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Synthesis of Hyperbranched Poly(phenylacetylene)s Containing Pendant Alkyne Groups by One-Pot Pd-Catalyzed Copolymerization of Phenylacetylene with Diynes
journal contribution
posted on 2012-06-26, 00:00 authored by Zhongmin Dong, Zhibin YeWe report in this article the convenient synthesis of
a class of
hyperbranched poly(phenylacetylene)s (HBPPAs) containing various branching
densities and different contents of pendant alkyne groups through
one-pot chain-growth copolymerization of phenylacetylene (PA) with
a diyne comonomer (1,3- or 1,4-diethynylbenzene (DEB)). The polymerization
was facilitated with the use of an in situ generated
cationic diphosphine-ligated Pd(II) catalyst system. Serving effectively
as difunctional cross-linker in the polymerization, the diyne comonomer
first undergoes monoinsertion to render pendant alkyne groups, which
can be further enchained to generate branching structures. A systematic
investigation has been undertaken to study the effects of various
polymerization parameters, including diyne/PA feed ratio, diyne type,
temperature, and solvent, on the polymerization, polymer structure
and topology. With either 1,3- or 1,4-DEB, a convenient tuning of
polymer topology from linear to hyperbranched can be achieved by simply
increasing diyne/PA feed ratio. Relative to 1,3-DEB, 1,4-DEB is more
effective in rendering branching structures since the pendant alkyne
groups suffer less steric effect from the polymer backbone and are
thus more reactive. As to the solvent, a dichloromethane/methanol
mixture (at vol. ratio of 13:3) was shown to better help the formation
of branching structures than methanol alone as the resulting polymers
can dissolve well in the former while precipitate in the latter. Because
of their possession of the valuable pendant alkyne groups, these polymers
have also been demonstrated for their use as building blocks in the
synthesis of core–shell structured star polymers containing
a HBPPA core and polystyrene arms through their Cu-catalyzed “click”
reaction with an azide-ended polystyrene.