Polymeric mesoions: Novel synthetic methods, photochemistry, and characterization in the solid state by dielectric and waveguide-mode spectroscopy

Article abstract of DOI:10.1021/ma0347013

Photosensitive mesoionic polymers in which the polymerizable methacrylic group is attached to the malonic acid component of the mesoionic function were prepared and characterized. Dielectric measurements were performed, and the results were compared to th

Full text of DOI:10.1021/ma0347013

7520
Macromolecules 2003, 36, 7520-7526
Polymeric Mesoions: Novel Synthetic Methods, Photochemistry, and
Characterization in the Solid State by Dielectric and Waveguide-Mode
Spectroscopy
Alexa n d er Th eis,† Ber n h a r d Men ges,‡ Silvia Mittler ,‡ Mich a l Mier zw a ,‡,§
Ta d eu sz P a k u la ,‡ a n d Helm u t Ritter *,†
Institute of Organic Chemistry and Macromolecular Chemistry, Heinrich Heine University,
Universitaetsstrasse 1, 40225 Duesseldorf, Germany, and Max Planck Institute for Polymer Research,
Ackermannweg 10, 55128 Mainz, Germany
Received May 26, 2003; Revised Manuscript Received August 4, 2003
ABSTRACT: Photosensitive mesoionic polymers in which the polymerizable methacrylic group is attached
to the malonic acid component of the mesoionic function were prepared and characterized. Dielectric
measurements were performed, and the results were compared to those of liquid-crystalline mesoionic
copolymers. The influence on the dielectric properties upon irradiation with UV light, which causes the
photoconversion of the mesoionic groups to bis(â-lactame) structures, was determined. The glass-transition
temperatures determined by dielectric spectroscopy were compared to those obtained by DSC. It could
be observed by waveguide-mode spectroscopy that irradiating the mesoionic methacrylates results in
remarkable effects on the film thickness and refractive index of spin-coated polymer films.
Sch em e 1. P h otoch em ica l Isom er iza tion of Mesoion ic
6-Oxo-1,6-d ih yd r op yr im id in -3-iu m -4-ola tes
In tr od u ction
In past decades, photosensitive materials have seen
an increase in practical and scientific importance. They
are useful for optical data storage and in photolitho-
graphic processes. Changes in different properties are
desired, for example, changes in volume, solubility,
color, or refractive index.
Our recent interest is focused on polymeric mesoions.
They can be converted into bis(â-lactames) by light
irradiation in a wavelength regime between 320 and 490
nm depending on the substitution (Scheme 1).
structure on the photocyclization of the mesoionic
compounds and the physical properties, which were
analyzed by dielectric and waveguide spectroscopy, are
described.
To obtain stable, easy to handle, film-forming materi-
als, the photoreactive mesoionic group must be co-
valently attached to a polymer. During the last several
years we have described the synthesis and polymeriza-
tion behavior of various styrene substituted mesoionic
6-oxo-1,6-dihydropyrimidin-3-ium-4-olates.1-3 Recently,
different methods for the synthesis of polymerizable
mesoionic methacryl derivatives have also been devel-
oped.4,5 We also prepared polymers that are based on
phenols as the polymerizable group6 or polycondensates
bearing mesoionic groups in the main chain.7,8 An
alternative method is to modify technical polymers with
dispersed crystals of photosensitive mesoions.9
For the estimation of changes in the physical proper-
ties by irradiation, different methods have been devel-
oped. For example, waveguide-mode spectroscopy can
be used to determine changes in the refractive index
and film thickness of spin-coated polymer films.6,8,9
Other methods involve changes in the solubility or
spectroscopic characteristics.1,4
Exp er im en ta l Section
Meth od s. Chemicals were used as received from Acros,
Fluka, and Aldrich. Technical solvents were distilled before
use. For chromatography, silica gel with particle sizes of 30-
60 (Baker) or 32-63 µm (ICN), 60 Å was used. 1H and 13C
NMR spectra were recorded on a Bruker AC200 or AM400 at
room temperature. The deuterated solvent was used as the
lock and the internal standard for the δ scale relative to TMS.
Infrared spectra were recorded using Nicolet FT-IR spectrom-
eter 5DXC (DTGS detector) or 5SXB (MCT detector). The ATR
measurements were performed with a Specac golden-gate
diamond ATR unit on the 5SXB spectrometer. Mass spectra
were obtained on a Finnigan MAT 95 (FD). UV-vis spectra
were obtained with a Shimadzu UV-2102 PC UV-vis spec-
trometer. Elementary analysis was done in the micro analyti-
cal laboratory of the Institute of Organic Chemistry, University
of Mainz. SEC measurements were made on a PSS installation
with chloroform (30 °C) as the eluent. One hundred microliters
was injected onto a column arrangement of PSS SDV 5µ 100-,
1000-, and 10 000-Å porosity. A TSP UV 2000 UV-vis detector
and a Shodex RI 71 differential refractometer were used as
detectors. The data were evaluated with PSS-WinGPC 6.20.
