Induction of smectic layering in nematic liquid crystals using immiscible components. 1. Laterally attached side-chain liquid crystalline poly(norbornene)s and their low molar mass analogs with hydrocarbon/fluorocarbon substituents

Article abstract of DOI:10.1021/ja963687p

{5-[[[2',5'-Bis[(4''-(n-(perfluoroalkyl)alkoxy)benzoyl)oxy]benzyl]oxy ]carbonyl]bicyclo[2.2.1]hept-2-ene]s were polymerized by ring-opening metathesis polymerization in THF at 40°C using Mo(CHCMe₂Ph)(N-2,6(i)Pr₂Ph)(O(t)Bu)₂

Full text of DOI:10.1021/ja963687p

J. Am. Chem. Soc. 1997, 119, 3027-3037
3027
Induction of Smectic Layering in Nematic Liquid Crystals
Using Immiscible Components. 1. Laterally Attached
Side-Chain Liquid Crystalline Poly(norbornene)s and Their Low
Molar Mass Analogs with Hydrocarbon/Fluorocarbon
Substituents
Stephen V. Arehart and Coleen Pugh*
Contribution from the Department of Chemistry, Macromolecular Science and Engineering
Center, UniVersity of Michigan, Ann Arbor, Michigan 48109-1055
ReceiVed October 23, 1996X
Abstract: {5-[[[2′,5′-Bis[(4′′-(n-(perfluoroalkyl)alkoxy)benzoyl)oxy]benzyl]oxy]carbonyl]bicyclo[2.2.1]hept-2-
ene}s were polymerized by ring-opening metathesis polymerization in THF at 40 °C using Mo(CHCMe2Ph)(N-2,6-
iPr2Ph)(OtBu)2 as the initiator. 2,5-Bis[(4′-(n-(perfluoroalkyl)alkoxy)benzoyl)oxy]toluenes mimic both the phases
formed by the poly{5-[[[2′,5′-bis[(4′′-(n-(perfluoroalkyl)alkoxy)benzoyl)oxy]benzyl]oxy]carbonyl]bicyclo[2.2.1]hept-
2-ene}s and the general temperatures of their transitions, and are therefore excellent models of the polymers. In
contrast to their hydrocarbon analogs which exhibit only nematic mesophases, all of the polymers and their low
molar mass model compounds exhibit smectic C and smectic A mesophases. In both cases, all of the transition
temperatures decrease with increasing hydrocarbon length and increase with increasing fluorocarbon length.
Introduction
attached mesogen is much larger than the repeat unit along the
polymer backbone, it generally forces the backbone into an
extended helical conformation with the mesogens jacketing the
backbone.7 The centers of mass of the mesogens are therefore
staggered, which corresponds to a nematic mesophase.
Although the structure-property relationships1,2 of low molar
mass liquid crystals (LMMLCs) have been fairly well estab-
lished since their discovery in 1888,3 elucidation of the
elementary structural principles of side-chain liquid crystalline
polymers (SCLCPs)4 has only recently begun.5 In spite of the
maturity of the former field and the technological importance
of both areas in electrooptical displays,6 chemical concepts have
not been developed for converting the type of mesophases
exhibited by LMMLCs, much less SCLCPs, for a given
chemical structure. We are therefore establishing chemical tools
for transforming the mesophases exhibited by both LMMLCs
and SCLCPs. The most significant transformation will be from
nematic to smectic mesophases, and vice versa, although one
can envision developing chemical concepts for converting
positionally disordered mesophases to positionally ordered
phases (and vice versa), and from orthogonal to tilted meso-
phases (and vice versa).
This paper will demonstrate that smectic layering can be
induced in both SCLCPs with laterally attached mesogens (Table
1)9 and the corresponding low molar mass analogs (Table 2)1,10
by terminating the mesogen’s hydrocarbon substituents with
immiscible fluorocarbon segments. This is based on the
observation that saturated molecules containing hydrocarbon and
fluorocarbon segments of at least six to eight carbons organize
into layers due to the incompatibility of the two segments;11-15
the lamellar structure of microphase separated H(CH2)20(CF2)12F
has been observed directly using transmission electron micros-
copy.11 In addition, diblock H(CH2)n(CF2)mF and triblock
F(CF2)m(CH2)n(CF2)mF molecules with 4 e n e 14 and m g 6
melt into a smectic B12 or smectic G13 mesophase before
disordering completely into the isotropic state,11-15 as do the
corresponding polymers.16 Similar small molecules17 and
polymers18 in which the immiscible segments are connected
through ester groups also form smectic mesophases or lamellar
Induction of smectic mesophases in SCLCPs with laterally
attached mesogens is particularly challenging; attaching the
mesogen laterally to a polymer backbone is commonly believed
to strongly favor formation of a nematic mesophase,7 or even
prevent ordering into smectic layers.8 Since the laterally
(7) (a) Hessel, F.; Finkelmann, H. Polym. Bull. 1985, 14, 375. (b) Hessel,
F.; Herr, R.-P.; Finkelmann, H. Makromol. Chem. 1987, 188, 1597. (c)
Keller, P.; Hardouin, F.; Mauzac, M.; Achard, M. F. Mol. Cryst. Liq. Cryst.
1988, 155, 171. (d) Hardouin, F.; Mery, S.; Achard, M. F.; Mauzac, M.;
Davidson, P.; Keller, P. Liq. Cryst. 1990, 8, 565.
(8) Hessel, F.; Finkelmann, H. Makromol. Chem. 1988, 189, 2275.
(9) Pugh. C.; Shrock, R. R. Macromolecules 1992, 25, 6593.
(10) Pugh, C.; Kiste, A. L. Unpublished results.
* To whom correspondence should be addressed.
X Abstract published in AdVance ACS Abstracts, March 15, 1997.
(1) Demus D.; Zaschke H. Flussige Kristalle in Tabellen II; VEB
Deutscher Verlag: Leipzig, 1984.
(2) Gray, G. W.; Goodby, J. W. Smectic Liquid Crystals. Textures and
Structures; Leonard Hall: Glasgow, 1984.
(3) Reinitzer, F. Monatsch Chem. 1888, 9, 421.
(11) Ho¨pken, J.; Mo¨ller, M. Macromolecules 1992, 25, 2482.
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Liq. Cryst. 1989, 168, 63. (b) Viney, C.; Twieg, R. J.; Russell, T. P.;
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(4) First SCLCP reported: Bacceredda, M.; Magagnini, P. L.; Pizzirani,
G.; Giusti, P. J. Polym. Sci., Polym. Lett. Ed. 1971, 9, 303.
(5) (a) Percec, V.; Pugh, C. In Side Chain Liquid Crystal Polymers;
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S0002-7863(96)03687-6 CCC: $14.00 © 1997 American Chemical Society

3028 J. Am. Chem. Soc., Vol. 119, No. 13, 1997
Arehart and Pugh
Table 1. Molecular Weight and Phase Transitions of
Polynorbornenes with Laterally Attached
Amphiphilic hydrocarbon/fluorocarbon substituents have also
been incorporated into liquid crystals and SCLCPs based on
rigid-rod mesogens, either within the same substituent(s)24-29
or with an extended perfluoro-n-alkyl substituent at one terminus
of the mesogen and an n-alkyl chain at the other.26-31 Although
all of these compounds exhibit smectic mesophases (and some
are inherently ferroelectric25,26), their hydrocarbon analogs
generally also exhibit smectic mesophases and therefore have
not contributed to developing a concept for switching the type
of mesophase formed.25-28,30 Nevertheless, a few researchers
have noticed that incorporation of amphiphilic hydrocarbon/
fluorocarbon substituents into calamitic mesogens “enhances”
the formation of smectic mesophases and “suppresses” formation
of nematic mesophases in systems whose hydrocarbon analogs
display smectic-nematic phase sequences,24,29,31 or only a
nematic mesophase.29 Termination of hydrocarbon substituents
with fluorocarbon units also stabilizes columnar mesophases.32
We have chosen the polymers shown in Table 1 as the most
challenging system possible for inducing smectic layering using
immiscible components; both the molecular architecture7-9,33
and the use of only a short spacer5,33 disfavor smectic meso-
morphism. In addition, the polynorbornenes shown in Table 1
were prepared by a controlled ring-opening metathesis polym-
erization (ROMP)34 and are the most well-defined SCLCPs
prepared to date with laterally attached mesogens; both the
molecular weight dependence of the phase transitions and the
effect of the length of the n-alkoxy substituents have been
determined.9 That is, the glass and nematic-isotropic transition
temperatures become independent of molecular weight at
approximately 25 repeat units; therefore, the phase behavior will
be representative of a polymer if the chains contain at least 25
2,5-Bis[(4′-n-alkoxybenzoyl)oxy]benzyl Mesogensa
n
DPn
5.1
8.2
14
39
45
100
32
44
Mn × 10-3
pdi
phase transitionsb (°C)
1
1
1
1
1
1
2
3
4
5
6
2.7
4.3
7.2
21
24
53
18
26
14
29
1.16
1.20
1.12
1.13
1.13
1.16
1.19
1.24
1.17
1.18
1.24
g 79 n 131 i
g 90 n 146 i
g 91 n 155 i
g 97 n 163 i
g 98 n 164 i
g 97 n 163 i
g 92 n 172 i
g 83 n 140 i
g 73 n 138 i
g 60 n 123 i
g 56 n 126 i
23
45
66
44
a Number average degree of polymerization (DPn), number average
molecular weight (Mn), and polydispersity (pdi ) Mw/Mn) determined
by gel permeation chromatography (GPC) relative to polystyrene,
from ref 9. b Observed on heating; g ) glass, n ) nematic, i ) iso-
tropic.
