Preparation and properties of poly(methacrylamide)s containing oligoaniline side chains

Article abstract of DOI:10.1021/ma030033+

New poly(methacrylamide)s containing oligoaniline side chains were synthesized and characterized. Oligoanilines were prepared by palladium-catalyzed amination, followed by reaction with methacryloyl chloride to give methacrylamide monomers. Polymers were

Full text of DOI:10.1021/ma030033+

Macromolecules 2003, 36, 6333-6339
6333
Preparation and Properties of Poly(methacrylamide)s Containing
Oligoaniline Side Chains
Ru Ch en a n d Br ia n C. Ben icew icz*
Department of Chemistry, New York State Center for Polymer Synthesis, Rensselaer Polytechnic
Institute, Troy, New York 12180
Received J anuary 16, 2003; Revised Manuscript Received J une 4, 2003
ABSTRACT: New poly(methacrylamide)s containing oligoaniline side chains were synthesized and
characterized. Oligoanilines were prepared by palladium-catalyzed amination, followed by reaction with
methacryloyl chloride to give methacrylamide monomers. Polymers were prepared by free radical
polymerization. The polymers were prepared in the leucoemeraldine state and were oxidized to the
emeraldine state by exposure to oxygen gas. The electrochemical characterization of these polymers by
cyclic voltammetry indicated that the redox behaviors were similar to the corresponding oligoanilines.
In tr od u ction
phologies such as lamellae and cylindrical micelles
which may lead to electrical and optical properties
absent in conjugated homopolymers.
Conducting polymers have been extensively studied
since the important discovery of Shirakawa et al.1 that
an organic polymer could display high conductivity at
room temperature when exposed to an appropriate
dopant. Because of their unique electrical and optical
properties, conducting polymers have a wide variety of
potential applications from electronic and optoelectronic
devices such as field effect transistors, electrolumines-
cent, electrochromic, and photovoltaic devices to sensors,
gas separation membranes, electromagnetic shielding
layers, and corrosion protective coatings.2-4
Polymers containing pendant conjugated oligomers
are of interest because of the variety of possible oligo-
mers, processability, and potential applications in elec-
tronic devices.7 The electrical and electrochemical prop-
erties can be tailored by adjusting the oligomer length,
incorporation of ring substituents, and alteration of the
basic chemical structure of the oligomer. Polymer
properties can be easily modified and improved through
copolymerization. The covalent bond attachment of the
oligomers to the polymer backbone also prevents the loss
of active species from the bulk polymer through migra-
tion and extraction. In this paper, we report the
synthesis of poly(methacrylamide)s with oligoaniline
side chains, polymers 1 and 2 (Figure 1). The effect of
oligoaniline side chain length on the redox behavior of
the polymer will be reported and discussed.
Early studies on conjugated polymers were plagued
by difficulties in processing the intractable materials
and imperfections in the conjugated polymer structures.
Conjugated oligomers were initially introduced as model
compounds to rationalize and predict the properties of
the intractable polymeric analogues. Because of the
monodisperse composition, well-defined structure, and
special physical, electronic, and optical properties,
conjugated oligomers also have potential applications
in molecular electronics and nanotechnology. Incorpora-
tion of conjugated oligomers into polymer structures
combines the properties of the specific oligomer and
desirable polymer properties such as mechanical strength
and film-forming properties. Shirota et al.5-7 showed
that oligothiophenes can be attached to vinyl and
methacrylate polymers as side chains. These polymers
showed an electrical conductivity in the range of semi-
conductors and have potential applications in electro-
chromic devices. Dufour et al.8 copolymerized 3-octylth-
iophene with a thiophene monomer containing an
oligoaniline side chain which displayed spectroelectro-
chemical properties of both polyaniline and poly-
(thiophene). Polymers with conjugated aniline oligomers
in the main chains have also been prepared by an acid-
induced polycondensation.9 This polymer displayed good
solubility in common organic solvents and electrical
conductivities up to 1 S/cm upon doping. Electroactive
polyimides derived from the bis-amino-terminated aniline
trimer were also reported by Wei et al.10 Yu et al.11,12
reported on the synthesis of rod-coil diblock copolymers
containing an oligo(p-phenylenevinylene) block and
polyisoprene or poly(ethylene glycol) block. These co-
polymers self-assembled into different nanoscale mor-
Exp er im en ta l Section
All chemicals were purchased from ACROS Organics unless
otherwise specified. p-Aminodiphenylamine (98%), benzophe-
none (99%), tetra-n-butylammonium tribromide (98+%), di-
tert-butyl bicarbonate (97%), 4-(dimethylamino)pyridine (DMAP,
99%), ammonium formate (99%), palladium acetate (Pd(OAc)2,
47.5% Pd), sodium tert-butoxide (98%), methacryloyl chloride
(Aldrich, 98+%), and triethylamine (99%) were all used as
received without further purification. 2,2′-Azobis(isobutyroni-
trile) (AIBN, Aldrich) was recrystallized from ethanol. Bis[(2-
diphenylphosphino)phenyl] ether (DPEphos)13 and N-(diphe-
nylmethylene)-4-bromoaniline (3)14 were synthesized according
to literature methods. Toluene and tetrahydrofuran (THF,
HPLC grade) were refluxed over sodium metal for 24 h
followed by distillation under argon. N,N-Dimethylformamide
(DMF) was treated with 5 Å molecular sieves and distilled
under reduced pressure. Deuterated chloroform (CDCl3, 99.9
at. % D) and deuterated methyl sulfoxide (DMSO-d6, 99.9 at.
