Chiral studies in amorphous solids: The effect of the polymeric glassy state on the racemization kinetics of bridged paddled binaphthyls

Article abstract of DOI:10.1021/ja0023231

Optical activity, used here for the first time to gain information about the amorphous solid state, allows previously unavailable insight into the dynamic properties of polymer glasses and their effect on a chemical process. This is accomplished by disper

Full text of DOI:10.1021/ja0023231

J. Am. Chem. Soc. 2001, 123, 49-56
49
Chiral Studies in Amorphous Solids: The Effect of the Polymeric
Glassy State on the Racemization Kinetics of Bridged Paddled
Binaphthyls
Ji-Woong Park,† Mark D. Ediger,*,‡ and Mark M. Green*,†
Contribution from the Herman F. Mark Polymer Research Institute, Polytechnic UniVersity, Six Metrotech
Center, Brooklyn, New York 11201, and Department of Chemistry, UniVersity of WisconsinsMadison,
1101 UniVersity AVenue, Madison, Wisconsin 53706-1396
ReceiVed June 27, 2000
Abstract: Optical activity, used here for the first time to gain information about the amorphous solid state,
allows previously unavailable insight into the dynamic properties of polymer glasses and their effect on a
chemical process. This is accomplished by dispersing in polymer glasses atropisomeric bridged binaphthyls
with appended oligophenyl paddles of varying sizes and studying the racemization kinetics as a function of
temperature. The racemization occurs by a simple one-dimensional twisting motion and, without effect on the
intrinsic mechanism, sweeps out a variable volume of the matrix as the paddle length is increased. The
racemization is limited by the polymer matrix only for probes with a minimum paddle size and only when the
time scale for racemization is comparable to the time scale for segmental motion of the polymer matrix. The
high barrier for this racemization is unique in probe studies of glasses and causes these overlapping time
scales to occur significantly below the glass transition temperature. These measurements yield a clear quantitative
view of the role of segmental dynamics on the racemization kinetics of the binaphthyls and allow the important
demonstration, via the transition from first-order to stretched exponential kinetics, that heterogeneous dynamics
persist deep within the glassy state.
Introduction
associated with motions of small portions of the polymer chain,
that is, the polymer segmental relaxation.6 Although it is
reasonable that one enters the glassy state with a heterogeneity
similar to that encountered in the supercooled liquid, little is
known about the nature of this heterogeneity below Tg.7 Thus,
physical aging in polymer glasses is, for example, routinely
interpreted with a model that does not allow heterogeneous
relaxation.8 Including this heterogeneity may well be essential
to explain technologically important and commonly observed
complex phenomena that occur as the glass very slowly relaxes
toward equilibrium. In addition, information storage schemes
based upon molecular transitions in polymer glasses9 would be
fundamentally limited by such heterogeneity.
Studies of isomerizing probes in rubbery and glassy polymers
often show a crossover from exponential to nonexponential
kinetics.10 This transition to nonexponential kinetics has always
been observed near Tg. But it has been argued that if nonex-
ponential kinetics results from spatial heterogeneity, that is, if
there are subensembles of molecules subject to different
environments, then the transition should occur when there is
Constrained motion is the signature characteristic of super-
cooled liquids and the glassy states they form on further
cooling.1 This phenomenon, which is a subject of considerable
interest,2,3 can be seen not only in the motions of the molecules
forming the glass but also in the motions of probe molecules
incorporated in these materials. Investigations using probe
molecules are especially common in the study of the melt and
glass states formed by polymers,4 and such efforts have proven
invaluable in understanding the changes that occur as the ergodic
melt is cooled into the nonequilibrium glassy state.
Many lines of evidence including these probe studies
demonstrate that liquids just above the glass transition temper-
ature Tg are dynamically heterogeneous with a characteristic
length scale of nanometers.5 The lifetimes of these heteroge-
neous regions increase as the temperature is lowered toward
the glass transition and are at least as long as the time scale
* Corresponding authors.
