate) Homopolymer-B
Poly(tert-Butyl Acrylate)-block-Poly(styrene) Copolymer (10:11)
Table 1 Sample Materials
Table 2 shows the analytical conditions used in the GPC analysis
of the samples shown in Table 1, and Fig. 1 shows the GPC
chromatograms. Because both the homopolymers and the
copolymer have weight-average molecular weights of around 1.0
× 10
4
, complete separation of the peaks was not possible by GPC.
GPC Analysis
Table 2 GPC Analytical Conditions
Column : Shim-pack GPC-8025
*1
(300 mm × 8.0 mm I.D., 6 µm)
Mobile phase : THF (without stabilizer)
Flow rate : 1.0 mL/min
Column temp. : 40 ˚C
Injection vol. : 10 µL
Vial : SHIMADZU LabTotal for LC 1.5 mL, Glass
*2
Detection : Refractive index (RID-20A)
Polarity : +
Cell temp. : 40 ˚C
Response : 1.5 sec
*1 P/N: 228-20805-91
*2 P/N: 227-34001-01
Homopolymer-A,B+Copolymer (10:11)
Copolymer (10:11)
Homopolymer-B
Homopolymer-A
0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0
min
0
10
20
30
µRIU
Fig. 1 GPC Chromatograms of Single Samples of Homopolymers
and Copolymer and Mixed Sample
