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Conductive Polymer Functionalization by Click Chemistry
Anders Egede Daugaard and Søren Hvilsted*
Danish Polymer Centre, Department of Chemical and Biochemical Engineering, Technical Uni V ersity of
Denmark, Building 423 Produktionstor V et, DK-2800 Kgs. Lyngby, Denmark
Thomas Steen Hansen and Niels B. Larsen
Polymer Department, POL-313, P.O. Box 49, Frederiksborg V ej 399, DK-4000 Roskilde, Denmark
Recei V ed December 7, 2007; Re V ised Manuscript Recei V ed April 21, 2008
ABSTRACT: Click chemistry is used to obtain new conductive polymer films based on poly(3,4-ethylenedi- oxythiophene) (PEDOT) from a new azide functional monomer. Postpolymerization, 1,3-dipolar cycloadditions in DMF, using a catalyst system of CuSO 4 and sodium ascorbate, and different alkynes are performed to functionalize films of PEDOT-N 3 and copolymers prepared from EDOT-N 3 and 3,4-ethylenedioxythiophene (EDOT). This approach enables new functionalities on PEDOT that could otherwise not withstand the polymerization conditions. Reactions on the thin polymer films have been optimized using an alkynated fluorophore, with reaction times of ∼20 h. The applicability of the method is illustrated by coupling of two other alkynes: a short chain fluorocarbon and a MPEG 5000 to the conductive polymer; this alters the advancing water contact angle of the surface by + 20 ° and - 20 °/- 25 °, respectively. The targeted chemical surface modifications have been verified by X-ray photoelectron spectroscopy analysis.
Introduction
Conductive polymers have been extensively studied during
the past few decades for applications such as biosensors,^1 strain
gauges,^2 organic solar cells,^3 or organic light-emitting diodes.^4
Many challenges have to be met in the development of new
functional conducting polymers, including synthesis of mono-
mers with the required functionality and establishment of
polymerization conditions compatible with the targeted function.
Specific problems may be instability of large biological mol-
ecules for biosensors under the typically harsh polymerization
conditions or inhibition of the polymerization process by a side
reaction with a functional group in the monomer. Functional-
ization of the conductive polymer may result either from
incorporation of the functional entity into the monomer during
monomer synthesis or by postpolymerization coupling of the
targeted functionality to built-in generic coupling sites in the
monomer unit. Recently, the term “click chemistry” was defined
by Sharpless et al.^5 as selection criteria for highly efficient
coupling reactions. Ideally, the click reaction can be performed
in water or organic solvents at room temperature, making the
method suitable for most applications. Click chemistry has
mainly been based on the use of 1,3-dipolar cycloadditions of
azides and alkynes under copper catalysis6,7^ and Diels-Alder
reactions. In polymer chemistry it has been used in numerous
ways e.g. for end-group functionalization,^8 polymer to polymer
couplings,^9 functionalization of linear polymers with selected
groups,^10 dendrons,^11 and poly(ethylene glycol) (PEG).^12 Also,
in reactions on surfaces the cycloaddition has been used with
good results e.g. to bond metal surfaces together.^13 It has been
used with carbon nanotubes^14 and for functionalization of self-
assembled monolayers on gold.15,16^ Recently click chemistry
has also been used for surface reactions on cotton^17 and
glass.18,19^ A bioactive surface has been prepared by introduction
of biotin by click chemistry on a polymer substrate.^20 For sensor
applications especially biological systems are of great interest,
and these often require mild reaction conditions, which can be
obtained using click chemistry.^21 A comprehensive review on
macromolecular click chemistry has recently been published by
Binder et al.^22
The new developed conducting polymer is based on PEDOT,
used in numerous applications due to its high electrical
conductivity and high stability in ambient and aqueous environ-
ments.^23 During polymerization the polymer becomes insoluble,
and further functionalization becomes difficult. Combination of
the conductive properties of PEDOT and the advantages of
modularity, high selectivity, and high yields of click chemistry
permits preparation of new PEDOTs for many different ap-
plications, e.g., surfaces with conductive properties or sensors.
Both pre- and postfunctionalization have been studied by others.
With regards to biological active molecules the most successful
methods so far is physical absorption after polymerization or
entrapment during polymerization.^24 Covalent postfunctional-
ization has been achieved through peptide bonding. 25,26^ The
click approach is a good alternative that gives a controlled
functionalization without protective groups through high selec-
tivity. In our group we have focused on the use of PEDOT for
different applications27–30^ and the use of click chemistry for
polymer functionalization.^31 Here we present a standardized
method for postpolymerization functionalization of PEDOT to
obtain conductive polymer surfaces with various functionalities.
