New fluorinated liquid crystalline copoly(vinylcyclopropane)s with unusual macromolecular structure

Article abstract of DOI:10.1080/15421400490436197

New liquid crystal polymers with unusual macromolecular structure were prepared by copolymerization of a fluorinated vinylcyclopropane (1) with methyl methacrylate (2). The copolymers pol(1-co-2) formed a mesophase despite the high dilution of the perfluorinated side chains along the polymer main chain. The onset of mesomorphism is attributed to the microphase separation of the incompatible fluorocarbon-hydrocarbon components.

Full text of DOI:10.1080/15421400490436197

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New Fluorinated
Liquid Crystalline
Copoly(vinylcyclopropane)s
with Unusual Macromolecular
Structure
a
a
a
G. Galli , S. Gasperetti , M. Bertolucci & E.
a
Chiellini
a
Dipartimento di Chimica e Chimica Industriale ,
Università di Pisa , Pisa, Italy
Published online: 18 Oct 2010.
To cite this article: G. Galli , S. Gasperetti , M. Bertolucci & E. Chiellini (2004)
New Fluorinated Liquid Crystalline Copoly(vinylcyclopropane)s with Unusual
Macromolecular Structure, Molecular Crystals and Liquid Crystals, 411:1, 413-419,
DOI: 10.1080/15421400490436197
To link to this article: http://dx.doi.org/10.1080/15421400490436197
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Mol. Cryst. Liq. Cryst., Vol. 411, pp. 413=[1455]–419=[1461], 2004
Copyright # Taylor & Francis Inc.
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080=15421400490436197
NEW FLUORINATED LIQUID CRYSTALLINE
COPOLY(VINYLCYCLOPROPANE)S WITH UNUSUAL
MACROMOLECULAR STRUCTURE
G. Galli, S. Gasperetti, M. Bertolucci, and E. Chiellini
Dipartimento di Chimica e Chimica Industriale, Universit a` di Pisa,
5
6126 Pisa, Italy
New liquid crystal polymers with unusual macromolecular structure were pre-
pared by copolymerization of a fluorinated vinylcyclopropane (1) with methyl
methacrylate (2). The copolymers pol(1-co-2) formed a mesophase despite the
high dilution of the perfluorinated side chains along the polymer main chain.
The onset of mesomorphism is attributed to the microphase separation of the
incompatible fluorocarbon-hydrocarbon components.
Keywords: fluorinated polymer; liquid crystal; macromolecular structure; microphase separ-
ation; poly(vinylcyclopropane)
INTRODUCTION
Vinylcyclopropanes [1] containing electron-withdrawing or radical-stabiliz-
ing groups are known to easily undergo radical ring-opening polymerization
yielding polymers consisting predominantly, though not exclusively, of 1,5-
linear structures. Isomer cyclic structures have also been shown to form
[
2]. Therefore, poly(vinylcyclopropane)s are complex copolymer systems,
the properties of which could be affected substantially by the macromole-
cular structure.
We are interested in vinylcyclopropanes containing perfluorinated-
chain side groups [3,4]. In fact, incorporation of suitable fluoro-substituents
can additionally impart low energy surface properties to the polymer films
by enriching the surface of orderly assembled perfluorinated chain
segments. In this work we have prepared new liquid crystal polymers by
Financial support from the EU (Contract G5RD-2001-00554) and the Italian MIUR (PRIN
001-03-4479) is gratefully acknowledged.
2
Address correspondence to G. Galli, Dipartimento di Chimica e Chimica Industriale,
Universit a` di Pisa, 56126 Pisa, Italy.
413=[1455]

