Synthesis and polymerization of unsaturated phthalides

Article abstract of DOI:10.1023/B:RJAC.0000008306.12906.74

Procedures were developed for preparing unsaturated phthalides: phthalideneacetic acid and methylene phthalide, which are promising monomers for radical polymerization. The structures of the monomers were studied, and their copolymerization with methyl methacrylate was performed.

Full text of DOI:10.1023/B:RJAC.0000008306.12906.74

Russian Journal of Applied Chemistry, Vol. 76, No. 8, 2003, pp. 1299 1303. Translated from Zhurnal Prikladnoi Khimii, Vol. 76, No. 8, 2003,
pp. 1336 1340.
Original Russian Text Copyright
2003 by Puzin, Chebaeva, Egorov, Khatchenko.
MACROMOLECULAR CHEMISTRY
AND POLYMERIC MATERIALS
Synthesis and Polymerization of Unsaturated Phthalides
Yu. I. Puzin, T. V. Chebaeva, A. E. Egorov, and E. A. Khatchenko
Ufa State Petroleum Technical University, Ufa, Bashkortostan, Russia
Institute of Organic Chemistry, Ufa Scientific Center, Russian Academy of Sciences, Ufa, Bashkortostan, Russia
Received October 9, 2002; in final form, March 2003
Abstract Procedures were developed for preparing unsaturated phthalides: phthalideneacetic acid and
methylene phthalide, which are promising monomers for radical polymerization. The structures of the mono-
mers were studied, and their copolymerization with methyl methacrylate was performed.
Much attention is given today to polymeric materi-
als whose components change the structure and phys-
icochemical properties, depending on external condi-
tions (pressure, temperature, acidity of the medium,
etc.). Of particular interest in this respect are phthal-
ides showing ring chain isomerism [1]. Phthalide-
containing polymers exhibit unique electrical [2] and
optical [3] properties, high heat resistance, and high
softening points [4]. These polymers are most often
prepared by polycondensation. However, their high
heat resistance is combined with high glass transition
and flow points, and also with poor solubility in
the majority of industrially used organic solvents.
The monomeric purity is the necessary condition
for their application.
EXPERIMENTAL
Phthalic anhydride was recrystallized from absolute
ethanol before use; mp 239 C. Acetic anhydride was
distilled; bp 140 C. The polymerization initiators,
azobis(isobutyronitrile) (AIBN) and benzoyl peroxide
(BP), were repeatedly recrystallized from methanol
and vacuum-dried to constant weight.
Methyl methacrylate (MMA) was purified to re-
move the stabilizer by shaking with 5 10% KOH,
washed with water to neutral reaction, dried over
CaCl2, and double-distilled in a vacuum. The fraction
with bp 42 C (13.3 kPa) was used for polymerization.
In contrast to phthalide-containing polymers, many
vinyl polymers, in particular, polyacrylates have low
glass transition and flow points and good solubility,
but poor heat resistance. These polymers are most
often prepared by radical polymerization. Therefore,
it seems appropriate to modify vinyl polymers, such
as poly(meth)acrylates, polystyrene, etc., with phthal-
ides, and development of procedures allowing modifi-
cation in the stage of synthesis is an urgent problem.
Phthalideneacetic acid. Published data on syn-
thesis of I and II are contradictory. Phthalideneacetic
acid was prepared for the first time at the end of
the XIX century [5 8], but its properties have been
studied poorly. In this study, we prepared I by the
Perkin Gabriel reaction from phthalic and acetic an-
hydrides in the presence of a metal acetate:
Phthalides can be incorporated into a polymeric
molecule in the course of radical polymerization both
via their involvement in chain initiation or transfer [3]
and through (co)polymerization of unsaturated phthal-
ides. With the aim to prepare poly(methyl methacry-
late) modified with phthalide-containing compounds,
we prepared two phthalide-containing monomers:
phthalideneacetic acid I and methylene phthalide II:
H
COOH
O
O
O
C
C
O
C
CH3C
CH3C
CH3COOM
CH3COOH
O
O +
C
O
C
O
H
COOH
The reaction was performed in several steps. First,
a flask was charged with phthalic anhydride (2 3%
excess relative to the reaction stoichiometry), acetic
anhydride, and potassium acetate (20 30% excess rel-
ative to phthalic anhydride). The mixture was heated
for 1.5 h on a boiling water bath. Then a tenfold vol-
C
C
CH2
C
O
C
O
C
O
O
I
II
1070-4272/03/7608-1299 $25.00 2003 MAIK Nauka/Interperiodica

