Polymeric nitrons. 2. Synthesis, irradiation and waveguide mode spectroscopy of polymeric nitrons derived from polymeric benzaldehydes and N-isopropylhydroxylamine

Article abstract of DOI:10.1021/ma0116710

Various vinylbenzaldehydes were prepared using the Heck reaction: 4-vinylbenzaldehyde (14), 3-vinylbenzaldehyde (15), 2-vinylbenzaldehyde (18a), 2-hydroxy-4-vinylbenzaldehyde (16) and 4-[(4-vinylbenzyl)oxy]benzaldehyde (6). The four monomers (6, 14, 15, 16) were polymerized using AIBN as initiator at 70 °C for 24 h to yield the corresponding homopolymers (7, 19, 23, 25) and a copolymer (20) with styrene. The molecular weights are about 10 000. The polymer analogous condensation of the aldehyde groups with an excess of N-isopropylhydroxylamine (8) at room temperature produces polymeric nitrons (9, 21, 22, 24, 26) in almost quantitative yields. All nitron functions were irradiated, and the intramolecular cyclization of the nitrons to the corresponding oxaziridines was examined. Waveguide mode spectroscopy of poly(4-vinylbenzaldehyde-N-isopropylnitron) (21) shows that the changes in film thickness are low but the changes in refractive indices are significant after irradiation. Oxaziridine 10 has high thermal stability with respect to ring opening. No structural change was detected after irradiation of the hydrexyphenyl-modified polynitron (26). A low molecular weight model compound (2-hydroxybenzaldehyde-N-methylnitron, 28) was prepared id order to examine this abnormal photochemical behavior and also showed that it is highly resistant to UV irradiation.

Full text of DOI:10.1021/ma0116710

3448
Macromolecules 2002, 35, 3448-3455
Polymeric Nitrons. 2. Synthesis, Irradiation and Waveguide Mode
Spectroscopy of Polymeric Nitrons Derived from Polymeric
Benzaldehydes and N-Isopropylhydroxylamine
Mich a el Hein en ber g,† Ber n h a r d Men ges,‡ Silvia Mittler ,‡ a n d Helm u t Ritter *,†
Institute of Organic Chemistry and Macromolecular Chemistry II, Heinrich-Heine-Universita¨t
Du¨sseldorf, Universita¨tsstrasse 1, 40225 Du¨sseldorf, Germany; and Max Planck Institute of Polymer
Research, Ackermannweg 10, D-55128 Mainz, Germany
Received September 25, 2001
ABSTRACT: Various vinylbenzaldehydes were prepared using the Heck reaction: 4-vinylbenzaldehyde
(14), 3-vinylbenzaldehyde (15), 2-vinylbenzaldehyde (18a ), 2-hydroxy-4-vinylbenzaldehyde (16) and 4-[(4-
vinylbenzyl)oxy]benzaldehyde (6). The four monomers (6, 14, 15, 16) were polymerized using AIBN as
initiator at 70 °C for 24 h to yield the corresponding homopolymers (7, 19, 23, 25) and a copolymer (20)
with styrene. The molecular weights are about 10 000. The polymer analogous condensation of the aldehyde
groups with an excess of N-isopropylhydroxylamine (8) at room temperature produces polymeric nitrons
(9, 21, 22, 24, 26) in almost quantitative yields. All nitron functions were irradiated, and the intramolecular
cyclization of the nitrons to the corresponding oxaziridines was examined. Waveguide mode spectroscopy
of poly(4-vinylbenzaldehyde-N-isopropylnitron) (21) shows that the changes in film thickness are low
but the changes in refractive indices are significant after irradiation. Oxaziridine 10 has high thermal
stability with respect to ring opening. No structural change was detected after irradiation of the
hydroxyphenyl-modified polynitron (26). A low molecular weight model compound (2-hydroxybenzaldehyde-
N-methylnitron, 28) was prepared in order to examine this abnormal photochemical behavior and also
showed that it is highly resistant to UV irradiation.
Sch em e 1. Beh a vior of Nitr on s d u r in g Ir r a d ia tion
1. In tr od u ction
The demand on storage capacity of data media
increased exponentially during the past decades. To
master this challenge in the future, new switchable
polymeric materials are needed.1 Dipolar nitrons may
be used to develop photosensitive materials change
polarity during irradiation.2-4 Typical photoinduced
isomerization products of nitrons are summarized in
Scheme 1. The photoinduced cyclization of the aryl-N-
aryl-substituted nitrons (R ) R′ ) aryl) leads to forma-
tion of substituted oxaziridines, which are unstable and
rapidly decompose (Scheme 1).5 Irradiation gives a
mixture of products, which are poorly applicable for
photoactive materials. However, the N-alkyl-substituted
nitrons formed stable oxaziridines.
The properties of polymers with a high concentration
of reactive nitron groups near the backbone should be
strongly influenced by irradiation. This paper presents
the synthesis of vinylbenzaldehyde nitron precursors.
Regarding former studies, nitrons inhibit the free radi-
cal polymerization.5 However, at 60 °C the 1,3-dipolar
polycycloaddition of nitrons with (meth)acryl and vinyl
groups is the preferred reaction. Enzymatic catalyzed
polycondensations at room temperature were possible
with phenol derivatives of nitrons.6
measured coupling angles of different waveguide modes
the effective refractive indices Ni,j of these modes can
be calculated and converted into the thickness and the
refractive index of the thin film using the dispersion
relation. S- or p-polarized waveguide modes can also be
used to determine the anisotropy of the thin polymer
film.8,9 This paper reports the synthesis and photo-
chemical behavior of new polymers bearing N-aliphatic
substituted nitrons as photosensitive moieties.
2. Exp er im en ta l Section
2.1. Ma ter ia ls. All solvents of p.a. quality (Riedel de Haen,
Seelze, Germany) were stored over molecular sieves, 3 or 4 Å.
Technical solvents and styrene were distilled before use.