Table 2. Thermotropic Behavior of
1,4-Bis[(4′-n-alkoxybenzoyl)oxy]toluenesa
(23) Ho¨pken, J.; Mo¨ller, M.; Lee, M.; Percec, V. Makromol. Chem. 1992,
193, 275.
(24) Liu, H.; Nohira, H. Liq. Cryst. 1996, 20, 581.
n
phase transitionsb (°C)
(25) (a) Tournilhac, F. G.; Bosio, L; Nicoud, J. F.; Simon, J. Chem. Phys.
Lett. 1988, 145, 452. (b) Chiang, Y. H.; Ames, A. E.; Gaudiana, R. A.;
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1
2
3
4
5
6
7
8
k 166 n 252 i
k 187 n 248 i
k 138 n 209 i
k 115 n 206 i
k 90 n 178 i
k 88 n 173 i
k 86 n 161 i
k 40 n 157 i
a n ) 1-6 from ref 1; n ) 7, 8 from ref 10. b Observed on heating;
k ) crystalline, n ) nematic, i ) isotropic.
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crystals, as do aliphatic polyesters,19 poly(meth)acrylates,20 poly-
(R-fluoroacrylate)s,21 poly(R-fluoroalkoxy)acrylates,22 and poly-
(vinyl ether)s23 with linear fluorocarbon side chains.
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(31) (a) Janulis, E. P., Jr.; Novack, J. C.; Papapolymerou, G. A.; Tristani-
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are laterally attached through a decyloxycarboxylate spacer that exhibits a
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(34) Pugh, C. Macromol. Symp. 1994, 77, 325.

Smectic Layering in Nematic Liquid Crystals
J. Am. Chem. Soc., Vol. 119, No. 13, 1997 3029
Scheme 1. Ring-Opening Metathesis Polymerization of
5-{[[2′,5′-Bis[(4′′-(n-(perfluoroalkyl)alkoxy)benzoyl)oxy]-
benzyl]oxy]carbonyl}bicyclo[2.2.1]hept-2-enes
Scheme 2. Synthesis of the 2,5-Bis[(4′-(n-(perfluoroalkyl)-
alkoxy)benzoyl)oxy]toluene Model Compounds and
5-{[[2′,5′-Bis[(4′′-(n-(perfluoroalkyl)alkoxy)benzoyl)oxy]-
benzyl]oxy]carbonyl}bicyclo[2.2.1]hept-2-enes
repeat units. Both transition temperatures decrease with in-
creasing n-alkoxy substituent length; isotropization decreases
with odd-even alternation, such that the even-membered
substituents have broader and more stable mesophases. Since
the polymerizations are controlled, the polynorbornenes shown
in Scheme 1 can be prepared by ROMP without varying any
structural feature(s) in addition to the incorporation of im-
miscible hydrocarbon/fluorocarbon components.
Results and Discussion
Synthesis and Thermotropic Behavior of Model Com-
pounds. Model compounds which take into account only the
mesogen and spacer of a given SCLCP mimic the latter’s
thermotropic behavior well.35,36 The 2,5-bis{[4′-(n-(perfluoro-
alkyl)alkoxy)benzoyl]oxy}toluenes should therefore be ap-
propriate model compounds for the poly(norbornene)s shown
in Scheme 1; they are based on identical mesogens with identi-
cal n-(perfluoroalkyl)alkoxy substituents and are further sub-
stituted with a methyl group to mimic the benzylic spacer of
the polymers.
Table 3. Thermal Transitions and Thermodynamic Parameters of
2,5-Bis[(4′-(n-(perfluoroalkyl)alkoxy)benzoyl)oxy]toluenesa
phase transitions, °C (∆H, kJ/mol)
n
m
4
5
6
8
6
6
6
6
k 110 (44.1)
k 101 (23.9)
k 102 (48.9)
k 104 (50.4)
sC 205 (0.46)
sC 197 (0.43)
sC 200 (0.46)
sC 190 (0.60)
sA 214 (8.76)
sA 208 (10.9)
sA 204 (10.4)
sA 193 (9.96)
i
i
i
i
Due to the insolubility of the corresponding 4-[n-(perfluo-
roalkyl)alkoxy]benzoic acids, the 2,5-bis{[4′-(n-(perfluoroalkyl)-
alkoxy)benzoyl]oxy}toluene model compounds were prepared
by constructing the mesogen first and then introducing the
fluorocarbon substituents. As shown in Scheme 2, ethyl
4-hydroxybenzoate was etherified with an n-bromo olefin,
followed by saponification of the resulting ethyl 4-(n-alkenyl-
oxy)benzoates. The mesogen was then generated by coupling
the 4-(n-alkenyloxy)benzoic acids with methyl hydroquinone
in the presence of dicyclohexylcarbodiimide as the dehydrating
agent. Perfluorinated segments were introduced by free radical
addition of a perfluoroalkyl iodide across the double bonds of
the n-alkenyloxy substituents, followed by reduction of the
iodides using tributyltin hydride under free radical conditions.
The equilibrium thermal transitions obtained on heating the
12 model compounds are summarized in Table 3. The data
obtained on heating are from samples which are at thermody-
namic equilibrium and represent samples crystallized from
solution and/or from the melt after short annealing times. That
is, crystallization from the melt to the most thermodynamically
4
5
6
8
7
7
7
7
k 124 (45.1)
k 119 (35.7)
k 130 (45.5)
k 120 (51.5)
sC 215 (0.69)
sC 208 (0.89)
sC 206 (0.63)
sC 199 (0.75)
sA 222 (6.67)
sA 216 (8.38)
sA 212 (6.78)
sA 200 (7.70)
i
i
i
i
4
5
6
8
8
8
8
8
k 132 (46.8)
k 122 (32.6)
k 130 (58.5)
k 124 (55.5)
sC 218 (1.10)
sC 214 (1.30)
sC 211 (1.45)
sC 201 (1.59)
sA 226 (8.66)
sA 221 (8.12)
sA 217 (8.88)
sA 205 (9.20)
i
i
i
i
a Observed on heating; k ) crystalline, sC ) smectic C, sA ) smectic
A, i ) isotropic.
stable phase is slower than the time scale of the differential
scanning calorimetry (DSC) experiment and is therefore either
incomplete, or the sample crystallizes to a less stable crystalline
phase if sufficient annealing time is not allowed. Fluorocar-
bons37,38 and molecules containing hydrocarbon-fluorocar-
bon11,13,14,39 components often crystallize into multiple phases
and/or undergo solid-solid phase transitions, with the solution-
(37) Schwickert, H.; Strobl, G.; Kimig, M. J. Chem. Phys. 1991, 95,
2800.
(35) (a) Pugh, C.; Arehart, S.; Liu, H.; Narayanan, R. J. Macromol.
Sci.sPure Appl. Chem. 1994, A31, 1591. (b) Pugh, C.; Liu, H.; Arehart, S.
V.; Narayanan, R. Macromol. Symp. 1995, 98, 293.
(38) Dee, G. T.; Sauer, B. B.; Haley, B. J. Macromolecules 1994, 27,
6106.
(39) (a) Vilalta, P. M.; Weiss, R. G. Liq. Cryst. 1992, 12, 531. (b)
Guittard, F.; Sixou, P.; Cambon, A. Liq. Cryst. 1995, 19, 667.
(36) Pugh, C.; Kiste, A. L. Prog. Polym. Sci., in press.

3030 J. Am. Chem. Soc., Vol. 119, No. 13, 1997
Arehart and Pugh
relatively narrow and decreases as the length of the hydrocarbon
segment increases.
Figure 2a plots the temperature of isotropization as a function
of the number of methylenic units (n) in the hydrocarbon portion
of the substituents for fluorocarbon lengths m ) 6-8, as well
as for their hydrocarbon analogs (m ) 0); these trends are also
representative of the melting and sC-sA transitions. In general,
all of the transition temperatures decrease with increasing
hydrocarbon length and increase with increasing fluorocarbon
length. That is, the transition temperatures decrease toward the
melting point of polyethylene (HDPE mp 138 °C)43 as the
molecule becomes more like polyethylene and increase toward
the melting point of Teflon (332 °C)43 as it becomes more like
poly(tetrafluoroethylene). Therefore, there is a general increase
in the transition temperatures as the ratio (m/n) of the lengths
of fluorocarbon to aliphatic hydrocarbon increases (Figure 2b).
Table 3 also lists the enthalpy changes associated with the
phase transitions of the model compounds. In general, the
change in enthalpy of crystalline melting is essentially constant
as a function of the fluorocarbon length for a given hydrocarbon,
but appears to increase with an odd-even alternation as the
hydrocarbon length increases. In contrast, the change in
enthalpy of the sC-sA transition is invariant to changes in the
hydrocarbon length for a given fluorocarbon, but increases as
the length of the fluorocarbon increases. The change in enthalpy
of isotropization is independent of both hydrocarbon and
fluorocarbon length. These trends indicate that the aliphatic
hydrocarbon segments disorder primarily at the melting transi-
tion, whereas the fluorocarbon segments disorder primarily at
the sC-sA transition.