1300
PUZIN et al.
Table 1. Properties of I and II
Found, %
NMR spectrum, , ppm
1H 13C
UV
spectrum,
, nm
IR
spectrum,
, cm
Com-
pound
Calculated, %
mp,
C
1
C
H
O
C
O
C166.76
6.32
H
97.21
H
I
63.47
63.16
3.02
3.18
282
(C=C)
1705
(COOH)
1800
C
C
O
C
O
280
8.28
139.76C154.77
122.79
136.14
H
H
7.97
7.85
4.0
O
O
(C=O)
133.20
C
O
124.94 C165.41
8.05
O
II
74.16
73.97
4.02
4.14
311
(C=O and Ar)
1780
(C=O)
4.80 (cis-H)
5.25 (trans-H)
56
94.86 (C=CH2)
Table 2. Geometries of I and II
II
I
Bond
bond length,
bond angle, deg
bond length,
bond angle, deg
C=C
1.3
1.1
130.2
108.7*
130.2
1.3
1.1
1.5
122.7
108.8*
119.6
=C H
=C CO
115.6
115.8
124.8**
116.5
=C O
O H
1.4
1.0
109.9
Deviation from plane
No
COOH, 58
*
**
In the ring.
Relative to the C=C bond.
ume of hot water was added, and the hot mixture was
filtered. The precipitate was washed with hot water
and ethanol. A light brown product was obtained; it
was washed with a small amount of hot glacial acetic
acid. After cooling and filtration, a yellow substance
was obtained; its melting point, 249 C, is reasonably
consistent with published data [6, 7]. The product was
repeatedly recrystallized from glacial acetic acid in the
presence of activated carbon. Colorless lustrous plates
were obtained; mp 280 C (with decomposition). Fur-
ther recrystallizations did not increase the melting
point. The product was identified by IR, 13C NMR,
or the product was unsuitable for polymerization be-
cause of the presence of inhibiting impurities.
In this study, to prepare and purify methylene
phthalide, we chose the procedure described in [9].
It involved high-vacuum dehydration of acetophen-
one-o-carboxylic acid:
O
CH2
C CH3
C
O
C
+SOCl2
H2O
C OH
O
1
O
and H NMR spectroscopy and by elemental analysis
(Table 1).
The product sublimes and is condensed as color-
less needles, mp 56 C (yield about 60%); it is hy-
groscopic and sublimes in a vacuum at about 300 C
(1 5 mm Hg). Some characteristics of II are listed
in Table 1.
Methylene phthalide. Synthesis of methylene
phthalide and its polymers has been attempted by
numerous researchers. However, either the suggested
procedures gave the monomer in low yield (10 15%)
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SYNTHESIS AND POLYMERIZATION OF UNSATURATED PHTHALIDES
1301
The kinetics of bulk polymerization was monitored
gravimetrically [10]. The temperature was maintained
at 60 0.5 C. The composition was calculated from
the analytical data.
Table 3. Characteristics of copolymerization of MMA
with unsaturated phthalides at 70 C [initiator azobis-
(isobutyronitrile), 0.5 wt %] and decomposition (onset)
temperatures of the copolymers
The UV spectra (solutions in CH3COOH) were
recorded on a Shimadzu UV VIS NIR 3100 spec-
trometer using a 1-cm quartz cell. The IR spectra
(mulls in mineral oil) were recorded on a Specord
Phthalide
content
in monomer
mixture, mol %
Initial co-
polymeriza-
tion rate,
Phthalide
content in
copolymer,
mol %
Tdec
C
,
1
% min
1
M-80 spectrophotometer (Germany). The H and 13C
NMR spectra were taken on a Bruker AM-400 spec-
trometer (300 MHz, CD3OD, internal reference hexa-
methyldisiloxane).
Phthalideneacetic acid
0
10
20
30
40
60
0.0950
0.0925
0.0800
0.0540
0.0220
0.0067
0
1.8
3.3
4.2
6.9
190
218
226
235
230
220
The temperature of the decomposition onset was
determined by the method of tangents with an MOM
Q-1500D derivatograph (Hungary); sample weight
1
100 mg, heating rate 5 deg min .
18.0
The probabilities of addition of propagating radi-
cals with different structures of terminal units to co-
monomer molecules were calculated as described in
[10].
Methylene phthalide
0
10
15
20
40
60
80
90
0.1070
0.1098
0.1064
0.1002
0.0891
0.0788
0.0745
0.0704
0
4.2
7.0
190
220
228
235
240
238
242
240
The overwhelming majority of studies concerned
phthalideneacetic acid are limited to its synthesis.
In most cases, the acid was immediately subjected
to thermal decarboxylation in a vacuum to obtain
methylene phthalide [7, 8]. The properties and struc-
ture of the acid remained unknown, like those of
methylene phthalide. Therefore, we first examined the
structures of these compounds.
9.6
21.6
37.6
60.2
77.7
4.00 ppm; 30 C, 4.72 ppm; and 40 C, 5.73 ppm. This
indicates that the intramolecular hydrogen bond in
the acid molecule becomes weaker.
1
The H NMR spectrum of II (Table 1) shows that
the methylene hydrogen atoms ( -position relative to
the phthalide ring) are nonequivalent (cis and trans
arrangement relative to the oxygen atom of the phthal-
ide ring).
The molecular geometry of I and II was optimized
by PM3 calculations. The results (Table 2) show that
the oxygen atom deviates from the ring plane by ap-
proximately 2 ; the bond angle at the ring oxygen
atom is 108 , and the C O bond length, 1.44 . An
important result is that the phthalideneacetic acid
molecule, in contrast to the methylene phthalide mol-
ecule, has functional groups that extend from the
molecular plane; this must affect the electrical prop-
erties of I at elevated pressures and temperatures.
In the case of phthalideneacetic acid, two isomers
with the cis and trans arrangement of the carboxy
group relative to the oxygen atom of the phthalide
ring are possible. The nuclear Overhauser effect
( = 8%) observed on the aromatic proton (8.28 ppm,
3-position) upon irradiation at the frequency of
the olefinic proton signal (6.32 ppm) unambiguously
suggests steric proximity of these protons, i.e., the cis
structure of the product. In other words, the syn-
thesized phthalideneacetic acid is a pure cis isomer.
Furthermore, the chemical shift of the carboxyl proton
signal is unusually small, which may be due to
interaction of this proton with the oxygen atom of
the phthalide ring. Unfortunately, we failed to follow
the changes in the chemical shift of this signal de-
pending on the solvent polarity because of extremely
low solubility of I in other solvents. However,
the chemical shift varies with temperature: 25 C,
Unfortunately, we failed to prepare the homopoly-
mer of phthalideneacetic acid by radical polymeriza-
tion. However, we obtained copolymers of I with
MMA. Some data on the reaction and copolymer
compositions are listed in Table 3. It is seen that the
copolymerization rate decreases with increasing con-
tent of I in the reaction mixture. This may be due to
the fact that the purity of I is insufficient for radical
polymerization. Therefore, we additionally performed
repeated chromatographic purification of the mono-
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 76 No. 8 2003