Benzaldehyde (98+%), 4-brombenzaldehyde (99%), 3-brom-
benzaldehyde (96+%), 2-brombenzaldehyde (97%), 4-hydroxy-
benzaldehyde (99%), 2-hydroxybenzaldehyde (99%), 2-hydroxy-
4-brombenzaldehyde (98%), styrene (99%), triethylamine (99%),
and tri(o-toloyl)phosphine (99%) were purchased from Acros
Organics, Geel, Belgium, acetoneoxime (98+%), AIBN (98+%),
NaCNBH3 (95%) and 4-vinylbenzyl chloride (95+%) from
Fluka GmbH, Deisenhofen, Germany, as well as N-methyl-
hydroxylamine hydrochloride (98%) and palladium acetate
(98%) from Aldrich, Taufkirchen, Germany. These chemicals
were used without further purification. N-Isopropylhydroxy-
lamine10 (8) and benzaldehyde-N-methylnitron11 (3) were
prepared as described in the literature.
Optical data storage can be achieved by changes in
the refractive index or thickness of the photosensitive
material. This behavior of polynitrons and other pho-
tosensitive polymers like mesoions can be excellently
examined by waveguide mode spectroscopy during UV
irradiation.7,8 This method is based on the selective
excitation of waveguide modes in thin films. From the
* Fax: +49 211 811 4788. E-mail: H.Ritter@uni-duesseldorf.de.
† Heinrich-Heine-Universita¨t Du¨sseldorf.
‡ Max Planck Institute of Polymer Research.
10.1021/ma0116710 CCC: $22.00 © 2002 American Chemical Society
Published on Web 03/22/2002

Macromolecules, Vol. 35, No. 9, 2002
Polymeric Nitrons 3449
2.2. Syn th esis of 4-[(4-Vin ylben zyl)oxy]ben za ld eh yd e-
N-isop r op yln itr on (9). 2.2.1. Syn th esis of 4-[(4-Vin ylben -
zyl)oxy]ben za ld eh yd e (6). p-Vinylbenzyl chloride (4, 15.2
g, 0.1 mol), p-hydroxybenzaldehyde (5, 12.2 g, 0.1 mol), and
K2CO3 (25 g, 0.18 mol) were suspended in acetone (150 mL)
and then refluxed for 7 h. After removing of the inorganic salts,
the solvent was evaporated, yielding a brownish pulp. Column
chromatography in chloroform/petrol ether (1/2, v/v) gave, after
drying in a vacuum (oil pump), 13.3 g (56%) of a yellow colored
CH2). IR (KBr): 3061, 3011 (aryl), 2828, 2729 (alkyl), 1702
(CdO aldehyde), 1572 (ring), 787, 673 (1,3-disubstituted
benzenes), further intensive signals at 1384, 1192, 991, 922
cm-1
.
2.3.3. Syn t h esis of 2-H yd r oxy-4-vin ylb en za ld eh yd e
1
(16). Yield: 54%. H NMR (200 MHz, DMSO-d6): δ ) 10.90
(b, 1H, -OH), 10.20 (s, 1 H, -CHO), 7.65 (m, 2 H, ArH), 6.97
(d, J ) 8.8 Hz, 1 H, ArH), 6.68 (dd, J ) 17.6 Hz, J ) 11.2 Hz,
1 H, -CHdCH2), 5.90 (d, J ) 17.6 Hz, 2H, -CHdCH2), 5.43
(d, J ) 11.2 Hz, 3H, -CHdCH2). IR (NaCl): 3377 (b, OH)
3090, 3066, 3043 (aryl), 2959, 2927, 2872 (alkyl), 1663 (CdO
aldehyde), further intensive signals at 1635, 1468, 1375, 1281,
1
oil (6). RF value (technical chloroform) ) 0.59. H NMR (200
MHz, CDCl3 [ppm]): δ ) 9.87 (s, 1H, -CHO), 7.83 (d, J ) 8.8
Hz, 2H, ArH), 7.39 (m, 4H, ArH), 7.06 (d, J ) 8.8 Hz, 2H, ArH),
6.75 (dd, J ) 11.2 Hz, J ) 17.6 Hz, 1H, -CHdCH2), 5.77 (d,
J ) 17.6 Hz, 1H, -CHdCH2), 5.27 (d, J ) 11.2 Hz, 1H, -CHd
CH2), 5.12 (s, 2H, O-CH2-).
1156, 893, 831, 768, 713 cm-1
.
2.3.4. Syn th esis of 2-Vin ylben za ld eh yd e (18a ). The Heck
reaction leads to the formation of 2-ethylstyrene (18b) and
2-vinylbenzaldehyde (18a ), which were quite difficult to sepa-
rate. Data for 2-Ethylstyrene follow. 1H NMR (200 MHz,
DMSO-d6): δ ) 7.50 (m, 1 H, ArH), 7.20 (m, 3 H, ArH), 7.01
(dd, J ) 17.6 Hz, J ) 11 Hz, 1 H, -CHdCH2), 5.66 (d, J )
17.6 Hz, 2H, -CHdCH2), 5.30 (d, J ) 11 Hz, 3H, -CHdCH2),
2.72 (q, J ) 7.5 Hz, 2 H, -CH2-CH3), 1.21 (t, J ) 7.5 Hz, 3 H,
-CH2-CH3). IR (NaCl): 3086, 3063, 3015 (aryl), 2965, 2931,
2873, 2854 (alkyl), 1484, 1452 (alkyl), 773, 753 (1,2-disubsti-
tuted benzenes), further intensive signals at 1625, 1123, 990,
2.2.2. Hom op olym er iza tion of 4-[(4-Vin ylben zyl)oxy]-
ben za ld eh yd e (6). Monomer 6 (0.95 g, 4 mmol) in benzene
(5 mL) was polymerized with AIBN (15 mg, 9 × 10-5 mol) for
24 h at 70 °C. Precipitating in methanol gave 0.4 g (42%) of
poly{4-[(4-vinylbenzyl)oxy]benzaldehyde} (7).