Experimental Section
General Methods. Thin layer chromatography (TLC) was performed on Merck plates coated with silica gel F254. Kieselgel for column chromatography was Merck Kieselgel 60 (230- 400 mesh). 1 H NMR was run on a 250 MHz cryomagnet from Spectrospin and Brucker at room temperature. Infrared spectroscopy (IR) was performed on a Perkin-Elmer Spectrum One model 2000 Fourier transform infrared system with a universal attenuated total reflection sampling accessory on a ZnSe/diamond composite. Differential scanning calorimetry (DSC) was performed on a DSCQ1000 from TA Instruments. The thermal analyses were performed at a heating and cooling rate of 10 °C/min. The melting temperatures ( T m ) are reported as the peak temperatures of the endothermic melting peaks. The conductivity was measured with a four-point probe (Jandel Engineering Ltd., Linslade, UK) con- nected to a four-point source meter (Keithley 2400, Cleveland, OH).
- Corresponding author. E-mail: [email protected]. Film thickneses were measured with an Ambios XP-2 (Ambios
Macromolecules 2008 , 41 , 4321- 4327 4321
10.1021/ma702731k CCC: $40.75 2008 American Chemical Society Published on Web 05/29/
Technology, Inc., Santa Cruz, CA) profilometer using a stylus force of 0.5 mg. Optical microscopy images was recorded with a AxioCam MRc 5 camera mounted on a Zeiss Axioskop 40 microscope (Oberkochen, Germany). Fluorescence analysis was conducted with a Zeiss Filter Set 09 (excitation 450-490 nm, emission >515 nm). XPS analysis was performed on a Thermo Fisher Scientific K Alpha (East Grinstead, UK) using monochro- matized aluminum KR radiation in a 400 μm spot on the sample. Survey and high-resolution spectra were acquired and analyzed using the manufacturer’s Avantage software package. Spectra were generally acquired with electron charge compensation in operation to avoid sample charging, except for a series of measurements to determine the detrimental effects of electron flooding on azide functional gruops. Atomic force microscopy analysis proceeded on a PSIA XE-150 instrument operating in intermittent contact mode with BudgetSensor Tap-300 cantilevers. Chemicals. Chemicals except for Baytron C were acquired from Aldrich and were used as received unless otherwise specified. Baytron C was purchased from H.C. Starck. Fluorescein methyl ester was prepared in accordance with Moore et al.^32 3,4-(1-Bromomethylethylene)dioxythiophene, 1 (EDOT-Br). 3,4-Dimethoxythiophene (0.41 g, 2.8 mmol), 3-bromo-1,2-pro- panediol (1.11 g, 7.2 mmol), and p -toluenesulfonic acid (0.08 g, 0.4 mmol) were dissolved in toluene (30 mL) and stirred at 100 °C for 48 h. Toluene was removed in vacuo, and the residue was dissolved in CH 2 Cl 2 and extracted with Na 2 CO 3 and H 2 O. The organic phase was dried with MgSO 4 , filtered, and concentrated in vacuo, and the crude product was purified by column chromatog- raphy with a gradient eluent of heptane/ethyl acetate (EtOAc). The product was isolated as a colorless oil (0.24 g, 37%). IR (cm-^1 ): 3112 (C-H stretch). 1 H NMR (CDCl 3 , 250 MHz, δH , ppm): 3.4-3.6 (m, 2H, CH 2 - Br); 4-4.44 (m, 3H, O-CH 2 - CH-O); 6.36/6.37 (2 × d, 4 J ) 3.7 Hz, 2H, S-CH). 3,4-(1-Azidomethylethylene)dioxythiophene, 2 (EDOT-N 3 ). 