† Polytechnic University.
‡ University of Wisconsin.
(1) Kauzmann, W. Chem. ReV. 1948, 43, 219.
(5) For leading references see: (a) Ediger, M. D. Annu. ReV. Phys. Chem.
2000, 51, 99. (b) Sillescu, H. J. Non-Cryst. Solids 1999, 81, 243. (c) Bohmer,
R. Curr. Opin. Solid State Mater. Sci. 1998, 3, 378. (d) Li, K.-L.; Jones,
A. A.; Inglefield, P. T.; English, A. D. Macromolecules 1989, 22, 4198.
(6) Wang, C.-Y.; Ediger, M. D., J. Phys. Chem. B 1999, 103, 4177.
(7) Hall, D. B.; Dhinojwala, A.; Torkelson, J. M. Phys. ReV. Lett. 1997,
79, 103.
(8) Mekenna, G. B. ComprehensiVe Polymer Science, 1st ed.; Perga-
mon: Oxford, 1989; Vol. 2, p 311.
(9) Song, O.-K.; Wang, C. H.; Pauley, M. A. Macromolecules 1997,
30, 6913.
(10) (a) Priest, W. J.; Sifain, M. M. J. Polym. Sci., A-1 1971, 9, 3161.
(b) Paik, C. S.; Morawetz, H. Macromolecules 1972, 5, 171. (c) Eisenberg,
C. D. Makromol. Chem. 1978, 179, 2489.
(2) Angell, C. A. Science 1995, 267, 1924.
(3) Ediger, M. D.; Angell, C. A.; Nagel, S. R. J. Phys. Chem. 1996,
100, 13200.
(4) The two broad catagories of probe studies in polymers are (i)
translational and rotational motions and (ii) motions involving shape
changes, that is, isomerizations of the probe. For leading references to the
former large literature see: (a) Heuberger, G.; Sillescu, H. J. Phys. Chem.
1996, 100, 15255. (b) Cicerone, M. T.; Blackburn, F. R.; Ediger, M. D. J.
Chem. Phys. 1995, 102, 471. For leading references to the considerable
literature on probe isomerizations see: (c) Hall D. B.; Hooker, J. C.;
Torkelson, J. M. Macromolecules 1997, 30, 667. (d) Bokobza, L.; Pham
Van Cong, C.; Giordano, C.; Monnerie, L.; Vandendriessche, J.; De
Schryver, F. C. Polymer 1988, 29, 251.
10.1021/ja0023231 CCC: $20.00 © 2001 American Chemical Society
Published on Web 12/08/2000

50 J. Am. Chem. Soc., Vol. 123, No. 1, 2001
Park et al.
Table 1. Molar Extinction Coefficients and Molar Ellipticities of Paddled Bridged Binaphthyls in Solutions in Cyclohexanea
molar
extinction
coeffient
molar
extinction
coeffient
molar
ellipticity
molar
ellipticity
paddled
paddled
binaphthyl
(wavelength/nm)
(wavelength/nm)
binaphthyl
(wavelength/nm)
(wavelength/nm)
(R)-BNO
103 000 (218)
13 000 (306)
9 700 (328)
56 000 (215)
98 000 (252)
28 000 (294)
1.3 × 106 (217)
-1.3 × 106 (229)
7.4 × 104 (327)
-7.4 × 104 (228)
6.0 × 105 (248)
-7.4 × 105 (264)
1.0 × 105 (311)
(R)-BPBNO
64 000 (272)
57 000 (300)
1.6 × 105 (225)
-2.1 × 105 (238)
1.8 × 105 (263)
-3.4 × 105 (291)
3.0 × 104 (340)
-1.7 × 105 (237)
-1.1 × 105 (271)
-2.6 × 105 (301)
1.8 × 104 (347)
(R)-PBNO
(R)-PPBNO
150 000 (213)
120 000 (303)
a Methylene chloride for BPBNO.
an overlap between the segmental relaxation time of the polymer
matrix and the time scale of the isomerization motion, which
may or may not correspond to Tg.11 Up to now the probe
isomerization time scales have been so fast that they intersect
the segmental motions very close to the conventionally deter-
mined Tg. Here we present a probe with a well-defined and
simple invariant isomerization mechanism in which the length
scale can be varied without effect on this mechanism. Because
the time scale for isomerization is far longer than has been
previously available, these probes can explore dynamics deep
in the glassy state.