1
SEC (RI): Mn ) 11 800, PD ) 2.29. DSC: Tg ) 74 °C. H
NMR (200 MHz, CDCl3): δ ) 9.78 (b, 1 H, -CHO), 7.71 (b, 2
H, ArH), 6.92 (b, 4 H, ArH), 6.53 (b, 2 H, ArH), 4.92 (b, 2H,
-CH2-), 2.50-1.00 (b, 3H, -CH2-CH-). IR (KBr): 2924
(alkyl, aryl), 1691 (CdO) ester), 1602 (ring), 1509 (ring), 876,
832 (ring), further intensive signals at 1577, 1425, 1314, 1258,
912 cm-1
.
2.4. P olym er iza tion of th e Differ en t Vin ylben za ld e-
h yd es (14, 15, 16). 2.4.1. P olym er iza tion of 4-Vin ylben -
za ld eh yd e (14). Hom op olym er iza tion . p-Vinylbenzalde-
hyde (2.64 g, 20 mmol) was dissolved in benzene (10 mL) and
bubbled with argon for 20 min. It was polymerized with AIBN
(82 mg, 0.5 mmol) as initiator for 24 h at 70 °C. Precipitating
in diethyl ether gave 2.0 g (75%) of the colorless polymer 19.
SEC (RI): Mn ) 5500, Mw ) 5900, PD ) 1.07. SEC (UV):
Mn ) 5000, PD ) 1.15. DSC: no transition. 1H NMR (200 MHz,
CDCl3): δ ) 9.84 (b, 1 H, -CHO), 7.50 (b, 2 H, ArH), 6.55 (b,
2 H, ArH), 2.5-1.0 (m, 3H, -CH-CH2-). IR (KBr): 2926,
2849, 2829, 2736 (alkyl), 1704 (CdO aldehyde), 1605 (ring),
further intensive signals at 1575, 1307, 1214, 1170, 1015, 842,
1161, 1015 cm-1
.
2.2.3. P olym er An a logou s Rea ction of P oly{4-[(4-vi-
n ylben zyl)oxy]ben za ld eh yd e} (7) w ith N-Isop r op ylh y-
d r oxyla m in e (8) To P r od u ce P olyn itr on 9. A solution of
poly{4-[(4-vinylbenzyl)oxy]benzaldehyde} (7, 0.31 g, 1.3 mmol)
and N-isopropylhydroxylamine (8, 0.3 g, 4 mmol) in chloroform
(1.5 mL) was stirred for 2 days at room temperature and then
precipitated in diethyl ether, yielding 0.35 g (conversion 89%)
of the polymeric nitron (9).
SEC (RI): Mn ) 16 000, PD ) 2.03. SEC (UV): Mn ) 16 000,
1
PD ) 2.15. DSC: Tdec ) 170 °C. H NMR (200 MHz, CDCl3):
δ ) 9.78 (b, 0.11 H, -CHO), 8.16 (b, 1.75 H, ArHnit), 7.66 (b,
0.89 H, CHdN, 0.22 H, ArHald), 6.94 (b, 4 H, ArH), 6.50 (b, 2
H, ArHald and ArHnit), 4.82 (b, 2H, -CH2-), 4.41 (b, 0.89 H,
N-CH(CH3)2) 2.00-1.00 (m, 3 H, -CH2-CH-, 5.5 H, N-
CH(CH3)2). IR (KBr): 2979, 2930, 2870 (alkyl, aryl), 1602
(ring), 1506 (ring), 1147 (N-O stretch), 844 (ring), further
829 cm-1
.
Cop olym er iza tion . p-Vinylbenzaldehyde (2.0 g, 15 mmol)
and styrene (1.6 g, 15 mmol) were dissolved in benzene (20
mL) and bubbled with argon for 20 min. The mixture was
polymerized with AIBN (123 mg, 0.75 mmol) as described
before, yielding 2.8 g (∼78%) of the colorless polymer 20
(styrene:4-vinylbenzaldehyde ) 0.85:1).
intensive signals at 1456, 1310, 1252, 1171, 1086, 1016 cm-1
.
UV (methylene chloride): λmax/nm ) 306.
2.3. Heck Rea ction of Differ en t Br om oben za ld eh yd es
w ith Eth en e. In a typical procedure,12 a pressure vessel was
charged with 0.01 mol of bromobenzaldehyde (11-13, or 17),
palladium(II) acetate (22 mg, 10-4 mol), tris(o-toloyl)phosphine
(60 mg, 2 × 10-4 mol) dissolved in DMF (30 mL), and
triethylamine (9.1 g, 0.09 mol). The solution was bubbled with
argon for more than 15 min, and a pressure of about 40 bar
ethylene was applied. The autoclave was heated to 110 °C for
24 h. Then the mixture was added to 120 mL of water and
extracted four times with ethyl acetate, and the organic phase
was extracted two times with water and saturated NaCl
solution, dried with MgSO4, and evaporated. The brownish
liquid was distilled and/or purified by chromatography with
chloroform as eluant. Nevertheless about 5 mol % of the
bromobenzaldehyde educt was present which did not disturb
further polymerization.
SEC (RI): Mn ) 15 600, PD ) 1.30. SEC (UV): Mn ) 14 900,
1
PD ) 1.68. DSC: Tg ) 110 °C. H NMR (200 MHz, CDCl3): δ
) 9.87 (b, 1 H, -CHO), 7.49 (b, 2 H, ArHald), 7.01 (b, 2.55 H,
ArHstyrene), 6.51 (b, 2 H, ArHald, 1.7 H, ArHstyrene), 2.5-1.0 (m,
5.6 H, -CH-CH2-). IR (KBr): 3058, 3025 (aryl), 2924, 2849,
2827, 2733 (alkyl), 1704 (CdO aldehyde), 1605 (ring), further
intensive signals at 1575, 1452, 1306, 1213, 1169, 1015, 842,
829, 763, 703 cm-1
.
