Langmuir film polymerization of 1,22-bis(2-aminophenyl)docosane: A two- dimensional cross-linked polyalkylaniline [3]

Full text of DOI:10.1021/ja990142x

8108
J. Am. Chem. Soc. 1999, 121, 8108-8109
Scheme 1
Langmuir Film Polymerization of
1,22-Bis(2-aminophenyl)docosane: A
Two-Dimensional Cross-linked Polyalkylaniline
L. J. Kloeppner and R. S. Duran*
Center for Macromolecular Science and Engineering
Department of Chemistry, UniVersity of Florida
GainesVille, Florida 32611
ReceiVed January 14, 1999
Ultrathin films have been proposed for many applications such
as in nonlinear optical1-5 and electroluminescent devices6,7 and
sensors.8,9 However, most applications require the films to be
mechanically, thermally, and chemically stable under environ-
mental conditions, which is often difficult to achieve. Polymeric
systems are usually more stable than low molar mass analogues
due to covalent bonding in the film plane and are often preferred.10
Further, network polymers in 3-dimensions are generally more
stable to thermal and physical stress than their non-cross-linked
counterparts, and therefore, free-standing monolayers of this type
should also have improved stability. Though the potential for these
types of films is great, there are few published reports that deal
with Langmuir films that form 2-dimensional network poly-
mers.11-15 Self-assembled organic monolayers on solid substrates
show some of these characteristics, but require specific substrates
and therefore cannot be a general method to produce stable, free-
standing films.16-18
(i) TsCl, pyridine, and CHCl3; (ii) LiBr, acetone, and heat; (iii) PPh3
CH3CN, and heat; (iv) potassium tert-butoxide, 2-nitrobenzaldehyde, and
THF; (v) H2, 10% Pd on carbon, and 95% ethanol.
This communication presents the Langmuir film polymerization
of a dipolar monomer, 1,22-bis(2-aminophenyl)docosane (BAD),
which forms a 2-dimensional network polymer of polyalkylaniline.
The surface behavior of BAD is presented and compared with
that of the monopolar surfactant, 2-pentadecylaniline (PDA),
which is routinely polymerized in Langmuir films.19-21
(1) Nalwa, H. S. AdV. Mater. 1993, 5, 341.
(2) Hodge, P.; Ali-Adib, Z.; West, D.; King, T. Macromolecules 1993, 26,
6, 1789.
(3) Bosshard, C.; Otomo, A.; Stegeman, G. I.; Ku¨pfer, M.; Flo¨rsheimer,
M.; Gu¨nter, P. Appl. Phys. Lett. 1994, 64, 2076.
(4) Eaglesham, A.; Jaworek, T.; Cresswell, J.; Allen, S.; Burgess, A.;
Ferguson, I.; Ryan, T. G.; Hutchings, M.; Petty, M. C.; Yarwood, Y. Langmuir
1996, 12, 2292.
(5) Srikhirin, T.; Mann, J. A., Jr.; Lando, J. B. J. Polym. Sci., Polym. Chem.
Ed. 1999, 37, 1057.
Figure 1. Surface pressure (π) vs mean molecular area (A) isotherms of
BAD and PDA on 0.01 M H2SO4 at 25 °C.
(6) Pavier, M. A.; Weaver, M. S.; Lidzey, D.; Richardson, T.; Searle, T.
M.; Bradley, D. D. C.; Huang, C. H.; Li, H.; Zhou, D. Thin Solid Films 1996,
284-285, 644.