1302
PUZIN et al.
mer. A certain increase in the copolymerization rate
was, indeed, observed but attempted preparation of the
homopolymer failed.
The constants of copolymerization of MMA with I
were determined by the Fineman Ross method [10]
(Fig. 1) to be 0.36 0.06 and 5.80 0.08, respectively.
Calculation of the probabilities of monomer addition
to propagating radicals of various structures shows
(Fig. 2) that incorporation of MMA into the chain is
much more probable than incorporation of I.
Fig. 1. Determination of the constants of MMA copoly-
merization with phthalideneacetic acid by the Fineman
Ross method.
At the same time, the copolymerization constants
show that the monomers interact with each other (the
product of the constants is significantly greater than
unity), probably owing to their high polarity. Using
the Q e scheme, we calculated the parameters e =
1.26 (parameter characterizing the polarity of I) and
Q = 0.79 (parameter characterizing the conjugation in
the propagating radical with the radical center loca-
lized in the phthalideneacetic acid unit) [10]. Phthali-
deneacetic acid is close to MMA in the value of Q
(QMMA = 0.74) but significantly exceeds it in polarity
(eMMA = 0.40), being in this respect close to aceto-
nitrile (e = 1.20).
Fig. 2. Probability A of addition of a propagating radical
with the of terminal unit (1, 2) MMA and (3, 4) phthal-
ideneacetic acid to (1, 3) MMA and (2, 4) phthalideneacetic
In contrast to phthalideneacetic acid I, methylene
phthalide polymerizes in the presence of radical initi-
ators, such as BP or AIBN. The reaction was per-
acid molecule. (c ) Concentration of I.
I
3
formed in DMF in the presence of 3.7 10 M BP.
The polymerization noticeably accelerated after reach-
ing 30% conversion of the monomer (gel effect), sug-
gesting the radical mechanism of the reaction. The
polymer was precipitated with acetone and reprecipi-
tated several times. Dry poly(methylene phthalide)
has a high glass transition point (305 C), and its
softening is accompanied by decomposition (as indi-
cated by significant weight loss). We failed to prepare
films from this polymer (under conditions similar to
those used with other polymers) for studying electrical
properties; therefore, it seems necessary to prepare
copolymers of II, primarily with MMA.
Fig. 3. Content A of methylene phthalide units in the co-
polymer vs. the content B of methylene phthalide in
the initial monomer mixture.
A study of copolymerization of MMA with II
showed that, with increasing content of II, the process
decelerates but does not fully stop (Table 3), which
allows preparation of the copolymer with different
monomer ratios. Figure 3 shows that the copolymer is
enriched in MMA units at any composition of the
monomer mixture, and the ratio of the copolymeriza-
tion constants meets the condition r1 > 1 and r2 < 1.
The copolymerization constants were determined
by the Mayo Lewis method [10] (Fig. 4) to be 2.69
0.05 (for MMA) and 0.70 0.07 (for II). In this case,
too, the product of the copolymerization constants is
Fig. 4. Determination of the constants of MMA copoly-
merization with methylene phthalide by the Mayo Lewis
method.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 76 No. 8 2003