2.4.2 P olym er iza tion of 3-Vin ylben za ld eh yd e (15). The
polymerization of 3-vinylbenzaldehyde (15, 0.6 g, 4.5 mmol)
in benzene (2.5 mL) with AIBN (17 mg, 0.1 mmol) was carried
out as described in section 2.4.1 (homopolymerization), yielding
0.42 g (70%) of 23.
SEC (RI): Mn ) 12 600, PD ) 3.42. SEC (UV): Mn ) 11 800,
1
PD ) 3.45. DSC: no transition. H NMR (200 MHz, CDCl3):
δ ) 9.76 (b, 1 H, -CHO), 7.47 (b, 1 H, ArH), 7.02 (b, 2 H,
ArH), 6.60 (b, 1 H, ArH), 2.5-1.0 (m, 3H, -CH-CH2). IR
(KBr): 3060, 3030, 3010 (aryl), 2925, 2848, 2814, 2728 (alkyl),
1699 (CdO aldehyde), 1601 (ring), 798, 698 (1,3-disubstituted
benzenes), further intensive signals at 1585, 1450, 1391, 1232,
2.3.1. Syn th esis of 4-Vin ylben za ld eh yd e (14). Yield:
66%. 1H NMR (200 MHz, CDCl3): δ ) 9.98 (s, 1 H, -CHO),
7.83 (d, J ) 8.3 Hz, 2 H, ArH), 7.54 (d, J ) 8.3 Hz, 2 H, ArH),
6.76 (dd, J ) 17.6 Hz, J ) 10.7 Hz, 1 H, -CHdCH2), 5.90 (d,
J ) 17.6 Hz, 2H, -CHdCH2), 5.43 (d, J ) 10.7 Hz, 3H, -CHd
CH2). IR (NaCl): 3089, 3010 (aryl), 2824, 2736 (alkyl), 1702
(CdO aldehyde), 1605 (ring), 842 (ring), further intensive
1153 cm-1
.
2.4.3. P olym er iza tion of 2-Hyd r oxy-4-vin ylben za ld e-
h yd e (16). The polymerization of 2-hydroxy-4-vinylbenzalde-
hyde (16, 0.81 g, 5.5 mmol) in dioxane (4.5 mL) with AIBN
(21 mg, 0.13 mmol) was carried out as described in section
2.4.1, yielding 0.49 g (60%) of polymer 23.
SEC (RI): Mn ) 8000, Mw ) 34 700, PD ) 4.32. SEC (UV):
Mn ) 8400, Mw ) 33 500, PD ) 4.00. DSC: no transitoin points
found. 1H NMR (200 MHz, DMSO-d6): δ ) 10.41 (b, 1 H,
-OH), 9.97 (b, 1 H, -CHO), 6.63 (b, 3 H, ArH), 2.5-1.0 (m,
signals at 1566, 1213, 1167, 991, 922 cm-1
.
2.3.2. Syn th esis of 3-Vin ylben za ld eh yd e (15). Yield:
83%. 1H NMR (200 MHz, CDCl3): δ ) 9.97 (s, 1 H, -CHO),
8.07 (t, J ) 1.7 Hz, 1 H, ArH), 7.91 (dd, J ) 7.8, J ) 1.5 Hz,
1 H, ArH), 7.56 (dt, J ) 7.8 Hz, J ) 2.4 Hz, 1 H, ArH), 6.77
(dd, J ) 17.6 Hz, J ) 10.7 Hz, 1 H, -CHdCH2), 5.79 (d, J )
17.6 Hz, 1 H, -CHdCH2), 5.79 (d, J ) 10.7 Hz, 1 H, -CHd

3450 Heinenberg et al.
Macromolecules, Vol. 35, No. 9, 2002
F igu r e 1. Setup for waveguide mode spectroscopy with simultaneous irradiation of the sample.
3H, -CH-CH2). IR (KBr): 3442 (OH), 2925, 2852 (alkyl), 1658
(CdO aldehyde), 1590 (ring), 1485 (alkyl), 835, 772 (substi-
2.6. Syn th esis of 2-Hyd r oxyben za ld eh yd e-N-isop r o-
p yln itr on (28). 2-Hydroxybenzaldehyde (27, 3.05 g, 25 mmol)
and N-isopropylhydroxylamine (8, 1.88 g, 25 mmol) were
dissolved in ethanol (10 mL) and stirred at room temperature
over night. The solvent was evaporated and purified by column
chromatography with chloroform, yielding 1.9 g (43 %) pure
yellowish crystals of 2-hydroxybenzaldehyde-N-isopropylnitron
(28) with a melting point of 46 °C.
tuted benzenes), further intensive signals at 1281, 1210 cm-1
.
2.5. P olym er a n a logou s Rea ction of th e P olya ld eh yd es
to th e P olyn itr on s. 2.5.1. P olym er a n a logou s Rea ction
of 19 to P oly(4-vin ylben za ld eh yd e-N-isop r op yln itr on ).
Hom op olym er 21. A solution of polymer 19 (0.34 g, 2.6 mmol)
and N-isopropylhydroxylamine (8, 0.6 g, 8 mmol) in chloroform
(3 mL) was stirred for 24 h at room temperature under
exclusion of light. Precipitating in diethyl ether gave polymer
21, showing a conversion to the nitron of 100%.
1H NMR (200 MHz, DMSO-d6): δ ) 12.61 (s, 1 H, -OH),
8.20 (s, 1 H, -CHdN), 7.37 (m, 2 H, ArH), 6.82 (m, 2 H, ArH),
4.36 (heptett, J ) 6.3 Hz, 1 H, dN-CH(CH3)2), 1.36 (d, J )
6.3 Hz, 6 H, -CH(CH3)2). 13C NMR (200 MHz, DMSO-d6): δ
) 158.6 (1 C, C-OH), 138.3 (1 C, -CHdN), 133.2, 132.2, 118.7,
118.5, 117.2 (5 C, arom. ring), 64.8 (1 C, dN-CH(CH3)2), 20.4
(2 C, -CH(CH3)2). IR (KBr): 3453 (OH), 3061 (aryl), 2987, 2936
(alkyl), 1596, 1580 (ring), 757 (1,2-disubstituted benzenes),
further intensive signals at 1479, 1430, 1286, 1152, 1056, 994,
920, 848, 771 cm-1. UV (methylene chloride): λmax/nm ) 283,
333. Anal. Calcd for C10H13NO2 (179): C, 67.02; H, 7.31; N,
7.82; O, 17.85. Found: C, 66.60; H, 8.05; N, 7.73; O, 17.62.