% D) were used as received. Elemental analysis was performed
by Midwest Microlabs. NMR spectra were recorded on a Varian
500 spectrometer using solvent residues as references. A
Shimadzu GCMS-QP-5000 spectrometer was used to confirm
the chemical structure and purity of all compounds prepared
in this work. Fourier transform infrared (FTIR) spectrometry
was performed using a Bio-Rad FTS3000 spectrometer. UV-
vis spectra were recorded on Perkin-Elmer Lamda 4C UV/vis
spectrophotometer. Thermal analysis was carried out in a
nitrogen atmosphere with a heating rate of 20 °C/min on a
10.1021/ma030033+ CCC: $25.00 © 2003 American Chemical Society
Published on Web 07/23/2003

6334 Chen and Benicewicz
Macromolecules, Vol. 36, No. 17, 2003
6.68 (d, J ) 8.5 Hz, 2H, Ar), 1.39 (s, 9H, -OC(CH3)3). 13C NMR
(125 MHz, CDCl3): δ 169.1, 153.7, 149.7, 142.5, 139.6, 137.9,
136.2, 131.7, 131.1, 129.7, 129.5, 128.9, 128.4, 128.1, 127.8,
127.6, 121.7, 118.3, 81.6, 28.3. IR (KBr, cm-1): 3059, 3028,
2977, 2926, 1709, 1490, 1324, 1161, 701. Anal. Calcd for C30H27
-
BrN2O2: C, 68.31; H, 5.16; Br, 15.15; N, 5.31. Found: C, 68.24;
H, 5.07; Br, 15.14; N, 5.27.
N-(Dip h en ylm et h ylen e)-N′-(ter t-b u t oxyca r b on yl)-N′-
(p h en yl)-p-p h en ylen ed ia m in e (6). Compound 4 (24.00 g,
68.93 mmol) was dissolved in THF (200 mL). Di-tert-butyl
bicarbonate (18.00 g, 82.47 mmol) and 4-(dimethylamino)-
pyridine (1.26 g, 10.3 mmol) were added. The solution was
refluxed for 24 h. The solvent was removed by rotary evapora-
tion. The crude solid was recrystallized in ethyl acetate/
hexanes and dried in vacuo at 50 °C for 24 h. Product: slightly
1
yellow needles, 29.52 g (95%); mp 154-155 °C. H NMR (500
MHz, CDCl3): δ 7.74 (d, J ) 7.1 Hz, 2H, Ar), 7.46 (t, J ) 7.0
Hz, 1H, Ar), 7.40 (t, J ) 7.6 Hz, 2H, Ar), 7.32-7.20 (m, 5H,
Ar), 7.18-7.06 (m, 5H, Ar), 6.97 (d, J ) 8.5 Hz, 2H, Ar), 6.67
(d, J ) 8.3 Hz, 2H, Ar), 1.40 (s, 9H, -OC(CH3)3). 13C NMR
(125 MHz, CDCl3): δ 168.9, 154.0, 149.3, 143.3, 139.7, 138.5,
136.3, 131.0, 129.7, 129.5, 128.9, 128.7, 128.4, 128.1, 127.6,
126.4, 125.3, 121.6, 81.0, 28.4. IR (KBr, cm-1): 3059, 3027,
2982, 2924, 1707, 1497, 1319, 1163, 695. Anal. Calcd for
F igu r e 1. Chemical structures of the poly(methacrylamide)s
containing oligoaniline side chains.
C
30H28N2O2: C, 80.33; H, 6.29; N, 6.25. Found: C, 80.31; H,
thermal gravimetric analysis (TGA) Perkin-Elmer 7 series
instrument with Pyris software or a Mettler-Toledo DSC 822e
and TGA/SDTA 851e. The molecular weight of the polymers
was measured on a Waters GPC system equipped with a
refractive index detector (Waters 2410) and three Styragel
columns packed with 5 µm particles (HR1: effective molecular
weight 100-5000; HR3: effective molecular weight 500-
30 000; HR4: effective molecular weight 5000-500 000) using
THF as the eluent at a flow rate of 0.3 mL/min. The column
temperature was set at 30 °C. Molecular weights were reported
relative to polystyrene standards. Cyclic voltammetry was
conducted on a Zahner IM6e electrochemical workstation with
a three-electrode electrochemical cell using SCE and Pt wire
as the reference and counter electrodes, respectively. The
working electrode was prepared by casting the polymer as a
film on the surface of Pt electrode. Sulfuric acid aqueous
solution (1.0 M) was used as the supporting electrolyte. The
scan rate was 100 mV/s.