SYNTHESIS AND POLYMERIZATION OF UNSATURATED PHTHALIDES
greater than unity, suggesting mutual interaction of ACKNOWLEDGMENTS
1303
the monomers; however, it is apparently weaker than
that with I.
The authors are grateful to S.N. Salazkin (Nesmeya-
nov Institute of Organometallic Compounds, Russian
Academy of Sciences, Moscow) for valuable advices.
Methylene phthalide is characterized by Q = 1.35
and e = +1.20. It is somewhat more polar than I, but
its growing radical is more active in chain propaga-
tion.
The study was supported financially by the Russian
Foundation for Basic Research (project no. 98-03-
33322).
As expected, the copolymers show higher heat
resistance, compared to poly(methyl methacrylate)
(Table 3). However, with increasing content of phthal-
ideneacetic acid, the decomposition onset tempera-
ture starts to decrease, probably owing to decarbox-
ylation.
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1. Valter, R.E., Kol’chato-tsepnaya izomeriya v orga-
nicheskoi khimii (Ring Chain Isomerism in Organic
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Pis’ma Zh. Eksp. Teor. Fiz., 1990, vol. 52, p. 742.
CONCLUSIONS
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4. Buhler, K.-U., Spezialplaste, Berlin: Akademie, 1978.
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(1) Procedures were developed for synthesis and
purification of phthalideneacetic acid and methylene
phthalide, promising monomers for radical polymeri-
zation.
p. 391.
(2) The structures of the phthalides were studied;
phthalideneacetic acid has the cis structure.
6. Gabriel, S. and Neuman, A., Ber., 1893, vol. 26,
p. 951.
7. Gabriel, S., Ber., 1884, vol. 17, p. 2521.
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(3) (Co)polymerization of unsaturated phthalides
with methyl methacrylate was performed; the copoly-
merization constants and Q e parameters were calcu-
lated; the activity of I and II as monomers was eval-
uated.
9. Vinogradova, S.V., Salazkin, S.N., Korshak, V.V.,
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(4) The methyl methacrylate copolymers obtained
show enhanced heat resistance.
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