Poly(1,1′-bi-2-naphthol)s: Synthesis, characterization, and application in Lewis acid catalysis

Article abstract of DOI:10.1021/jo961407i

6,6′-Dibromo-1,1′-bi-2-naphthol derivatives, where the hydroxyl groups are protected by alkyl, methoxymethyl, and acyl groups, have been polymerized using nickel(0) or nickel(II) complexes as catalysts. The molecular weights of the resulting polymers have

Full text of DOI:10.1021/jo961407i

8370
J . Org. Chem. 1996, 61, 8370-8377
Articles
P oly(1,1′-bi-2-n a p h th ol)s: Syn th esis, Ch a r a cter iza tion , a n d
Ap p lica tion in Lew is Acid Ca ta lysis
Qiao-Sheng Hu,1a Dilrukshi Vitharana,1a Xiao-Fan Zheng,1a Chi Wu,1b
Chi Man Simon Kwan,1b and Lin Pu*,1a
Center for Main Group Chemistry and the Department of Chemistry, North Dakota State University,
Fargo, North Dakota 58105, and the Department of Chemistry, the Chinese University of Hong Kong,
Shatin, N.T., Hong Kong
Received J uly 23, 1996X
6,6′-Dibromo-1,1′-bi-2-naphthol derivatives, where the hydroxyl groups are protected by alkyl,
methoxymethyl, and acyl groups, have been polymerized using nickel(0) or nickel(II) complexes as
catalysts. The molecular weights of the resulting polymers have been analyzed by gel permeation
chromatography and laser light scattering. Hydrolysis of these polymers has produced the optically
active poly(1,1′-bi-2-naphthol)s [poly(BINOL)s]. The poly(BINOL)s are soluble in basic water
solution and have been characterized by NMR, IR, UV, and CD spectroscopic methods. The reaction
of a (R)-poly(BINOL) with diethylaluminum chloride, trimethylaluminum, and titanium tetra-
isopropoxide generates novel polymeric Lewis acid complexes. These complexes represent a new
generation of polymeric catalysts where the catalytic centers are highly organized in an optically
active and sterically regular polymer chain. When used to catalyze the Mukaiyama aldol
condensation, the polymeric aluminum catalyst shows greatly enhanced catalytic activity over the
monomeric complex.
In tr od u ction
Due to the restricted rotation around the 1,1′-bond,
1,1′-binaphthyl molecules are chiral and the chirality of
these compounds has been utilized in many asymmetric
processes.2-4 A number of chiral binaphthyl metal
complexes have been demonstrated to be excellent cata-
lysts for enantioselective organic transformations. Fig-
ure 1 lists several binaphthyl-based chiral metal com-
plexes: the ruthenium binaphthylphosphine complex
(R)-1 is applied in asymmetric hydrogenations,5 the
aluminum binaphthyl complex (R)-2 is used in asym-
metric Diels-Alder reactions,6 the titanium binaphthyl
complex (S)-3 is used in asymmetric aldol reactions,7 and
the trimeric binaphthyl lanthanum complex (R)-4 is
applied in asymmetric Michael reactions.8 These cata-
lysts have induced very good enantioselectivity in these
reactions.
F igu r e 1. Examples of chiral binaphthyl catalysts.
On the basis of the unique structure of binaphthyl
compounds, we have constructed novel main chain chiral
conjugated polymers.9-12 For example, propeller poly-
mers such as (R)-5 have been designed and synthesized
in our laboratory.12 In (R)-5 (Chart 1), all of its binaph-
thyl units have a R configuration, and the dipole units
of this polymer are expected to progressively rotate along
the polymer axis to generate a fascinating three-
dimensional propeller structure. Polymers of this struc-
ture may lead to interesting electrical and optical prop-
erties. Besides the development of the binaphthyl-based
X Abstract published in Advance ACS Abstracts, November 1, 1996.
(1) (a) North Dakota State University. (b) The Chinese University
of Hong Kong.
(2) (a) Rosini, C.; Franzini, L.; Raffaelli, A.; Salvadori, P. Synthesis
1992, 503. (b) Whitesell, J . K. Chem. Rev. 1989, 89, 1581. (c)
Bringmann, G.; Walter, R.; Weirich, R. Angew. Chem., Int. Ed. Engl.
1990, 29, 977.
(3) (a) Takaya, H.; Ohta, T.; Noyori, R. In Catalytic Asymmetric
Synthesis; Ojima, I., Ed.; VCH: New York, 1993; pp 1. (b) Ishihara,
K.; Kurihara, H.; Yamamoto, H. J . Am. Chem. Soc. 1996, 118, 3049.
(c) Maruoka, K.; Itoh, T.; Shirasaka, T.; Yamamoto. J . Am. Chem. Soc.
1988, 110, 310.
(4) Santelli, M.; Pons, J .-M. Lewis Acids and Selectivity in Organic
Synthesis; CRC Press: New York, 1995.
(5) Ohta, T.; Takaya, H.; Kitamura, M.; Nagai, K.; Noyori, R. J . Org.
Chem. 1987, 52, 3174.
(6) Maruoka, K.; Itoh, T.; Shirasaka, T.; Yamamoto, H. J . Am. Chem.
Soc. 1988, 110, 310.
(9) Hu, Q.-S.; Vitharana, D.; Liu, G.; J ain, V.; Wagaman, M. W.;
Zhang, L.; Lee, T. ; Pu, L. Macromolecules 1996, 29, 1082.
(10) Hu, Q.-S.; Vitharana, D.; Liu, G.; J ain, V.; Pu, L. Macromol-
ecules 1996, 29, 5075.
(7) (a) Carreira, E. M.; Lee, W.; Singer, R. A. J . Am. Chem. Soc.
1995, 117, 3649. (b) Carreira, E. M.; Singer, R. A. J . Am. Chem. Soc.
1995, 117, 12360.
(8) Sasai, H.; Arai, T.; Shibasaki, M. J . Am. Chem. Soc. 1994, 116,
1571.
(11) Ma, L.; Hu, Q.-S.; Musick, K.; Vitharana, D.; Wu, C.; Kwan, C.
M. S.; Pu, L. Macromolecules 1996, 29, 5083.
(12) (a) Ma, L.; Hu, Q.-S.; Vitharana, D.; Pu, L. Polymer Prepr. 1996,
37(2), 462. (b) Ma, L.; Hu, Q. -S.; Vitharana, D.; Wu, C.; Kwan, C. M.