N-(Dip h en ylm et h ylen e)-N′-(ter t-b u t oxyca r b on yl)-N′-
(4-b r om op h en yl)-p -p h en ylen ed ia m in e (5). p-Aminodi-
phenylamine (22.32 g, 121.1 mmol) and benzophenone (20.00
g, 109.8 mmol) were dissolved in toluene (125 mL). Molecular
sieves, 5 Å (30.0 g), were added to the solution. The mixture
was refluxed for 48 h under a nitrogen atmosphere. The
solution was decanted, and the molecular sieves were washed
with ethyl ether until the filtrate was colorless. The organic
solutions were combined and concentrated. The solid residue
was dissolved in ethyl acetate and washed with NaOH solution
(2 M) and finally brine. The organic solution was dried with
anhydrous sodium sulfate and concentrated. The crude solid
was recrystallized in methanol/ethyl acetate. The yellow
crystals were dried in vacuo at 50 °C for 24 h. The yield of
product 4 was 35.69 g (93%). Compound 4 (10.00 g, 28.72
mmol) was dissolved in dichloromethane (80 mL), and tetra-
n-butylammonium tribromide (15.24 g, 31.61 mmol) was added
in one portion. The solution was stirred at room temperature
for 1 h, and then sodium sulfite solution (22%, 50 mL) was
added with stirring for 30 min, followed by the addition of
sodium hydroxide solution (2 M, 25 mL). The organic phase
was washed with distilled water, dried over anhydrous sodium
sulfate, and concentrated. The residue was dissolved in THF
(80 mL), to which di-tert-butyl bicarbonate (7.52 g, 34.5 mmol)
and 4-(dimethylamino)pyridine (0.58 g, 4.7 mmol) were added.
The solution was refluxed for 24 h and concentrated. The
residue was recrystallized in methanol/ethyl acetate and dried
in vacuo at 50 °C for 24 h. The yield of the slightly yellow
crystals was 13.28 g (88%); mp 163-165 °C. 1H NMR (500
MHz, CDCl3): δ 7.74 (d, J ) 7.3 Hz, 2H, Ar), 7.50-7.33 (m,
5H, Ar), 7.31-7.20 (m, 3H, Ar), 7.11 (dd, J ) 7.9, 1.3 Hz, 2H,
Ar), 7.02 (d, J ) 8.8 Hz, 2H, Ar), 6.94 (d, J ) 8.5 Hz, 2H, Ar),
6.32; N, 6.26.
N-(Dip h en ylm et h ylen e)-N′-(ter t-b u t oxyca r b on yl)-N′-
[4-(N-ter t-bu toxyca r bon yla n ilin o)]p h en yl-p-p h en ylen e-
d ia m in e (8). Compound 6 (24.00 g, 53.50 mmol), ammonium
formate (40.61 g, 644.0 mmol), and palladium on carbon (5%,
2.83 g, 1.33 mmol Pd) were charged into a round-bottomed
flask and purged with argon. THF (100 mL) and methanol (250
mL) were added, and the reaction mixture was refluxed for
24 h. The solution was concentrated, and the residue was
dissolved in dichloromethane, filtered through Celite, and then
concentrated. The solid was ground and washed with hexanes
and then filtered. The white powder was dried in vacuo at 50
°C for 24 h. Yield of product 7 was 15.00 g (98%). Compound
7 (5.00 g, 17.6 mmol), palladium acetate (69.8 mg, 0.311 mmol),
and DPEphos (246.0 mg, 0.457 mmol) were charged into a flask
and purged with argon. Compound 3 (4.92 g, 14.6 mmol) was
added, followed by toluene (30 mL). The solution was warmed
to 50 °C to aid the dissolution. Sodium tert-butoxide (3.00 g,
31.2 mmol) was added in one portion. Additional toluene (20
mL) was added to wash the flask wall. The reaction mixture
was heated to 110 °C with stirring for 24 h. The solvent was
removed by rotary evaporation. The residue was dissolved in
dichloromethane, washed with distilled water, and dried over
anhydrous sodium sulfate and concentrated. The residue was
dissolved in THF (100 mL), and di-tert-butyl bicarbonate (4.12
g, 18.9 mmol) and 4-(dimethylamino)pyridine (0.38 g, 3.1
mmol) were added. The reaction mixture was refluxed for 24
h. The solvent was removed, and the solid was recrystallized
in methanol. Product 8 was obtained as a pink solid 6.92 g
(74%); mp 149-151 °C. 1H NMR (500 MHz, CDCl3): δ 7.74
(d, J ) 7.3 Hz, 2H, Ar), 7.47 (t, J ) 7.1 Hz, 1H, Ar), 7.40 (t, J
) 7.4 Hz, 2H, Ar), 7.33-7.22 (m, 5H, Ar), 7.21-7.06 (m, 9H,
Ar), 6.96 (d, J ) 8.5 Hz, 2H, Ar), 6.67 (d, J ) 8.3 Hz, 2H, Ar),
1.44 (s, 9H, -OC(CH3)3), 1.38 (s, 9H, -OC(CH3)3). 13C NMR
(125 MHz, CDCl3): δ 168.9, 154.0, 149.4, 143.0, 140.6, 140.0,
139.7, 138.2, 136.3, 131.0, 129.7, 129.5, 128.9, 128.4, 128.1,
127.7, 127.2, 127.0, 126.3, 125.9, 121.6, 81.4, 81.1, 28.4, 28.3.