Synthesis and Thermotropic Behavior of Monomers. As
shown in Scheme 2, the fluorinated monomers were synthesized
directly from the model compounds by free radical bromination
at the benzylic position, followed by phase transfer catalyzed
esterification with potassium bicyclo[2.2.1]hept-2-ene-5-car-
boxylate. Table 4 summarizes their equilibrium thermotropic
behavior, which is generally observed on the first heating scan
from solution-crystallized samples, and on subsequent heating
scans after sufficient annealing times. Compared to the model
compounds (Table 3), all of the monomers undergo phase
transitions at lower temperatures and with a lower change in
enthalpy, albeit with the same general trends. Both the
decreased temperatures and decreased changes in enthalpy are
due to destabilization of all of the phases by the bulky lateral
norbornene substituent. In most cases, the sC-sA transition
occurs at the same or a slightly lower temperature as that of
crystalline melting; the sA mesophase is therefore monotropic
and observed only on cooling.44 However, the sA mesophase
is enantiotropic in all cases. In contrast, the corresponding
hydrocarbon monomers exhibit only nematic mesophases, which
are generally monotropic.9
Figure 1. Polarized optical micrographs (200×) observed on cooling
2,5-bis[(4′-(n-(perfluorohexyl)butoxy)benzoyl)oxy]toluene from the
isotropic melt: (a, top) 211 °C, sA focal-conic fan texture; (b, bottom)
200 °C, schlieren sC texture obtained by cooling from a homeotropically
aligned sA mesophase.
crystallized phase being more stable and more ordered than
phases that crystallize rapidly from the melt.
As confirmed by the representative polarized optical micro-
graphs shown in Figure 1a,b, all of the model compounds exhibit
sA and sC mesophases, respectively. However, the focal conic
fan texture shown in Figure 1a is only observed if the glass
slides are pretreated with a hydrocarbon film (see the Experi-
mental Section). If the glass slides are not pretreated, small
baˆtonnets initially form upon cooling from the isotropic melt,
but the texture rapidly becomes completely homeotropic40 with
further annealing. This tendency to align homeotropically is
apparently due to the high affinity of fluorine for silicon and
has been noted previously in crystals37 and liquid crystals26,41
with terminal fluorocarbon groups. Both natural textures
(homeotropic and focal conic fan)2,42 of the sA mesophase are
therefore observed. The schlieren texture shown in Figure 1b
is consistent with a sC mesophase.2,42
Comparison of Tables 2 and 3 demonstrates that terminating
the n-alkoxy substituents with immiscible fluorocarbon segments
is extremely effective at inducing smectic layering in nematic
LMMLCs. Whereas the 2,5-bis[(4′-n-alkoxybenzoyl)oxy]tolu-
enes form only nematic mesophases, the 2,5-bis{[4′-(n-
(perfluoroalkyl)alkoxy)benzoyl]oxy}toluenes exhibit a sC-sA
phase sequence instead. The temperature range of the sC
mesophase is quite broad, whereas that of the sA mesophase is
Synthesis and Thermotropic Behavior of Polymers. The
5-{[[2′,5′-bis[(4′′-(n-(perfluoroalkyl)alkoxy)benzoyl)oxy]benzyl]-
oxy]carbonyl}bicyclo[2.2.1]hept-2-enes were polymerized by
ROMP using Mo(CHCMe2Ph)(N-2,6-iPr2Ph)(OtBu)2 as the
initiator (Scheme 1). Polymerization of these amphiphilic
monomers was challenging due to solubility problems similar
to those encountered in the synthesis of the model compounds.
Since 1,3-xylene hexafluoride (276% swelling), diethyl ether
(133%), chloroform (48%), and toluene (23%) swell vulcanized
(40) A homeotropic texture appears black between cross polarizers
because the long axis of the mesogens are oriented parallel to the direction
of light.
(41) Blinov, L. M. Electro-optical and Magneto-optical Properties of
Liquid Crystals; Wiley: New York, 1983.
(42) Demus, D.; Richter, L. Textures of Liquid Crystals; Verlag Che-
mie: Weinheim, 1978.
(43) Polymer Handbook, 3rd ed.; Brandrup, J., Immergut, E. H., Eds.;
Wiley-Interscience: New York, 1989.
(44) The transition temperature from the monotropic sC mesophase to
the sA mesophase can be observed by reheating the cooled sample before
it recrystallizes, i.e. immediately after it forms the sC phase upon cooling.

Smectic Layering in Nematic Liquid Crystals
J. Am. Chem. Soc., Vol. 119, No. 13, 1997 3031
Figure 2. Temperatures of isotropization of 2,5-bis[(4′-(n-(perfluoroalkyl)alkoxy)benzoyl)oxy]toluenes as a function of (a) the number of methylenic
units (n) in the hydrocarbon substituents at various fluorocarbon lengths (m methylenic units) and (b) the ratio (m/n) of the lengths of the fluorocarbon
and aliphatic hydrocarbon segments; (4) m ) 0, (O) m ) 6, (]) m ) 7, (0) m ) 8.
Table 4. Thermal Transitions and Thermodynamic Parameters of
5-{[[2′,5′-Bis[(4′′-(n-(perfluoroalkyl)alkoxy)benzoyl)oxy]benzyl]-
oxy]carbonyl}bicyclo[2.2.1]hept-2-enesa
Polymerizations of monomers containing perfluorohexyl
substituents remained homogeneous in THF at 40 °C, resulting
in polymers which were sufficiently well-defined for thermal
analysis. Polymerizations of monomers containing perfluoro-
heptyl substituents also remained homogeneous in THF at 40
°C. However, these polymers were contaminated with trace
amounts of oligomers which were removed before analyzing
their thermotropic behavior. In contrast, polymerizations of
monomers containing perfluorooctyl segments became turbid
after 30-45 min, resulting in bimodal molecular weight
distributions. These polymers were therefore also purified by
fractional precipitation to remove lower molecular weight
oligomers, and in one case (n ) 6, m ) 8), to remove a trace
amount of high molecular weight polymer.
phase transitions, °C (∆H, kJ/mol)
n
m
4
5
6
8
6
6
6
6
k 83 (23.6)
k 49 (15.5)
k 78 (18.4)
k 67 (21.0)
[sC 73 (0.077)]
sA 163 (5.42)
sA 156 (6.06)
sA 154 (5.06)
sA 146 (5.65)
i
i
i
i
[sC 60 (0.076)]
[sC 51 (0.067)]
4
5
6
8
7
7
7
7
k 89 (23.8)
k 69 (12.3)
k 89 (34.8)
k 43 (39.6)
[sC 85 (0.077)]
[sC 66 (0.51)]
[sC 64 (0.059)]
sA 180 (6.01)
sA 178 (5.78)
sA 164 (5.89)
sA 157 (4.60)
i
i
i
i
4
5
6
8
8
8
8
8
k 83 (19.2)
k 76 (24.3)
k 89 (26.1)
k 89 (49.3)
[sC 85b]
[sC 78 (0.065)]
[sC 90 (0.055)]
[sC 88 (0.11)]
sA 188 (6.22)
sA 189 (6.20)
sA 184 (6.15)
sA 170 (5.77)
i
i
i
i
Table 6 summarizes the final molecular weights and molec-
ular weight distributions of the polymers used for thermal
analysis. Although all of the polymerizations were performed
with [M]0/[I]0 ≈ 50 in order for the thermotropic behavior to
be independent of molecular weight (DPn g 25), the final GPC-
determined molecular weights relative to polystyrene were
generally lower (DPn ) 8-52). Nevertheless, these polymers
enabled us to test the concept of inducing smectic layering in
SCLCPs with laterally attached mesogens using immiscible
components. In addition, the molecular weight distributions of
the final polymers are monomodal and somewhat narrow.
a Observed on heating; k ) crystalline, sC ) smectic C, sA ) smectic
A, i ) isotropic; [monotropic]. b Τransition detected only by polarized
optical microscopy.
poly(1,1-dihydroperfluoroacrylate)45 and are therefore potentially
good solvents for other polymers containing hydrocarbon-
fluorocarbon components, similar solvents were used in pre-
liminary polymerizations in order to optimize the polymerization
conditions. However, THF was used instead of diethyl ether,
and methylene chloride was used instead of chloroform due to
chloroform’s acidic proton.
Comparison of the data in Tables 1 and 7 demonstrates that
terminating the n-alkoxy substituents with immiscible fluoro-
carbon segments is also very effective at inducing smectic
layering in polynorbornenes with laterally attached mesogens.
The representative polarized optical micrographs shown in
Figure 3a,b confirm that all of the SCLCPs exhibit sA and sC
mesophases, respectively. Due to the higher viscosity of the
polymers, sA baˆtonnets (Figure 3a) are readily observed on
cooling from the isotropic melt without treating the glass slides
with a hydrocarbon film, although the texture becomes homeo-
tropic with further annealing. However, the polynorbornene
backbone is unstable at the high temperatures above isotropiza-
tion, and identifiable schlieren textures of the sC mesophase were
therefore best developed by annealing briefly (5-10 min) at
190 °C on the first heating scan. Therefore, the sC mesophase
is readily observed by polarized optical microscopy (Figure 3b),
although it is not detected in most of the polymers by DSC.
As summarized in Table 5, oligomers precipitate out of
solution during the room temperature polymerizations in THF,
methylene chloride, and toluene. Although the molecular weight
distributions appear to be narrow in some cases, all are
multimodal. Nevertheless, these ill-defined oligomers were
essential in determining the lowest temperature at which such
polymers dissolve in various solvents, and therefore in deter-
mining optimum polymerization conditions. As shown in Table
5, preliminary polymerizations in 1,3-bis(trifluoromethyl)-
benzene and THF remained homogeneous at 40 °C. Although
the polydispersity (pdi ) Mw/Mn) broadens to 1.3-1.5 by the
higher temperature, the molecular weight distributions are
monomodal. In addition, the molecular weight of the polymer
prepared in 1,3-bis(trifluoromethyl)benzene appears to match
the theoretical value determined by the monomer to initiator
ratio ([M]0/[I]0) better than that prepared in THF. However,
subsequent polymerizations in 1,3-bis(trifluoromethyl)benzene
were inconsistent. In contrast, the THF polymerizations are
reproducible and all subsequent polymerizations were therefore
performed in THF at 40 °C.