Scheme 1 shows the synthetic route by which BAD was
prepared. In this route, two molecules of 1-(2-nitrophenyl)-1,11-
dodecadiene were coupled at the terminal olefin by a metathesis
reaction using a ruthenium alkylidene catalyst.22 1H NMR studies
of this coupling reaction suggest that this self-metathesis reaction
occurs selectively at the terminal olefin and not at the olefin next
to the aromatic ring. PDA was synthesized by a route previously
reported.19
The surface pressure (π) vs mean molecular area (A) isotherms
of BAD and PDA on a 0.10 M H2SO4 subphase had pressure
onset areas at ca. 150 and 74 Å2 molecule-1, respectively (Figure
1). As expected, the pressure onset area of BAD was about twice
that of the PDA, indicating that both of the anilinium groups were
adsorbed to the interface with the long chain oriented away from
the surface. Isobaric creep experiments of the monomers showed
that the BAD film was more stable over time than PDA under
similar conditions. For example, at a surface pressure of 15 mN
m-1, the monolayer film of BAD crept ca. 0.048 Å2 anilinium
(7) Onoda, M.; Yamaue, T.; Tada, K.; Kawai, T.; Yoshino, K. Synth. Met.
1997, 84, 983.
(8) Nomura, T.; Takebayashi, M.; Saitoh, A. IEEE Trans. Ultrason.,
Ferroelect., Freq. Control 1998, 45, 1261.
(9) Di Natale, C.; Paolesse, R.; Macagnano, A.; Troitsky, V. I.; Berzina,
T. S.; D’Amico, A. Anal. Chim. Acta 1999, 384, 249.
(10) Fuchs, H.; Ohst, H.; Prass, W. AdV. Mater. 1991, 3, 10.
(11) Steitz, R.; Peterson, I. R.; Voigt-Martin, I.; Mo¨hwald, H. Thin Solid
Films 1989, 178, 289.
(12) Dubault, C.; Casagrande, M.; Veyssie, M. J. Phys. Chem. 1975, 79,
2254.
(13) Rosilio, C.; Ruaudel-Teixier, A. J. Polym. Sci., Polym. Chem. Ed. 1975,
13, 2459.
(14) Emmerling, W. N.; Pfannemu¨ller, B. Colloid Polym. Sci. 1983 261,
677.
(15) Porteu, F.; Palacin, S.; Ruaudel-Teizier, A.; Barraud, A. Makromol.
Chem., Macromol. Symp. 1991, 46, 37.
(16) Bain, C. D.; Whitesides, G. M. Angew. Chem., Int. Ed. Engl. 1989,
28, 506.
(17) Ulman, A. An Introduction to Ultrathin Organic Films; Academic
Press: Boston, 1991.
(18) Ulman, A. Characterization of Organic Thin Films; Butterworth-
Heinemann: Boston, 1995.
(19) Kloeppner, L. J.; Duran, R. S. Langmuir 1998, 14, 6734.
(20) Zhou, H.; Stern, R.; Batich, C.; Duran, R. S. Makromol. Chem., Rapid
Commun. 1990, 11, 409.
(22) Schwab, P.; France, M. B.; Ziller, J. W.; Grubbs, R. H. Angew. Chem.,
Int. Ed. Engl. 1995, 34, 2039.
(21) Bodalia, R. R.; Duran, R. S. J. Am. Chem. Soc. 1993, 115, 11467.
10.1021/ja990142x CCC: $18.00 © 1999 American Chemical Society
Published on Web 08/18/1999

Communications to the Editor
J. Am. Chem. Soc., Vol. 121, No. 35, 1999 8109
Figure 2. Surface pressure (π) vs mean molecular area (A) isotherms of
poly(BAD) and poly(PDA) on 0.01 M H2SO4 and 0.03 M (NH4)2S2O8 at
25 °C. -d[ANI]/dt vs time for the polymerization of BAD at 10 mN
m-1 and 25 °C.
Figure 3. Removal of poly(BAD) from the surface of the Langmuir
trough. The polymer comes off the subphase in self-supporting, elastic
sheets which easily draw down to fibers.
The infrared spectrum of the poly(BAD) polymerized on a 0.2
M HCl and 0.03 M (NH4)2S2O8 subphase reveals the characteristic
C-C ring stretching of the polyaniline backbone at 1498 and
1597 cm-1. The asymmetric and symmetric stretch and bending
vibrations of the alkyl groups were recorded at 2924, 2852, and
1461 cm-1, respectively.
unit-1 min-1, while PDA had a film creep of 0.30 Å2 anilinium
unit-1 min-1 23
.