1 (0.22 g, 0.9 mmol) and NaN 3 (0.08 g, 1.2 mmol) were dissolved in DMF (10 mL) and stirred at room temperature (RT) for 17 h. The reaction mixture was diluted with H 2 O (15 mL), and the aqueous DMF was extracted with EtOAc (5 × 15 mL). The organics were combined and extracted with H 2 O (3 × 15 mL) and brine (1 × 15 mL), dried with MgSO 4 , filtered, and concentrated in vacuo to give the product as a colorless oil (0.18 g, 97%). IR (cm-^1 ): 3114 (C-H stretch); 2097 (-N 3 stretch). 1 H NMR (CDCl 3 , 250 MHz, δH, ppm): 3.4-3.6 (m, 2H, CH 2 - N 3 ); 4-4.44 (m, 3H, O-CH 2 - CH-O); 6.36/6.39 (2 × d, 4 J ) 3.7 Hz, 2H, S-CH). General Polymerization Method for 2, to PEDOT-N 3 , 3. The polymerization method was based on an earlier published method for the polymerization of EDOT.^33 A number of microscope slides were thoroughly cleaned using acetone, isopropanol, ethanol, and water. The glass slides were surface modified by vapor phase hexamethyldisilazane (HMDS) in a dedicated oven (Yield Engi- neering Systems 6112). 2 (20 mg,0.15 mmol), Baytron C (0.48 mL, ∼40 wt % Fe(III)Tos in butanol), and butanol (0.48 mL) were mixed and spin-coated on the glass-slides (10 s at 1000 rpm). The samples were placed on a hot plate at 65 °C for 5 min and subsequently washed with water and blown dry in a nitrogen flow, yielding films with a thickness of 200-250 nm. General Copolymerization Method for Poly(3,4-ethylenedi- oxythiophene- co -3,4-(1-azidomethylethylene)dioxythiophene). The copolymerization method was based on an earlier published method for the polymerization of EDOT.^33 A solution of 3,4- ethylenedioxythiophene (EDOT, 0.22 mL), Baytron C (6.5 mL), butanol (6.5 mL), and pyridine (0.15 mL) was mixed with the EDOT-N 3 solution mentioned above to yield solutions containing 5 ( 4 ), 10 ( 5 ), 20 ( 6 ), 40 ( 7 ), 60 ( 8 ), and 80 mol % ( 9 ) EDOT-N 3 of the total monomer content. The polymerization mixtures were then spin-coated onto the HDMS treated glass slides (10 s at 1000 rpm). The samples were placed on a hot plate at 65 °C for 5 min and subsequently washed with water and blown dry in a nitrogen flow. General Ester Synthesis, 2,2,3,3,3-Pentafluoropropyl Pent- 4-ynoate, 10. A solution of 4-pentynoic acid (0.60 g, 6.1 mmol), dimethylaminopyridine (DMAP, 0.12 g, 0.9 mmol), and 2,2,3,3,3-
pentafluoropropanol (0.97 g, 6.5 mmol) in CH 2 Cl 2 (15 mL) was stirred at RT, and a solution of N,N ′-dicyclohexylcarbodiimide (DCC, 1.58 g, 7.6 mmol) in CH 2 Cl 2 was added dropwise. The reaction mixture was stirred overnight at RT, filtered, and concen- trated in vacuo. The crude product was purified by column chromatography using a gradient eluent of pentane/ether and gave a colorless oil (1.24 g, 88%). IR (cm-^1 ): 3314 (CtC-H stretch); 2119 (CtC stretch); 1761 (O-CdO stretch); 1197, 1143, 1107 (C-F stretch). 1 H NMR (CDCl 3 , 250 MHz, δH , ppm): 1.99 (t, 4 J ) 2.6 Hz, 1H, H-C≡); 2.54 (m, 2H, ≡C-CH 2 - ); 2.67 (m, 2H,