Chirality is an approach not previously considered as a means
to study the properties of the glassy state although this material
state is amorphous and, as for the fluid solutions classically
used for chiral optical studies, is free of birefringence. However,
the glassy state has served to study the nature of chirality. In
fact, optical activity studies in the glassy state were first
published by Biot in 1832 to counter arguments that birefrin-
gence is solely a characteristic of the crystalline state and thus
to demonstrate the inherent molecular basis of optical activity12
and, as would be understood later, chirality.
restrictions to motion in the glassy state of a much studied model
polycarbonate.
Results and Discussion
Synthesis and Characteristics of the Binaphthyls. Oli-
gophenyl “paddles” were appended to the 6 and 6′ positions of
the nearly enantiomerically pure 1,1′-bridged binaphthyls as
outlined in Scheme 1. Attachment of the paddles to the
binaphthyl core was carried out using conventional Suzuki
coupling.14 Either the paddle group (method A) or the binaphthyl
core (method B) was functionalized with boronic acid depending
on the difficulty of the synthesis of each of the paddles.
Since all the reactions involving the binaphthyl moieties were
performed at temperatures below 100 °C, the loss of enantio-
meric excess of the probes that originated from the starting
compound (R)-1,1′-bi-2-naphthol (93% ee) was negligible. Table
1 shows the UV and CD characteristics of the probes while
Scheme 2 exhibits information on the size of the static molecules
and also the distances along the arc traversed from the ends of
these paddles as each enantiomer is converted to its mirror
image.
Racemization is an isomerization process in which the
interconverting chiral molecules, that is, enantiomers, are of
identical energy. The process is thus entirely driven by an
increase in entropy. In the racemization of bridged binaphthyls
in particular, molecules that owe their chirality to a nonplanar
arrangement of the individually planar naphthalene rings, the
racemization path is a one-dimensional twisting motion so that
both the thermodynamic and kinetic aspects of the process are
simple and well studied.13 Below we show that structural
adaptations to the bridged binaphthyls allow the length scale
of the racemizing motion to be varied without effect on the
mechanism of the process. Most important, the time scale of
the racemization is quite long so the segmental motions of the
polymer matrix are more rapid than the racemization rate even
below Tg. Moreover, the racemization can be energized by light
as well as thermally allowing a wide variation in the enantiomer
lifetime at constant temperature. Observations of how the
racemization characteristics of the varied binaphthyls are
affected by the polymer matrix are shown in this work to yield
new information concerning the time and length scales of
In each of the binaphthyls shown in Scheme 2 the circular
dichroism (CD) spectrum was almost identical to that in a dilute
solution in decalin (see below) and as well was unaffected by
rotation of the sample in the beam of the CD spectrometer
demonstrating the absence of birefringent effects that would arise
from aggregation or crystallization of these molecules in the
polymer matrix.15 In addition, dissolution of the probes in the
polymers was found to have no effect on the polymer Tg.16 See
the Experimental Section for details on the synthesis and
characteristics of the probe molecules and the dissolution
methods involving the glass and melt states of the polymers.
Kinetic Studies in Small-Molecule Solvents. The racem-
ization kinetics of the four probes studied, BNO, PBNO,
BPBNO, and PPBNO (Scheme 2), were characterized by
excellent fits to first-order kinetics, with the rates within
experimental error for any one probe in small-molecule solvents
of varied structure and polarity.