The polymeric films were prepared from 5 to 10 wt % solutions
of the polymer in chloroform by spin coating with a BLE Delta
10 spin coater using a spin rate of 600 rpm at the highest
acceleration for 1 min. For the liquid-crystalline copolymers,
dioxane was used as the solvent, and exhaust air separation
was used during the spin-coating process for 10 min. Dielectric
measurements have been performed using a temperature-
controlled sample cell and a Novocontrol system composed of
an Alpha frequency response analyzer and a Quattro temper-
In this study, a new synthetic route for the synthesis
of methacryl-based mesoionic monomers, which has a
strong impact on the photochemical properties, is pre-
sented. In addition, the effects of the overall chemical
* Corresponding author. E-mail: H.Ritter@uni-duesseldorf.de.
Tel.: +49 211 8114760. Fax: +49 211 8115840.
† Heinrich Heine University.
‡ Max Planck Institute for Polymer Research.
§ On a leave from the Institute of Physics, Silesian University,
Uniwersytecka 4, 40-007 Katowice, Poland.
10.1021/ma0347013 CCC: $25.00 © 2003 American Chemical Society
Published on Web 09/11/2003

Macromolecules, Vol. 36, No. 20, 2003
Polymeric Mesoions 7521
F igu r e 1. Setup for waveguide-mode spectroscopy with simultaneous irradiation of the mesoionic polymer sample.
by a combination of all modes. The irradiation of the film was
carried out with a HeCd laser at a wavelength λ of 442 nm
with linear polarization at 0° angle of incidence and a power
of 10 mW.
ature controller. Two different sample geometries were used:
The liquid-crystalline sample was sandwiched between two
copper electrodes of 20 mm diameter and had a thickness of
50 µm. Teflon spacers were used to control the geometry of
the sample. The copolymer with methyl methacrylate was
deposited by spin coating a concentrated solution onto a gold-
covered copper electrode, and it had thickness of about 3 µm.
The upper electrode was placed in contact with the surface of
the film and had a diameter of 20 mm. The dielectric measure-
ments were carried out at different temperatures from 173 to
373 K (the LC-sample) and from 203 to 403 K (spin-coated
samples) for frequencies from 10-2 to 106 Hz. The dielectric
properties are characterized by the complex dielectric permit-
tivity ꢀ* ) ꢀ′ - iꢀ′′ (ꢀ′ is the real and ꢀ′′ is the imaginary part)
as a function of frequency ω and temperature T. The frequency-
dependent permittivity spectra were analyzed using the
empirical Havriliak-Negami function10 (eq 1):
Syn th esis.
Tosyl chloride (76.26 g, 0.4 mol) and 47.27 g of 1,6-hexane-
diol (0.4 mol) were dissolved in 160 mL of acetonitrile at room
temperature. Afterward, the mixture was cooled in an ice bath,
and 81 g (0.8 mol) of triethylamine was added under stirring
in a nitrogen atmosphere for 2 h. Then the ice bath was re-
moved, and the reaction mixture was stirred for another 2 h
at room temperature. Later, the acetonitrile was distilled of
in vacuum, and the residue was dissolved in 250 mL of
chloroform. The solution was cooled again and stirred for 5
min together with a mixture of 280 g of ice and 100 mL of
concentrated HCl. The aqueous phase was separated and ex-
tracted with chloroform. The combined chloroform phases were
washed with water three times and dried with magnesium
sulfate. The crude product, which was obtained after removing
the chloroform in vacuum, was purified by column chroma-
tography over silica gel (chloroform). Yield: 47.1 g (43%), col-
ꢀ*(T, ω) - ꢀ∞(T)
∆ꢀ(T)
1
)
(1)
[1 + (iωτHN(T))R]γ
where τHN(T) is the relaxation time and ∆ꢀ(T) ) ꢀo(T) - ꢀ∞(T)
is the relaxation strength of the process under investigation.
Exponents R and γ describe the symmetrical and asymmetrical
broadening of the distribution of relaxation times, respectively.
Only the imaginary parts of the spectra were used in the fitting
procedure. The film was irradiated on the copper electrode
using a doped mercury vapor mean pressure lamp, type TQ718
Z4 of a Heraeus Nobelight VG 700 irradiation reactor and an
UB4 interference filter, manufactured by Prinz Optics (absorp-
tion <375 nm). The waveguide-mode spectroscopy experiments
were carried out using a home-built spectrometer (Figure 1).
