Chemistry Reference
In-Depth Information
Application of Fractionation Techniques to the
Study of Olefin Polymerization Kinetics and
Polymer Degradation
Hisayuki Nakatani,
1
Hitoshi Matsuoka,
2
Shoutarou Suzuki,
3
Toshiaki Taniike,
3
Liu Boping,
3
Minoru Terano
*
3
Summary: Temperature rising elution fractionation (TREF) has been regarded as a
powerful technique for study of semicrystalline polymers. In this paper, two examples
of unique applications of TREF were introduced. One was the study on the influence
of extraction of internal donor on the variation of isospecific active sites of a MgCl
2
-
supported Ziegler catalyst, and the other was the estimation of the relationship
between polymer micro-tacticity and degradation rate of isotactic polypropylene
(iPP). The former example revealed the conversion from high to low isospecific site by
the extraction of internal donors, whereas the latter showed a negative correlation
between the level of isotacticity and the degradation rate. These results demon-
strated that TREF was useful in these research applications.
Keywords: catalyst; degradation; fractionation polymers; isotactic; polypropylene
Introduction
of isotacticities. This distribution directly
reflects the existence of various isospecific
active sites on the catalyst, with individual
fractions of narrow isotactic distributions
being produced by each corresponding
active site type. TREF application for
such iPP reveals the distribution profile
of isospecific active sites on the Ziegler
catalyst.
[4,5]
Another substantial advantage of TREF
is the fractionation of iPP with broad iso-
tacticity distribution into several fractions
of different isotacticities. In our previous
studies,
[6,7]
the effect of tacticity on thermal
oxidative degradation of polypropylene was
investigated using highly isotactic, syndio-
tactic and atactic polypropylene resins,
suggesting that the degree of oxidation of
iPP was the severest. On the basis of this
result, it was concluded that the tacticity
affects one reaction path in the degradation
process. However, the relationship between
the level of tacticity and the rate of degra-
dation had not been systematically clarified.
The elucidation of this phenomenon requ-
ires the use of a systematic iPP series
Analytical TREF has been a useful tech-
nique for the quantitative structural ana-
lysis of semicrystalline polymers.
[1-3]
In
addition, TREF is a well-known procedure
to fractionate each polymer component by
differences of crystallizability. TREF has
been regarded as the method of choice for
the analysis and fractionation of polymer
crystalline distribution.
It should be noticed here that the
crystallizability of isotactic polypropylene
(iPP) strongly depends on its isotacticity.
In the case of iPP synthesized by MgCl
2
-
supported Ziegler catalysts, the iPP obta-
ined often shows a broad distribution