4
14=[1456]
G. Galli et al.
copolymerization of a vinylcyclopropane 1 containing a perfluorinated chain
segment and methyl methacrylate (2). The copolymerization proceeded via
unusual ring-opening and ring-closing steps, and these fluorinated poly-
mers represent a novel class of materials forming liquid crystalline phases.
EXPERIMENTAL PART
The synthesis of monomer 1 and copolymer pol(1-co-2)b are described as
typical examples.
Monomer 1
1
,1-Diethoxycarbonyl-2-vinylcyclopropane 3. 1.98 g (0.09 mol of metallic
sodium was added in small portions to 30 ml of absolute ethanol over 1 h
under dry nitrogen atmosphere. After complete reaction, 13.40 g
(0.08 mol) of diethyl malonate was added dropwise. The mixture was let
to react for an additional 1 h at room temperature and then heated to
ꢀ
4
0 C. 9.06 g (0.04 mol) of trans-1,4-dibromobutene in 40 ml of absolute
ethanol was added in 1 h. The reaction mixture was kept for 1 day at reflux.
The precipitate was then filtered off and the solvent was evaporated under
vacuum. The crude residue was purified by repeated distillations giving
ꢀ
1
.87 g (22% yield) of 3: b.p. 69–72 C=0.5 mm.
1-Ethoxycarbonyl-1-(2-perfluorodecyl)ethoxycarbonyl-2-vinylcyclo-
propane 1. 3.92 g (0.07 mol) of KOH was added in small portions to a sol-
ꢀ
ution of 15.05 g (0.07 mol) of 3 in 25 ml of ethanol at ꢁ5 C. The reaction
was then let to proceed at room temperature for 12 h. The solution was
concentrated to small volume and acidified with HCl to pH ꢂ2.5. The
organic phase separated was dried over Na SO and then evaporated to
2
4
dryness, giving 11.50 g (90% yield) of acid 4.
5
.02 g (22 mmol) of dicyclohexylcarbodiimide (DCCI) in 15 ml of anhy-
drous dichloromethane was added dropwise to a solution of 4.62 g
25 mmol) of 4, 0.02 g (1.0 mmol) of pyrrolidinopyridine (PPy) and
(
1
methane under dry nitrogen atmosphere at 0 C. The reaction was let to
2.86 g (23 mmol) of 2-(perfluorodecyl)ethanol in anhydrous dichloro-
ꢀ
ꢀ
proceed for an additional 3 h at 0 C and then for 1 day at room temperature.
The precipitate was filtered off and the organic phase was washed with 5%
HCl, 5% NaHCO , water, dried over Na SO and finally evaporated to dry-
3
2
4
ness. The crude residue was purified by liquid chromatography on silica gel
with ethyl acetate=hexane (2=3 v=v) as eluent. 5.97 g (36% yield) of pure 1
as a colorless viscous liquid was obtained.
1
H-NMR (CDCl ): 1.2 (3H, CH ), 1.6–1.8 (2H, CH cyclopropane),
3
3
2
2
.3–2.7 (3H, CH cyclopropane þ CH CF ), 4.2 (2H, COOCH ), 4.4
2
2
2
(
2H, COOCH CH CF ), 5.1–5.5 ppm (3H, CH =CH).
2
2 2 2

New Fluorinated Copoly (Vinylcyclopropane)s
415=[1457]
FT-IR (liquid film): 3092 and 2964 (mC-H vinyl and aliphatic), 1730 (mC-
ꢁ1
O), 1640 (mC=C vinyl), 1372 (dC-H cyclopropane), 662 cm (xCF ).
2
(C H F O ) (530.27): Calcd. C 38.50, H 2.85, F 46.58; Found C 38.40,
17 15 13 4
H 2.95, F 47.0.
Copolymer Pol(1-co-2)d
1.08 g (1.48 mmol) of 1, 0.04 (0.37 mmol) di 2, 8 mg (0.02 mmol) of AIBN in
3.0 ml of anhydrous trifluorotoluene were introduced into a Pyrex vial.
After three freeze-thaw pump cycles the vial was sealed under vacuum,
ꢀ
and the polymerization was let to proceed for 22 h at 65 C. The polymer
was then precipitated into methanol and purified by repeated precipita-
tions from chloroform into methanol (3% yield).
1
H-NMR (CDCl ): 0.8 (12H, CH (2)), 0.9–2.4 (14H, CHCH (1) þ CH
3
3
2
2
3
(
(
(
2)), 2.5 (2H, CH CF ), 3.6 (12H, COOCH (2)), 4.2 (2H, COOCH CH
2 2 3 2
1)), 4.4 ppm (2H, COOCH CH CF (1)). FT-IR (polymer film): 2994–2952
2
2
2
ꢁ1
mC-H aliphatic), 1728 (mC=O), 668 cm (xCF ).
2
Characterizations
1
13 19
NMR ( H, C, F) spectra were recorded with a Varian VXR 300 spec-
trometer. Size exclusion chromatography (SEC) was carried out with a
Jasco PU-1580 liquid chromatograph equipped with four PL gel 5 mm
Mixed-C columns, a Jasco 830-RI refractive index detector and a Perkin
Elmer LC75 UV detector. Polystyrene standards were used for calibration.
Differential scanning calorimetry (DSC) measurements were performed
ꢀ
with a Mettler DSC-30 instrument (10 C=min). The phase transition
temperatures were taken as the maximum temperature in the DSC enthal-
pic peaks. The glass transition temperature (T ) was taken as the half-
g
devitrification temperature.
RESULTS AND DISCUSSION
The fluorinated vinylcyclopropane monomer 1 was synthesized following
the reaction pathway in Figure 1. Trans-1,4-dibromobutene was reacted
with the diethyl malonate sodium salt to give 1,1-diethoxycarbonyl-2-vinyl-
cyclopropane 3. This was selectively hydrolyzed and the corresponding
monocarboxylic acid 4 was esterified with 2-(perfluorodecyl)ethanol to
afford the eventual vinylcyclopropane 1.
ꢀ
Monomer 1 was free-radically copolymerized (AIBN at 65 C) with
methyl methacrylate (2) in trifluorotoluene. Different comonomer feed
mixtures were used, which gave copolymers pol(1-co-2) with varying