S.; Pu, L. Manuscript submitted.
S0022-3263(96)01407-7 CCC: $12.00 © 1996 American Chemical Society

Poly(1,1′-bi-2-naphthol)s
J . Org. Chem., Vol. 61, No. 24, 1996 8371
Ch a r t 1
polymers in electrical and optical applications, we are
also interested in using these chiral materials in asym-
metric catalysis. There are important advantages using
polymer-supported catalysts in industrial processes.13 For
example, because of the easy separation of the polymeric
catalysts from the reaction system, these catalysts can
be used in flow reactor synthesis. Studies have shown
that polymer-supported catalysts may have more durable
catalytic activity than the monomeric metal complexes.
Chiral polymeric catalysts have been studied before, but
very few show good enantioselectivity. The traditional
polymeric chiral catalysts are synthesized by covalently
bonding a chiral metal complex to an achiral and steri-
cally irregular polymer backbone. As shown by 6, a
polystyrene-supported chiral rhodium catalyst,14 the
catalytic centers in these catalysts are randomly oriented,
and the influence of the microenviroment of the catalytic
sites on the catalysis is difficulty to study. We have
Resu lts a n d Discu ssion
In order to synthesize poly(BINOL)s, (R)-7 is prepared
from the bromination of (R)-1,1′-bi-2-naphthol in over
95% yield.16,17 The attempt to directly polymerize this
molecule using a catalytic amount of nickel(II) chloride
and excess zinc produces mostly (R)-1,1′-bi-2-napthol with
less than 5% of oligomers. The hydroxyl groups of (R)-7
are therefore protected with different protecting groups,
and the resulting monomers are polymerized by using
different coupling processes to make chiral polybinaph-
thyls. Removal of the protecting groups in the polymers
gives the desired poly(BINOL)s which are used to syn-
thesize polymeric Lewis acid catalysts for the Mukaiyama
aldol condensation.
1. P r ep a r a t ion of a n Alk yl-P r ot ect ed P oly-
(BINOL). An alkyl-protected chiral binaphthyl mono-
mer has been synthesized. The reaction of (R)-7 with
iodohexane in a refluxing acetone/K2CO3 mixture gener-
ates (R)-6,6′-dibromo-2,2′-bis(hexyloxy)-1,1′-binaphthyl,
(R)-8.9 The specific optical rotation of the monomer (R)-8
is [R]D ) +25.9° (c ) 0.52, THF). (R)-8 undergoes
polymerization in the presence of a stoichiometric amount
of bis(1,5-cyclooctadiene)nickel(0) (Scheme 1).15b The
reaction is carried out in a DMF solution of (R)-8 (1.42
mmol), bis(1,5-cyclooctadiene)nickel(0) (1.76 mmol), 2,2′-
bipyridine (2.09 mmol), and 1,5-cyclooctadiene (4.9 mmol).
After the mixture is heated at 70 °C under nitrogen for
21 h, a chiral polybinaphthyl (R)-9 is obtained. Gel
carried out a program to introduce metal centers into the
rigid and sterically regular polybinaphthyls to prepare
a new generation of polymeric chiral catalysts. In this
article, several strategies to prepare the optically active
and sterically regular poly(1,1′-bi-2-naphthol)s [poly-
(BINOL)s] are described. The hydroxyl functional groups
in these polymers allow us to incorporate aluminum and
titanium Lewis acid metal centers. The use of these
polymeric complexes in the Mukaiyama aldol condensa-
tion is studied.15
(13) (a) Blossey, E. C.; Ford, W. T. In Comprehensive Polymer
Science. The Synthesis, Characterization, Reactions and Applications
of Polymers; Allen, G., Bevington, J . C., Ed.; Pergamon Press: New
York. 1989; Vol. 6, p 81. (b) Pittman, C. U., J r. In Comprehensive
Organometallic Chemistry; Wilkinson, G., Stone, F. G. A., Abel, E. W.,
Ed.; Pergamon Press: Oxford, 1983; Vol. 8, p 553.
(14) (a) Dumont, W.; Poulin, J . C.; Dang, T. P.; Kagan. H. B. J . Am.
Chem. Soc. 1973, 95, 8295. (b) Dang, T. P.; Kagan, H. B. Fr. Pat.
1 199 756.
(15) Preliminary accounts of this work have been published: (a) Hu,
Q.-S.; Zheng, X.-F.; Pu, L. J . Org. Chem. 1996, 61, 5200. (b) Vitharana,
D.; Hu, Q.-S.; Pu, L. Polymer Prepr. 1996, 37(1), 855.
(16) (a) Pradellok, W.; Kotas, A.; Walczyk, W.; J edlinski, Z. Chem.
Abstr. 1979, 90, 121289t. (b) Sogah, G. D. Y.; Cram, D. J . J . Am. Chem.
Soc. 1979, 101, 3035.
(17) An efficient resolution of 1,1′-bi-2-naphthol has been developed
in this laboratory: Hu, Q.-S.; Vitharana, D. R.; Pu, L. Tetrahedron:
Asymmetry 1995, 6, 2123.

8372 J . Org. Chem., Vol. 61, No. 24, 1996
Hu et al.
Sch em e 2. Th e Su zu k i Cou p lin g Rea ction to
Sch em e 1. Syn th esis of a n Op tica lly Active
P oly(bin a p h th yl) (R)-9
P r ep a r e a Ch ir a l P olybin a p h th yl
The circular dichroism spectrum of (R)-9 in methylene
chloride exhibits very strong Cotton effects. The chiral
configuration of this polymer is also quite stable. When
a toluene solution of the polymer is heated at reflux for
24 h, only 6% loss of the optical rotation is observed.
The racemic monomer rac-8 has also been polymerized
by using the nickel(0)-mediated polymerization. The
resulting polymer rac-9 has a molecular weight of Mw
)
11 000 and Mn ) 4700 (PDI ) 2.3) as measured by GPC.
The NMR and UV spectra of rac-9 are almost identical
to those of (R)-9.
