C O M M U N I C A T I O N S
In summary, we have shown that high molecular weight PPEs
can be obtained by nucleophilic aromatic substitution. The polymers
are easily purified as the only side product is a gas (TMSF), and
the catalyst can be removed with a simple aqueous treatment. Their
well-defined C6F5 endgroups might be selectively functionalized
with other nucleophiles, or the polymers can be used as mac-
romonomers. This synthetic route may enjoy broad applicability
in synthesis of acetylenic scaffolds of varying geometries.15 It may
show particular importance for incorporating alkynyl monomers
that are unstable16 if desilylated prior to Hagihara-Sonogashira
coupling. For example we have coupled 9,10-trialkylsilylacetylene-
functionalized anthracene and the analogous 6,13-functionalized
pentacene with perfluoro-pyridine and -toluene in 60-80% isolated
yields (unoptimized).
Figure 1. Pn vs C6F6:1c molar ratio (TMAF catalyst), estimated by NMR
end-group analysis ([) and GPC (4), compared to Carothers equation
(dashed line). See Supporting Information for treatment of GPC data. The
inset shows the Carothers equation with r ) molar ratio of excess monomer
to limiting monomer.
Acknowledgment. This work was supported in part by the
American Chemical Society (Grant PRF 43047-G), Kentucky
Science and Engineering Foundation, and the National Science
Foundation (Grant CHE 0616759). This work is dedicated in
memory of Prof. George B. Butler and his contributions to polymer
chemistry.
Scheme 2. Model Reactiona
Supporting Information Available: Experimental procedures,
spectroscopic and analytical data. This material is available free of
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The model reaction is violently exothermic when conducted at
high concentration, producing substantial amounts of 6 and 7. At
dilutions approaching those of the polymerizations, combined
conversions to 6 and 7 are lowered to ∼6%. These side-products
correspond to branching points or cross-links in the analogous
polymerizations, which could also cause deviation from Carothers
equation. However, the actual percentage of such defects in the
polymers is less than 1/150 repeat units based on integration of
diminutive 19F NMR signals. For comparison, model “defect” 6 (1
mol %) is readily detected in a solution of model polymer repeat
unit 5 by 19F NMR after relatively few transients. The low
percentage of defects in the polymers might be attributed to steric
bulk of monomers 1. From other bis-silyl-acetylene monomers, we
have prepared hyperbranched or cross-linked PAE gels, which may
have their own merits14 and will be described in a future com-
munication.
Unlike poly1a,6a poly1b,1c are highly soluble in common organic
solvents at room temperature. The solution absorbance/photolumi-
nescence spectra of poly1b,1c differ significantly (Supporting
Information). The 2-ethyl-hexyl chains of poly1c present greater
steric bulk in the vicinity of the polymer backbone, altering
rotational freedom around backbone bonds and/or the benzene-
oxygen bonds. The former may affect backbone conjugation, while
the latter can affect the mesomeric/inductive influence of the side
chains on the chromophoric backbone. The result is a larger apparent
Stokes shift and nearly featureless absorbance and PL profiles. A
future communication will link solid-state optical and thermal
properties to packing arrangements determined by wide-angle X-ray
scattering studies.
(16) Taylor, M. S.; Swager, T. M. Angew. Chem., Int. Ed. 2007, 46, 8480-3.
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