The sC mesophase was also confirmed by preliminary X-ray
scattering of the n ) 5 SCLCPs at room temperature, in which
the sC alignment is frozen in the glassy state. The X-ray patterns
of unoriented samples exhibit a sharp inner ring corresponding
to the lamellar thickness and a diffuse outer ring, which
(45) Bovey, F. A.; Abere, J. F.; Rathmann, G. B.; Sandberg, C. L. J.
Polym. Sci. 1955, 15, 520.

3032 J. Am. Chem. Soc., Vol. 119, No. 13, 1997
Arehart and Pugh
Table 5. Exploratory Polymerizations of 5-{[[2′,5′-Bis[(4′′-(n-(perfluoroalkyl)alkoxy)benzoyl)oxy]benzyl]oxy]carbonyl}bicyclo-
[2.2.1]hept-2-enes and Characterization of the Resulting Polymersa
GPC
n
m
solvent
THF
CH2Cl2
toluene
1,3-(CF3)2Ph
THF
temp (°C)
solution
turbid
turbid
precipitates
homogeneous
homogeneous
[M]0/[I]0
theor Mn × 10-4
Mn × 10-4
pdi
6
6
6
4
4
8
7
7
6
6
25
25
25
40
40
32
40
40
50
25
4.8
5.5
5.5
6.2
3.1
0.2
2.9
2.9
5.8
1.3
2.1
1.3
1.3
1.5
1.3
a Number average molecular weight (Mn) and polydispersity (pdi ) Mw/Mn) determined by gel permeation chromatography (GPC) relative to
polystyrene.
Table 6. Polymerization of 5-{[[2′,5′-Bis[(4′′-(n-(perfluoroalkyl)-
alkoxy)benzoyl)oxy]benzyl]oxy]carbonyl}bicyclo[2.2.1]hept-2-enes
and Characterization of the Resulting Polymers in THF at 40 °Ca
GPC
n
m
[M]0/[I]0
yield (%)
Mn × 10-4
DPn
pdi
4
5
6
8
6
6
6
6
50b
44
50
50
90
75
81
77
5.58
4.31
2.59
5.27
52
35
19
39
1.39
1.32
1.39
1.49
4
5
6
8
7
7
7
7
50
50
48
52
69
88
72
54
1.84
2.26
1.97
3.95
14
16
14
27
1.45
1.62
1.28
1.22
4
5
6
8
8
8
8
8
51
49
49
50
59
76
83
77
1.27
1.20
2.13
2.59
9
8
14
17
1.18
1.48
2.06
1.37
a Number average molecular weight (Mn), number average degree
of polymerization (DPn), and polydispersity (pdi ) Mw/Mn) determined
by gel permeation chromatography (GPC) relative to polystyrene.
b Polymerized in 1,3-bis(trifluoromethyl)benzene at 40 °C.
Table 7. Thermal Transitions and Thermodynamic Parameters of
Poly{5-[[[2′,5′-bis[(4′′-(n-(perfluoroalkyl)alkoxy)benzoyl)oxy]-
benzyl]oxy]carbonyl]bicyclo[2.2.1]hept-2-ene}sa
phase transitions, °C (∆H, kJ/mru)
n
m
4
5
6
8
6
6
6
6
g 106
g 96
g 90
g 77
sC 227 (6.97)
sC 228b
sA 234 (4.09)
sA 231 (4.42)
sA 223 (4.36)
sA 216 (4.22)
i
i
i
i
sC 216b
sC 213b
Figure 3. Polarized optical micrographs (200×) observed on cooling
poly{5-[[[2′,5′-bis[(4′′-(n-(perfluorohexyl)butoxy)benzoyl)oxy]benzyl]-
oxy]carbonyl]bicyclo[2.2.1]hept-2-ene} from the isotropic melt: (a) 229
°C, baˆtonnets in homeotropic texture of sA mesophase; (b) 200 °C,
sanded schlieren sC texture obtained by cooling from a homeotropically
aligned sA mesophase.
4
5
6
8
7
7
7
7
g 90
g 96
g 93
g 97
sC 242 (3.21)
sC 239b
sA 251 (0.52)
sA 248 (4.35)
sA 236 (3.56)
sA 232 (3.45)
i
i
i
i
sC 230b
sC 228b
4
5
6
8
8
8
8
8
g 93
g 93
g 98
g 98
sC 251b
sC 258b
sC 250b
sC 231b
sA 264 (3.87)
sA 262 (3.81)
sA 261 (3.78)
sA 234 (0.69)
i
i
i
i
a Observed on heating; g ) glass, sC ) smectic C, sA ) smectic A,
i ) isotropic. b Transition detected only by polarized optical microscopy.
demonstrates that the mesogens are disordered within the layer
planes. As shown by the diffractograms in Figure 4, the m )
6, m ) 7, and m ) 8 polymers have sharp reflections at 43.1,
45.8, and 48.9 Å, respectively, which correspond to tilt angles
of 31.2, 30.8, and 29.0° relative to the layer normal.
Figure 5a plots the temperature of isotropization as a function
of the number of methylenic units (n) in the hydrocarbon portion
of the substituents for fluorocarbon lengths m ) 6-8, as well
as for their hydrocarbon analogs (m ) 0); these trends are also
representative of the melting and sC-sA transitions. As with
the low molar mass model compounds, all of the transition
temperatures decrease with increasing hydrocarbon length as
the polymer becomes more like polyethylene and increase with
increasing fluorocarbon length as it becomes more like poly-
Figure 4. Small angle X-ray scattering curves of poly{5-[[[2′,5′-bis-
[(4′′-(n-(perfluoroalkyl)pentoxy)benzoyl)oxy]benzyl]oxy]carbonyl]bicyclo-
[2.2.1]hept-2-ene}s (n ) 5) recorded in the glassy state at room
temperature.

Smectic Layering in Nematic Liquid Crystals
J. Am. Chem. Soc., Vol. 119, No. 13, 1997 3033
Figure 5. Temperatures of isotropization of poly{5-[[[2′,5′-bis[(4′′-(n-(perfluoroalkyl)alkoxy)benzoyl)oxy]benzyl]oxy]carbonyl]bicyclo[2.2.1]hept-
2-ene}s as a function of (a) the number of methylenic units (n) in the hydrocarbon substituents at various fluorocarbon lengths (m methylenic units)
and (b) the ratio (m/n) of the lengths of the fluorocarbon and aliphatic hydrocarbon segments; (4) m ) 0, (O) m ) 6, (]) m ) 7, (0) m ) 8.
Figure 6. Comparison of the differential scanning calorimetry traces observed on heating (a) 2,5-bis[(4′-(n-(perfluorohexyl)alkoxy)benzoyl)oxy]-
toluenes and (b) poly{5-[[[2′,5′-bis[(4′′-(n-(perfluorohexyl)alkoxy)benzoyl)oxy]benzyl]oxy]carbonyl]bicyclo[2.2.1]hept-2-ene}s at 10 °C/min.46
(tetrafluoroethylene). This results in a general increase in the
transition temperatures as the ratio (m/n) of the lengths of fluoro-
carbon to aliphatic hydrocarbon increases (Figure 5b), although
the increase is more scattered than that of the model compounds.
Figure 6 compares representative DSC traces of the fluori-
nated model compounds and poly(norbornene)s46 and demon-
strates that both the mesophases and the temperatures of the
transitions are nearly identical. The 2,5-bis[(4′-(n-(perfluoro-

3034 J. Am. Chem. Soc., Vol. 119, No. 13, 1997
Arehart and Pugh
pump-thaw cycles immediately before use. All other reagents and
solvents were commercially available and used as received.
Techniques. All polymerizations were performed under a N2
atmosphere in a Vacuum Atmospheres drybox. All other reactions were
performed outside the drybox under a N2 atmosphere. 1H-NMR spectra
(δ, ppm) were recorded on either a Bruker AC-200 (200 MHz) or a
Bruker AM-300 (300 MHz) spectrometer. Unless noted otherwise, all
spectra were recorded in CDCl3 with TMS as an internal standard.
Relative molecular weights were determined by gel permeation
chromatography (GPC) at 35 °C using THF as solvent (1.0 mL/min),
a set of 50, 100, 500, 104 and linear (50-104) Å Styragel 5 µ columns,
a Waters 486 tunable UV/vis detector set at 290 nm, and a Waters 410
differential refractometer.
The thermotropic behavior of all compounds was determined by a
combination of differential scanning calorimetry (DSC) and polarized
optical microscopy. A Perkin-Elmer DSC-7 differential scanning
calorimeter was used to determine the thermal transitions which were
read as the maximum or minimum of the endothermic or exothermic
peaks, respectively. Glass transition temperatures (Tgs) were read as
the middle of the change in heat capacity. All heating and cooling
rates were 10 °C/min. Unless stated otherwise, thermal transitions were
read from reproducible second or later heating scans and first or later
cooling scans, respectively. Both enthalpy changes and transition
temperatures were determined using indium and zinc as calibration
standards. A Leitz Laborlux 12 Pol S polarized optical microscope
(magnification 200×) equipped with a Mettler FP82 hot stage and a
Mettler FP90 central processor was used to observe the thermal
transitions and to analyze the anisotropic textures.2,42 Thin samples
were prepared either by capillary flow or by melting a minimum amount
of compound between a clean glass slide and a cover slip and rubbing
the cover slip with a spatula. When it was necessary to prevent
homeotropic alignment of the smectic A phase, glass slides and
coverslips were pretreated by soaking them in concentrated HNO3 for
1 h, washing sequentially with distilled water, 2-propanol, and hexane,
and then air-drying.