Ta ble 1. UV Sp ectr a l Da ta of th e P olym er (R)-9,
2,2′-Bis(h exyloxy)-1,1′-bin a p h th yl (10) a n d
2-(Hexyloxy)n a p h th a len e (11)
2. Usin g th e Su zu k i Cou p lin g Rea ction to P r e-
p a r e th e P olybin a p h th yl. The Suzuki coupling reac-
tion19 has been utilized to prepare the chiral polybinaph-
thyl. When a 1:1 mixture of (R)-8 and (R)-12,9 a diboronic
acid monomer, is reacted in the presence of Pd(PPh3)4
catalyst, the Suzuki reaction occurs to generate (R)-9′
(Scheme 2). GPC analysis of (R)-9′ shows Mw ) 17 600
and Mn ) 7600 (PDI ) 2.3). [R]D ) -281° (c ) 0.50,
THF). The NMR and UV spectroscopic data (R)-9′ are
essentially the same as those of (R)-9. Racemic mono-
mers rac-8 and rac-12 also undergo the Suzuki coupling
to generate polymer rac-9′. GPC analysis of rac-9′ shows
Mw ) 21 500 and Mn ) 8100 (PDI ) 2.6). The Suzuki
coupling reaction produces higher molecular weight
polybinaphthyls than the nickel(0)-mediated polymeri-
zation.
(R)-9
10
11
λmax (nm) 240 (sh), 262, 252, 273 (sh), 284,
240, 266, 274,
318, 330
284, 316
293 (sh), 328 (sh),
340
permeation chromatography (GPC) analysis shows that
the molecular weight of (R)-9 is Mw ) 15 000 and Mn )
6800 (PDI ) 2.2). The specific optical rotation of the
polymer is [R]D ) -215° (c ) 0.52, CH2Cl2). This polymer
rotates the plane of polarized light to the opposite
direction of the monomer with a much larger optical
rotation.
1
The H NMR spectrum of (R)-9 displays well-resolved
proton signals with a few low intensity peaks probably
arisen from the end groups. Based on analogy to
substituted monomeric binaphthyl molecules, each peak
in the aromatic region can be assigned. The 13C NMR
spectrum of (R)-9 is also well-resolved. The polymer has
a glass transition temperature (Tg) at 119 °C as indicated
by differential scanning calorimetry. The thermal stabil-
ity of (R)-9 is very high. Thermogravimetric analysis
shows that (R)-9 does not start to lose mass until ca. 392
°C.
The UV-vis spectrum of (R)-9 exhibits maximum
absorptions at λmax ) 240 (sh), 262, 284, and 316 nm.
Comparison of the UV spectrum of (R)-9 with those of
2,2′-bis(hexyloxy)-1,1′-binaphthyl, 10, and 2-(hexyloxy)-
naphthalene, 11, can provide some insight on the main
chain conformation of this class of polybinaphthyls. As
shown in Table 1, the UV spectrum of the polymer (R)-9
In order to find out whether the polymerization of the
racemic monomers rac-8 and rac-12 is stereoselective,
and whether polymer rac-9′ is a stereoregular polymer
or it is actually made of randomly distributed R and S
binaphthyl units in the polymer chain, we have studied
the Suzuki coupling of 2 equivalents of rac-8 with 1 equiv
of (R)-12. After the reaction is completed, an oligomer
13 is obtained. GPC analysis of 13 shows Mw ) 3600
and Mn ) 2300 (PDI ) 1.5). Its specific optical rotation
is [R]D ) -97.7° (c ) 1.0, THF). About 20% of unreacted
rac-8 is recovered which shows the specific optical rota-
tion is [R]D ) -0.7°. Thus there is no enrichment of
either R or S enantiomer after the reaction. On the basis
of this experiment, we conclude that the coupling of rac-8
with rac-12 is not stereoselective and the polymer rac-9′
is made of randomly distributed R and S binaphthyl
units.
3. P r ep a r a tion of a Meth oxym eth yl Gr ou p P r o-
tected P oly(BINOL). A methoxy methyl protected
chiral binaphthyl monomer is also synthesized (Scheme
3). In the presence of sodium hydride, the reaction of
chloromethyl methyl ether with (R)-7 produces a chiral
in methylene chloride solution resembles that of 11 more
than it resembles that of 10. This indicates that there
is no extended conjugation at both the R,R′-naphthyl
connection and the â,â′-naphthyl connection in the
polymer main chain. Therefore, all of the adjacent
naphthalene rings in the polymer are most likely to be
orthogonal to each other.
(18) Maruyama, T.; Zhou, Z.; Kubota, K.; Yamamoto, T. Chem. Lett.
1992, 643.
(19) Selected references on the Suzuki coupling reactions: (a)
Miyaura, N.; Yanagi, T.; Suzuki, A. Synth. Commun. 1981, 11, 513.
(b) Wallow, T. I.; Novak, B. M. J . Am. Chem. Soc. 1991, 113, 7411. (c)
Huber, J .; Scherf, U. Macromol. Rapid Commun. 1994, 15, 897.

Poly(1,1′-bi-2-naphthol)s
Sch em e 3. P r ep a r a tion of th e Ch ir a l
J . Org. Chem., Vol. 61, No. 24, 1996 8373
Sch em e 4. P r ep a r a tion of th e Ch ir a l
P olybin a p h th yl (R)-15
P olybin a p h th yl (R)-17
Sch em e 5. P r ep a r a tion of th e Ch ir a l
Ta ble 2. Molecu la r Weigh ts of th e P olym er s P r ep a r ed
fr om th e P olym er iza tion of (R)-15 Usin g Differ en t
Am ou n ts of NiCl2 a s th e Ca ta lysts
P oly(1,1′-bi-2-n a p h th ol) (R)-18
amount of NiCl2
(mol %)
Mw
Mn
PDI
2
5
10
50
2400
4400
6000
5400
1900
2700
3800
3500
1.2
1.6
1.6
1.5
binaphthyl monomer (R)-14.20 The specific optical rota-
tion of (R)-14 is [R]D ) +23.1° (c ) 1.0, THF). The use of
a catalytic amount of nickel(II) chloride and excess zinc21
to carry out the polymerization of (R)-14 is studied. The
molecular weights of the resulting polybinaphthyl is
found to be dependent on the amount of nickel(II)
chloride. Table 2 summarizes the molecular weights of
the polymers measured by GPC when different amount
of nickel(II) chloride is used. In the presence of 10 mol
% of nickel(II) chloride and excess zinc, the polymer (R)-
15 is obtained with a molecular weight of Mw ) 6000 and
Mn ) 3800 (PDI ) 1.6). (R)-15 is soluble in common
organic solvents such as THF, methylene chloride, and
chloroform and has been characterized by spectroscopic
MeOH. The molecular weight of (R)-17 is Mw ) 6400
and Mn ) 3600 (PDI ) 1.8) as shown by GPC analysis.