IR (KBr, cm-1): 3059, 3027, 2976, 2925, 1711, 1494, 1325,
1162, 697. Anal. Calcd for C41H41N3O4: C, 76.97; H, 6.46; N,
6.57. Found: C, 76.70; H, 6.65; N, 6.54.
N-(Met h a cr yloyl)-N′-(ter t-b u t oxyca r b on yl)-N′-[4-(N-
ter t-b u t oxyca r b on yla n ilin o)]-p -p h en ylen ed ia m in e (9).
Compound 8 (5.00 g, 7.82 mmol), ammonium formate (7.39 g,
117 mmol), and palladium on carbon (5%, 0.86 g, 0.40 mmol
Pd) were charged into a round-bottomed flask and purged with
argon. THF (100 mL) and methanol (250 mL) were added, and
the reaction mixture was refluxed for 24 h. The solution was
concentrated, and the residue was dissolved in dichloro-
methane, filtered through Celite, and concentrated. The solid
was ground and washed with hexanes and then filtered. The

Macromolecules, Vol. 36, No. 17, 2003
Poly(methacrylamide)s 6335
Sch em e 1a
a
(i) Ph2CO, toluene, reflux, 48 h; (ii) n-Bu4NBr3, CH2Cl2, rt, 1 h; (iii) (Boc)2O, DMAP, THF, reflux, 24 h; (iv) NH4HCO2, Pd/C,
THF/MeOH, reflux, 24 h; (v) Pd(OAc)2, DPEphos, NaOt-Bu, toluene, 110 °C, 24 h; (vi) methacryloyl chloride, THF, Et3N, 0 °C, 24
h.
white powder was dried in vacuo at 50 °C for 24 h; yield 3.48
g (94%). This amine (3.00 g, 6.31 mmol) was dissolved in THF
(25 mL) under a nitrogen atmosphere. Triethylamine (1.70 g,
16.8 mmol) was added, and the reaction mixture was cooled
with a ice bath. Methacryloyl chloride (0.79 g, 7.6 mmol) in
THF (25 mL) was added slowly into the solution. After
completion, the reaction mixture was stirred at room temper-
ature for 24 h. The precipitate was filtered off and washed
with THF. The solutions were combined, and the solvent was
removed with rotary evaporation. The residue was dissolved
in dichloromethane, washed with HCl solution (1 M), Na2CO3
solution (1 M), and distilled water. The solution was dried with
anhydrous sodium sulfate. The solvent was removed, and the
residue was separated by column chromatography (silica gel,
ethyl acetate/hexanes, 1:1). The product was obtained as a
white powder: 2.34 g, (68%); mp 178-180 °C (decomposition).
1H NMR (500 MHz, DMSO-d6): δ 9.84 (s, 1H, -NH), 7.66 (d,
J ) 8.8 Hz, 2H, Ar), 7.34 (t, J ) 7.8 Hz, 2H, Ar), 7.25-7.10
(m, 9H, Ar), 5.79 (s, 1H, cis dCH), 5.51 (s, 1H, trans dCH),
1.94 (s, 3H, dC-CH3), 1.37 (s, 18H, -OC(CH3)3). 13C NMR
(125 MHz, DMSO-d6): δ 166.8, 153.0, 152.9, 142.7, 140.4,
140.0, 137.8, 137.0, 128.9, 127.4, 127.1, 127.1, 126.8, 125.9,
120.5, 120.0, 80.4, 80.4, 27.8, 27.8, 18.7. IR (KBr, cm-1): 3331,
3043, 2977, 2930, 1711, 1511, 1327, 1162, 1057. Anal. Calcd
for C32H37N3O5: C, 70.70; H, 6.86; N, 7.73. Found: C, 70.90;
H, 6.88; N, 7.72.