Polymer samples were ground and packed into 1.5 mm quartz
capillary tubes (Charles Supper) and flame-sealed under atmospheric
conditions for X-ray scattering. The filled capillaries were heated at
150 °C for 30 min and then cooled to 30 °C at a nominal rate of 5
°C/min. Room temperature (20 °C) scattering experiments (1000
pulses/run) were performed within 6 h of this procedure using a Ni-
filtered beam of Cu KR radiation from a Rigaku Geigerflex CN4012K1
spectrometer, operating at 1 kW (40 kV, 25 mA). The camera (Anton
Paar, Austria) was equipped with Kratky-type (e.g. infinitely long slit)
collimation. The scattered intensity was recorded using a position-
sensitive detector (M-Broun, Germany, model OED 50), and a baseline
using an empty capillary tube was subtracted from each run. The
channel/angle ratio was 0.0075° 2θ/channel with a resolution of 100-
200 nm.
Synthesis of Monomers and Precursors. Ethyl 4-(n-Alkenyloxy)-
benzoates (n ) 4-6, 8). The ethyl 4-(n-alkenyloxy)benzoates were
prepared in 56-78% yield as in the following example. A solution of
4-bromo-1-butene (20 g, 0.15 mol) in ethanol (170 mL) was added
dropwise over 2 h to a refluxing solution of ethyl 4-hydroxybenzoate
(24 g, 0.14 mol) and potassium carbonate (24 g, 0.17 mol) in ethanol
(150 mL). After 18 h of reflux, the reaction mixture was poured into
ice water (600 mL). This solution was extracted three times with diethyl
ether (500 mL total). The organic layer was washed twice with dilute
aqueous sodium bicarbonate (100 mL each) and once with water. After
the mixture was dried over sodium sulfate, the ether was removed on
a rotary evaporator and the resulting liquid was purified by column
chromatography using silica gel as the stationary phase and methylene
chloride/hexane (1:1) as the eluant. The solvent was removed in vacuo
to yield 18 g (56%) of ethyl 4-(n-but-3′-enyloxy)benzoate as a clear,
slightly yellow oil. 1H-NMR: 1.38 (t, CO2CH2CH3), 2.56 (q, CH2-
CHd), 4.06 (t, OCH2), 4.35 (q, CO2CH2), 5.15 (m, dCH2), 5.81 (m,
dCH), 6.91 (d, 2 aromatic H ortho to OR), 7.98 (d, 2 aromatic H ortho
to CO2R′).
alkyl)alkoxy)benzoyl)oxy]toluenes are therefore excellent mod-
els of the poly{5-[[[2′,5′-bis[(4′′-(n-(perfluoroalkyl)alkoxy)-
benzoyl)oxy]benzyl]oxy]carbonyl]bicyclo[2.2.1]hept-2-ene}s
shown in Scheme 1. In most cases, the melting points of the
model compounds are simply replaced by a glass transition in
the polymers, whereas the clearing temperatures of the polymers
are approximately 20 °C higher than those of the low molar
mass analogs. (The sC-sA transition of the polymers is
generally not detected by DSC.) In contrast, the clearing
temperatures of the nonfluorinated poly{5-{[[2′,5′-bis[(4′′-n-
alkoxybenzoyl)oxy]benzyl]oxy]carbonyl}bicyclo[2.2.1]hept-2-
ene}s (Table 1) are depressed by 50-90 °C relative to those of
the 1,4-bis[(4′-n-alkoxybenzoyl)oxy]toluenes (Table 2). There-
fore, the ordering effect of the fluorocarbon segments is so
strong that the polymer backbone appears to have little influence.
In this case, the thermotropic behavior of the polymers should
also be independent of molecular weight, even at the low degrees
of polymerization sometimes used in this study.
Conclusions
Compounds which normally form only nematic mesophases
can be forced to order into smectic layers by incorporating
immiscible fluorocarbon units into their hydrocarbon chemical
structure. Smectic layering is induced not only in low molar
mass liquid crystals, but also in side-chain liquid crystalline
polymers with laterally attached mesogens. The latter archi-
tecture is the most convincing system possible for demonstrating
this concept since lateral attachment of the mesogens to a
polymer backbone had previously precluded smectic layering.
The segregation effect is so strong that the polymer backbone’s
influence is minimal, with the polymers’ transition temperatures
being similar to those of the model compounds, and only the
melting transition being replaced by a glass transition.
Experimental Section
Materials. Acryloyl chloride (96%), 4-bromo-1-butene (97%),
8-bromo-1-octene (98%), 5-bromo-1-pentene (97%), methyl hydro-
quinone (99%), tetrabutylammonium hydrogen sulfate (TBAH, 99%),
and tributyltin hydride (97%) were used as received from Aldrich.
6-Bromo-1-hexene (95%), heptadecafluoro-1-iodooctane (>98%), and
1-iodotridecafluorohexane (>98%) were used as received from Fluka.
4-(Dimethylamino)pyridine (DMAP, 99%) and ethyl 4-hydroxybenzoate
(99%) were used as received from Lancaster Synthesis. Dicyclohexyl-
carbodiimide (DCC, 99%) was used as received from Janssen.
1-Iodoperfluoroheptane (97%) was used as received from PCR Inc.
(Gainesville, FL). 2,2′-Azobisisobutyronitrile (AIBN, Johnson Mathey,
99%) was recrystallized from methanol below 40 °C. Benzaldehyde
(Aldrich, >99%) was distilled under N2 before use. Cyclopentadiene
was freshly cracked from dicyclopentadiene (Aldrich, 95%). Mo-
(CHCMe2Ph)(N-2,6-iPr2Ph)(OtBu)2 was synthesized by a literature
procedure,47 except that hexane was used throughout the synthesis
instead of pentane. Hexane used in all drybox procedures was washed
with 5% HNO3 in H2SO4, stored over CaCl2, and then distilled from
purple sodium benzophenone ketyl under N2. CH2Cl2 was washed with
10% HNO3 in H2SO4, stored over CaCl2, and then distilled from CaH2
under N2. Reagent grade tetrahydrofuran (THF) and toluene were dried
by distillation from purple sodium benzophenone ketyl under N2. THF
and 1,3-bis(trifluoromethyl)benzene used as polymerization solvents
were vacuum transferred from purple sodium benzophenone ketyl on
a high vacuum line and then vigorously degassed by several freeze-
(46) The DSC traces (enthalpies) of both the model compounds and poly-
(norbornene)s are normalized within each series but not relative to each
other; the polynorbornene traces are magnified relative to the model
compounds.
(47) (a) Schrock, R. R.; Murdzek, J. S.; Bazan, G. C.; Robbins, J.;
DiMare, M.; O’Regan, M. J. Am. Chem. Soc. 1990, 112, 3875. (b) Fox, H.
H.; Yap, K. B.; Robbins, J.; Cai, S.; Schrock, R. R. Inorg. Chem. 1992, 31,
2287.
Ethyl 4-(n-Pent-4′-enyloxy)benzoate. 1H-NMR: 1.38 (t, CO2-
CH2CH3), 1.90 (m, CH2CH2O), 2.25 (q, CH2CHd), 4.02 (t, OCH2),
4.34 (q, CO2CH2), 5.05 (m, dCH2), 5.85 (m, dCH), 6.90 (d, 2 aromatic
H ortho to OR), 7.98 (d, 2 aromatic H ortho to CO2R′).

Smectic Layering in Nematic Liquid Crystals
J. Am. Chem. Soc., Vol. 119, No. 13, 1997 3035
Ethyl 4-(n-Hex-5′-enyloxy)benzoate. 1H-NMR: 1.38 (t, CO2-
CH2CH3), 1.57 (m, CH2), 1.82 (m, CH2CH2O), 2.12 (q, CH2CHd),
4.01 (t, OCH2), 4.34 (q, CO2CH2), 5.00 (m, dCH2), 5.83 (m, dCH),
6.89 (d, 2 aromatic H ortho to OR), 7.98 (d, 2 aromatic H ortho to
CO2R′).
Ethyl 4-(n-Oct-7′-enyloxy)benzoate. 1H-NMR: 1.45 (t, CO2-
CH2CH3), 1.45 (m, [CH2]3, 1.80 (m, CH2CH2O), 2.05 (q, CH2CHd),
4.00 (t, OCH2), 4.34 (q, CO2CH2), 4.97 (m, dCH2), 5.79 (m, dCH),
6.90 (d, 2 aromatic H ortho to OR), 7.97 (d, 2 aromatic H ortho to
CO2R′).