(14) (a) Suzuki, A. Acc. Chem. Res. 1982, 15, 178-184. (b) Sharp, M.
J.; Cheng, W.; Snieckus, V. Tetrahedron Lett. 1987, 28, 5093-5096.
(15) Kuball, H.-G.; Ho¨fer, T. In Circular Dichroism-Principles and
Applications, revd ed.; Berova, N., Nakanishi, K., Woody, R. W., Eds.;
Wiley: New York, 2000; Chapter 5 and references therein. Observation of
birefringent-derived large distortions from the isotropic solution phase CD
spectrum was observed in the glassy state for a p-terphenyl-paddled
binaphthyl (TPBNO), which was found to be the least soluble of the paddled
binaphthyls, excluding it from contributing to the racemization studies in
the polycarbonate matrix.
(16) The DSC for the mixture of BPBNO (1% weight to polymer) and
the polycarbonate that was prepared from their solutions in chloroform gave
almost the same glass transition temperature as the polymer without
BPBNO: ∼145 °C.
(11) (a) Richert, R. Macromolecules 1988, 21, 923. (b) Richert, R.; Heuer,
A. Macromolecules 1997, 30, 4038.
(12) Martin Lowry, T. Optical Rotatory Power; Longmans, Green and
Co. Publishers, 1935; reprinted by Dover Publications: New York, 1964;
p 104.
(13) (a) Carter, R. E.; Liljefors, T. Tetrahedron 1976, 32, 2915. (b) Colter,
A. K.; Clemens, L. M. J. Phys. Chem. 1964, 68, 651. (c) The racemization
properties of binaphthyls have been used before as a probe of a different
material state, liquid crystals. Naciri, J.; Spada, G. P.; Gottarelli, G.; Weiss,
R. G. J. Am. Chem. Soc. 1987, 109, 4352.

Chiral Studies in Amorphous Solids
J. Am. Chem. Soc., Vol. 123, No. 1, 2001 51
Scheme 1. Synthesis of the 2,2′-Bridged 1,1′-Binaphthyls with Varying Paddles Attached to the 6 and 6′ Positionsa
a Synthesis of the pentaphenyl paddle is shown in the box.
Analysis of the twisting about the single bond connecting
the two naphthalene rings with an empirical force field program
showed the force constant for this motion to be independent of
the appended variable oligophenyl paddles.17 The computer-
generated plot of potential energy versus dihedral angle yielded
identical force constants regardless of the probe size when the
dihedral angle centered at the C(1)-C(1′) bond was varied near
55°. This can be shown from the same force field to be the
most stable ground-state conformation independent of paddle
size. It reasonably follows that the energy of activation for the
racemization of the various probes should be identical while
the preexponential factors should be reduced in proportion to
the weight and therefore the number of phenyl rings in the
paddle. This was experimentally confirmed as demonstrated in
the Arrhenius plots in Figure 1 for racemization in dilute solution
in decalin, with the energy of activation for all probes close to
33 kcal/mol and the preexponential factor varying in the range
between 13.2 and 12.3 in logarithmic values, decreasing with
increasing probe size.
Since the preexponential factors are obtained by extrapolating
the data to infinite temperature, that is, to 1000/T f 0 in the
Arrhenius plot in Figure 1a, even small scattering in the
experimental points can cause significant errors, which may be
large compared to the effect caused by the size of the paddles.
Therefore, the rates of racemization for the probes at a constant
temperature were compared to analyze the effect of the probe
size on the preexponential factors. An inverse square relationship
was found between the rate constant and the length of the
paddles, which was revealed by the slope of the line of -0.5 in
the plot of log(rate constant) versus log(paddle length) or log-
(molar mass of the paddle) (Figure 1b). Since the activation
(17) The calculations were carried out on the Spartan 5.0 program with
a Merck force field. We are grateful to K. Nakanishi of Columbia University
for allowing use of this facility.

52 J. Am. Chem. Soc., Vol. 123, No. 1, 2001
Park et al.