1H, trans dCH), 1.95 (s, 3H, dCCH3), 1.38 (s, 27H, -OC-
(CH3)3). 13C NMR (125 MHz, DMSO-d6): δ 166.8, 153.0, 152.9,
152.9, 142.6, 140.5, 140.4, 140.3, 140.0, 139.7, 137.8, 137.0,
128.9, 127.4, 127.2, 127.1, 127.1, 126.9, 125.9, 120.5, 120.0,
80.5, 80.5, 80.4, 27.8, 27.8, 27.7, 18.7. IR (KBr, cm-1): 3335,
3043, 2977, 2930, 1712, 1511, 1327, 1162, 1057. Anal. Calcd
for C43H50N4O7: C, 70.28; H, 6.86; N, 7.62. Found: C, 70.32;
H, 6.95; N, 7.60.
P olym er iza tion of Com p ou n d 9. AIBN (10.0 mg, 6.09 ×
10-2 mmol) was dissolved in DMF (10 mL). Compound 9 (1.00
g, 1.84 mmol) was then dissolved in 2 mL of AIBN/DMF
solution. The reaction mixture was degassed by three freeze-
pump-thaw cycles, sealed under nitrogen, and heated to 70
°C for 24 h with stirring. The polymer was precipitated from
methanol/water (2:1) three times, filtered, and dried in a
vacuum oven at 60 °C for 24 h. The yield was 0.65 g (65%).
The GPC analysis gave Mn ) 2.8 × 104, Mw ) 5.2 × 104, and
PDI ) 1.9. 1H NMR (500 MHz, DMSO-d6): δ 9.02 (s, 1H,
-NH-), 7.41 (b, 2H, Ar), 7.25 (b, 2H, Ar), 7.12 (b, 9H, Ar),
1.96 (b, 2H, -CH2-), 1.32 (b, 21H, -CH3). IR (KBr, cm-1):
2977, 1711, 1510, 1327, 1161, 1056, 847. Anal. Calcd for
C
32H37N3O5: C, 70.70; H, 6.86; N, 7.73. Found: C, 70.95; H,
6.80; N, 7.33.
P olym er iza tion of Com p ou n d 11. AIBN (10.0 mg, 6.09
× 10-2mmol) was dissolved in DMF (20 mL). Compound 11
(0.504 g, 0.686 mmol) was then dissolved in 2 mL of AIBN/
DMF solution. The reaction mixture was degassed by three
freeze-pump-thaw cycles, sealed under nitrogen, and heated
to 70 °C for 24 h with stirring. The polymer was precipitated
from methanol/water (2:1) three times, filtered, and dried in
a vacuum oven at 60 °C for 24 h. The yield was 0.38 g (76%).
The GPC analysis gave Mn ) 5.8 × 103, Mw ) 1.1 × 104, and
PDI ) 1.9. 1H NMR (500 MHz, DMSO-d6): δ 9.09 (s, 1H,
-NH-), 7.45 (b, 2H, Ar), 7.24 (b, 2H, Ar), 7.10 (b, 13H, Ar),
1.97 (b, 2H, -CH2-), 1.31 (b, 30H, -CH3). IR (KBr, cm-1):
2977, 1712, 1510, 1326, 1161, 1055, 847. Anal. Calcd for
Compounds 10 and 11 were obtained by the same proce-
dures.
Com p ou n d 10. Obtained as pink solid in 63% yield; mp
184-185 °C (decomposition). 1H NMR (500 MHz, CDCl3): δ
7.74 (d, J ) 7.3 Hz, 2H, Ar), 7.46 (t, J ) 7.1 Hz, 1H, Ar), 7.40
(t, J ) 7.4 Hz, 2H, Ar), 7.33-7.22 (m, 5H, Ar), 7.21-7.06 (m,
13H, Ar), 6.95 (d, J ) 8.5 Hz, 2H, Ar), 6.67 (d, J ) 8.4 Hz, 2H,
Ar), 1.44 (s, 9H, -OC(CH3)3); 1.43 (s, 9H, -OC(CH3)3); 1.39
(s, 9H, -OC(CH3)3). 13C NMR (125 MHz, CDCl3): δ 169.5,
154.0, 143.0, 140.8, 140.6, 140.3, 139.7, 138.2, 136.3, 131.1,
129.8, 129.6, 129.0, 128.9, 128.4, 128.1, 127.7, 127.2, 126.4,
126.0, 121.6, 81.5, 81.5, 81.2, 28.4, 28.4. IR (KBr, cm-1): 3059,
3027, 2977, 2928, 1711, 1506, 1325, 1162, 698. Anal. Calcd
for C52H54N4O6: C, 75.16; H, 6.55; N, 6.74. Found: C, 74.94;
H, 6.63; N, 6.75.
C
43H50N4O7: C, 70.28; H, 6.86; N, 7.62. Found: C, 69.91; H,
6.94; N, 7.60.
Resu lts a n d Discu ssion
Oligom er a n d Mon om er Syn th esis. Several meth-
ods have been used for the preparation of oligoanilines.