4-(n-Alkenyloxy)benzoic Acids (n ) 4-6, 8). The 4-(n-alkenyl-
oxy)benzoic acids were prepared in 73-97% yield as in the following
example. Ethyl 4-(n-but-3′-enyloxy)benzoate (19 g, 85 mmol) and
sodium hydroxide (7.3 g, 0.18 mol) in ethanol (230 mL) and water
(230 mL) were refluxed for 12 h. After being cooled to room
temperature, the solution was acidified to a pH of 2 with concentrated
HCl. The resulting precipitate was collected and recrystallized from
ethanol (150 mL) to yield 12 g (73%) of 4-(n-but-3′-enyloxy)benzoic
acid as white crystals. 1H-NMR: 2.59 (q, CH2CHd), 4.09 (t, OCH2),
5.16 (m, dCH2), 5.90 (m, CHd), 6.94 (d, 2 aromatic H ortho to OR),
8.05 (d, 2 aromatic H ortho to CO2H).
4-(n-Pent-4′-enyloxy)benzoic Acid. 1H-NMR: 1.92 (m, CH2-
CH2O), 2.24 (q, CH2CHd), 4.04 (t, OCH2), 5.05 (m, dCH2), 5.86 (m,
CHd), 6.93 (d, 2 aromatic H ortho to OR), 8.05 (d, 2 aromatic H ortho
to CO2H).
4-(n-Hex-5′-enyloxy)benzoic Acid. 1H-NMR: 1.60 (m, CH2), 1.81
(m, CH2CH2O), 2.07 (q, CH2CHd), 4.02 (t, OCH2), 4.97 (m, dCH2),
5.82 (m, CHd), 6.94 (d, 2 aromatic H ortho to OR), 8.06 (d, 2 aromatic
H ortho to CO2H).
4-(n-Oct-7′-enyloxy)benzoic Acid. 1H-NMR: 1.45 (m, [CH2]3),
1.81 (m, CH2CH2O), 2.07 (q, CH2CHd), 4.02 (t, OCH2), 4.97 (m,
dCH2), 5.82 (m, dCH), 6.94 (d, 2 aromatic H ortho to OR), 8.05 (d,
2 aromatic H ortho to CO2H).
2,5-Bis[(4′-(n-alkenyloxy)benzoyl)oxy]toluenes (n ) 4-6, 8). The
2,5-bis[(4′-(n-alkenyloxy)benzoyl)oxy]toluenes were synthesized in 84-
90% yield as in the following example. 4-(n-But-3′-enyloxy)benzoic
acid (7.4 g, 39 mmol), methyl hydroquinone (2.4 g, 20 mmol), DMAP
(4.7 g, 38 mmol), p-toluenesulfonic acid (0.73 g, 3.8 mmol), and DCC
(9.5 g, 46 mmol) in dry CH2Cl2 (130 mL) were stirred at room
temperature for 12 h. The solvent was removed using a rotary
evaporator, and the resulting solid was purified by column chroma-
tography using silica gel as the stationary phase and CH2Cl2 as the
eluant. The resulting solid was recrystallized from a mixture of ethanol
(200 mL) and toluene (25 mL) to yield 8.2 g (90%) of 2,5-bis[(4′-(n-
but-3′′-enyloxy)benzoyl)oxy]toluene as white crystals. 1H-NMR: 2.27
(s, ArCH3), 2.61 (m, CH2CHd, 4 H), 4.11 (t, OCH2, 4 H), 5.19 (m,
dCH2, 4 H), 5.92 (m, dCH, 2 H), 6.99 (dd, 4 aromatic H ortho to
OR), 7.14 (m, 3 aromatic H of central ring), 8.15 (dd, 4 aromatic H
ortho to CO2Ar).
resulting addition adduct was precipitated from the reaction mixture
by adding methanol (40 mL). After the mixture was cooled to room
temperature, the precipitate was collected and recrystallized from a
mixture of ethanol (60 mL) and toluene (40 mL) to yield 7.2 g (73%)
of H4F6-I as white crystals. Due to the thermal lability of the iodine
groups, the thermotropic behavior of the addition adducts was not
determined. The 1H-NMR spectra of the adducts with n ) 4 and m )
6-8 (H4F6-I, H4F7-I, H4F8-I) are identical: 2.30 (m, ArCH3, CH2-
CH2O, 7 H), 2.99 (m, CH2CF2, 4 H), 4.25 (t, OCH2, 4 H), 4.62, (bm,
CH(I), 2 H), 7.02 (dd, 4 aromatic H ortho to OR), 7.14 (m, 3 aromatic
H of central ring), 8.18 (dd, 4 aromatic H ortho to CO2Ar).
1
The H-NMR spectra of the perfluoroalkyl iodides with n ) 5 and
m ) 6-8 (H5F6-I, H5F7-I, H5F8-I) are identical: 2.07 (m, [CH2]2, 8
H), 2.24 (s, ArCH3), 2.92 (m, CH2CF2, 4 H), 4.11 (t, OCH2, 4 H), 4.42
(bm, CH(I), 2 H), 6.98 (dd, 4 aromatic H ortho to OR), 7.13 (m, 3
aromatic H of central ring), 8.16 (dd, 4 aromatic H ortho to CO2Ar).
1
The H-NMR spectra of the perfluoroalkyl iodides with n ) 6 and
m ) 6-8 (H6F6-I, H6F7-I, H6F8-I) are identical: 1.80 (m, [CH2]3,
12 H), 2.25 (s, ArCH3), 2.90 (m, CH2CF2, 4 H), 4.09 (t, OCH2, 4 H),
4.37 (bm, CH(I), 2 H), 6.98 (dd, 4 aromatic H ortho to OR), 7.13 (m,
3 aromatic H of central ring), 8.16 (dd, 4 aromatic H ortho to CO2Ar).
1
The H-NMR spectra of the perfluoroalkyl iodides with n ) 8 and
m ) 6-8 (H8F6-I, H8F7-I, H8F8-I) are identical: 1.52 (m, [CH2]3,
12 H), 1.80 (m, CH2CH(I) and CH2CH2O, 8 H), 2.24 (s, ArCH3), 2.87
(m, CH2CF2, 4 H), 4.06 (t, OCH2, 4 H), 4.35, (bm, CH(I), 2 H), 7.00
(dd, 4 aromatic H ortho to OR), 7.13 (m, 3 aromatic H of central ring),
8.15 (dd, 4 aromatic H ortho to CO2Ar).
2,5-Bis[(4′-(n-(perfluoroalkyl)alkoxy)benzoyl)oxy]toluenes (n )
4-6, 8; m ) 6-8). The 2,5-bis[(4′-(n-(perfluoroalkyl)alkoxy)benzoyl)-
oxy]toluenes were prepared in 80-92% yield as in the following
example. A heterogeneous solution of H4F6-I (5.6 g, 4.9 mmol), AIBN
(0.28 g, 1.7 mmol), and tributyltin hydride (4.4 mL, 17 mmol) in toluene
(10 mL) were heated at 70 °C under nitrogen for 2 h in a 50 mL Schlenk
flask sealed with a rubber septum. The precipitate was collected,
washed with hexanes (100 mL), and recrystallized from toluene (70
mL) to yield 4.6 g (85%) of 2,5-bis[(4′-(n-(perfluorohexyl)butoxy)-
1
benzoyl)oxy]toluene as white crystals. The H-NMR spectra of the
2,5-bis[(4′-(n-(perfluoroalkyl)butoxy)benzoyl)oxy]toluenes with m )
6-8 are identical: 1.88 (m, [CH2]2CH2O, 8 H), 2.23 (m, CH2CF2 and
ArCH3, 7 H), 4.10 (t, OCH2, 4 H), 6.98 (dd, 4 aromatic H ortho to
OR), 7.14 (m, 3 aromatic H of central ring), 8.16 (dd, 4 aromatic H
ortho to CO2Ar). Anal. (C41H30F26O6) C, H: calcd 44.26, 2.72; found
44.29, 2.82. Anal. (C43H30F30O6) C, H: calcd 42.59, 2.49; found 42.29,
2.60. Anal. (C45H30F34O6) C, H: calcd 41.18, 2.30; found 41.01, 2.37.
The 1H-NMR spectra of the 2,5-bis[(4′-(n-(perfluoroalkyl)pentoxy)-
benzoyl)oxy]toluenes with m ) 6-8 are identical: 1.68 (m, [CH2]2, 8
H), 1.86 (m, CH2CH2O, 4 H), 2.12 (m, CH2CF2, 4 H), 2.24 (s, ArCH3),
4.08 (t, OCH2, 4 H), 6.98 (dd, 4 aromatic H ortho to OR), 7.14 (m, 3
aromatic H of central ring), 8.16 (dd, 4 aromatic H ortho to CO2Ar).
Anal. (C43H34F26O6) C, H: calcd 45.28, 3.00; found 45.26, 3.00. Anal.
(C45H34F30O6) C, H: calcd 43.56, 2.76; found 43.30, 2.83. Anal.
(C47H34F34O6) C, H: calcd 42.11, 2.56; found 42.22, 2.56.
2,5-Bis[(4′-(n-pent-4′′-enyloxy)benzoyl)oxy]toluene. 1H-NMR: 1.93
(m, CH2CH2O, 4 H), 2.27 (m, CH2CHd and ArCH3, 7 H), 4.07 (t,
OCH2, 4 H), 5.06 (m, dCH2, 4 H), 5.86 (m, dCH, 2 H), 6.98 (dd, 4
aromatic H ortho to OR), 7.14 (m, 3 aromatic H of central ring), 8.15
(dd, 4 aromatic H ortho to CO2Ar).