- CH 2 - COO-); 4.57 (tq, 4 J ) 1 Hz, 3 J ) 12.9 Hz, 2H, O-CH 2 - CF 2 ). Methyl 2-(3-Oxo-6-(prop-2-ynyloxy)xanthen-9-yl)benzoate, 11. Fluorescein methyl ester (2.00 g, 5.8 mmol), triphenylphosphine (TPP, 4.55 g, 17.3 mmol), and propargyl alcohol (0.98 g, 17. mmol) were stirred in acetonitrile/THF (50/50) at 0 °C. Diethyla- zodicarboxylate (DEAD, 3 mL, 17.3 mmol) was added slowly, and the mixture was stirred overnight at RT. The crude mixture was poured onto a Kieselgel column and chromatographed using an eluent of 80/20 CH 2 Cl 2 /ether, followed by a gradient of CH 2 Cl 2 / EtOAC. The product was collected from the top of the column with EtOAc as a yellow crystalline compound (1.08 g, 49%, T m ) 206 °C). IR (cm-^1 ): 3193 (-C≡C-H stretch); 2123 (C≡C stretch); 1729 (O-CdO stretch). 1 H NMR (CDCl 3 , 250 MHz, δH , ppm): 3.59 (s, 3H, O-CH3); 5.00 (s, 2H, ≡C-CH 2 - O); 6.26 (s, 1H, Ar-H); 6.40 (m, 1H, Ar-H); 6.7-7.0 (m, 3H, Ar-H); 7.28 (s, 1H, Ar-H); 7.50 (m, 1H, Ar-H); 7.7-8.0 (m, 2H, Ar-H); 8. (s, 1H, Ar-H). r -Methoxypoly(ethylene glycol)- ω -pent-4-ynoate, 12. The product was prepared according to the general procedure for ester synthesis by DCC coupling, using a commercially available methoxypoly(ethylene glycol) ( M n ) 5010, PDI ) 1.1), 1.2 equiv of 4-pentynoic acid, DCC and 1 equiv of DMAP relative to the end group. The crude product was purified by precipitation in cold dry diethyl ether and dried in vacuo to give 12 as a solid polymer (3.54 g, 87%, T m ) 56 °C, M n ) 5290, PDI ) 1.1). IR (cm-^1 ): 1738 (O-CdO stretch); 1099 (C-O stretch). 1 H NMR (CDCl 3 , 250 MHz, δH , ppm): 1.96 (t, 2.5 Hz, 1H, H-C≡); 2.4-2.6 (m, 4H, - OC-CH 2 - CH 2 - C≡); 3.35 (s, 3H, - OCH 3 ) ; 3.4-3.8 (m, O-CH 2 - CH 2 - O); 4.23 (t, 4.8 Hz, 2H, - COO-CH 2 - ). Click Reaction of 2 with 10 and 13. 2 (49.8 mg, 0.25 mmol) and 10 (62.8 mg, 0.27 mmol) were dissolved in H 2 O/THF (50/50, 25 mL), aqueous CuSO 4 (0.21 mL, 1 M, 0.21 mmol) and sodium ascorbate (0.43 mL, 1 M, 0.43 mmol) were added, and the reaction mixture was stirred at RT overnight. THF was removed in vacuo, and the residue was dissolved in CH 2 Cl 2 , extracted with brine, H 2 O, dried with MgSO 4 , filtered, and concentrated in vacuo. The crude product contained a minor residue of starting material that could be removed by column chromatography (EtOAc/heptane); the product was a colorless oil (77.7 mg, 72%). IR (cm-^1 ): 3112 (C-H stretch); 1756 (O-CdO stretch); 1190, 1140, 1106 (C-F stretch). (^1) H NMR (CDCl 3 , 250 MHz, δH , ppm): 2.87 (m, 2H, ≡C-CH 2 - ); 3.08 (m, 2H, - CH 2 - COO-); 3.84 (dd, 12 Hz, 6.2 Hz, 1H,
- CH 2 - N); 4.26 (dd, 12 Hz, 1.9 Hz, 1H, - CH 2 - N); 4.4-4.7 (m, 5H, - CH 2 - O, - CH-O, CH 2 - CF 2 ); 6.37/6.39 (2 × d, 4 J ) 3. Hz, 2H, S-CH); 7.47 (s, 1H, N-CH)C). General Procedure for Click Reaction of Polymers 3, 4, 5, 6, 7, 8, and 9 with 11 To Give Respectively 14, 15, 16, 17, 18, 19, and 20. 11 (2.2 mg, 5.7 μmol) was dissolved in DMF (0. mL) and mixed with a solution of CuSO 4 (10 μL, 0.1 M, 1 μmol) and sodium ascorbate (20 μL, 0.1 M, 2 μmol) in DMF (0.1 mL). The reaction mixture was placed on the surface of 3 and left there for 20 h. The surface was rinsed with H 2 O and DMF and finally dried with pressurized air. The films were reoxidized by immersion in 10 mL of 10% Baytron C in water (∼4 wt % Fe(III)Tos) in 5 min, followed by rinsing with H 2 O and drying with pressurized air. Click Reaction of 3 and 10, 21. The product was prepared according to the general click procedure on 3 using 10 (4.0 mg, 17.4 μmol), CuSO 4 (10 μL, 0.1 M, 1 μmol), and sodium ascorbate (20 μL, 0.1 M, 2 μmol) in DMF for 20 h.
4322 Daugaard et al. Macromolecules, Vol. 41, No. 12, 2008
in ratio to below 1:3 after switching on charge compensation.
