Macromolecules, Vol. 38, No. 3, 2005
Communications to the Editor 659
Table 1. Palladium Content before and after Treatment
with 1 for Polymer Samples of the
Poly(phenylenevinylene), Poly(phenyleneethynylene),
and Poly(alkylthiophene) Type and the Device
Resistance According to the Device Geometry (See
Supporting Information)
Pd content before/after
(ppm)
resistance before/after
polymer
(kΩ)
PPV
PPE
PAT
17860/<0.1
268/<0.1
4073/<0.1
0.10/30
0.03/45
0.06/24
The polymers employed for the demonstration were
prepared by typical palladium routes (see Supporting
Information) and cover a broad range of conjugated
polymers: poly(phenylenevinylene) (PPV), poly(phen-
yleneethynylene)s (PPE), and poly(alkylthiophene) (PAT).
While the palladium content depends on the amount of
catalyst used and on the conditions of the experiment,
the levels observed before treatment are typical. Re-
moval using 1 is efficient, and this is reflected in the
device resistance and device function. Electrolumines-
cent and photovoltaic devices could be prepared after
palladium removal using this method.
In conclusion, our report describes the efficient re-
moval of the palladium nanoparticle/catalyst contained
in polymer materials by a palladium route. We further
demonstrate the possibility of a quantitative determi-
nation of the palladium nanoparticles/catalyst content
at the 1 ppb (w/w) level using simple UV-vis spectro-
photometry. It should be emphasized that the method
is general and that it can be applied to any sample,
small molecule or macromolecular. The only require-
ment is solubility of the sample.
Figure 1. UV-vis spectrum of 1 and 3 in chloroform at room
temperature showing their extinction coefficients. Compound
3 shows a moderately strong absorption with a maximum at
801 nm where compound 1 does not absorb, making this
technique applicable for the analytical determination of re-
sidual palladium content in materials where palladium ca-
talysis has been employed.
azothioformamide skeleton can be envisaged that can
encompass different solubility requirements of the
derived palladium complexes, making its removal easy
in terms of solubility/insolubility. Having demonstrated
the successful reaction of 1 with metallic palladium
nanoparticles/catalyst it remained to evaluate possible
side reactions of 1 with the conjugated polymer product.
The most likely reaction between an unsaturation such
as vinylene or ethynylene groups is an electrocyclic
condensation reaction of the Diels-Alder type. We
performed model reactions between 1 and stilbene or
tolane in both the presence and absence of palladium.
We were not able to demonstrate detectable amounts
of the corresponding electrocyclic condensation products
(see Supporting Information). The major problem with
such side reactions during polymer synthesis is that
they are accumulated, and their alleviation is difficult
to envisage. The removal of palladium using 1 is thus
possible. While the treatment can be performed at
elevated temperature, it works best at room tempera-
ture and was normally complete within 1 h. The
progress of the palladium dissolution could be conve-
niently followed using simple UV-vis spectroscopy. This
has the advantage that the complex exhibits a moder-
ately strong absorption in a wavelength region normally
not explored for saturated polymers and rarely for
conjugated polymers and organic materials (ꢀ797nm,THF
) 8500 M-1 cm-1, ꢀ801nm,chloroform ) 10 300 M-1 cm-1).
The method presented here can thus be used for
preparative work where alleviation of residual pal-
ladium catalyst is of interest and for analytical purposes
where the palladium content can be determined by
simple treatment with 1 followed by UV-vis analysis.
In the case where there is an overlap, a correct analyti-
cal determination of the palladium content is still
possible provided that the UV-vis spectrum of the
sample is known and can be accurately subtracted.
We have shown the applicability of 1 for the removal
of residual palladium catalyst through 3 that in our case
is a complex readily soluble in common organic solvents
including methanol commonly used to precipitate poly-
mer materials. Using the method of analysis presented
here, it is possible to determine the palladium content
with a detection limit of 0.1 ppm (w/w) using 50 mg
sample. Employing larger samples and concentration of
the supernatant the detection limit can be lowered to 1
ppb (w/w). The results are summarized in Table 1.
Acknowledgment. The work was supported by the
Danish Technical Research Council (STVF).
Supporting Information Available: Details of the one-
pot synthesis to 1, preparation of 3, general procedure for the
removal of palladium remnants from conjugated polymer
materials, analysis of the palladium content in a conjugated
polymer sample at the 0.1 ppm level, the device geometry, and
UV-vis in THF. This material is available free of charge via
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