The 1H-NMR spectra of the 2,5-bis[(4′-(n-(perfluoroalkyl)hexoxy)-
benzoyl)oxy]toluenes with m ) 6-8 are identical: 1.62 (m, [CH2]3,
12 H), 1.86 (m, CH2CH2O, 4 H), 2.10 (m, CH2CF2, 4 H), 2.25 (s,
ArCH3), 4.06 (t, OCH2, 4 H), 6.98 (dd, 4 aromatic H ortho to OR),
7.14 (m, 3 aromatic H of central ring), 8.15 (dd, 4 aromatic H ortho to
CO2Ar). Anal. (C45H38F26O6) C, H: calcd 46.25, 3.28; found 46.20,
3.35. Anal. (C47H38F30O6) C, H: calcd 44.49, 3.02; found 44.08, 3.01.
Anal. (C49H38F34O6) C, H: calcd 43.00, 2.78; found 42.86, 2.78.
2,5-Bis[(4′-(n-hex-5′′-enyloxy)benzoyl)oxy]toluene. 1H-NMR: 1.61
(m, CH2, 4 H), 1.85 (m, CH2CH2O, 4 H), 2.17 (q, CH2CHd, 4 H),
2.24 (s, ArCH3), 4.07 (t, OCH2, 4 H), 5.04 (m, dCH2, 4 H), 5.84 (m,
dCH, 2 H), 6.98 (dd, 4 aromatic H ortho to OR), 7.13 (m, 3 aromatic
H of central ring), 8.15 (dd, 4 aromatic H ortho to CO2Ar).
2,5-Bis[(4′-(n-oct-7′′-enyloxy)benzoyl)oxy]toluene. 1H-NMR: 1.47
(m, [CH2]3, 12 H), 1.83 (m, CH2CH2O, 4 H), 2.08 (m, CH2CHd, 4
H), 2.25 (s, ArCH3), 4.04 (t, OCH2, 4 H), 4.99 (m, dCH2, 4 H), 5.83
(m, dCH, 2 H), 6.98 (dd, 4 aromatic H ortho to OR), 7.13 (m, 3
aromatic H of central ring), 8.15 (dd, 4 aromatic H ortho to CO2Ar).
Perfluoroalkyl Iodide Addition Adducts (n ) 4-6, 8; m ) 6-8).
The perfluoroalkyl iodide addition adducts were prepared in 51-87%
yield as in the following example. 2,5-Bis[(4′-(n-but-3′′-enyloxy)-
benzoyl)oxy]toluene (3.4 g, 7.2 mmol), 1-iodotridecafluorohexane (10
g, 22 mmol), AIBN (0.38 g, 2.3 mmol), and toluene (1.8 mL) were
combined in a 25 mL Schlenk flask sealed with a rubber septum. The
solution was degassed by several freeze-pump-thaw cycles, and the
flask was then filled with nitrogen and heated at 70 °C for 18 h. The
1
The H-NMR spectra of the 2,5-bis[(4′-((n-(perfluoroalkyl)octyl)-
oxy)benzoyl)oxy]toluenes with m ) 6-8 are identical: 1.52 (m, [CH2]5,
20 H), 1.84 (m, CH2CH2O, 4 H), 2.06 (m, CH2CF2, 4 H), 2.24 (s,
ArCH3), 4.05 (t, OCH2, 4 H), 6.98 (dd, 4 aromatic H ortho to OR),
7.14 (m, 3 aromatic H of central ring), 8.15 (dd, 4 aromatic H ortho to
CO2Ar). Anal. (C49H46F26O6) C, H: calcd 48.05, 3.79; found 47.95,
3.88. Anal. (C51H46F30O6) C, H: calcd 46.24, 3.49; found 46.04, 3.50.
Anal. (C53H46F34O6) C, H: calcd 44.68, 3.25; found 44.58, 3.29.
2,5-Bis[(4′-(n-(perfluoroalkyl)alkoxy)benzoyl)oxy]benzyl Bro-
mides (n ) 4-6, 8; m ) 6-8). The 2,5-bis[(4′-(n-(perfluoroalkyl)-
alkoxy)benzoyl)oxy]benzyl bromides were prepared in 39-80% purity
(corresponding to 24-68% overall yield) as in the following example.

3036 J. Am. Chem. Soc., Vol. 119, No. 13, 1997
Arehart and Pugh
A solution of bromine (6.6 mL, 10 mmol) in benzene (200 mL) was
added dropwise over 5 h to a refluxing solution of 2,5-bis[(4′-(n-
(perfluorohexyl)butoxy)benzoyl)oxy]toluene (4.6 g, 4.0 mmol) in
benzene (80 ml) in the presence of a 275 W sunlamp. The solution
was then poured immediately into 5% aqueous sodium bisulfite (600
mL). The colorless organic layer was separated and dried over sodium
sulfate. The solvent was removed using a rotary evaporator, and the
crude solid was purified by column chromatography using silica gel
as the stationary phase and CH2Cl2/hexanes (1:1) as the eluant. Once
it was established by TLC that the product was eluting from the column,
the solvent ratio was switched to 100% CH2Cl2. The solvent was
removed using a rotary evaporator, and the crude solid was recrystal-
lized from a mixture of ethanol (25 mL) and toluene (25 mL) to yield
3.5 g of crude product containing 74% 2,5-bis[(4′-(n-(perfluorohexyl)-
butoxy)benzoyl)oxy]benzyl bromide (53% overall yield) and 26%
dibrominated material. This product was used without further purifica-
tion. The 1H-NMR spectra of the 2,5-bis[(4′-(n-(perfluoroalkyl)butoxy)-
benzoyl)oxy]benzyl bromides with m ) 6-8 are identical: 1.88 (m,
[CH2]2CH2O, 8 H), 2.19 (m, CH2CF2, 4 H), 4.10 (t, OCH2, 4 H), 4.45
(s, CH2Br), 7.00 (dd, 4 aromatic H ortho to OR), 7.28 (m, 3 aromatic
H of central ring), 8.18 (dd, 4 aromatic H ortho to CO2Ar).
Potassium Bicyclo[2.2.1]hept-2-ene-5-carboxylate (73:27 Endo:
Exo). A solution of bicyclo[2.2.1]hept-2-ene-5-carboxylic acid (6.4
g, 47 mmol) in methanol (30 mL) was titrated to a phenolphthalein
endpoint with 1.5 M potassium hydroxide in methanol. The resulting
salt was precipitated from methanol using cold diethyl ether (1500 mL),
collected, and dried in vacuo to yield 7.4 g (91%) of potassium bicyclo-
[2.2.1]hept-2-ene-5-carboxylate as a white solid; mp >260 °C.
5-{[[2′,5′-Bis[(4′′-(n-(perfluoroalkyl)alkoxy)benzoyl)oxy]benzyl]-
oxy]carbonyl}bicyclo[2.2.1]hept-2-enes (62-82% Endo). The mono-
mers were prepared in 29-45% yield as in the following example. A
solution of 2,5-bis[(4′-(n-(perfluorohexyl)butoxy)benzoyl)oxy]benzyl
bromide (3.5 g, 2.9 mmol ArCH2Br), TBAH (0.13 g, 0.38 mmol),
potassium bicyclo[2.2.1]hept-2-ene-5-carboxylate (0.60 g, 3.4 mmol),
and dimethyl sulfoxide (1.6 mL) in tetrahydrofuran (14 mL) was heated
at 60 °C for 12 h. The reaction mixture was passed through a column
of basic activated alumina using CH2Cl2 as eluant. The solvent was
removed using a rotary evaporator, and the resulting solid was purified
by column chromatography using silica gel as the stationary phase and
a gradient of CH2Cl2/hexanes as the eluant. The solvent was removed
using a rotary evaporator, and the crude product was recrystallized from
a mixture of hexanes (15 mL) and toluene (2 mL) to yield 1.6 g (45%)
of 5-{[[2′,5′-bis[(4′′-(n-(perfluorohexyl)butoxy)benzoyl)oxy]benzyl]-
oxy]carbonyl}bicyclo[2.2.1]hept-2-ene as white crystals. In preparation
for polymerization, this recrystallization was repeated twice in a drybox
using stringently dried solvents. The 1H-NMR resonances at 1.21 (m),
1.85 (m), 2.90 (m), and 3.15 (s) are due to the nonolefinic norbornene
protons of both isomers; 5.81 (m, dCH, endo), 6.10 (m, dCH, endo),
6.04 (m, dCH, exo), 6.13 (m, dCH, endo). The 1H-NMR resonances
due to the mesogen of the 5-{[[2′,5′-bis[(4′′-(n-(perfluoroalkyl)butoxy)-
benzoyl)oxy]benzyl]oxy]carbonyl}bicyclo[2.2.1]hept-2-enes with m )
6-8 are identical: 1.87 (m, CH2, 4 H), 1.86 (m, CH2CH2O, 4 H), 2.18
(m, CH2CF2, 4 H), 4.10 (t, OCH2, 4 H), 5.07 (s, ArCH2), 6.98 (dd, 4
aromatic H ortho to OR), 7.29 (m, 3 aromatic H of central ring), 8.16
(dd, 4 aromatic H ortho to CO2Ar). Anal. (C49H38F26O8) C, H: calcd
47.13, 3.07; found 47.10, 3.14. Anal. (C51H38F30O8) C, H: calcd 45.42,
2.84; found 45.51, 2.79. Anal. (C53H38F34O6) C, H: calcd 43.94; H,
2.64; found 43.31, 2.78.
The 1H-NMR spectra of the 2,5-bis[(4′-(n-(perfluoroalkyl)pentoxy)-
benzoyl)oxy]benzyl bromides with m ) 6-8 are identical: 1.67 (m,
[CH2]2, 8 H), 1.89 (m, CH2CH2O, 4 H), 2.13 (m, CH2CF2, 4 H), 4.08
(t, OCH2, 4 H), 4.45 (s, CH2Br), 6.99 (dd, 4 aromatic H ortho to OR),
7.30 (m, 3 aromatic H of central ring), 8.18 (dd, 4 aromatic H ortho to
CO2Ar).