A grating with a periodicity Λ of 597 nm that was ion etched
into the substrate11 was used to couple a HeNe laser beam (λ
) 632.8 nm) simultaneously in s- (TE) and p-polarized (TM)
directions from the air into the waveguide by using a polarizer
at an angle of 45°. The waveguide-mode spectrum was
determined by scanning the angle of incidence of the incoming
laser beam onto the grating while measuring the out-coupled
1
orless oil. H NMR (200 MHz, CDCl3, δ): 1.17-1.73 (m, 8 H,
3,4,5,6-H), 2.41 (s, 3 H, 18-H), 3.57 (t, 2 H, 2-H, J ) 6.6 Hz),
3.98 (t, 2 H, 7-H, J ) 6.6 Hz), 7.31 (d, 2 H, 12,14-H, J ) 8.0
Hz), 7.75 (d, 2 H, 11,15-H, J ) 8.0 Hz). IR (NaCl): λ-1 (cm-1
)
) 3550, 3376 (O-H), 3066 (ar. C-H), 2936, 2862 (aliph. C-H),
1357 (SO2), 1177 (SO2), additional signals at 1598, 1495, 1462,
1307, 1292, 1211, 1198, 1098, 1057, 1020, 967, 928, 817, 790,
755, 727, 665.
power with
a photodetector situated at the end of the
waveguide.12 From the coupling angles and the known param-
eter of the grating, the effective refractive indices of all modes
Nij can be calculated according to eq 2.
λ
Λ
Ni,j ) nc ‚ sin Θ + m ‚
(2)
Absolute DMF (43 mL) was poured into an annealed flask,
and 0.51 g of sodium hydride (95%; 20.2 mmol) was added with
the exclusion of moisture. The suspension was cooled in an
ice bath, and then 3.97 g (18.4 mmol) of di-(tert-butyl) malonate
was injected with stirring through a septum with an injection
needle for a period of 10 min. Afterward, the ice bath was re-
moved, and the mixture was stirred for 2 h at room temper-
ature. Then, the reaction mixture was cooled again with an
ice bath, and 5 g (18.4 mmol) of 1,6-hexanediol monotosylate
was added within 10 min through the septum. The ice bath
nc is the refractive index of the cladding (here, air with nc )
1), λ is the wavelength of the coupled light, Λ is the grating
period, and m is the diffraction order. With a knowledge of
the optical constants of the substrate, the thickness and
refractive index for both polarization directions can be calcu-
lated iteratively as long as at least two modes for each direction
can be detected. If more than two modes were detected, the
errors in the thickness and refractive index were calculated

7522 Theis et al.
Macromolecules, Vol. 36, No. 20, 2003
was removed, and the mixture was stirred for 12 h. Then the
DMF was distilled off in vacuum, and the crude product was
diluted with diethyl ether and washed with a half-saturated
solution of ammonium chloride. The aqueous phase was ex-
tracted with diethyl ether, and the combined ether fractions
were dried with magnesium sulfate. After removing the ether,
the crude product was purified by column chromatography
over silica gel (petroleum ether/ethyl acetate 7:3 v/v). Yield:
2.8 g (48%), colorless oil. 1H NMR (200 MHz, CDCl3, δ): 1.21-
1.62 (m, 26 H, 3,4,5,6,12,16,18,19,21,22-H), 1.75 (dt, 2 H, 7-H),
3.06 (t, 1 H, 8-H, J ) 7.6 Hz), 3.59 (t, 2 H, 2-H, J ) 6.3 Hz).
IR (NaCl): λ-1 (cm-1) 3432 (O-H), 2978, 2933, 2860 (C-H),
1744, 1728 (CdO); additional signals at 1478, 1458, 1393,
1369, 1345, 1292, 1257, 1142, 1057, 849, 757. MS (FD) m/z
(%): [M + H+] 317 (100).
125.60 (C-1), 136.35 (C-2), 167.94 (C-3), 174.74 (C-12,16). IR
(KBr): λ-1 [cm-1] 3450, 3183, 3104 (O-H), 2936, 2861 (C-H),
1717 (CdO), 1636 (CdC); additional signals at 1455, 1407,
1325, 1301, 1180, 1046, 1014, 944, 817.
2-Nitrilo-N,N′-diphenylacetamidine (2.56 g, 11.5 mmol),13
4.77 g (23.1 mmol) of DCC, and 5 mg of hydroquinone were
dissolved with stirring in 23 mL of dry dichloromethane.