The Langmuir polymerization of PDA and the experimental
details have been reported.19 The polymerizations of BAD and
PDA were carried out on a 0.10 M sulfuric acid and 0.03 M
ammonium peroxydisulfate subphase solution. The surface pres-
sure was held constant while the film area was monitored over
time. In the case of aniline-type monomers, the area that a polymer
repeat unit occupies at the interface is less than that of the
monomer,20 making this a useful technique to monitor the reaction
kinetics.
The two polymerizable anilinium groups of BAD, allow for it
to add to the polymer backbone in several ways. One possible
ordering would involve incorporating the anilinium groups such
that the linked groups are next to each other in a single polymer
chain. This ordering would probably lead to a material with
mechanical properties similar to those of poly(PDA). A second
possible ordering would incorporate connected anilinium groups
into the backbones of different polyaniline chains, which would
lead to cross-linked polyaniline. The insolubility of the material
and the fact that it could be lifted from the aqueous interface in
one piece suggests that the second ordering is occurring to an
appreciable extent and that a cross-linked polymer was formed.
Such an architecture is an example of a 2-dimensional network
polymer connected in two ways. A layer of rather stiff connections
forms the polyaniline chains; these are sandwiched between an
aqueous subphase and a layer of flexible alkyl chains that connect
the backbones. Varying the length of the alkyl chain or copoly-
merizing it with PDA may provide an interesting means of
controlling the ultimate porosity of the resulting network polymer.
Preliminary results show that BAD can be polymerized to form
a novel insoluble organic material in a Langmuir film. The surface
behavior of this dipolar molecule is much like that of PDA under
similar conditions, while the polymer exhibits an increase in its
mechanical strength compared to that of poly(PDA). This increase
in mechanical strength could lead to a wider acceptance of highly
ordered LB films in technical applications.
The polymerization rate can be calculated from the change in
A of the surfactant at a constant applied surface pressure from
the equation19
d[(A0 - A)/(A0 - A∞)]
dt
[ANI]
dt
2
A
-
)
(
)
( )
where [ANI] is the concentration of anilinium groups at the
interface and A0 and A∞ are the surface areas of the monomer at
the beginning and end of the reaction. Figure 2 shows the polymer
formation rate with time. The plot indicates that the polymeri-
zation rate increased with time early in the reaction, suggesting
that autoacceleration occurred. This effect has been observed in
the solution polymerization of aniline24 and in the Langmuir film
polymerization of PDA.19,20 The π-A isotherm of poly(BAD)
had a pressure onset area of ca. 70 Å2 molecule-1 or 35 Å2 repeat
unit-1, while the onset area of poly(PDA) was 35 Å2 repeat unit-1
(Figure 2).
Once the polymerization was complete, the polymer could be
expanded and compressed with little hysteresis. A dark blue
material was collected from the interface by first compressing
the polymer film to ca. 2 cm with the trough barriers, and then a
glass frit connected to vacuum was used to pull the material from
the surface (Figure 3). Unlike poly(PDA), this material was gel
like and could be essentially collected in one piece. The material
was insoluble in the solvents that usually dissolve polyaniline
(NMP and sulfuric acid) and in the solvents typically used for
poly(PDA) (chloroform and THF), making molecular weight
analysis by GPC impossible.
Acknowledgment. We are grateful for financial support provided in
part by the Office of Naval Research, the National Science Foundation,
and KSV Instruments Ltd., Helsinki, Finland. Thanks to Mark D. Watson
for his help in the metathesis coupling reaction.
Supporting Information Available: Synthetic details and charac-
1
terization of each step in Scheme 1, including H and 13C NMR, MS,
melting point, and CHN, and the FTIR and hysteresis of poly(BAD) (6
pages, print/PDF). This material is available free of charge via the Internet
at http://pubs.acs.org.
(23) Bodalia, R. Ph.D. Dissertation, University of Florida, Dec 1993.
(24) Tzou, K.; Gregory, R. V. Synth. Met. 1992, 47, 267.
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