Scheme 2. Structures of the Bridged Binaphthyl Probesa
a Also shown are the length of the paddles, the distance along the
arc traversed as one enantiomer is converted to its mirror image, and
the molar mass of the paddles.
Figure 2. (a) Arrhenius plot of the racemization data of the four
paddled bridged binaphthyls in bisphenol A polycarbonate films. (b)
KWW â parameters plotted against inverse temperature. (c) KWW â
parameters for the photoracemization of the probes in bisphenol A
polycarbonate films. The x axes in all three panels are drawn with the
same scale for comparison.
range for the probes dissolved in the bisphenol A polycarbonate.
While the smallest probe, BNO, follows an Arrhenius depen-
dence over the temperature range investigated with the same
energy of activation and preexponential factor determined in
decalin (Figure 1a), the larger probes exhibit different behavior
at high and low temperature. At high temperature, these probes
resemble BNO and exhibit nearly Arrhenius behavior with
apparent activation energies similar to those observed in low-
viscosity solvents. At low temperature, the larger probes show
considerably slower rates than would be expected on the basis
of extrapolation from the high-temperature regime.
Superimposed on the rate data for the racemization in Figure
2a is the independently determined rate of the segmental motion
of the polymer matrix. The temperature dependence of the
segmental relaxation, which does not obey Arrhenius depen-
dence, is often described by the empirical Williams-Landel-
Ferry (WLF) equation.19 This motion corresponds to small
segments of the overall chain rather than motion of the entire
macromolecule. The latter is far slower and depends on the
molecular weight of the polymer. The rate information about
the segmental motions is obtained by various techniques such
as transient mechanical spectroscopy, photon correlation spec-
troscopy, NMR, dielectric spectroscopy, or neutron scattering,
Figure 1. (a) Arrhenius plot of the rates of racemization for the four
probes (Scheme 2) in dilute solution in decalin. (b) log k versus log-
(paddle length (d)) or log(paddle mass (M)). Each data point arises
from a first-order kinetic plot of the racemization at 135 °C.
energies are constant for the binaphthyls of different sizes as
determined experimentally (Figure 1a) as are the force constants
for twisting about the 1,1′-bond independent of paddle size as
determined by computation,17 this result must arise solely from
the effect of the paddle on the preexponential factor, which is
consistent with the relationship between vibrational frequency
and mass, ν (force constant/mass)1/2. This is an example of
a “ponderal effect”, which is the retardation of a chemical
process caused by the weight of rotors.18 With this basic
information in hand on the properties of the binaphthyls (Scheme
2) in small-molecule solvents, we carried the studies into the
glassy state.
(18) (a) de la Mare, P. B. D.; Fowden, L.; Hughes, E. D.; Ingold, C. K.;
Mackie, J. D. H. J. Chem. Soc. 1955, 3200. (b) Werstiuk, N. H.; Dhanoa,
D.; Timmins, G. Can. J. Chem. 1983, 61, 2403. (c) O’Neal, H. E.; Benson,
S. W. J. Phys. Chem. 1968, 72, 1866. (d) Berson, J. A.; Tompkins, D. C.;
Jones, G. J. Am. Chem. Soc. 1970, 92, 5799. (e) Paquette, L. A.; Thompson,
G. L. J. Am. Chem. Soc. 1971, 93, 4920.
Kinetic Studies in Polymer Matrixes. Figure 2a shows the
thermally activated racemization rates over a wide temperature

Chiral Studies in Amorphous Solids
J. Am. Chem. Soc., Vol. 123, No. 1, 2001 53
which monitor local rather than large scale motions of the
chain.20 The steep change of the segmental rate as a function
of temperature near the transformation from the melt to the glass
state typifies glasses formed by polymers and is characteristic
of glasses characterized as fragile.2
Thus, while the segmental motions of the polycarbonate are
much faster than the rate of racemization at the temperatures in
the melt state, the steeply slowing rate of segmental motion as
the system approaches the glass boundary crosses that of the
racemization somewhat below Tg. We have designated this
crossover temperature as Tx in Figure 2a and observe that this
approximate temperature corresponds to a relatively sudden
slowing of the racemization rate for all the probes except the
smallest, BNO. In contrast to the importance of this time scale
overlap, the macroscopic transition from the rubbery to the
glassy state of the polymer matrix, Tg, has no detectable effect
on the racemization rates of any of the probes.