4
16=[1458]
G. Galli et al.
FIGURE 1 Reaction scheme for the synthesis of monomer 1.
contents of fluorinated 1 units (Table 1). The copolymer compositions
1
were evaluated by H-NMR by integrating the areas of the resonance sig-
nals of the COOCH groups from 1 at 4.15 and 4.40 ppm relative to that
2
of the COOCH group from 2 at 3.60 ppm. In any copolymer sample the
3
content of units 2 was much greater than in the corresponding feed mix-
tures, because of the higher reactivity of 2 with respect to 1. No olefin sig-
nal (5.30 ppm) or allyl signal (2.50 ppm) from 1,5-ring-opened units (see
[2]) from 1 was ever detected, but a broad signal around 1.6–2.7 ppm
due to other reactions exhausting the olefin double bond [5].
The radical copolymerization of vinylcyclopropanes (Fig. 2, X ¼ Cl,
COOEt) is supposed to proceed via opening of the vinylcyclopropane ring
followed by intermolecular cyclization with 2 [5]. According to this,
addition of initiator radical to the vinyl double bond on the cyclopropane
ring is followed by 1,5-ring-opening to yield a homoallyl radical that further
attacks at 2 to give a 2-terminated radical. Intramolecular cyclization of this
radical proceeds by two possible pathways, that is leading to six-membered
(route [A]) or five-membered (route [B]) alicyclic units. The occurrence
of the former ring structure seems to be preferred [5,6], even though
formation of the latter cannot be definitely ruled out. This radical cyclo-
polymerization is rather unusual in that it involves both ring-opening and
ring-closing processes.
TABLE 1 Physico-chemical Characteristics of Copolymers Pol(1-co-2)
1 (mol%)
in the feed
1(mol%)
in the cop.
a
a
Copolymer
Yield (%)
M
n
(g=mol)
w n
M =M
pol(1-co-2)a
pol(1-co-2)b
pol(1-co-2)c
pol(1-co-2)d
20
40
60
80
3
2
5
3
ꢂ5
10
15
20
20000
18000
nd
2.12
1.98
nd
nd
nd
a
By SEC in tetrahydrofuran with PS standards.

New Fluorinated Copoly (Vinylcyclopropane)s
417=[1459]
FIGURE 2 Copolymerization scheme of vinylcyclopropanes with 2.
In our experiments, the copolymerization yields were deliberately kept
low (< ꢂ5%) in order to estimate the reactivity ratios r of the two como-
nomers. The values we evaluated by the Kelen-T u¨ d oꢀ s method (r ¼ 0.5,
1
r ¼ 12.1) confirmed the greater reactivity of 2 relative to 1. In fact,
2
1
2
-terminated radicals would add to 2 two times faster than to 1, and
-terminated radicals would add to 2 twelve times faster than to 1.
Therefore, a simplified structure of copolymers pol(1-co-2) consists of
isolated six-membered (mixed 1–2) units flanked by sequences of 2 units,
e.g. three units 2 in pol(1-co-2)d (Fig. 3).
The copolymers exhibited thermotropic mesophases above T (Table 2).
g
ꢀ
In any case the mesophase was highly stable (T ꢃ 183 C) and persistent
i
ꢀ
over a broad temperature range (T – T ꢃ 79 C). Previous studies by
i
g
X-ray diffraction on homopolymer pol(1)have confirmed the occurrence
of two mesophases, namely SmB and SmA [4]. By contrast, there was
d
d
one smetic mesophase in copolymers pol(1-co-2) (Fig. 4). Thus, incorpor-
ation of limited proportions (down to as low as 5–10 mol%) of fluorinated
FIGURE 3 Schematic structure of copolymers pol(1-co-2).