This polymer is soluble in methylene chloride, chloroform,
and THF. The specific optical rotation of (R)-16 is [R]D
) -353° (c ) 0.5, THF). The racemic monomer rac-16
has also been polymerized to generate rac-17. GPC
analysis shows that the molecular weight of rac-17 is Mw
) 7400 and Mn ) 3200 (PDI ) 2.3).
All of the molecular weights of the polybinaphthyls
described above are measured by GPC relative to poly-
styrene standards. Because the three-dimensional struc-
ture of the rigid polybinaphthyls are expected to be quite
different from that of polystyrene, the GPC data may not
reflect the actual molecular weights of these polymers.
A laser light scattering (LLS) study of the polymers (R)-
17 and rac-17 has been carried out to determine the
absolute molecular weights of these polymers.22 Table 3
summarizes the LLS study results and the GPC data.
As shown in the table, the GPC data deviate ca. 10-20%
from the LLS data. Since the difference is small, the
GPC analysis using polystyrene standard can be used as
a convenient and good estimate for the molecular weights
of these polybinaphthyls.
1
methods including H and 13C NMR. Its specific optical
rotation is [R]D ) -301.9° (c ) 1.0, THF). The molecular
weight of (R)-15 is significantly lower than (R)-9 and (R)-
9′, but its optical rotation is much higher. This indicates
that the methoxymethyl protecting groups have signifi-
cant effects on the stereo and electronic structure of the
polymer.
4. P r epar ation of an Acyl-P r otected P oly(BINOL).
An acyl-protected chiral binaphthyl monomer (R)-16 is
synthesized from the reaction of (R)-7 with acetic anhy-
dride in the presence of triethylamine. (R)-16 is polym-
erized by using nickel(II) chloride and excess zinc (Scheme
4). The reaction is carried out under nitrogen by heating
a mixture of (R)-16 (18.0 mmol), zinc (61.2 mmol), NiCl2
(1.80 mmol), PPh3 (7.2 mmol), and bipyridine (1.8 mmol)
in DMF at ca. 85 °C. The resulting polymer (R)-17 is
purified by dissolution in CH2Cl2 and precipitation with
5. H yd r olysis To Gen er a t e t h e P oly(BINOL)s.
The acetate protecting groups of (R)-17 can be easily
hydrolyzed. Heating a mixture of the THF solution of
(R)-17 and aqueous potassium hydroxide at reflux gener-
ates the first optically active and sterically regular poly-
(BINOL) (R)-18 (Scheme 5). Although this polymer
cannot be dissolved in organic solvents, it is soluble in
(20) Kitajima, H.; Aoki, Y.; Ito, K.; Katsuki, T. Chem. Lett. 1995,
1113.
(21) (a) Wang, Y.; Quirk, R. P. Macromolecules 1995, 28, 3495. (b)
Phillips, R. W.; Sheares, V. V.; Samulski, E. T.; DeSimone, J . M.
Macromolecules 1994, 27, 2354.
(22) (a) Chu, B. Laser Light Scattering, 2nd ed.; Academic Press:
New York, 1974. (b) Pecora, R.; Berne, B. J . Dynamic Light Scattering.
Plenum Press: New York, 1976. (c) Wu, C.; Chan, K.; Xia, K. Q.
Macromolecules 1995, 28, 1032.

8374 J . Org. Chem., Vol. 61, No. 24, 1996
Hu et al.
Ta ble 3. Com p a r ison of th e GP C Da ta a n d th e LLS Stu d y Resu lts of th e P olym er s (R)-17 a n d r a c-17
Mw
(GPC)
Mn
(GPC)
PDI
(GPC)
Mw
(LLS)
A2
<D>
Mw/Mn
(estimated)
polymers
(mol cm-3 g-2
)
(µm2/s)
<Rh> (nm)
µ2Γ2
(R)-17
rac-17
6400
7400
3600
3200
1.79
2.29
7130
5930
-2.86 E-3
-6.27 E-3
202
205
2.28
2.24
0.10
0.089
∼1.4
∼1.4
A2 is the second virial coefficient; D is the translational diffusion coefficient; Rh is the hydrodynamic radius and µ2/ Γ is the width of
the line-width distribution.
Sch em e 6. Th e Mu k a iya m a Ald ol Con d en sa tion of
19 a n d 20
In the presence of hydrochloric acid, (R)-15 undergoes
facile hydrolysis to generate the optically active poly-
(BINOL). The ether functional groups of (R)-9 and (R)-
9′ are difficult to hydrolyze. To convert these polymers
to the poly(BINOL)s, (R)-9 and (R)-9′ have to be treated
with excess boron tribromide and followed by reaction
with water.23 Although both (R)-9 and (R)-9′ have much
higher molecular weights than (R)-15 and (R)-17, the
poly(BINOL)s prepared from them are still soluble in
basic water solution. Among the methods we have
described for the preparation of the optically active poly-
(BINOL)s, the synthesis of (R)-17 and its hydrolysis is
the most practical one because of the readily available
monomer, inexpensive catalysts, and easy hydrolysis.
1
F igu r e 2. The H NMR spectrum of (R)-18 in a 0.5 M NaOD
deuterium water solution.
6. P oly(BINOL) in Ca ta lysis. We have used the
chiral poly(BINOL) (R)-18 to prepare novel polymeric
Lewis acid catalysts for the Mukaiyama aldol reaction24,25
of benzaldehyde, 19, and 1-phenyl-1-(trimethylsilyloxy)-
ethylene, 20. The reaction of 19 and 20 can be catalyzed
by Lewis acids to generate 21 (Scheme 6).25 This class
of reactions is very useful in the formation of carbon-
carbon bonds between carbonyl compounds.
(R)-18 can be converted to polyaluminum complexes
(Scheme 7). The reaction (R)-18 with diethylaluminum
chloride produces a heterogeneous polymeric aluminum
complex (R)-22.26 The reaction of (R)-18 with trimethyl-
aluminum gives (R)-23. When these polymeric alumi-
num complexes are used to catalyze the Mukaiyama
condensation of 19 with 20 in methylene chloride solu-
tion, (R)-22 shows higher catalytic activity than (R)-23.