2.7. Mea su r em en ts. NMR spectra were recorded on a
Bruker AM400 FT-NMR spectrometer (400 MHz) or on a
Bruker AC200 FT-NMR spectrometer (200 MHz) with CDCl3
or DMSO-d6 as internal standard. IR spectra were run on a
Nicolet 5SBX- or a 5DXC-FTIR spectrophotometer and the UV
spectra on a Nicolet UV540 UV-vis spectrometer. The irradia-
tions were carried out in a 700 mL reactor with a 700 W
mercury medium pressure lamp TQ718Z4 from Heraeus (using
an edge filter with a transmission of λ < 300 nm) in 2 × 10-4
molar solution in CH2Cl2. Elemental analyses were carried out
with a Foss Heraeus vario EL and the uncorrected melting
points with a Bu¨chi melting point determinator. SEC mea-
surements were performed using a PSS apparatus with a
Shodex refractive index (RI) detector and a TSP UV2000 UV-
vis detector at 75 °C under the following conditions: HEMA
10 µm, 8 × 50 mm precolumn with a porosity of 40 Å, three
HEMA 10 µm, 8 × 300 mm columns with porosities of 40, 102,
3000 Å, and DMF eluent containing 0.1 wt % LiBr at a flow
rate of 1.0 mL/min. The calibration curves for SEC analysis
were obtained using PSS polystyrene standards (374-106 D).
The polymeric films were prepared using an ∼16 wt %
solution of the polymer in DMF on a BLE Delta 10 spin-coater
(600 rpm, highest acceleration). The waveguide mode spec-
troscopy experiments were carried out using a home-built
setup shown in Figure 1. The irradiation was carried out with
an unfocused HBO 100 W mercury short arc lamp from Osram.
A grating with a periodicity Λ of 1091.5 nm ion etched into
the substrate13 before spincoating the polymeric waveguide
was used to couple a HeNe laser beam (λ ) 632.8 nm) in the
s- (TE) and/or p-polarized (TM) direction from the air into the
waveguide.
SEC (RI): Mn ) 16 300, PD ) 9.24. DSC: Tdec ) 190 °C. 1H
NMR (200 MHz, DMSO-d6): δ ) 7.97 (b, 1 H, ArH), 7.72 (b,
1H, -CHdN-), 6.55 (b, 2 H, ArH), 4.27 (b, 1 H, dN-
CH(CH3)2), 2.5-1.0 (m, 6 H, dN-CH(CH3)2, 3H, -CH-CH2).
IR (KBr): 2978, 2932 (alkyl), 1605 (ring), 1452 (-CH2-), 1148
(N-O-stretch), 852 (substituted benzenes), further intensive
signals at 1641, 1585, 1312, 1175, 1086, 929 cm-1
.
Cop olym er 22. The condensation of polymer 20 (2.0 g )
9.0 mmol aldehyde groups) and N-isopropylhydroxylamine (8,
1.2 g, 16 mmol) in chloroform (13 mL) was carried out as
described before, yielding the polymeric nitron 22 (conver-
sion: 100%, styrene: 4-vinylbenzaldehyde ) 0.85:1).
SEC (RI): Mn ) 18 800, PD ) 1.40. SEC (UV): Mn ) 16 300,
1
PD ) 1.54. DSC: Tdec ) 195 °C. H NMR (200 MHz, DMSO-
d6): δ ) 7.90 (b, 2 H, ArHnitron), 7.36 (b, 1 H, -CHdN), 6.99
(b, 2.55 H, ArHstyrene), 6.49 (b, 1.7 H, ArHstyrene, 2 H, ArHnitron),
4.19 (b, 1H, dN-CH(CH3)2), 2.5-1.0 (m, 6H, dN-CH(CH3)2,
5.6 H, -CH-CH2). IR (KBr): 3024 (aryl), 2977, 2928 (alkyl),
1604 (ring), 1452 (-CH2-), 1149 (N-O stretch), 849, 703
(substituted benzenes), further intensive signals at 1635, 1582,
1310, 1175, 1088 cm-1. UV (methylene chloride): λmax/nm )
302.
2.5.2. P olym er An a logou s Rea ction of 23 to P oly(3-
vin ylben za ld eh yd e-N-isop r op yln itr on ) (24). The conden-
sation of polymer 23 (0.26 g, 2.0 mmol) and N-isopropylhy-
droxylamine (8, 0.5 g, 6.7 mmol) in chloroform (2 mL) was
carried out as described in section 2.5.1, yielding the polymeric
nitron 24 (conversion: 100%).
SEC (RI): Mn ) 13 400, PD ) 3.53. DSC: no transition. 1H
NMR (200 MHz, DMSO-d6): δ ) 8.22 (b, 1 H, -CHdN), 7.05
(b, 3H, ArH), 6.54 (b, 1 H, ArH), 4.20 (b, 1 H, dN-CH(CH3)2),
2.5-1.0 (m, 3H, -CH-CH2, 6 H, dN-CH(CH3)2). IR (KBr):
3424 (OH), 3072 (aryl), 2979, 2933, 2872 (alkyl), 1582 (ring),
1452 (alkyl), 808, 701 (1,3-disubstituted benzenes), further
intensive signals at 1635, 1365, 1309, 895 cm-1. UV (methylene
chloride): λmax/nm ) 298.
2.5.3. P olym er An a logou s Rea ction of 25 to P oly(2-
h yd r oxy-4-vin ylb en za ld eh yd e-N-isop r op yln it r on ) (26).