4
18=[1460]
G. Galli et al.
TABLE 2 Liquid Crystal Properties of Copolymers Pol(1-co-2)
ꢀ
ꢀ
Copolymer
1 (mol%) in the cop.
T
g
( C)
T
i
( C)
i
DH (J=g)
pol(2)
0
10
105
–
187
–
pol(1-co-2)b
pol(1-co-2)c
pol(1-co-2)d
pol(1)
110
105
66
1.3
1.1
0.6
6.7
15
20
184
183
187
a
a
100
78
a
ꢀ
Additional mesophase transition at 118 C (DH ¼ 0.7 J=g).
units 1 in combination with non-mesogenic units 2 in the copolymers did
not disrupt their mesogenic character, even though it was depressed. A
detailed investigation of the mesophase structures by X-ray diffraction will
be given elsewhere.
The formation of thermotropic mesophase(s) in the present polymers
simply incorporating 2-(perfluorodecyl)ethyl chains is somewhat surpris-
ing. In fact it is very rarely observed and has been previously reported in
a structurally related polyacrylate only [7]. The mesogenic capability of
fluorocarbon chains is usually attributed to the rigid-rodlike character of
their helical conformation in combination with their immiscibility with
other molecular constituents [8].
We also explain the onset of liquid crystallinity in pol(1-co-2) by the
strong microphase separation of the fluorocarbon side groups from the
hydrocarbon polymer backbone.
FIGURE 4 DSC curves of pol1 (—) and pol(1-co-2)d (—).

New Fluorinated Copoly (Vinylcyclopropane)s
419=[1461]
It is noteworthy that the T of the copolymers was not affected by
i
the chemical composition and remained almost equal to that of pol(1)
(Table 2). Normally, T in copolymers is found to decrease gradually with
i
increasing content of non-mesogenic units [9], and the variation of chemical
composition is in fact a common means of tuning the mesophase behavior
of copolymers. The apparent insensitivity of the T of pol(1-co-2) to
i
composition may be due to their chemical constitution of two incompatible
hydrocarbon-fluorocarbon components. Their phase separation into distinct
sub-layers would confine the perfluorinated tails in an ordered array, thus
amplifying their mesogenic character.
Liquid crystalline polymers with a purely alicyclic main chain and pen-
dant side groups are rather unusual [10], and the influence of the various
stereochemical features of the polymer backbone on their mesophase beha-
vior is completely unknown.
CONCLUSIONS
We have prepared new copoly(vinylcyclopropane)s with unusual macromo-
lecular structure, which form mesophases despite the high dilution of the
fluorinated side groups along the polymer main chain. Microphase separ-
ation at the molecular level appears to be a strong driving force even
in polymers that do not contain typical mesogenic units of liquid crystal
molecules.
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[
1] Moszner, N., Zeuner, F., Volkel, T., & Rheinberger, V. (1999). Macromol. Chem. Phys.,
00, 2173.
2
[2] Sanda, F., Takata, T., & Endo, T. (1993). Macromolecules, 26, 1818.
[3] Andruzzi, L., D’Apollo, F., Galli, G., & Gallot, B. (2001). Macromolecules, 34, 7707.
[4] Galli, G., Gasperetti, S., Bertolucci, M., Gallot, B., & Chiellini, E. (2002). Macromol.
Rapid Commun., in press.
[
[
[
5] Sanda, F., Takata, T., & Endo, T. (1994). Macromolecules 27, 3982.
6] Takahashi, T. (1970). J. Polym. Sci., Part A-1, 8, 739.
7] Volkov, V. V., Plat e´ , N. A., Takahara, A., Kajiyama, T., Amaya, N., & Murata, Y. (1992).
Polymer, 33, 1316.
8] Wang, J. & Ober, C. K. (1999). Liq. Cryst., 26, 637.
[
[
9] Galli, G. (2001). in ‘‘Advanced Functional Molecules and Polymers’’, Nalwa H. S. (Ed.),
Overseas Publishers Association: Singapore, Vol. I, 271.
10] Buxton, I. P., Hall, A. W., & Lacey, D. (1997). Macromol. Chem. Phys., 198, 2307.
[