At -78 °C, 100% conversion is observed in 3.5 h when
the reaction is carried out in the presence of 16 mol % of
(R)-22, but only ca. 30% conversion is observed when
using 16 mol % of (R)-23. The catalytic activity of (R)-
22 is also much higher than its corresponding monomeric
aluminum complex (R)-24 made from the reaction of (R)-
1,1′-bi-2-naphthol with diethylaluminum chloride. At
-78 °C, there is only ca. 5% conversion for the reaction
of 19 and 20 catalyzed by 16 mol % of (R)-24. Thus, there
F igu r e 3. The CD spectrum of (R)-18 in 0.5 M aqueous KOH
solution.
basic water solution. It is purified by precipitation of its
aqueous potassium hydroxide solution with hydrogen
chloride. The specific optical rotation of (R)-18 is [R]D )
-139.8° (c ) 0.5, 0.5 M aqueous KOH). Figure 2 is the
1H NMR spectrum of (R)-18 in a D2O solution of 0.5 M
NaOD. A singlet at δ 8.12 corresponds to H-5 in the
naphthalene ring. Four additional signals are observed
for the remaining four protons on the aromatic ring.
Smaller peaks in the spectrum are due to the end groups
of the polymer. This relatively well-resolved NMR
spectrum is consistent with the polymer structure. The
UV spectrum of the polymer in 0.5 M aqueous KOH
solution displays λmax ) 274 and 340 nm. The UV
spectrum of (R)-18 shows a significant red-shift of
maximum absorptions from that of (R)-9 due to the
negative charges on the oxygen atoms of (R)-18 in the
strong basic solution. The circular dichroism spectrum
of (R)-18 in 0.5 M aqueous KOH solution is shown in
Figure 3. Two positive and two negative Cotton effects
are observed.
(23) Lingenfelter, D. S.; Helgeson, R. C.; Cram, D. J . J . Org. Chem.
1981, 46, 393.
(24) Selected references on Lewis acid-catalyzed asymmetric Mu-
kaiyama aldol condensations: (a) a review: Bach, T. Angew. Chem.,
Int. Ed. Engl. 1994, 33, 417. (b) Reetz, M. T.; Kyung, S.-H.; Bolm, C.;
Zierke, T. Chem. Ind. 1986, 824. (c) Mikami, K.; Matsukawa, S. J . Am.
Chem. Soc. 1994, 116, 4077. (d) Parmee, E. R.; Hong, Y.; Tempkin, O.;
Masamune, S. Tetrahedron Lett. 1992, 33, 1729. (e) Corey, E. J .; Cywin,
C. L.; Roper, T. D. Tetrahedron Lett. 1992, 33, 6907.
(25) Furuka, K.; Maruyama, T.; Yamamoto, H. J . Am. Chem. Soc.
1991, 113, 1041.
(26) Maruoka, K.; Itoh, T.; Shirasaka, T.; Yamamoto, H. J . Am.
Chem. Soc. 1988, 110, 310.

Poly(1,1′-bi-2-naphthol)s
J . Org. Chem., Vol. 61, No. 24, 1996 8375
Sch em e 7. P r ep a r a tion of P olybin a p h th ol
Alu m in u m (III) Ca ta lysts (R)-22 a n d (R)-23
bi-2-naphthol with Ti(O-iPr)4 in the presence of 4 Å
molecular sieves,27 can catalyze the reaction of 19 and
20 at rt.
This completely opposite behavior of the polybinaph-
thyl aluminum complex and the polybinaphthyl titanium
complex provides additional insights on the mechanism
of Lewis acid catalysis. It has been proposed that when
a binaphthyl titanium complex such as (R)-26 is used to
carry out organic transformations, the actual catalytically
active species should be a dimeric complex.28 Our
observation that no reaction takes place when (R)-25 is
used in the condensation of 19 and 20 supports this
assumption. Because in the rigid polymer (R)-25, all of
its titanium centers are isolated and the binaphthyl
titanium units cannot dimerize to form the active catalyst
for the reaction. On the other hand, the catalysis of
aluminum complexes is believed to proceed through the
coordination of substrates to the empty p orbital of the
metal center. In solution, monomeric aluminum com-
plexes such as (R)-24 can undergo oligomerization through
the formation of stable Al-O-Al bridging bonds which
reduces the Lewis acidity and deactivates the catalysts.
However, in (R)-22, the rigid polymeric structure and its
insolubility prevent the formation of such Al-O-Al
bridging bonds. The empty p orbitals of the metal centers
in this polyaluminum complex are therefore available to
activate 19 for the Mukaiyama condensation. No enan-
tioselectivity has been observed for this polymeric cata-
lyst, and further modification of the catalyst is in
progress.
Sch em e 8. Syn th esis of a P olym er ic Tita n iu m
Com p lex (R)-25
Su m m a r y
The synthesis of polybinaphthyls containing alkoxyl,
methoxymethoxyl, and acetyloxy substituents have been
studied. We have shown that these polymers can be
made by using nickel(0) or nickel(II) complexes mediated
coupling processes as well as the Suzuki coupling reac-
tion. GPC analysis and LLS study are used to analyze
the molecular weights of these polymers. Hydrolysis of
the functional groups of the polybinaphthyls leads to the
first optically active and sterically regular poly(BINOL)s.
These chiral poly(BINOL)s are soluble in basic water
solution and have been characterized by different spec-
troscopic methods. The aluminum and titanium poly-
meric complexes are synthesized by using a poly(BINOL)
as the precursor. A polymeric aluminum complex shows
greatly enhanced catalytic activity over its monomeric
binaphthyl complex when used in the Mukaiyama aldol
condensation. The polybinaphthyl titanium complex,
however, loses its catalytic activity while its monomeric
complex is catalytically active. These studies have
provided further understanding of the mechanism of
Lewis acid catalysis in organic reactions.
Exp er im en ta l Section
is a dramatic increase of catalytic activity from the
monomeric complex to the polymeric complex.
The general data about the analytical instruments and the
LLS experiment were published.10 THF and ether were dried
with sodium benzophenone. Methylene chloride was dried
However, when a polymeric titanium complex (R)-25,
prepared from the reaction of (R)-18 with Ti(O-iPr)4 in
the presence of 4 Å molecular sieves (Scheme 8),27 is used
to catalyze the condensation of 19 and 20, no reaction
occurs at all even in a refluxing methylene chloride
solution for one day. In contrast, the monomeric tita-
nium complex (R)-26, made from the reaction of (R)-1,1′-
(28) (a) Terada, M.; Mikami, K.; Nakai, T. J . Chem. Soc., Chem.