The condensation of polymer 25 (0.35 g, 2.35 mmol) and
N-isopropylhydroxylamine (8, 0.6 g, 8 mmol) in THF (2.5 mL)
was carried out as described in section 2.5.1, yielding the
polymeric nitron 26 (conversion: 100%).
The waveguide mode spectrum was determined by scanning
the angle of incidence of the incoming laser beam onto the
grating while measuring the outcoupled power with a photo
detector situated at the end of the waveguide.14 From the
coupling angles and the known parameter of the grating and
the substrate, the effective refractive indices of all modes Nij
were calculated according to eq 115
SEC (RI): Mn ) 12 800, Mw ) 29 600, PD ) 2.30. DSC: Tdec
1
) 190 °C. H NMR (200 MHz, DMSO-d6): δ ) 12.58 (b, 1 H,
-OH), 6.63 (b, 1 H, -CHdN), 6.61 (b, 3H, ArH), 4.36 (b, 1 H,
dN-CH(CH3)2), 2.5-1.0 (m, 3H, -CH-CH2, 6 H, -CH(CH3)2).
IR (KBr): 3439 (OH), 2981, 2925 (alkyl), 1589 (ring), 1495
(alkyl), 830, 781 (substituted benzenes), further intensive
signals at 1611, 1454, 1404, 1281, 1152, 1065 cm-1. UV
(methylene chloride): λmax/nm ) 286, 343.
Nij ) nc sin R + mλ/Λ
(1)

Macromolecules, Vol. 35, No. 9, 2002
Polymeric Nitrons 3451
where 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. If the optical
constants of the substrate are known, the thickness and the
refractive indices for both polarization directions can be
calculated iteratively as long as at least two modes can be
detected for each polarization direction. If there is a redun-
dancy of modes, you can make an error calculation.
sponding polymeric nitron (9) in > 90% yields. The
resulting polymeric nitron still contained some residual
benzaldehyde groups.
3. Resu lts a n d Discu ssion
3.1. Syn th esis a n d Ir r a d ia tion . To study the influ-
ence of irradiation on the structure of N-aryl-substituted
nitrons,5 a low molecular weight benzaldehyde-N-me-
thylnitron (3) was prepared by condensation of benzal-
dehyde (1) and N-methylhydroxylamine (2).
Figure 2 demonstrates that the cyclization reaction
of the polymeric nitron 9 to the corresponding oxaziri-
dine (10) (2 × 10-4 molar solution in CH2Cl2) is fast.
After only about 30 s of irradiation, the ring formation
was nearly complete. The 1H NMR spectra indicate that
only traces of the nitron were still present. Further
irradiation leads to decomposition of the three-mem-
bered ring (see Scheme 1 and compound 3b).
The photochemical cyclization of the nitron (3) was
very fast. After 1 min of irradiation with a 700 W
mercury medium-pressure lamp in a 5 × 10-4
M
solution in ethanol, the nitron cyclized preferentially to
the phenylmethyloxaziridine (3a) and only small amounts
of the N-methylbenzamide (3b) were formed. However,
further irradiation leads to decomposition of 3a to 3b
(Table 1).
Ta ble 1. Yield of P r od u cts 3a a n d 3b a fter Ir r a d ia tion of
th e Ben za ld eh yd e-N-m eth yln itr on (3)
irradiation time
1 min
2 min
3 min
oxaziridine (3a ) [%]
benzamide (3b) [%]
85
15
55
45
40
60
The polyaldehydes should condense with N-alkylhy-
droxylamines to produce the desired polynitrons in good
yields. For this purpose, 4-[(4-vinylbenzyl)oxy]benzal-
dehyde (6) was prepared from 4-vinylbenzyl chloride (4)
and 4-hydroxybenzaldehyde (5), and then polymerized
in benzene to produce poly{4-[(4-vinylbenzyl)oxy]ben-
zaldehyde} (7).
4-Vinylbenzaldehyde (14), 3-vinylbenzaldehyde (15),
and 2-hydroxy-4-vinylbenzaldehyde (16) were synthe-
sized via Heck reactions of 4-bromobenzaldehyde (11),
3-bromobenzaldehyde (12), and 2-hydroxy-4-bromoben-
zaldehyde (13). Small amounts of educt impurities
(bromobenzaldehydes 11, 12, and 13) did not disturb
the polymerization and were easily separated from the
polymeric aldehydes.
The Heck reaction of ethylene with 2-bromobenzal-
dehyde (17) was not successful. The main product was
o-ethylstyrene rather than the desired vinylbenzalde-
The polyaldehyde (7) was then condensed with N-
isopropylhydroxylamine (8) in solution to the corre-

3452 Heinenberg et al.
Macromolecules, Vol. 35, No. 9, 2002
F igu r e 2. Change of UV absorption of polynitron 9 during
irradiation.
was compared with the total integral of the aromatic
region minus four protons of the aldehyde component.
hyde 18a . The vicinal aldehyde seems to interact with
the Pd complex, which results in a decarbonylation and
insertion of ethylene (18b). Because of the presence of
the hydroxy group in 13, only a low yield was achieved
indicating a strong interaction with the Pd. Therefore,
polymerizations with 18b were not yet carried out.
Analogously, 3-vinylbenzaldehyde (14) was polymer-
ized to yield the polymeric aldehyde 23 and then
condensed with N-isopropylhydroxylamine (8) to the
polynitron (24). The conversion to the nitron was
approximately 100%. No aldehyde functions of 24 could
1
be detected by H NMR and IR spectroscopy.
Figure 3 shows the degradation of the nitron band at
298 nm due to UV irradiation. After 45 s, the intramo-
lecular cyclization to the oxaziridine ring was nearly
complete. This corresponds to a cyclization rate of about
1 mmol in 5 min.
