A Bicyclo[4.2.0]octene-Derived Monomer Provides Completely
Linear Alternating Copolymers via Alternating Ring-Opening Metathesis
Polymerization (AROMP)
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Abstract
Strained bicyclic carbomethoxy olefins
were utilized as substrates
in alternating ring-opening metathesis polymerization and found to
provide low-dispersity polymers with novel backbones. The polymerization
of methyl bicyclo[4.2.0]oct-7-ene-7-carboxylate with cyclohexene in
the presence of the fast-initiating Grubbs catalyst (H<sub>2</sub>IMes)(3-Br-Pyr)<sub>2</sub>Cl<sub>2</sub>RuCHPh leads to
a completely linear as well as alternating copolymer, as demonstrated
by NMR spectroscopy, isotopic labeling, and gel permeation chromatography.
In contrast, intramolecular chain-transfer reactions were observed
with [5.2.0] and [3.2.0] bicyclic carbomethoxy olefins, although to
a lesser extent than with the previously reported monocyclic cyclobutenecarboxylic
ester monomers [Song, A.; Parker, K. A.; Sampson, N. S. J. Am. Chem. Soc. 2009, 131, 3444]. Inclusion of cyclohexyl rings fused to the copolymer backbone
minimizes intramolecular chain-transfer reactions and provides a framework
for creating alternating functionality in a one-step polymerization