Commun. 1990, 1623. (b) Mikami, K.; Terada, M. Tetrahedron 1992,
48, 5671. (c) Kitamoto, D. H.; Imma, H.; Nakai, T. Tetrahedron Lett.
1995, 36, 1861.
(29) References on Al-O-Al bridging bonds in aluminum alkoxide
and aryloxide complexes: (a) Oliver, J . P.; Kumar, R.; Taghiof, M. In
Coordination Chemistry of Aluminum; Robinson, G. H., Ed.; VCH
Publishers: New York, 1993; p 167. (b) J effery, E. A.; Mole, T. Aust.
J . Chem. 1968, 21, 2683. (c) Pasynkiewicz, S.; Starowieyski, K. B.;
Skoweonska-Ptasinska, M. J . Organomet. Chem. 1973, 52, 269. (d)
Pasynkiewicz, S.; Starowieyski, K. B.; Skoweonska-Ptasinska, M. J .
Organomet. Chem. 1974, 65, 155.
(27) Keck, G. E.; Tarbet, K. H.; Geraci, L. S. J . Am. Chem. Soc. 1993,
115, 8467.

8376 J . Org. Chem., Vol. 61, No. 24, 1996
Hu et al.
with calcium hydride. 1,5-Cyclooctadiene, 2,2′-bipyridine,
triphenylphosphine, and anhydrous DMF were purchased from
Aldrich and used directly. Biscyclooctadienenickel(0), nickel-
(II) chloride, and tetrakis(triphenylphosphine)palladium(0)
were purchased from Strem and used directly. The optical
purity of the binaphthyl monomers in this paper is larger than
99% as measured by HPLC using Chiralcel OD column made
by Chiral Technologies Inc.
P r ep a r a tion a n d Ch a r a cter iza tion of (R)-9. Under
nitrogen, to a 50 mL Schlenk flask were added (R)-8 (855 mg,
1.42 mmol), bis(cyclooctadiene)nickel(0) (489 mg, 1.76 mmol),
2,2′-bipyridine (330 mg, 2.09 mmol), and 1,5-cyclooctadiene
(0.60 mL, 4.9 mmol) in DMF (9 mL), and the reaction mixture
was heated at 70 °C for 21 h. Aqueous HCl (1 N, 25 mL) was
then added to the reaction mixture at rt and was extracted
with CH2Cl2 (2 × 25 mL). The Organic layer was passed
through a plug of silica gel and concentrated under vacuum.
The polymer was precipitated out with MeOH and isolated
(70% yield). Mp 136-137 °C. [R]D ) +23.1° (c ) 1.0, THF).
1H NMR (400 MHz, CDCl3) δ 8.03 (d, 2H, J ) 1.9 Hz), 7.86 (d,
2H, J ) 9.1 Hz), 7.59 (d, 2H, J ) 9.1 Hz), 7.28 (dd, 2H, J )
9.1, 1.9 Hz), 6.97 (d, 2H, J ) 9.1 Hz), 5.08 (d, 2H, J ) 6.7 Hz),
4.97 (d, 2H, J ) 7.0 Hz), 3.15 (s, 6H). 13C NMR (100 MHz,
CDCl3) δ 152.98, 132.46, 130.93, 129.97, 129.80, 128.80, 127.21,
120.75, 118.10, 118.07, 95.05, 56.03. FT-IR (KBr) cm-1 2991.8
(w), 2957.1 (m), 2901.1 (m), 2827.8 (w), 1585.6 (s), 1494.9 (s),
1363.8 (m), 1246.1 (s), 1192.1 (m), 1149.7 (s), 1064.8 (s), 1022.3
(s), 958.7 (m), 920.1 (m), 877.7 (m), 817.9 (m), 679.0 (w), 517.0
(w). Anal. Calcd for C24H20O4Br2: C, 54.14; H, 3.76. Found:
C, 54.20; H, 3.71.
P r ep a r a tion of th e P olybin a p h th yl (R)-15. Under
nitrogen, a mixture of (R)-14 (200 mg, 0.4 mmol), zinc (88 mg,
1.36 mmol), NiCl2 (5.2 mg, 0.04 mmol), triphenylphosphine (42
mg, 0.16 mmol), and bipyridine (6 mg, 0.04 mmol) in DMF
(10 mL) was stirred at 85-90 °C. After 24 h, CH2Cl2 (20 mL)
was added and the mixture was filtered. The solution was
concentrated and filtered again to remove some insoluble
impurities. Methanol was added to the methylene chloride
solution to precipitate out the polymer. This process was
repeated twice to give (R)-15 as a white solid in 90% yield.
GPC: Mw ) 6000 and Mn ) 3800 (PDI ) 1.6). [R]D ) -301.9°
(c ) 1.01, THF). 13C NMR (100 MHz, CDCl3) δ 152.87, 136.61,
133.25, 130.27, 129.83, 126.26, 126.16, 125.89, 121.20, 117.79,
95.31, 55.99. 1H NMR (400 MHz, CDCl3) δ 8.15 (s, 2H), 8.00
(m, 2H, small peaks at 7.94, 7.89), 7.60 (m, 2H), 7.26 (m, 4H,
small peaks at 7.35, 7.22, 7.20), 5.10 (m, 2H), 5.00 (m, 2H),
3.16 (s, 6H) (small peaks are due to the end groups). FT-IR
(KBr) cm-1 2957.1 (w), 2916.6 (w), 1591.4 (m), 1473.7 (m),
1240.3 (s), 1151.6 (s), 1076.4 (m), 1016.6 (s), 922.3 (w), 821.7
(w). Anal. Calcd for C24H20O4: C, 77.42; H, 5.38. Found: C,
75.54; H, 5.45.
after centrifugation. The yield of (R)-9 is 58%. GPC: Mw
)
15 000 and Mn ) 6800 (PDI ) 2.2). [R]D ) -215° (c ) 0.52,
CH2Cl2). FT-IR (KBr) cm-1 2928 (s), 2858 (s), 1589 (s), 1491-
(m), 1400 (m), 1327, 1271, 1244, 1093, 1083, 879, 819, 559.