Afterward, 3.15 g (11.5 mmol) of 2-[6-(isopropenylcarbonyloxy)-
hexyl]malonic acid was added batchwise for a period of 15 min
with the exclusion of moisture. After 30 min of additional
stirring, the precipitated urea was filtered off and washed with
a small amount of dichloromethane. The combined dichloro-
methane fractions were concentrated in vacuum, and then 250
mL of petroleum ether was added under stirring. After 15 min,
the petroleum ether was decanted, and the red residue was
dried in vacuum. For further purification, the crude product
was chromatographed over silica gel (ethyl acetate/petroleum
Methacrylic acid (0.544 g, 6.3 mmol), 1 mg of hydroquinone
monopropyl ether, 2 g (6.3 mmol) of di-(tert-butyl)-2-(6-hy-
droxyhexyl) malonate, and 76 mg (0.63 mmol) of 4-(dimethyl-
amino)pyridine were dissolved in 2.5 mL of dry dichloro-
methane. Then a solution of 1.31 g (6.3 mmol) of dicyclohexyl-
carbodiimide in 1 mL of dry dichloromethane was added with
stirring for a period of 15 min. The temperature of the reaction
mixture was kept at room temperature by a water bath, and
the mixture was stirred for an additional 2 h. Afterward, the
precipitated urea was filtered off and washed with a small
amount of dichloromethane. The combined fractions were ev-
aporated and dried in vacuum. For purification, the product
was chromatographed with a silica gel column with chloroform.
1
ether 7/3 v/v). Yield: 1.10 g (21%); red, highly viscous oil. H
NMR (200 MHz, DMSO-d6, δ): 1.25-1.79 (m, 8 H, 6,7,8,9-H),
1.86 (s, 3 H, 17-H), 2.35 (t, 2 H, 10-H, J ) 6.8 Hz), 4.07 (t, 2
H, 5-H, J ) 6.1 Hz), 5.64 (s, 1 H, 1-H), 6,00 (s, 1 H, 1-H), 7.57-
7.70 (m, 10 H, ar.-H). 13C NMR (50 MHz, DMSO-d6, δ) 17.92
(C-17), 24.40/25.23/27.18/27.99/28.65 (C-6, C-7, C-8, C-9, C-10),
64.25 (C-5), 101.37 (C-11), 106.91 (C-26), 125.42 (C-1), 128.26/
129.25 (C-21,25,29,33, C-22,24,30,32), 130.53 (C-23,31), 135.94
(C-2), 136.02 (C-20,28), 157.64 (C-14), 166.53 (C-3). The C-12
1
Yield: 1.46 g (60%), colorless oil. H NMR (200 MHz, CDCl3,
δ): 1.24-1.38 (m, 6 H, 7,8,9-H), 1.42 (s, 18 H, 15,21,23,24,-
26,27-H), 1.53-1.84 (m, 4 H, 6,10-H), 1.90 (s, 3 H, 16-H), 3.07
(t, 1 H, 11-H, J ) 7.6 Hz), 4.09 (t, 2 H, 5-H, J ) 6.6 Hz), 5.51
(s, 1 H, 1-H), 6.06 (s, 1 H, 1-H). 13C NMR (50 MHz, CDCl3, δ):
18.28 (C-16), 25.71/27.05/28.44/28.49/28.89 (C-6, C-7, C-8, C-9,
C-10), 27.89 (C-15,21,23,24,26,27), 53.91 (C-11), 64.65 (C-5),
81.17 (C-14,20), 125.10 (C-1), 136.50 (C-2), 167.46 (C-3), 168.93
(C-12,18). IR (NaCl): λ-1 [cm-1]: 2978, 2933, 2860 (C-H),
1745, 1725 (CdO), 1639 (CdC); additional signals at 1456,
1393, 1369, 1322, 1297, 1254, 1167, 1057, 1012, 940, 850, 816,
757.
and C-16 signals could not be detected. IR (ATR): λ-1 [cm-1
]
3060 (ar. C-H), 2927, 2856 (aliph. C-H), 1694 (CdO), 1651
(mesoion CdO), 1593 (ar. CdC); additional signals at 1551,
1489, 1455, 1399, 1358, 1322, 1296, 1263, 1167, 1061, 1002,
943. UV (dichloromethane): λmax [nm] (log ꢀ) 262 (3.67), 303
(3.43), 491 (2.97). MS (FD) m/z (%): [M+] 458 (100). EA: Calcd
for C27H27N3O4 (457.53): C, 70.88; H, 5.95; N, 9.18. Found:
C, 70.50; H, 6.29; N, 9.51.