The relative nitrogen content also decreases with analysis time
(see Table 1, second column), where especially the intensity of
the peak at 405 eV is weakened. This deviation from the 1:
ratio is in agreement with the results obtained by Shannon et
al.^19 The XPS results clearly show the difference in binding
energies from PEDOT-N 3 to the product triazole, where no
residual azide was detected. The absence of azide nitrogens thus
shows that the reaction has proceeded, though it cannot be
concluded that all azides have reacted, since nonreacted azides
could be degraded during the analysis. In combination with the
data from the model reaction, fluorescence spectroscopy,
thickness measurements, and UV/vis data (examples given in
Figures 4, 5, and 8), this clearly shows that the click reaction
has been performed on the polymer substrate.
The conductivity of the films is not surprisingly affected by
the treatment. Before reaction the conductivity of the films is
around 60 S/cm. During the reaction the films are reduced with
sodium ascorbate, causing a dramatic reduction in conductivity
to around 0.2-0.3 S/cm. Some of the conductivity is however
regained by reoxidation in an aqueous solution of Fe(III) tosylate
ending at ∼15 S/cm. The actual loss in film conductance is
Scheme 3. Fluorophore Synthesis
Scheme 4. Schematic of the Film Reaction of 3 with 11, Where R Substitutes 11 a
a (^) The gray area indicates where the film has been exposed to the reaction mixture and thus also that there are unreacted azides around this area.
Figure 1. Fluorescence microscopy of the (a) clicked surface ( 14 ) and (b) the reference prepared without CuSO 4 under otherwise equivalent conditions. The drop of the reaction mixture did not cover the lower right corner in (a), and thus this part of the film has not been functionalized. The images are recorded using equal lighting and camera settings.
Figure 2. AFM topography image of the clicked surface of 14.
Figure 3. N (1s) high-resolution peak for PEDOT-N 3 ( 3 ) and the product triazole ( 21 ).
Table 1. XPS Results of PEDOT-N 3 (3) and the Triazoles 21 and 22 (All Numbers in atom %) theoretical 3 a^ 3 b^ 3 c^ 21 22 , DMF 22 , H2 O C 56 61.5 (58.7) 62.0 59.5 64.4 63. O 18 19.5 (18.4) 20.9 17.5 26.6 21. N 18 9.3 (13.6) 8.6 6.7 4.6 8. S 8 9.6 (9.1) 8.5 5.7 4.5 7. F 10. a (^) Inclusive 33% tosylate from reoxidation based on XPS analysis of pure PEDOT films showing tosylate to EDOT ratios of approximately 1: in oxidized conductive films. b^ Reference sample, PEDOT-N 3 without any further treatment. Quantification in parentheses refer to analysis without electron charge compensation. c^ Reference sample, PEDOT-N 3 exposed to equivalent reaction conditions except that CuSO 4 was omitted.
4324 Daugaard et al. Macromolecules, Vol. 41, No. 12, 2008
considerably smaller than the reduction in conductivity, since
the film thickness is increased by 75% after the click reaction,
which in its own effect gives a reduction in conductivity.
Mechanical stirring is not possible with the polymer film,
and all mixing of reagents is thus dependent on diffusion.
Therefore, the necessary catalyst concentration within reasonable
time frames was investigated. UV/vis spectroscopy of the films
produced with a catalyst amount of 5, 20, and 100% catalyst
relative to the alkyne ( 11 ) is presented in Figure 4 and compared
to a thin layer of 11 spin-coated on a glass slide. The UV/vis
spectrum shows that the 20% and 100% samples have the same
three characteristic peaks as 11 , although they are blue-shifted
by 5 - 10 nm. The strong absorption peaks supports the
assumption that more than a surface layer of fluorescein is
present after the reaction.
The UV/vis absorption of the three fluorescein peaks reaches
a maximum already at 20% catalyst, and conducting the reaction
with 100% catalyst made no significant difference. Two
explanations for this result seem feasible. Either 20% is
sufficient, given the diffusion, to make the reaction proceed to
completion within reasonable time or the concentration of azides
is lower than assumed and all reactive sites can be initialized
with 20% of the alkynes. The concentration of azides on the
surface estimated based on the film thickness, film size, and
the density of PEDOT that gives approximately 0.1-0.2 mg/
cm^2 of azide polymer. In addition to this, access to all the azides
in the film must be limited by sterical hindrance and diffusion
into the polymer film, and it is expected that some of the sites
may be inaccessible.