2-Hydroxy-4-vinylbenzaldehyde (16) was polymerized
radically yielding polymer 25 with relatively low mo-
lecular weight (Mn ) 8400), which is similar to that of
poly(4-vinylbenzaldehyde) (19) and poly(3-vinylbenzal-
dehyde) (23). The conversion of 25 with the N-isopro-
4-Vinylbenzaldehyde (14) was homo- and copolymer-
ized with styrene in benzene at 70 °C for 24 h. The
molecular weight (Mn) of 19 was only about 5500. This
indicates that aldehydes transfer their carbonyl hydro-
gen. Only copolymerization of 20 with styrene produced
polymers with molecular weights up to 15 000, which
shows a lower transfer rate because of lower aldehyde
concentration. For the preparation of polymer films the
low Mn values are favorable, because the polymer is
better processable.
As described above, the polymer analogous reaction
of 19 and 20 with N-isopropylhydroxylamine (8) quan-
titatively produces to the corresponding polymeric ni-
trons 21 and 22.
No residual aldehyde at 9.85 ppm could be detected
1
by H NMR or at 1704 cm-1 by IR spectroscopy of 20.
The aromatic signals ortho to the aldehyde function
shifted from 7.53 to 7.97 ppm, and the former aldehyde
proton appears at 7.72 ppm. The composition of copoly-
1
mer 20 was calculated by H NMR spectroscopy. The
F igu r e 3. Change of UV absorption of polynitron 24 during
integrated signal of the aldehyde proton at 9.85 ppm
irradiation.

Macromolecules, Vol. 35, No. 9, 2002
Polymeric Nitrons 3453
pylhydroxylamine (8) was also nearly 100% as deter-
1
mined by IR and H NMR spectroscopy.
Surprisingly, nitron 26 seems to be stable against UV
light (Figure 4). Only the intensity of the UV absorption
bands at 290 and 345 cm-1 are lowered in the same
ratio. This indicates that the hydroxyphenyl-substituted
polymeric nitron does not cyclize to the polyoxaziridine.
The nitron is partially degraded. The 1H NMR spectrum
shows that the signal of nitron 26 is overlaid with
several new sharp small signals not yet assigned.
F igu r e 4. Change of UV absorption of polynitron 26 during
irradiation.
spectra show that cyclization takes place without any
side reaction. To avoid undesired decomposition, the
irradiation time was limited; however, small amounts
of the nitron are still present in polymer 22a .
3.2. Rin g Op en in g of Nitr on s. According to the
literature,16 the cyclization of nitrons to oxaziridines
may be thermally reversible. To evaluate this predicted
thermal ring opening of polymer bound oxaziridine
functions, a KBr pellet of polymer 10 was heated to 100
°C for 2 h, 120 °C for 4 h, and 150 °C for 2 h. The IR
spectra were recorded to show the possible ring opening
after thermal treatment (Figure 6).
The N-O stretch vibration of nitrons appears in the
region of about 1147 cm-1. This band is degraded after
irradiation because of oxaziridine formation. The IR
spectrum of the oxaziridine 10 shows no bands in this
region. After heating 10 for 8 h, a small signal appears
at 1148 cm-1, which strongly indicates that a few ring
molecules were opened thermally. Additionally, two
signals disappeared due to heating; the OH vibration
at 3432 cm-1 belongs to the crystal water of the nitrons,
which disappears above 100 °C. The aldehyde signal at
1691 cm-1 due to the presence of untransformed poly-
aldehyde components in the polymer disappeared, prob-
ably due to oxidation. There are no significant changes
in the fingerprint region. Therefore, a significant ther-
mal ring opening of the oxaziridine to the nitron does
not seem to take place.
To study the behavior of polymer 26 in detail, a low
molecular model compound 2-hydroxybenzaldehyde-N-
isopropylnitron (28) was prepared from 2-hydroxyben-
zaldehyde (27) and N-isopropylhydroxylamine (8). How-
ever, UV irradiation of a solution of 28 showed that only
the two UV absorption bands decrease slightly which
is consistent with the behavior of the corresponding
polynitron 26 (Figure 4). In contrast, the nitron group
of p-hydroxybenzaldehyde-N-methylnitron undergoes a
nonretarded cyclization during UV irradiation.8 There-
fore, the hydroxy function ortho to the nitron must be
responsible for this photostability. The structure of 28
indicates that the o-OH group will form a H-bond with
the N-O group. This ortho effect may also be respon-
sible for the stability against UV irradiation in solution.
Hydrogen bridges between the hydroxy group and
nitron oxygen were verified with semiempirical methods
(PC Spartan Pro, Version 1.07, calculated on the PM3-
level). Thus, the typical 1,3-dipolar structure of the
nitron group is clearly disturbed, which evidently
prohibits a photoinduced cyclization of 28.
The 1H NMR spectra (Figure 5) of the polynitron
before (22) and after irradiation (22a ) shows that about
80% of the nitron has cyclized to the corresponding
oxaziridine. The intensity of the nitron signals is drasti-
cally reduced: The methine proton of the isopropyl
group shifted from 4.2 to 2.3 ppm and the “azomethine”
proton from 7.4 to 4.4 ppm. The degree of cyclization
was calculated with these two signals. The aromatic
protons (H-16) suffer a small shift to a higher field. The
3.3. Wa vegu id e Mod e Sp ectr oscop y. Due to the
photoinduced intramolecular cyclization of the polar
nitron groups to the less polar oxaziridine ring, the
refractive index should change. Spin-coated films of 21
with a thickness of about 1.2 µm were prepared for
waveguide mode spectroscopy using DMF as solvent.