Di-(tert-butyl)-2-[6-(isopropenylcarbonyloxy)hexyl] malonate
(6.77 g, 17.6 mmol) and 5 mg of hydroquinone monopropyl
ether were added to 18 mL of trifluoroacetic acid (90%) and
stirred for 2 h with the exclusion of moisture at room temp-
erature. Then the reaction mixture was dilluted with 10 mL
of toluene, and the azeotropic boiling solvents were distilled
off in vacuum. This procedure was repeated two times to re-
move residual trifluoroacetic acid. The product was dried in
vacuum and purified by column chromatography over silica
gel with a solvent gradient from chloroform to chloroform/
methanol (4/1 v/v). Yield: 4.1 g (86%), colorless crystals, mp:
60 °C. 1H NMR (200 MHz, CDCl3, δ): 1.25-1.45 (m, 6 H, 7,8,9-
H), 1.65 (tt, 2 H, 6-H), 1.81-2.03 (m, 5 H, 10,14-H), 3.43 (t, 1
H, 11-H, J ) 7.3 Hz), 4.13 (t, 2 H, 5-H, J ) 6.6 Hz), 5.56 (s, 1
H, 1-H), 6.09 (s, 1 H, 1-H), 9.64 (br, 2 H, COO-H). 13C NMR
(50 MHz, CDCl3, δ): 18.26 (C-14), 25.62/27.85/28.41/28.57/
28.76 (C-6, C-7, C-8, C-9, C-10), 51.52 (C-11), 64.88 (C-5),
Mesoionic 2-cyano-1,3-diphenyl-5-[6-(isopropenylcarbonyl-
oxy)hexyl]-6-oxo-1,6-dihydropyrimidin-3-ium-4-olate (0.994 g,
2.17 mmol) and 7.18 mg (0.040 mmol) of AIBN were dissolved
in 11 mL of absolute DMF. The solution was twice frozen in
liquid nitrogen and degassed two times. Afterward, the solu-
tion was polymerized for 24 h at 60 °C, and the accrued
polymer was precipitated in a mixture of 75 mL of methanol

Macromolecules, Vol. 36, No. 20, 2003
Sch em e 2. Syn th esis of Novel Mesoion ic Mon om er s
Polymeric Mesoions 7523
and 150 mL of water. After drying in vacuum, the polymer
was purified by dissolving in 5 mL of dichloromethane and
reprecipitating in 150 mL of diethyl ether. The product was
dried in vacuum again. Yield: 0.44 g (44%), red powder. 1H
NMR (400 MHz, DMSO-d6, δ): 0.45-2.20 (m, 1,6,7,8,9,17-H),
2.34 (m, 10-H), 3.82 (m, 5-H), 7.10-7.73 (m, ar.-H). IR (ATR):
λ-1 [cm-1] 3067 (ar. C-H), 2930, 2858 (aliph. C-H), 1695 (Cd
O), 1657 (mesoion CdO), 1595 (ar. CdC); additional signals
at 1489, 1456, 1389, 1359, 1259, 1153, 1073, 1002, 969, 753,
692. UV (dichloromethane): λmax [nm] (log ꢀ) 261 (3.67), 313
(3.04), 485 (3.09). DSC: Tg ) 78 °C. SEC (chloroform, PS
standard): Mn ) 11 000, Mw ) 24 000, PD ) 2.1.
of water. After drying in vacuum, the polymer was purified
by dissolving in 5 mL of dichloromethane and reprecipitating
in 200 mL of diethyl ether. The product was dried in vacuum
again. Yield: 0.56 g (66%), red powder. 1H NMR (400 MHz,
DMSO-d6, δ): 0.72 (s, syndiot. 17,40-H), 0.90 (s, heterot. 17,-
40-H), 1.12 (s, isot. 17,40-H), 1.22-2.20 (m, 1,6,7,8,9,35-H),
2.35 (m, 10-H), 3.51 (s, 39-H), 3.86 (m, 5-H), 7.24-7.68 (m,
ar.-H). IR (ATR): λ-1 [cm-1] 2989, 2929, 2866 (aliph. C-H),
1726 (CdO), 1663 (mesoion CdO), 1596 (ar. CdC); additional
signals at 1489, 1448, 1385, 1243, 1190, 1149, 1060, 985, 840,
753, 694. UV (dichloromethane): λmax [nm] 258, 312, 484.
DSC: Tg ) 104 °C. SEC (chloroform, PS standard): Mn
12 000, Mw ) 25 000, PD ) 2.1.
)
Resu lts a n d Discu ssion
Novel polymers in which the polymerizable meth-
acrylic group is attached to the malonic acid component
of the mesoionic function were prepared. This procedure
allows the use of various low-molecular-weight amidines
as condensating compounds. In contrast to former meth-
acrylic monomers, which were synthesized via the use
of isothioureas,4,5 this method does not require any
sulfur atoms in the molecule.