Using 20% catalyst loading the reaction time was monitored
using UV/vis as shown in Figure 5. The reaction proceeds
mainly within the first 20 h, and then the increase in intensity
gradually decreases over time. This rate decrease is believed to
be due to steric hindrance in the bulk of the polymer film as
the loading increases and less free sites are available for reaction.
It would demand unreasonable long reaction times to obtain
complete reaction of all azides, and thus the loading obtained
after 20 h has been found sufficiently high.
Film thickness measurements by profilometry corroborate
these results (see Figure 6) by showing a slow progression
toward larger film thickness for reactions occurring over several
days.
The results from polymer films of pure EDOT-N 3 show a
very high density of accessible reactive sites. Many applications
may benefit from a lower density of sites with controllable
average spacing, e.g., uses targeting the immobilization of
large biomolecules as sensors or cellular stimulants. In order
to be able to load the surface with a lower amount of azides,
the copolymerization of EDOT and EDOT-N 3 was investigated.
As mentioned earlier, EDOT-N 3 was less reactive than EDOT
and thus polymerized without pyridine. In the copolymer
formulation mixture it was necessary to include some pyridine
in order to limit the EDOT polymerization since that would
otherwise be too fast. It was decided to simply mix the reaction
mixtures for homopolymerization of the two monomers in the
ratio desired of the copolymer. This is a tradeoff as polymer-
ization has to be slowed down sufficiently to control the EDOT
reactivity without inhibiting the polymerization of EDOT-N 3
completely. The reaction was performed as shown in Scheme
5, and as with the homopolymer the product is insoluble and
cannot be characterized using NMR or SEC.
Figure 4. UV/vis spectroscopy of the fluorophore ( 11 ) loading on PEDOT-N 3 ( 3 ) as effect of catalyst concentration using a constant reaction time of 20 h.
Figure 5. UV/vis spectroscopy of the fluorophore ( 11 ) loading on PEDOT-N 3 ( 3 ) as a function of reaction time using a constant catalyst loading of 20%.
Figure 6. Increased thickness of the triazole functional polymer ( 14 ) as a function of reaction time using a constant catalyst loading of 20%.
Figure 7. Increase in thickness by the click reaction as a function of EDOT-N 3 content in the copolymer.
Figure 8. UV/vis absorptions per nm film thickness of the clicked copolymers, 15 - 20.
Macromolecules, Vol. 41, No. 12, 2008 Conductive Polymer Functionalization 4325
coupling to give 22 also correlate well with the contact angle
measurements, where there is clearly a higher loading of MPEG
with DMF as solvent compared to H 2 O. The high-resolution
peak of nitrogen shows in both cases residual azide nitrogen
(not shown), which would be expected since diffusion of the
long MPEG chains of 12 into the PEDOT-N 3 is much more
difficult than with the smaller 10. Regarding the MPEG
experiments, the reaction is much more likely to occur only in
the upper surface or perhaps only on the surface. However, there
is an increased loading in the case of DMF compared to water.
One may speculate that this is due to water being inefficient in
swelling and wetting the PEDOT-N 3 surface. Access to reactive
groups would be limited to the azides on the actual surface;
thus, after reaction of about one layer of MPEG the reaction
would stop. The higher loading observed with MPEG reactions
in DMF could be an effect of better wetting and swelling of
the surface, which would give access to an increased number
of reactive sites.
Conclusion
We have developed the synthesis of a new azide monomer,
EDOT-N 3 , and demonstrated that it can be polymerized to
PEDOT-N 3 , which can be used as a precursor to obtain
conductive polymers with different functionalities. A click
reaction with a fluorescein derivative has been performed on
the surface, and the reaction conditions have been optimized
for other applications. It is possible to copolymerize EDOT-N 3
and EDOT in different ratios and to functionalize these after
polymerization. Through the copolymer it is possible to control
the number of reactive sites on the surface, in case a lower
loading is desirable. The copolymers have also been shown to
be a good way to obtain functional conductive polymers while
minimizing the loss in conductivity.
By coupling the fluorous alkyne and the MPEG alkyne to
the surface, we have shown the versatility of the method. We
believe that this method can be applied for other alkynes with
different functional groups. The approach is well suited for new
sensor devices, and we are currently working on the develop-
ment of different systems.
Acknowledgment. The Danish Research Council for Technol-
ogy and Production Sciences (through the framework program “Design and Processing of Polymers for Microfluidic Applications”, grant 26-04-0074) is thanked for financial support.
References and Notes
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