Honzl et al.15 prepared aniline oligomers by the reaction
of diethyl succinoylsuccinate and aromatic amines,
Com p ou n d 11. Obtained as white solid in 78% yield; mp
141-143 °C. 1H NMR (500 MHz, DMSO-d6): δ 9.84 (s, 1H,
-NH), 7.66 (d, J ) 8.8 Hz, 2H, Ar), 7.34 (t, J ) 7.8 Hz, 2H,
Ar), 7.25-7.10 (m, 13H, Ar), 5.81 (s, 1H, cis dCH), 5.51 (s,

6336 Chen and Benicewicz
Macromolecules, Vol. 36, No. 17, 2003
Ta ble 1. P r op er ties of P oly(m eth a cr yla m id e)s w ith
Oligoa n ilin e Sid e Ch a in s
a
a
b
Mn
Mw
PDIa T5% (°C)
t-Boc-protected polymer 1 2.8× 104 5.2× 104
1.9
1.9
150
151
261
317
t-Boc-protected polymer 2 5.8× 103 1.1× 104
polymer 1
polymer 2
2.0× 104 3.3 × 104 1.6
3.4× 103 4.6× 103
1.4
a
Number-average molecular weight (Mn), weight-average mo-
lecular weight (Mw), and polydispersity (PDI) of polymers according
to gel permeation chromatography relative to polystyrene stan-
b
dards with tetrahydrofuran as eluent. T5% is the temperature
at 5% weight loss.
F igu r e 2. TGA thermograms of (a) t-Boc-protected polymer
1, (b) t-Boc-protected polymer 2, (c) polymer 1, and (d) polymer
2, carried out in a nitrogen atmosphere.
followed by hydrolysis, decarboxylation, and aromati-
zation. This procedure was modified by Wudl et al.16
for the preparation of octaaniline. Condensation be-
tween arylamines and phenol using a condensing re-
agent was applied in the oligomer synthesis by Ochi et
al.17 Rebourt et al.18 prepared aniline trimers and
tetramers by a modified Ullmann reaction without base.
A method similar to the oxidative polymerization of
polyaniline was developed by Wei et al.19 However, the
product contained oligomers with different chain lengths,
and intensive purification steps were necessary to obtain
well-defined products. Also, oligomers containing sub-
stituent groups are difficult to prepare using this
method. Recently, palladium-catalyzed amination has
emerged as a powerful method for the formation of
aromatic C-N bonds. The versatility of the methodology
has been demonstrated by the synthesis of aniline
oligomers with different functional end groups.14 Nu-
merous catalyst/ligand systems have been studied for
this reaction. The most common system is tri(diben-
zylideneacetone)dipalladium (Pd2(dba)3) and 2,2′-bis-
(diphenylphosphino)-1,1′-binaphthyl (BINAP). In this
work the catalyst system palladium acetate (Pd(OAc)2)
and DPEphos was used for the coupling reaction of an
aromatic amine with an aryl bromide. Compared with
other catalysts, palladium acetate is stable in air and
not very expensive. DPEphos can be prepared by a two-
step, one-pot reaction in medium scale with low cost.
This ligand is also stable in air. Buchwald et al.20
reported that this catalyst was highly efficient for the
C-N coupling reaction. Its application in the synthesis
of aniline oligomers has not been reported. In our
experiments, the catalyst system Pd(OAc)2/DPEphos
was highly efficient for the synthesis of aniline oligo-
mers.
F igu r e 3. FTIR spectra of (a) t-Boc-protected polymer 2 and
(b) polymer 2.
F igu r e 4. UV-vis spectra of polymer 2 in DMF solution: (a)
reduced, (b) oxidized, and (c) doped with sulfuric acid.
of the primary amine group, bromination, and then
protection of the secondary amine as a tert-butyl car-
bamate. Compound 7 was coupled with bromides 3 and
5 using palladium-catalyzed aromatic amination, fol-
lowed by protection with a t-Boc group, affording the
protected aniline oligomers 8 and 10, respectively. The
free amines of these oligomers were recovered by
palladium-catalyzed hydrogenation. The resultant com-
pounds were reacted with methacryloyl chloride to form
the methacrylamide monomers.
The synthesis of the monomers explored in this work
is shown in Scheme 1. Compound 7 was prepared from
4-aminodiphenylamine, in which the primary amine
group was first converted to an imine and the secondary
amine was subsequently protected by a tert-butoxycar-
bonyl group, followed by recovery of the primary amine
by catalyzed hydrogenation. N-Diphenylmethylene-4-
bromoaniline (3) was prepared by protection of 4-bromo-
aniline by diphenylmethylene.14 Compound 5 was pre-
pared from 4-aminodiphenylamine by initial protection
In the synthetic procedures, the NH group was
protected as a tert-butyl carbamate, which is a widely

Macromolecules, Vol. 36, No. 17, 2003
Poly(methacrylamide)s 6337
F igu r e 5. Cyclic voltammogram of polymer 1, measured in aqueous H2SO4 (1.0 M) with scan rate of 100 mV/s. The proposed
oxidation mechanism is shown below.
used protecting group and can be readily removed by
pyrolysis or other mild chemical methods.14 The intro-
duction of the t-Boc group prevents oxidation of the
anilino units and side reactions involving the secondary
amines.14 The t-Boc group also improves the solubility
of intermediates and products. Most importantly, the
protection is necessary for the free radical polymeriza-
tion of the monomers. The diphenylamine moiety is an
effective free radical inhibitor,21 which prevents free
radical polymerization of the corresponding monomers.