The monomers were obtained via monotosylated 1,6-
hexanediol (5), which was used as the electrophilic
compound in the alkylation of di-(tert-butyl)-malonate
(6). The malonate (6) itself was deprotonated by NaH
in N,N-dimethylformamide (DMF) as the solvent. The
hydroxyl group of the resulting alkylated malonate (7)
was esterified with methacrylic acid (8) in the presence
of dicyclohexylcarbodiimide (DCC) as the condensation
agent and 4-(dimethylamino)pyridine as the catalyst.
Then, the tert-butyl protecting groups of di-(tert-butyl)-
2-[6-(isopropenylcarbonyloxy)hexyl]malonate (9) were
removed with trifluoroacetic acid, resulting in a malonic
acid with a polymerizable methacrylic group attached
to the end of an alkane spacer (10). This product was
cyclocondensed with 2-nitrilo-N,N′-diphenylacetami-
Mesoionic 2-cyano-1,3-diphenyl-5-[6-(isopropenylcarbonyl-
oxy)hexyl]-6-oxo-1,6-dihydropyrimidin-3-ium-4-olate (0.45 g,
0.988 mmol), 0.395 g (3.95 mmol) of methyl methacrylate, and
7.18 mg (0.040 mmol) of AIBN were dissolved in 11 mL of
absolute DMF. The solution was twice frozen in liquid nitrogen
and degassed two times. Afterward, the solution was poly-
merized for 24 h at 60 °C, and the accrued polymer was
precipitated in a mixture of 100 mL of methanol and 200 mL

7524 Theis et al.
Macromolecules, Vol. 36, No. 20, 2003
Sch em e 3. P r ep a r a tion of Mesoion ic Cop olym er s
Ta ble 1. P olym er P r op er ties
Sch em e 4. Liqu id -Cr ysta llin e Mesoion ic Cop olym er
16
polymer
yield [%]
homopolymer 13
copolymer 15
44
66
n/m (polymer)
Mn [g/mol]
Mw [g/mol]
PD
4:1
11 000
24 000
2.1
12 000
25 000
2.1
∆Cp (Tg) [°C]
78
104
dine,10 resulting in mesoionic 2-cyano-1,3-diphenyl-5-
[6-(isopropenylcarbonyloxy)hexyl]-6-oxo-1,6-dihydropy-
rimidin-3-ium-4-olate (Scheme 2).
In comparison to similar mesoions with aromatic
groups instead of the cyano function, which show an
absorption corresponding to the HOMO-LUMO transi-
tion at 365 nm, the strong electron-withdrawing effect
of the cyano function causes a strong bathochromic shift
to 491 nm, which results in an intensely red-colored
product.
denoted on the graph as R, â, and γ. The linear rise of
ꢀ′′ at low frequencies for the highest temperatures is
due to the DC conductivity in the sample.
The polymerization of monomer 12 was carried out
in DMF with 2,2′-azobisisobutyronitrile (AIBN) as the
initiator at 60 °C. Homopolymer 13 as well as copolymer
15 with methyl methacrylate (14) was prepared (Scheme
3). The polymer properties are listed in Table 1.
Because of their zwitterionic structure, a high dipole
moment for the mesoionic pyrimidiniumolates can be
expected. Thus, they should be orientable in an electric
field. For a detailed analysis, dielectric spectroscopic
measurements were carried out with copolymer 15 and
compared with the results obtained from poly[mesoionic
5-butyl-1-(4-ethoxyphenyl)-2-[4-(vinylcarbonyloxy)bu-
tylthio]-6-oxo-3-phenyl-1,6-dihydropyrimidin-3-ium-4-
olate-co-5-(cholesterolcarbonyl)-pentylacrylate (16).5 The
molecular structure of 16 is shown in Scheme 4.
The spectra of the dielectric loss ꢀ′′ of mesoionic liquid-
crystalline copolymer 16 measured at different temper-
atures are sketched in Figure 2. Three dielectrically
active relaxation processes can be distinguished and are
Measurements on copolymer 15 were performed on
spin-coated films. The transparent material allows an
excellent photochemical conversion of the mesoionic
film, which was remeasured after conversion. Examples
of the spectra measured at various temperatures both
before and after conversion are shown in Figure 3.
It was also found that the dielectric storage function
ꢀ′ decreases by irradiation. This phenomenon is inde-
pendent of the frequency and can therefore be a result
of the decreased molecular polarizability, which can be
explained by the conversion of π bonds to σ bonds,
whereby the system of conjugated double bonds in the
molecules is lost. The parameters of the Havriliak-
Negami fit of the observed processes are given in the
Table 2.

Macromolecules, Vol. 36, No. 20, 2003
Polymeric Mesoions 7525
F igu r e 2. Dielectric loss spectra of liquid-crystalline me-
soionic copolymer 16 at different temperatures.