Figure 7 shows the coupling angles of three different
Ta ble 2. Refr a ctive In d ices a n d Th ick n esses of th e P olym er F ilm of 21 befor e a n d a fter UV Ir r a d ia tion
before irradiation polarized light after irradiation polarized light
TE
TM
TE
TM
refractive index
thickness (nm)
1.6023 ( 0.0004
1426 ( 7
1.6067 ( 0.0008
1447 ( 14
1.5451 ( 0.002
1405 ( 28
1.5500 ( 0.002
1417 ( 47
Ta ble 3. Refr a ctive In d ices a n d Th ick n esses of th e P olym er F ilm of 24 befor e a n d a fter UV Ir r a d ia tion
before irradiation polarized light after irradiation polarized light
TE
TM
TE
TM
refractive index
thickness (nm)
1.6014 ( 0.0006
1474 ( 11
1.6064 ( 0.0006
1470 ( 10
1.5466 ( 0.0010
1488 ( 17
1.5507 ( 0.0011
1482 ( 19

3454 Heinenberg et al.
Macromolecules, Vol. 35, No. 9, 2002
F igu r e 5. Comparison of the 1H NMR spectra of polynitron 22 and the corresponding polyoxaziridine (22a ).
F igu r e 6. Changes in the IR spectra of polyoxaziridine 10 before and after heating for about 8 h.
TM (p-polarized) waveguide modes before and after
irradiation.
The intensive mode at 25.15° results from the glass
substrate, which does not shift during irradiation of the
polymer film. The shift of the different coupling angles
up to 2.5° indicates that the refractive index of the
polymer waveguide decreases after irradiation. An
online observation of the TE1 mode during irradiation
shows the kinetic behavior of the bleaching effect
(Figure 8).

Macromolecules, Vol. 35, No. 9, 2002
Polymeric Nitrons 3455
F igu r e 7. Waveguide mode spectra in p-polarization before and after irradiation of polymer 21.
If the nitron bears a hydroxy group in the ortho
position, photochemical cyclization was not possible,
because the typical 1,3-dipole is disturbed. The refrac-
tive index measured by waveguide mode spectroscopy
decreases greatly, whereas the thickness remains al-
most constant. Waveguide mode spectroscopy is an
excellent method for examinating the photochemical
behavior of the polymers bearing photosensitive nitron
functions. These kinds of nitrons do not seem to be
switchable, because a thermal ring opening of the
oxaziridines to the nitrons could not be detected. This
is a disadvantage for information storage, but the
rapidness of the cyclization to the oxaziridine is an
advantage.
Refer en ces a n d Notes
(1) Eickmans, J .; Bieringer, T.; Kostromine, S.; Berneth, H.;
Figu r e 8. Changes of the coupling angle of the TM1 waveguide
Thoma, R. J pn. J . Appl. Phys. Part 1 1999, 1835.
mode during irradiation.
(2) Hamer, J .; Macaluso, A. Chem. Rev. 1964, 64, 473.
(3) Splitter, J . S.; Calvin, M. J . Org. Chem. 1965, 30, 3426.
(4) Splitter, J . S.; Calvin, M. Tetrahedron Lett. 1968, 12, 1445.
For further kinetic measurements, the irradiation
should be carried out using a suitable laser instead of
filtered light of an unfocused 100 W mercury arc lamp.
However, the irradiation curve shows that after about
1 h the coupling angle has stabilized. This is much faster
than in mesoionic systems.7,17 The exact values of the
changes in the refractive index and of film thickness
are shown in Table 2.
(5) Heinenberg, M.; Ritter, H. Macromol. Chem. Phys. 1999, 200,
1792.
(6) Heinenberg, M.; Reihmann, M. H.; Ritter, H. Des. Monomer
Polym. 2000, 3 (4), 501.
(7) Au: Please not that issue numbers should only be given for
those journals in which each issue begins with page 1.
Otherwise it should be deleted. We were not certain which
case ref 6 fell into.
The refractive index decreases significantly due to
irradiation. In contrast, the film thickness remains
almost constant during isomerization, indicating that
the resulting three-membered ring occupies nearly the
same space as the nitron group. Between p- and s-
polarized light, a significant difference of about 0.005
was observed. This may be attributed to the anisotropic
structure of the waveguide resulting from the spin-
coating process. Waveguide mode spectroscopy of the
polymeric nitron 24 shows the same results and nearly
the same values for the refractive indices and the
thickness (Table 3) as the polymeric nitron 21 (Table
2).
(8) Bo¨hme, F.; Klinger, C.; Menges, B.; Mittler, S.; Theis, A.;
Ritter, H. Chem. Mater., in press.
(9) Ihlein, G.; Menges, B.; Mittler-Neher, S. Opt. Mater. 1995,
4, 685.
(10) Paul, S.; Halle, O.; Menges, B.; Einsiedel, H.; Mu¨llen, K.;
Knoll, W.; Mittler-Neher, S. Thin Solid Films 1996, 288, 150.
(11) Borch, R. F.; Bernstein, M. D.; Durst, H. D. J . Am. Chem.
Soc. 1971, 93, 2897.
(12) Brady, O. L.; Dunn, F. P.; Goldstein, R. F. J . Chem. Soc. 1926,
2386.
(13) Detert, H.; Sugiono, E. J . Prakt. Chem. 1999, 34, 358.
(14) Mai, X.; Moshrefzadeh, R.; Gibson, U. J .; Stegeman, G. I.;
Seaton, C. Appl. Phys. 1985, 24, 3155.
(15) Lee, T.-M.; Mittler-Neher, S.; Neher, D.; Stegemann, G. I.;
Roux, C.; Leclerc, M. Opt. Mater. 1992, 1, 65.
(16) Karthe, W; Mu¨ller, R. Integrierte Optik, 1st ed; Akademische
4. Con clu sion
Verlagsgesellschaft Geest & Portig: Leipzig, Germany, 1991.
In contrast to previous studies,7 the photo chemically
generated oxaziridines obtained from aryl-N-alkyl ni-
trons are relatively stable. Since the nitron acts as a
radical inhibitor, polymeric nitrons were obtained from
polyvinylaldehydes, which were condensed with N-
isopropylhydroxylamine in almost quantitative yield.
(17) Rundel, W. In Houben-Weyl, Methoden der organische Che-
mie, 4th ed.; Georg Thieme Verlag: Stuttgart, Germany,
1974; Vol. 10/4, p 314 ff.
(18) Theis, A.; Ritter, H. Des. Monomers Polym. 2001, 4 (2), 177.
MA0116710