COMMUNICATION
DOI: 10.1002/chem.201202506
Tailored Nanostructuring of End-Group-Functionalized High-Density
Polyethylene Synthesized by an Efficient Catalytic Version of Zieglerꢀs
“Aufbaureaktion”**
Saravana K. T. Pillai,[a] Winfried P. Kretschmer,[a] Martin Trebbin,[b]
Stephan Fçrster,[b] and Rhett Kempe*[a]
Polyethylene (PE) is the most widely used synthetic poly-
mer and is essential for our modern life style due to its low
cost and its broad applicability. Unfortunately, the compati-
bility with other important polymers or materials is limited.
Compatibility agents with a PE block and a block of that
other polymer or a block that is compatible with the materi-
al could solve this problem. Furthermore, PE-based block
copolymers may allow to nanostructure PE through micro-
phase separation and enable new applications of this com-
modity. Both approaches rely on an efficient synthesis of PE
having an end group that allows the easy introduction of the
second polymer block. A polymerization method that pro-
duces metal-terminated PE which can easily be converted
into PE carrying such reactive end groups is coordinative
chain-transfer polymerization (CCTP).[1,2] Pioneering work
was done by Eisenberg and Samsel,[3] as well as Mortreux
and co-workers.[4] Meanwhile, a few ethylene/propylene
CCTP catalyst systems by using rare-earth metals (REM)
and transition metals in combination with different chain-
transfer agents (CTA), such as Mg, Zn,[5,6,7] and Al alkyls,[8,9]
have been disclosed. Furthermore, enhancements of the
CCTP concept, such as “chain shuttling” and “ternary
CCTP”, have been developed.[10] Mechanistic studies have
been carried out by the Bochmanꢀs[11] and the Nortonꢀs
group.[12,13] The kinetic of chain growth catalyzed by
These inverse first-order dependencies prohibit the use of
high CTA/catalyst ratios. High amount of CTA resulted in
an overall poor polymerization activity. As a consequence,
most of the described CCTP catalyst systems worked with
CTA/catalyst ratio smaller than 500 and became inactive
with significantly higher CTA/catalyst ratio. This problem
could be solved by the design of new catalyst systems that
undergo fast chain growth compared to chain exchange and
still suppress b-H elimination/transfer processes. In such a
regime, multiple insertions may compensate efficiency loss
caused by high CTA/catalyst ratio.[14]
Herein, we report a new titanium-based catalyst system
that is highly active in the presence of very high CTA/cata-
lyst ratio and undergoes polyethylenyl chain transfer to tri-
AHCTUNGTREGeNNNU thylaluminum (TEA). No b-hydride elimination/transfer
products were observed. This polymerization process can be
viewed as an efficient catalytic version of Zieglerꢀs “Auf-
baureaktion”. Through oxidation with O2 and subsequent
hydrolytic work-up, the metallopolymers can be converted
to PE-OH in high yield. The generated PE-OH was used to
synthesize block copolymers with polylactide (PLA) as a
counterblock. Microphase separation gave different mor-
phologies by varying the PLA block length. Etching out of
the sacrificial PLA block gave rise to mesoporous polyethy-
lene and polyethylene nanofibers/ribbons.
[(EBI)Zr
(m-Me)2AlMe2][B
E
Nanoporous PE has been generated from hydrogenated
1,4-polybutadiene (hPB). Block copolymers from hPB and
polystyrene obtained by anionic polymerization allow excel-
lent structuring, but need rather harsh and difficult condi-
tions to control etching processes to remove the polystyrene
block.[15] Furthermore, polymeric bicontinuous microemul-
sion templates were generated by using hPB and block co-
polymers carrying a hPB block.[16] Unfortunately, the PE
mimic hPB suffers from the unavoidable presence of
branches. Ring-opening metathesis polymerization of cyclo-
octene was discussed as an alternative and gave rise to
pseudo PE blocks after hydrogenation. Triblock copolymers
carrying this block were successfully converted into porous
PE.[17] The fabrication of polyethylene nanofibers/ribbons
through the block copolymer approach has not been report-
ed yet.[18,19] End-group-functionalized PE synthesized by
CCTP was already used to make block copolymers,[5d,e,9c,20]
among them PE-PLA block copolymers.[5e]
bisACHTUNGTRENNUNG(indenyl)) has been studied. The reaction is first order in
[olefin] and [catalyst] and inverse first order in [AlR3].[12]
[a] S. K. T. Pillai, Dr. W. P. Kretschmer, Prof. Dr. R. Kempe
Lehrstuhl Anorganische Chemie II
Universitꢁt Bayreuth
Universitꢁtsstrasse 30, NW I
95440 Bayreuth (Germany)
Fax : (+49)921552157
[b] M. Trebbin, Prof. Dr. S. Fçrster
Lehrstuhl Physikalische Chemie I
Universitꢁt Bayreuth
Universitꢁtsstrasse 30, NW I
95440 Bayreuth (Germany)
[**] Aufbaureaction (German): buildup reaction.
Supporting information for this article is available on the WWW
Chem. Eur. J. 2012, 00, 0 – 0
ꢂ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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