F igu r e 4. Activation plot (relaxation times of the dielectric
processes vs temperature) for all detected relaxation processes
in polymers 15 and 16. The vertical arrows indicate reciprocal
values of the calorimetric glass-transition temperatures of the
two polymers.
Ta ble 3. Com p a r ison of th e Gla ss-Tr a n sition
Tem p er a tu r es fr om DSC Mea su r em en ts a n d Dielectr ic
Sp ectr oscop y
polymer
Tg (DSC) [°C]
Tg (dielectric) [°C]
15
16
104
45
107
37
only in liquid-crystalline polymer 16, the activation
energy EA ) 12.2 ( 0.2 kJ /mol K has been determined.
The â process in this polymer has a higher activation
energy of EA ) 21.70 ( 0.08 kJ /mol K. For the process
assigned as â in copolymer 15, the activation energies
EA ) 34.9 ( 0.4 and 32.7 ( 0.2 kJ /mol K have been
obtained for states before and after irradiation, respec-
tively.
F igu r e 3. Dielectric loss spectra for mesoionic copolymer 15
at various temperatures. Filled and open symbols correspond
to spectra measured before and after irradiation, respectively.
Ta ble 2. P a r a m eter s of th e Ha vr ilia k -Nega m i F it of th e
In both of the polymers that were studied, slower
processes were also detected; these are assigned here
as R processes because they show features typical of the
vitrification of polymer segments in glass-forming sys-
tems. They do not show linear dependencies in the
activation plot, and they slow with decreasing temper-
ature to relaxation-time values reaching nearly 100 s
at the corresponding calorimetric glass-transition tem-
peratures (indicated in the Figure by vertical arrows).14
Taking this into account, one can consider these slower
relaxations to be responsible for a cooperative segmental
motion in the studied polymers. Any precise molecular
assignment of the other relaxation processes is not
possible on the basis of our recent information. Consid-
ering, however, their rates and activation energies, we
can say that they have to correspond to structural units
smaller than the monomeric segments in the polymers.
The glass-transition temperatures of the studied system
determined by means of differential scanning calorim-
etry are compared in Table 3 with temperatures at
which the R relaxations reach relaxation times of 100
s. In the case of polymer 15, the values concern the
unirradiated sample. After irradiation, the R process
was slower (indicating a higher glass-transition tem-
perature) and was masked by the DC conductivity,
making a detailed distinction impossible.
Dielectr ic P r ocesses
sample
process T∆ꢀ (K)a
RHN
γHN
15
â
â
R
â
γ
2.5-3.5
1.6-4.9
0.34 ( 0.05 0.86 ( 0.03
15 irradiated
16
0.25 ( 0.05
1
1
1
1
450-780 0.28 ( 0.5
2.3-4.4
11-20
0.40 ( 0.4
0.25 ( 0.2
a
This parameter is temperature-dependent; therefore, the low-
and high-temperature limits are given.
The R process of sample 16 was strong; the remaining
processes were very weak. All processes are broad but
symmetric, which is indicated by relatively low values
of RHN and γHN, which are close to or equal to 1, re-
spectively. The variation in the parameters with tem-
perature is within the error limits (given in Table 2).
To characterize the temperature dependence of the
observed relaxation processes in the studied samples,
an activation plot (log τ vs T-1) is presented in Figure
4.
The low-temperature processes show linear depend-
encies in this plot and can therefore be described as
EA
log(τmax ) ) log(τ0) +
(3)
2.303 ‚ kT
A detailed analysis of the molecular polarizability was
performed by waveguide-mode spectroscopy. In liquid-
crystalline copolymer 175 prepared from mesoionic 1-(4-
where τ0 is the relaxation time at infinite temperature
and EA is the activation energy. For the γ process visible

7526 Theis et al.
Macromolecules, Vol. 36, No. 20, 2003
was detected, that is, 34 nm (4.3%) larger than before
irradiation. The refractive index decreased by about
0.014 down to 1.559, which correlates to a decrease in
the optical susceptibility ø of 3.0%. For both polymers,
the increase in film thickness could be explained by the
change from the planar mesoionic structure to the
angled bis(â-lactam) structure, which has a higher steric
demand. The reduction in the refractive index common
to all experiments is caused by the decreased molecular
polarizability and is amplified by the decreased density
of the polarizability carrying units.
Con clu sion s
F igu r e 5. Time-dependent changes in the refractive index
and the film thickness of copolymer 17 during irradiation.
Errors: ∆n ) (0.0009 and ∆d ) (29 nm.