The 1H-NMR spectra of the 2,5-bis[(4′-(n-(perfluoroalkyl)hexoxy)-
benzoyl)oxy]benzyl bromides with m ) 6-8 are identical: 1.57 (m,
[CH2]3, 12 H), 1.85 (m, CH2CH2O, 4 H), 2.08 (m, CH2CF2, 4 H), 4.07
(t, OCH2, 4 H), 4.45 (s, CH2Br), 6.99 (dd, 4 aromatic H ortho to OR),
7.30 (m, 3 aromatic H of central ring), 8.18 (dd, 4 aromatic H ortho to
CO2Ar).
1
The H-NMR spectra of the 2,5-bis[(4′-((n-(perfluoroalkyl)octyl)-
oxy)benzoyl)oxy]benzyl bromides with m ) 6-8 are identical: 1.53
(m, [CH2]5, 20 H), 1.85 (m, CH2CH2O, 4 H), 2.08 (m, CH2CF2, 4 H),
4.06 (t, OCH2, 4 H), 4.45 (s, CH2Br), 6.99 (dd, 4 aromatic H ortho to
OR), 7.29 (m, 3 aromatic H of central ring), 8.17 (dd, 4 aromatic H
ortho to CO2Ar).
1
The H-NMR resonances due to the mesogen of the 5-{[[2′,5′-bis-
[(4′′-(n-(perfluoroalkyl)pentoxy)benzoyl)oxy]benzyl]oxy]carbonyl}-
bicyclo[2.2.1]hept-2-enes with m ) 6-8 are identical: 1.64 (m, [CH2]2,
8 H), 1.87 (m, CH2CH2O, 4 H), 2.13 (m, CH2CF2, 4 H), 4.08 (t, OCH2,
4 H), 5.10 (s, ArCH2), 6.98 (dd, 4 aromatic H ortho to OR), 7.29 (m,
3 aromatic H of central ring), 8.14 (dd, 4 aromatic H ortho to CO2Ar).
Anal. (C51H42F26O8) C, H: calcd 48.05, 3.32; found 47.92, 3.29. Anal.
(C53H42F30O8) C, H: calcd 46.23, 3.08; found 45.95, 3.03. Anal.
(C55H42F34O8) C, H: calcd 44.73, 2.87; found 44.85, 3.03.
In addition to the above resonances, products from this reaction
contained singlets at 2.24 ppm due to residual starting material, and at
6.8 (CHBr2) and 7.8 ppm (1 aromatic H ortho to CHBr2) due to
dibrominated material.48 These compounds were used without further
purification.
Bicyclo[2.2.1]hept-2-ene-5-carbonyl Chloride (73:27 Endo:Exo).49
Freshly cracked cyclopentadiene (67 g, 1.0 mol) was added dropwise
over 1 h to an ice-cooled solution of acryloyl chloride (84 g, 0.93 mol)
in toluene (330 mL). The reaction was maintained at 0 °C for 3 h and
then heated to 100 °C for 0.5 h. Toluene was distilled off at
atmospheric pressure, and the residual liquid was distilled (42-44 °C/1
mmHg) to yield 114 g (78%) of bicyclo[2.2.1]hept-2-ene-5-carbonyl
chloride as a clear, colorless oil. 1H-NMR resonances at 1.33 (d), 1.41
(m), 2.20 (m), 2.73 (m), 2.97 (s), 3.27 (s), and 3.44 (m) are due to the
nonolefinic protons of both isomers; 6.01 (m, dCH, endo), 6.25 (m,
dCH, endo), 6.11 (m, dCH, exo), 6.20 (m, dCH, exo).
1
The H-NMR resonances due to the mesogen of the 5-{[[2′,5′-bis-
[(4′′-(n-(perfluoroalkyl)hexoxy)benzoyl)oxy]benzyl]oxy]carbonyl}-
bicyclo[2.2.1]hept-2-enes with m ) 6-8 are identical: 1.59 (m, [CH2]3,
12 H), 1.84 (m, CH2CH2O, 4 H), 2.10 (m, CH2CF2, 4 H), 4.06 (t, OCH2,
4 H), 5.11 (s, ArCH2), 6.98 (dd, 4 aromatic H ortho to OR), 7.29 (m,
3 aromatic H of central ring), 8.15 (dd, 4 aromatic H ortho to CO2Ar).
Anal. (C53H46F26O8) C, H: calcd 48.78, 3.55; found 48.47, 3.59. Anal.
(C55H46F30O8) C, H: calcd 47.02, 3.30; found 46.76, 3.30. Anal.
(C57H46F34O8) C, H: calcd 45.49, 3.08; found 45.19, 3.10.
1
Bicyclo[2.2.1]hept-2-ene-5-carboxylic Acid (71:29 Endo:Exo). A
solution of sodium hydroxide (5.0 g, 0.13 mol) in water (200 mL) was
added slowly to ice-cooled bicyclo[2.2.1]hept-2-ene-5-carbonyl chloride
(20 g, 0.13 mol), and the solution was stirred at room temperature for
4 h. The reaction mixture was extracted three times with diethyl ether
(300 mL total) and dried over sodium sulfate. After the solvent was
removed in vacuo, the residual liquid was distilled (86-90 °C/2 mmHg)
to yield 11 g (64%) of bicyclo[2.2.1]hept-2-ene-5-carboxylic acid as a
clear, colorless oil. 1H-NMR resonances at 1.41 (m), 1.92 (m), 2.25
(m), 3.01 (m), and 3.24 (s) are due to the nonolefinic protons of both
isomers; 6.00 (m, dCH, endo), 6.23 (m, dCH, endo), 6.13 (m, dCH,
exo), 6.23 (m, dCH, exo).
The H-NMR resonances due to the mesogen of the 5-{[[2′,5′-bis-
[(4′′-((n-(perfluoroalkyl)octyl)oxy)benzoyl)oxy]benzyl]oxy]carbonyl}-
bicyclo[2.2.1]hept-2-enes with m ) 6-8 are identical: 1.53 (m, [CH2]5,
20 H), 1.84 (m, CH2CH2O, 4 H), 2.07 (m, CH2CF2, 4 H), 4.05 (t, OCH2,
4 H), 5.09 (s, ArCH2), 6.98 (dd, 4 aromatic H ortho to OR), 7.28 (m,
3 aromatic H of central ring), 8.14 (dd, 4 aromatic H ortho to CO2Ar).
Anal. (C57H54F26O8) C, H: calcd 50.30, 4.00; found 50.48, 4.07. Anal.
(C59H54F30O8) C, H: calcd 48.50, 3.73; found 46.22, 3.61. Anal.
(C61H54F34O8) C, H: calcd 46.94, 3.49; found 46.82, 3.47.
Poly{5-[[[2′,5′-bis[(4′′-(n-(perfluoroalkyl)alkoxy)benzoyl)oxy]-
benzyl]oxy]carbonyl]bicyclo[2.2.1]hept-2-ene}s. Polymers were pre-
pared in 54-90% yield as in the following example. In a drybox, a
solution of 5-{[[2′,5′-bis[(4′′-(n-(perfluoroheptyl)pentoxy)benzoyl)oxy]-
benzyl]oxy]carbonyl}bicyclo[2.2.1]hept-2-ene (0.62 g, 4.5 mmol) in
THF (20 g) at 40 °C was added dropwise over 2 min to a solution of
Mo(CHCMe2Ph)(N-2,6-iPr2Ph)(OtBu)2 (5 mg, 9 µmol) in THF (0.53
(48) Wang, F.; Roovers, J. J. Polym. Sci., Polym. Chem. Ed. 1994, 32,
2413.
(49) Jacobine, A. F.; Glaser, D. M.; Nakos, S. T. ACS Polym. Mat. Sci.
Eng. 1989, 60, 211.

Smectic Layering in Nematic Liquid Crystals
J. Am. Chem. Soc., Vol. 119, No. 13, 1997 3037
g) at 40 °C. After the mixture was stirred at 40 °C for an additional
2 h, benzaldehyde (10 µL, 99 µmol) was added to terminate the
polymerization. The solution was removed from the drybox, and the
polymer was precipitated in hexanes (120 mL). The precipitate was
collected and reprecipitated from THF (5 mL) into hexanes (200 mL)
to yield 0.55 g (88%) of poly{5-[[[2′,5′-bis[(4′′-(n-(perfluoroheptyl)-
pentoxy)benzoyl)oxy]benzyl]oxy]carbonyl]bicyclo[2.2.1]hept-2-ene} as
a white powder; Mn ) 2.3 × 104, Mw/Mn ) 1.62.
acknowledges the National Science Foundation for an NSF
Young Investigator Award (1994-1999) and matching funds
from Bayer, Dow Chemical, DuPont (DuPont Young Professor
Grant), GE Foundation (GE Junior Faculty Fellowship), Phar-
macia Biotech, and Waters Corp. We are also deeply indebted
to Mr. Alan L. Kiste and Dr. Frank A. Brandys for their help
with thermal analysis, and microscopic and X-ray analysis,
respectively. X-ray data was acquired using equipment in the
group of Professor David C. Martin (UM, Materials Science
and Engineering) with the help of Dr. Brendan J. Foran.
Acknowledgment. Acknowledgment is made to the donors
of the Petroleum Research Fund, administered by the American
Chemical Society, for support of this research. C.P. also
JA963687P