Our preliminary experiments showed that the polym-
erization of methacrylamide monomers containing un-
protected oligoaniline side chains was not successful.22
When acyl groups were used as protective groups, the
polymerization proceeded normally. However, the solu-
bility of the resulting polymers was low, and the
polymers precipitated early from the reaction mixture.
Also, the removal of the acyl group required vigorous
hydrolytic conditions which cleaved the amide bond that
attached the oligoaniline moiety to the polymer back-
bone. In this work, the primary and secondary amines
were protected with diphenylmethylene and tert-bu-
toxycarbonyl groups, respectively, which allowed the
selective protection and mild deprotection of the various
oligomers, monomers, and polymers. The diphenyl-
methylene group was quantitatively removed by cata-
lyzed hydrogenation in the presence of palladium on
carbon.
using AIBN as initiator. These polymers showed good
solubility in common organic solvents, such as toluene,
THF, DMSO, and DMF. In contrast, similar polymers
with the acyl protecting group were not soluble in
toluene or THF.22 The number-average molecular weights
of protected polymers 1 and 2 were 2.8 × 104 and 5.8 ×
103, respectively. The molecular structures of the poly-
mers were confirmed by proton NMR and FTIR. To
obtain electroactive polymers, the protecting groups
were removed after the polymerization. Thermolysis of
protected oligoanilines in an inert atmosphere quanti-
tatively removed the t-Boc group, affording oligoanilines
in their reduced state. In the TGA study in nitrogen,
t-Boc-protected polymers 1 and 2 started to lose weight
at about 140 °C (Figure 2). The total weight loss in the
first step of decomposition for polymers 1 and 2 was 36%
(theoretical loss 37%, calculated from molecular weight
of repeating unit) and 39% (theoretical loss 41%),
respectively. This showed that the removal of the t-Boc
group was essentially quantitative. The thermograms
also indicated that the resulting polymers 1 and 2 were
stable up to about 250 °C. Polymers 1 and 2 were
prepared by heating the precursors in Schlenk tubes
under argon at 180 °C for 10 h. Molecular weight
characterization and thermal stability (temperature at
5% weight loss) of the polymers are summarized in
Table 1.
P olym er Ch a r a cter iza tion . The resulting poly-
mers, 1 and 2, were soluble in THF, DMSO, and DMF.
GPC analysis showed that the molecular weights were
slightly lower than those of their precursors, 2.0 × 104
P olym er Syn th esis. Methacrylamide monomers con-
taining the t-Boc-protected oligoaniline side chains were
polymerized by free radical polymerization in DMF

6338 Chen and Benicewicz
Macromolecules, Vol. 36, No. 17, 2003
and 3.4 × 103, respectively. This was attributed to the
loss of the bulky t-Boc groups, causing a decrease in the
hydrodynamic volume of the macromolecules in solution.
Proton NMR spectra of the polymers in DMSO-d6
showed that the proton resonance of the tert-butyl group
(1.31 ppm) disappeared completely. New resonances due
to amine groups appeared after thermolysis (7.72 and
7.28 ppm for polymer 1; 7.72, 7.60, and 7.30 ppm for
polymer 2). The FTIR spectrum was obtained by casting
a film on a KBr pellet (Figure 3). The protected polymers
exhibit peaks at 1712 and 1161 cm-1 which were
assigned to the stretching vibration of carbonyl and the
stretching of O-C(CH3)3 from the tert-butyl carbamate
protective groups. These peaks disappeared after the
thermolysis. A new peak appeared at 3385 cm-1 which
was attributed to the N-H stretching of the diphenyl-
amine moiety. The spectra of polymer 1 and the precur-
sor are similar to those of polymer 2 and its precursor.
Polymers 1 and 2 in the reduced state were dissolved
in DMF and then oxidized by bubbling oxygen into the
solution. The reduced polymer 1 exhibits a single strong
absorption at 317 nm of the UV-vis spectrum. Oxida-
tion of the colorless solution resulted in an intense blue-
purple solution, with a sharp peak at 308 nm and a
broad peak at 481 nm. The first peak was ascribed to
the π-π* transition in the benzenoid ring. The second
peak is associated with a benzenoid to quinoid excitonic
transition. The oxidized polymer was doped with sul-
furic acid, and the solution turned green. Three peaks
were displayed in the UV-vis spectrum at 270, 391, and
752 nm. The protonation of the oxidized polymer caused
the low wavelength absorption to split. The high wave-
length absorption red-shifted and extended toward the
near-IR with an increase in intensity. The spectrum of
polymer 2 was similar to that of polymer 1, except that
the absorption peaks shifted slightly to longer wave-
lengths (Figure 4). The chromophore (conjugated oligo-
aniline) in polymer 2 is one unit longer than that in
polymer 1. The absorption shift to longer wavelengths
with the increase in conjugation length has been
observed in many series of conjugated oligomers.23 The
reduced state of polymer 2 exhibited a single strong
absorption at 320 nm, while the oxidized state showed
a sharp peak at 311 nm and a broad peak at 565 nm.
