Angewandte
Communications
Chemie
Polymerization
Heterotelechelic Polymers by Ring-Opening Metathesis and
Regioselective Chain Transfer
Abstract: Heterotelechelic polymers were synthesized by
a kinetic telechelic ring-opening metathesis polymerization
method relying on the regioselective cross-metathesis of the
propagating Grubbsꢀ first-generation catalyst with cinnamyl
alcohol derivatives. This procedure allowed the synthesis of
hetero-bis-end-functional polymers in a one-pot setup. The
molecular weight of the polymers could be controlled by
varying the ratio between cinnamyl alcohol derivatives and
monomer. The end functional groups can be changed using
different aromatically substituted cinnamyl alcohol derivatives.
Different monomers were investigated and the presence of the
functional groups was shown by NMR spectroscopy and
MALDI-ToF mass spectrometry. Labeling experiments with
dyes were conducted to demonstrate the orthogonal address-
ability of both chain ends of the heterotelechelic polymers
obtained.
reported the syntheses of a,w-bis(trialkoxysilyl) telechelic
copolyolefins.[7]
All of these synthetic methods rely on so-called back-
biting or secondary metathesis reactions (chain transfer to the
polymer) and can be carried out with catalytic amounts of
transition-metal–carbene complexes. Owing to the mechanis-
tic necessity to undergo secondary metathesis reactions,
narrow-molecular-weight dispersities ( ! 2.0) of the poly-
mers cannot be achieved using this equilibrium-driven
synthetic strategy.
Depending on the metal–carbene initiator employed,
polymers from norbornene and its derivatives do not readily
undergo secondary metathesis reactions. However, using
[8]
WCl6/SnMe4 or Grubbsꢀ second-generation ruthenium car-
bene complex,[9] telechelic poly(norbornene)s could be syn-
thesized following the thermodynamically controlled proce-
dure described above.
T
elechelic polymers, that is, those carrying functional groups
Polymers not undergoing secondary metathesis reactions
can in principle be prepared in a living fashion, that is, with
narrow-molecular-weight distributions. For norbornenes, the
so-called pulsed monomer addition has been successfully
employed to prepare telechelic polymers with narrow molec-
ular-weight dispersity.[10] There, the transition-metal–carbene
complex is first pre-functionalized with an excess of a sym-
metrical functional CTA before the first pulse of monomer is
added. Functional initiation is followed by complete con-
sumption of the monomer and subsequent chain transfer to
the CTA thereby preparing a telechelic polymer and a new
functional initiator. Upon addition of a second pulse of
monomer, a second polymer is prepared, and so on. While the
carbene complex is recycled, and used for several monomer
pulses, the method is not catalytic in metal complex as such.
Heterotelechelic polymers carry two different functional
groups at either chain end. Such polymers are important
macromolecular flexible spacers that allow the attachment of
biologically active molecules,[11,12] fluorescent and other labels
or other functional compounds to one end of the polymer
while the other is attached to macroscopic surfaces, nano-
particle surfaces, proteins, and so on. The attachment of
proteins to surfaces is very important for applications in
proteomics or biomaterials synthesis and long hetero-bis-
endfunctional spacers, that is, heterotelechelic polymers are
an efficient way of connecting the two.
at either chain end, have been prepared using olefin meta-
thesis since before well-defined ruthenium, molybdenum, and
tungsten (and many other) carbene complexes were reported
mainly by Grubbs and Schrock. It was realized early on that
adding acyclic olefins to a polymerization mixture of strained
cyclic olefins would lower the molecular weight of the
resulting polymer via chain transfer events. Furthermore,
depending on the nature of the acyclic olefin, functional
groups could be placed on the chain ends of the synthesized
polymers.
Early examples for telechelic polymers by ring-opening
metathesis polymerization (ROMP) were reported by Hill-
myer and Grubbs. There, cyclooctadiene was polymerized in
the presence of suitably protected 1,4-cis-butenediols using
either well-defined tungsten or ruthenium carbene com-
[1]
plexes· Alternatively, statistical copolymers between cyclo-
octadiene and dioxepines were prepared and the polymeric
acetals hydrolyzed in a post-polymerization step.[2] More
recently, other functional groups such as epoxides and
methacrylates,[3] carboxylic acids and amines,[4] trithiocarbon-
ate RAFT initiators[5] or nitroxide controlled radical poly-
merization initiators[6] have been introduced by chain-transfer
agents (CTA). Carpentier and Guillaume most recently
Heterotelechelic polymers have been prepared via many
living polymerization techniques, such as RAFT,[13] ATRP,[14]
carbanionic polymerization,[15] and cationic polymeri-
zation.[16] Few synthetic strategies have been reported that
allow the synthesis of heterotelechelic polymers using ROMP.
Non-catalytic methods involve the functional initiation of
a polymerization followed by functional termination with
[*] P. Liu, M. Yasir, Dr. A. Ruggi, Prof. Dr. A. F. M. Kilbinger
Department of Chemistry, University of Fribourg
Chemin du MusØe 9, 1700 Fribourg (Switzerland)
E-mail: andreas.kilbinger@unifr.ch
Supporting information and the ORCID identification number(s) for
the author(s) of this article can be found under:
914
ꢀ 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2018, 57, 914 –917
Liu, Peng