Novel mesoionic monomers in which the polymeriz-
able methacrylic group is attached to the malonic acid
component of the mesoionic function were prepared and
characterized. The (co)polymers obtained by radical
polymerization with AIBN in an organic solvent had
molecular weights of Mn ) 11 000 to 12 000 and a
polydispersity of 2.1. Dielectric measurements on the
copolymer with methyl methacrylate revealed two di-
electrically active processes: an Arrhenius â process
below the glass-transition temperature and a non-
Arrhenius R process above it. In liquid-crystalline
copolymer 16, an additional fast γ process reflecting
localized motions of the liquid-crystalline side chain
appears. The relaxation times of the R processes deter-
mined by dielectric spectroscopy reached 100 s at
temperatures close to the Tg obtained by DSC. Irradi-
ated sample 15 shows a higher glass-transition tem-
perature (slower R process), and the values of dielectric
function ꢀ′ were reduced as a result of the reduced
polarizability of the molecule. It could be observed by
waveguide-mode spectroscopy that the irradiation of
mesoionic methacrylates results in an increase in film
thickness caused by the change in the molecular struc-
ture and an isotropic decrease in the refractive index.
In liquid-crystalline copolymer 17, both effects could be
detected with decreased strength.
F igu r e 6. Time-dependent change of the coupling angle of
the TE0 mode of polymer 13.
ethoxyphenyl)-2-[4-(isopropenylcarbonyloxy)ethylthio]-
5-methyl-6-oxo-3-phenyl-1,6-dihydropyrimidin-3-ium-4-
olate and 5-(cholesterolcarbonyl)pentyl methacrylate,
three waveguide modes of both polarization directions
could be detected, from which a film thickness of 1733
nm and an isotropic refractive index of 1.539 could be
calculated. The changes in the film thickness and
isotropic refractive index during irradiation are shown
in Figure 5.
Similar to formerly described observations on the
homopolymer of the mesoionic methacrylate,8 the ir-
radiation of the copolymer results in an increase in the
film thickness and a decrease in the refractive index.
In comparison to the homopolymer, the effects are
smaller because of the reduced amount of the mesoionic
chromophore. In conclusion, the film thickness increased
up to 20 nm (1.2%), and the refractive index signifi-
cantly decreases about 0.005. For a determination of the
percentage change, the optical susceptibility ø can be
calculated from eq 4.
Refer en ces a n d Notes
(1) Ritter, H.; Sperber, R.; Weisshuhn, C. M. Macromol. Chem.
Phys. 1994, 195, 3823.
(2) Ritter, H.; Sperber, R. Macromol. Rapid Commun. 1995, 16,
407.
(3) Deutschmann, T.; Ritter, H. Macromol. Chem. Phys. 2000,
201, 1200.
(4) Theis, A.; Ritter, H. Des. Monomers Polym. 2001, 4, 177.
(5) Theis, A.; Ritter, H. Macromolecules 2003, 36, 7552.
(6) Tonami, H.; Uyama, H.; Kobayashi, S.; Menges, B.; Mittler,
S.; Theis, A.; Ritter, H. Macromol. Chem. Phys. 2003, 204,
1079.
(7) Deutschmann, T.; Ritter, H. Macromol. Rapid Commun.
1996, 17, 723.
(8) Theis, A.; Ritter, H.; Bo¨hme, F.; Klinger, C.; Menges, B.;
Mittler, S. Chem. Mater. 2002, 14, 2109.
(9) (a) Murase, S.; Ban, M.; Horie, K. J pn. J . Appl. Phys. 1999,
38, 6772. (b) Kato, Y.; Horie, K. Macromol. Chem. Phys. 2002,
203, 2290.
(10) Havriliak, S.; Negami, S. Polymer 1967, 8, 161.
(11) Mai, X.; Moshrefzadeh, R.; Gibson, U. J .; Stegeman, G. I.;
Seaton, C. T. Appl. Opt. 1985, 24, 3155.
ø ) n2 - 1
(4)
Therefore, a decrease in the optical susceptibility ø of
1.1% was found.
In another experiment with polymer 13, the refractive
index of the unirradiated sample was determined to be
1.573. The film thickness was 795 nm. During irradia-
tion, the coupling angle of the TE0 mode was automati-
cally followed as illustrated in Figure 6.
(12) Lee, T. M.; Mittler-Neher, S.; Neher, D.; Stegeman, G. I.;
Roux, C.; Leclerc, M. Opt. Mater. 1992, 1, 65.
(13) Ehrensvaerd, G.; Stjernholm, R. Acta Chem. Scand. 1949, 3,
971.
(14) Broadband Dielectric Spectroscopy; Kremer, F., Scho¨nhals,
A., Eds.; Springer: Berlin, 2003; Chapter 4.
After irradiation, the waveguide-mode spectrum was
scanned again. In this case, a film thickness of 829 nm
MA0347013