UV-vis (CH2Cl2) nm, λmax ) 240 (sh), 262, 284, 316. Fluores-
cence λemi (CH2Cl2) nm 408. 1H NMR (270 MHz, CDCl3) δ 8.05
(s, 2H), 7.91 (d, J ) 9.5 Hz, 2H), 7.51 (d, J ) 8.8 Hz, 2H), 7.35
(d, J ) 8.8 Hz, 2H), 7.21 (d, J ) 8.8 Hz, 2H), 3.88 (m, 4H),
1.33 (br, 4H), 0.89 (br, 12H), 0.62 (br, 6H). 13C NMR (270 MHz,
CDCl3) δ 154.61, 136.14, 133.31, 129.56, 129.35, 126.05, 125.91,
125.65, 120.58, 116.19, 69.79, 31.31, 29.36, 25.31, 22.46, 13.92.
CD (CH2Cl2) [θ]λ ) +2.28 × 105 (253 nm), -1.85 × 105 (278
nm), -3.02 × 104 (318 nm), +2.07 × 104 (340 nm). Anal.
Calcd for C32H36O2: C, 84.91; H, 8.02. Found: C, 83.91; H,
7.98.
P r ep a r a t ion a n d Ch a r a ct er iza t ion of r a c-9. In
a
procedure similar to (R)-9, rac-9 was prepared in 80% yield.
GPC: Mw ) 11 000 and Mn ) 4700 (PDI ) 2.3). [R]D ) +12.2°
(c ) 0.50, CH2Cl2). UV-vis (CH2Cl2) nm, λmax ) 240 (sh), 262,
274, 280, 316. FT-IR (KBr) cm-1 2931 (s), 2868 (s), 1591 (s),
1462 (s), 1400 (s), 1269 (m), 1093 (m), 802 (m). Fluorescence
λemi (CH2Cl2) nm 408. 1H NMR (270 MHz, CDCl3) δ 8.12 (s
2H), 7.98 (d, J ) 8.8 Hz, 2H), 7.56 (d, J ) 8.1 Hz, 2H), 7.43 (d,
J ) 8.8 Hz, 2H), 7.29 (d, J ) 8.8 Hz, 2H), 3.95 (m, 4H), 1.33
(br, 4H), 0.87 (br, 12H), 0.61 (br, 6H). 13C NMR (270 MHz,
CDCl3) 154.58, 136.12, 133.28, 129.53, 129.32, 126.03, 125.91,
125.62, 120.52, 116.13, 69.76, 31.31, 29.32, 25.29, 22.45, 13.91.
P r ep a r a tion of (R)-9′. Under nitrogen, to a mixture of (R)-
12 (135 mg, 0.25 mmol) and (R)-8 (153 mg, 0.25 mmol) in THF
(4 mL) and K2CO3 (5 mL, 1 M aqueous solution) was added a
THF (1 mL) solution of Pd(PPh3)4 (10 mg, 0.0086 mmol, 3.5
mol %). After heated at reflux for 24 h, the reaction mixture
was cooled to rt and the organic layer was separated and
diluted with CH2Cl2 (50 mL). The organic solution was washed
with 1 N HCl (15 mL) and then concentrated by rotary
evaporation. Methanol was added to precipitate out the
polymer. Centrifugation and removal of the solvent gave a
solid which was redissolved in methylene chloride and pre-
cipitated with methanol. After centrifugation separation, the
polymer (R)-9′ was obtained and dried under vacuum at rt for
P r ep a r a tion of th e Ch ir a l Mon om er (R)-16. To a
solution of (R)-7 (9.31 g, 21.0 mmol) and Et3N (20 mL) in CH2-
Cl2 was added Ac2O (10 mL) at 0 C. The mixture was stirred
o
at 0 oC for 2 h and warmed up to rt for another 2 h. The
reaction was monitored by 1H NMR spectroscopy. After the
reaction was complete, the mixture was poured into H2O and
extracted with EtOAc (3 × 150 mL). The combined organic
layer was washed with brine (20 mL), 1 N HCl (2 × 50 mL),
brine (20 mL), saturated sodium bicarbonate solution (20 mL),
and brine (20 mL) and dried with Na2SO4. After evaporation
of the solvent, the residue was recrystallized from EtOAc/
hexanes (1:3) to give a white crystalline solid, (R)-16 (10.5 g ,
94.8%). Mp 182-183 °C. [R]D ) -77.2° (c ) 1.0, THF). FT-
IR (KBr) cm-1 1772.7 (s), 1585.6 (m), 1493.0 (m), 1400 (w),
1367.6 (m), 1323.2 (w), 1188.2 (s), 1066.7 (m), 1012.7(m), 937.5
(m), 877.7 (m). 1H NMR (CDCl3, 400 MHz) δ 1.88 (s, 6H, CH3),
7.02 (d, J ) 8.8 Hz, 2H, H-8), 7.36 (dd, J ) 1.9, 8.8 Hz, 2H,
H-7), 7.45 (d, J ) 9.2 Hz, 2H, H-3), 7.91 (d, J ) 9.2 Hz, 2H,
H-4), 8.10 (d, J ) 1.9 Hz, 2H, H-5). 13C NMR (CDCl3, 400
MHz) δ 20.67, 120.2, 123.2, 123.3, 127.9, 129.0, 130.2, 130.4,
131.8, 132.7, 147.1, 169.3. Anal. Calcd for C24H16O4Br2: C,
54.57; H, 3.05. Found: C, 54.30; H, 3.01.
P r ep a r a tion of th e Ch ir a l P olybin a p h th yl (R)-17.
Under nitrogen, to a mixture of (R)-16 (9.5 g, 18.0 mmol), zinc
(4.0 g, 61.2 mmol), NiCl2 (0.234 g, 1.80 mmol), PPh3 (1.872 g,
7.2 mmol), and bipyridine (0.288 g, 1.8 mmol) was added DMF
(60 mL). The mixture was stirred at 80-90 °C for 24 h. It
was then cooled to rt and diluted with CH2Cl2 (200 mL). After
filtration, the solid was washed with CH2Cl2 (2 × 50 mL). The
combined organic layer was washed with 1 N HCl (50 mL)
and brine (2 × 30 mL). The solution was concentrated and
precipitated with MeOH. Centrifugation and filtration gave
a solid which was redissolved in CH2Cl2 and precipitated with
MeOH twice. The resulting solid was dried under vacuum at
rt for 24 h to give (R)-17 as a white powder (4.85 g, 73.2%).
