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Synthesis, Characterization, and Ring-Opening Polymerization of the Cyclic Oligomers of Poly(Oxy-1,3-phenylenecarbonyl-1,4-phenylene)
journal contribution
posted on 1998-03-13, 00:00 authored by Mark F. Teasley, Dan Q. Wu, Richard L. HarlowThe cyclic oligomers (cyclomers) of the title composition were
prepared from 4-fluoro-3‘-hydroxybenzophenone by nucleophilic aromatic substitution.
Cyclomers prepared in dimethyl sulfoxide
and toluene at 150−160 °C using pseudo-high dilution contained a
high fraction of cyclic dimer, which
was isolated by vacuum sublimation. Cyclomers prepared in
o-dichlorobenzene at 180 °C using catalytic
18-crown-6 were suitable for polymerization. High-performance
liquid chromatography was used to
quantify the mixtures. The ring-opening polymerization of the
cyclic dimer was studied using nucleophilic
initiators. The conversions and relative molecular weight
distributions were measured using gel
permeation chromatography. Absolute molecular weights were
estimated on the basis of laser light-scattering measurements using cyclomer-free polymer samples. Cesium
fluoride and alkali-metal
carbonates gave incomplete conversion of the cyclic dimer to very high
molecular weight polymers.
Potassium and cesium 4-benzoylphenolate gave essentially complete
conversion and their stoichiometry
controlled the molecular weights. The amorphous polymers possessed
Tg = 132 °C and Mw
= 60 000−180 000. The initiators are differentiated by the competition
between the chain extension of the linear
species generated by initiation and propagation of the ring-opening
polymerization. The reactivity of
the cyclomers was correlated with their 1H and
13C NMR chemical shifts. The cyclic dimer is less
reactive
than the higher cyclomers due to its structure. X-ray
crystallography showed that the p-phenylene
rings
of the cyclic dimer are partially rotated out of conjugation with the
carbonyls due to steric interactions
with the m-phenylene rings. The steric and electronic
effects, and the chemistry of the cyclomers in
general, are due to the 3,4‘-catenation of the repeat
unit.