Chemistry Reference
In-Depth Information
Separation and Characterization of
Ethylene-Propylene Copolymers by High-Temperature
Gradient HPLC Coupled to FTIR Spectroscopy
Andreas Albrecht,
1
Lars-Christian Heinz,
1
Dieter Lilge,
2
Harald Pasch
*
1
Summary: The chromatographic separation of ethylene-propylene (EP) copolymers
with regard to chemical composition was accomplished by a new technique - high-
temperature gradient HPLC. Using a mobile phase of ethylene glycol monobutylether
(EGMBE) and 1,2,4-trichlorobenzene (TCB), and silica gel as the stationary phase,
copolymers with different ethylene contents were separated according to their
chemical compositions. Using a sample solvent of n-decanol and a column tempera-
ture of 140
C, chromatographic conditions were established that correspond to
separation in a precipitation-redissolution mechanism. With the aim to obtain
further information on the separation process, the HPLC system was coupled to
FTIR spectroscopy through a LC-Transform interface. The FTIR data confirmed that the
copolymers were separated according to the ethylene content of the eluted samples.
8
Keywords: ethylene-propylene copolymers; FTIR; high performance liquid chromatography;
polyolefins
Introduction
TREF experiment the sample is dissolved
at high temperature and precipitated using
a slow cooling process. In a second step,
fractions of the precipitated material are
eluted at increasing elution temperatures.
The fractionation occurs mainly regarding
sample crystallinity and cannot be used for
amorphous samples. In addition, the long
analysis times and the complexity of the
method prevent a routine use on a daily
basis. With crystallization analysis frac-
tionation (CRYSTAF), which is partially
similar to TREF but requires less analysis
time, determinations of the CCD of EP
copolymers, high density polyethylene
(HDPE), low density polyethylene (LDPE),
linear low density polyethylene (LLDPE)
and polypropylene (PP) were accomplish-
ed.
[15-19]
It should be noted that amorphous
EP copolymers that do not crystallize
cannot be separated using the mentioned
fractionation techniques. Other techniques
that separate polyolefins according to
chemical composition are selective extrac-
tion with appropriate solvents and solu-
tion-precipitation techniques.
[20-22]
These
Ethylene-propylene (EP) copolymers are
important polymeric materials. Depending
on the comonomer content of the EP
copolymers their properties change from
crystalline (low comonomer content) to
amorphous (high comonomer content).
The determination of the chemical compo-
sition distribution (CCD) of EP copolymers
requires fast and efficient analytical meth-
ods. The analysis of EP copolymers and
blends of polyethylene and polypropylene
by DSC is a well established and simple
method;
[1-6]
however, it is not a separation
method and, thus, cannot provide a CCD.
For separations according to chemical
composition, temperature rising elution
fractionation (TREF) is used.
[7-14]
In a