[R]D ) -353.0° (c ) 0.5, THF). IR (KBr) cm-1 1765.0 (s), 1593.3
(m), 1500.7 (m), 1466.0 (m), 1429.3 (w), 1367.6 (s), 1331.0 (w),
1201.7 (s), 1082.1 (w), 1041.6 (w), 1012.7 (s), 884.4 (m), 821.7
(s). 1H NMR (CDCl3, 400 MHz) δ 1.89 (s, 6H, CH3), 7.31 (m,
2H), 7.46 (m, H-2), 7.65 (br s, 2H), 8.06 (m, 2H, H-4), 8.21 (br
s, 2H, H-5). 13C NMR (CDCl3, 400 MHz) δ 20.77, 122.6, 123.4,
24 h. The yield of the polymer is 93% (210 mg). [R]D
)
-281.3° (c ) 0.5, THF). GPC: Mw ) 17 600 and Mn ) 7600
(PDI ) 2.3). The UV, IR,1H NMR and 13C NMR data of (R)-9′
are the same as those of (R)-9. Anal. Calcd for C32H36O2: C,
84.91; H, 8.02. Found: C, 84.30; H, 7.89.
P r ep a r a tion of r a c-9′. rac-9′ was prepared in a procedure
similar to that of (R)-9′ in 90% yield. GPC: Mw ) 21 500 and
Mn ) 8100 (PDI ) 2.6). Anal. Calcd for C32H36O2: C, 84.91;
H, 8.02. Found: C, 84.06, H, 7.76.
P r ep a r a tion of th e Ch ir a l Mon om er (R)-14. Under
nitrogen, to a THF solution (20 mL) of NaH (280 mg, 11.7
mmol) was slowly added (R)-7 (2.0 g, 4.6 mmol) at 0 °C. After
5 min, chloromethyl methyl ether (0.88 mL, 11.6 mmol) was
added. The mixture was stirred at rt for 12 h. A small amount
of water was then slowly added to quench the reaction and
the mixture was extracted with ethyl acetate and washed with
brine. After removal of solvent by rotary evaporation, the
product (R)-14 was recrystallized from hexanes as a white solid

Poly(1,1′-bi-2-naphthol)s
J . Org. Chem., Vol. 61, No. 24, 1996 8377
126.3, 126.6, 127.0, 130.0, 131.96, 132.7, 137.9, 147.0, 169.6.
Anal. Calcd for C24H16O4: C, 78.25; H, 4.38. Found: C, 77.30;
H 4.47.
P r ep a r a tion of th e Ch ir a l P olybin a p h th ol (R)-18. To
a THF solution (150 mL) of (R)-17 (4.30 g) was added a water
solution (50 mL) of KOH (5.0 g). The mixture was heated at
reflux for 24 h. The aqueous layer was separated, and 1 N
(275 mg, 92%). 21 is converted to its acetate derivative
through desilylation with n-Bu4NF followed by reaction with
Ac2O, and the ee of the acetate derivative is determined by
1H NMR analysis using Eu(hfc)3 as the chiral shift reagent
and by HPLC analysis using Chiralcel OD column.
Similar procedures were used for the reaction of 19 and 20
catalyzed by (R)-23 and (R)-24.
HCl (100 mL) was added to acidify the water solution.
A
B: Under nitrogen, to a flask containing (R)-18 (56.8 mg,
0.2 mmol based on repeat unit) and 4 Å molecular sieves (450
mg) in CH2Cl2 (4 mL) was added Ti(OiPr)4 (45.0 mg, 0.16
mmol), and the mixture was refluxed for 2 h. After cooled to
rt, 19 (0.1 mL, 1 mmol) was added. After 10 min, the mixture
was cooled to -78 °C and 20 (0.25 mL, 1.2 mmol) was added.
No reaction was observed at -78 °C (24 h), at rt (18 h), and at
reflux (24 h). A similar procedure was applied to prepare (R)-
26 and to use it for the reaction of 19 and 20. Although no
reaction was observed at -78 °C (24 h), about 50% conversion
was observed after the reaction mixture was warmed up to rt
for 18 h.
precipitate was generated which was collected by filtration.
The solid was then redissolved in 0.5 M KOH and precipitated
with 1 N HCl again. After washed with H2O, the solid was
dried under vacuum at rt for 24 h to give (R)-18 as a light
yellow powder (2.80 g, 85%). [R]D ) -139.8 °C (c ) 0.5, 0.5M
aqueous KOH). IR (KBr) cm-1 3421.9 (s), 1593.3 (s), 1500.7
(s), 1466.0 (s), 1381.1 (s), 1336.8 (s), 1250.0 (m), 1215.2 (s),
1157.4 (s), 943.2 (w), 819.8 (s). 1H NMR (400 MHz, 0.5 M
NaOD‚D2O) δ 7.09 (m, 2H), 7.15 (d, J ) 8.4 Hz, 2H), 7.46 (m,
2H), 7.81 (d, J ) 8.8 Hz, 2H), 8.12 (br s, 2H). UV (0.5 M
aqueous KOH) λmax 274, 340 nm. CD (0.5 M aqueous KOH)
[θ]λ ) 2.45 × 104 (252 nm), -2.57 × 104 (276 nm), -1.30 × 104
(336 nm), 9.06 × 103 (364 nm) and 6.62 × 103 (377 [sh] nm).
P r oced u r es for th e Mu k a iya m a Ald ol Con d en sa tion
of 19 a n d 20 Usin g th e Lew is Acid Ca ta lysts. A: Under
nitrogen, to a mixture of (R)-18 (56.8 mg, 0.2 mmol based on
the repeat unit) and CH2Cl2 (5 mL) was added Et2AlCl (19.3
mg, 0.16 mmol) at rt to prepare (R)-22. (This reaction was
carried out in CD2Cl2 where the 1H NMR spectrum had shown
the complete consumption of Et2AlCl after 3 h). After stirred
at rt for 3 h, the mixture was cooled to -78 °C, and 19 (0.1
mL, 1 mmol) and 20 (0.25 mL, 1.2 mmol) were added. The
reaction was complete within 3.5 h (monitored by TLC).
Aqueous workup and flash chromatogrphy gave 21 as an oil
Ack n ow led gm en t. Partial support of this work
from the National Science Foundation (DMR-9529805),
US Air Force (F49620-96-1-0360), and the donors of the
Petroleum Research Fund, administered by the Ameri-
can Chemical Society, are gratefully acknowledged. We
also thank Professor Philip Boudjouk and Professor
Mukund P. Sibi at NDSU for their help on GPC analysis
and optical rotation measurement.
J O961407I