The acidified solution displayed three peaks at 302, 420,
and 789 nm.
F igu r e 6. Cyclic voltammogram of polymer 2, measured in
aqueous H2SO4 (1.0 M) with scan rate of 100 mV/s. The
proposed oxidation mechanism is shown below.
electron-transfer processes were observed.24 The leuco-
emeraldine structure was converted first into the
emeraldine and then the pernigraniline structure, as
observed in polyaniline. In the repeat unit of polymer
1, the oligoaniline was attached to the backbone through
an amide group whose oxidation is not observed in the
potential range of the experiment. Thus, the redox
properties of this oligoaniline unit should resemble that
of N,N′-diphenyl-p-phenylenediamine, which has been
shown in this work.
Similarly, the redox properties of polymer 2 should
behave like N-phenyl-N′-(4-anilinophenyl)-p-phenylene-
diamine. Unfortunately, there are no reports on the
electrochemistry of this oligoaniline. Only one peak was
observed at 0.561 V for polymer 2 (Figure 6), which is
similar to many longer oligomers that undergo two-
electron transfer processes. Buchwald observed that
oxidation of oligoanilines occurs through even-electron
transitions when possible, while odd-numbered oligo-
mers generate radical cations only transiently and at
high potentials.14
Cyclic voltammetry (CV) has been widely used to
characterize the electrochemical properties of conduct-
ing polymers.2 In this paper, the polymers were char-
acterized by CV using a three-electrode electrochemical
cell. A thin film of polymer was formed by evaporation
of a THF-polymer solution on the surface of the Pt
working electrode. The CV experiment was carried out
in 1.0 M aqueous sulfuric acid solution with a scan rate
of 100 mV/s. The CV spectrum showed two oxidation
peaks at 0.385 and 0.597 V for polymer 1 (Figure 5).
This result is similar to the results for N,N′-p-phen-
ylenediamine, which displayed two reversible oxidation
peaks corresponding to two one-electron-transfer pro-
cesses.24 The first oxidation involves the transfer of a
single electron giving rise to a radical cation species.
The second oxidation results in the transfer of another
electron followed by the loss of two protons forming the
uncharged imine.
For comparison, poly(N-(4-anilinophenyl)methacryl-
amide), a polymer similar to polymer 1 and 2 except
that the side chain is dimeric rather than trimeric or
tetrameric, was synthesized according to the litera-
ture.25 The electrochemical properties of the polymer
have not been reported previously. Oxidation did not
In oligoanilines with longer conjugation lengths, e.g.,
N,N′-(4-anilinophenyl)-p-phenylenediamine, the elec-
tron transfer occurred in pairs, and two consecutive two-

Macromolecules, Vol. 36, No. 17, 2003
Poly(methacrylamide)s 6339
(3) Wrobleski, D. A.; Benicewicz, B. C.; Thompson, K. G.; Bryan,
occur when oxygen was bubbled through a polymer
solution, and the UV-vis spectrum was unchanged by
this treatment. Cyclic voltammetry showed that the
polymer was not oxidized under the same experimental
conditions as those for polymers 1 and 2.
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New methacrylamides containing oligoaniline side
chains were synthesized using a palladium-catalyzed
amination reaction, followed by reaction with methacryl-
oyl chloride. Polymers were prepared by free radical
solution polymerization. Blocking of the diphenylamine
structures allowed facile polymerization to moderate
molecular weights. The tert-butyl carbamate protective
groups were removed quantitatively by thermolysis at
180 °C, providing a method to prepare polymers with
well-defined oligoaniline side chains. The t-Boc protected
polymers were more soluble in organic solvents than the
analogous polymers with acyl protecting groups. These
leucoemeraldine polymers were oxidized by simply
bubbling oxygen gas through the polymer solutions. The
electrochemical characterization by cyclic voltammetry
demonstrated that the redox behavior of these side
chain polymers was similar to the oligomeric anilines.
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Ack n ow led gm en t. The authors gratefully acknowl-
edge Dr. Peter Zarras, China Lake Naval Air Warfare
Center, SERDP program, and Rensselaer Polytechnic
Institute Start-Up Funds for financial support. We also
acknowledge receipt of the 2001 Mettler-Toledo Thermal
Analysis Education Grant in honor of Professor Edith
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