Figure 2b presents a plot of the Kohlrausch-Williams-Watts
(KWW) â parameter vs 1/T.21 The deviation of â from unity
expresses the deviation from first-order racemization kinetics;
that is, the KWW equation reduces to a first-order relationship
when â ) 1. The results mirror those for the Arrhenius
dependence discussed above. Only the smallest probe BNO
shows â ) 1 over the entire temperature range exhibited (Figure
2b). All the larger probes exhibit a deviation to â < 1 near the
temperature Tx below which the Arrhenius plots in Figure 2a
exhibit a steeper temperature dependence.
The results for the thermally activated racemization rates in
Figure 2a,b are consistent with the following picture. At high
temperatures, racemization is much slower than segmental
relaxation. Any differences among different environments in
the polymer matrix are averaged on the time scale of racem-
ization, and thus simple exponential relaxation is observed. The
environment surrounding the racemizing probes is effectively
homogeneous in a situation perfectly analogous to a rate process
in a small-molecule solvent where the dynamic motions of the
solvent are far faster than the rate. However, if the racemization
rate were to continue with the same temperature dependence to
low temperature, probe racemization would proceed faster than
segmental relaxation. While the experiments show that this is
possible for the smallest probe (BNO), racemization of the larger
probes requires substantial cooperation from the surrounding
polymer segments, and hence segmental motions hinder the rate
of racemization below Tx. In addition, in the low-temperature
regime, since racemization occurs on roughly the same time
scale as segmental motion, each probe experiences different
environments that do not exchange significantly on the time
scale of the racemization. Thus, different rates of segmental
relaxation in different regions of the glass give rise to different
racemization rates for the larger probes and therefore to the
associated nonexponential kinetics. Previous work exploring
other dynamics near Tg has also invoked the relationship
between probe and segmental relaxation.22
the racemization below Tg may lead to physical aging23 with a
densification of the polycarbonate, and this could, in principle,
contribute to the observed deviation from first-order kinetics
since this would cause the environment of the probe molecules
to vary during the course of the racemization. How could these
alternative interpretations of the deviations from first-order
kinetics be distinguished?
Speeding the racemization process would reduce the changes
associated with aging of the polymer matrix over the lifetime
of the racemization since the whole racemization takes place
over a shorter time. If aging is contributing to the observations,
accelerated racemization should be characterized by â closer
to 1 at the same temperatures as in Figure 2b. Since bridged
binaphthyls are subject to photochemical racemization involving
excitation to the singlet state by irradiation into the binaphthyl
chromophore followed by intersystem crossing to the triplet,
which then has a far lower barrier for racemization than the
ground state involved in the thermal racemization,24 we studied
the photochemical racemization of the various bridged binaph-
thyls in the same polymer matrix.
As shown in Figure 2c, the deviation from first-order kinetics
now occurs at an even higher temperature than for the purely
thermal racemization in Figure 2b and closer to the macroscopi-
cally observed Tg. This can only be understood if the overlap
with the segmental relaxation of the polymer plays the critical
role since speeding the racemization causes these time scales
to overlap at a higher temperature. While the segmental motions
remain identical if the racemization is thermally or photochemi-
cally activated, the faster photochemical process will intersect
the segmental time scale at a higher temperature. As shown
below another approach allows this to be confirmed in an
entirely different way.
The time scale for segmental motion of any polymer at its
Tg is on the order of 100 s.2,19 Thus, if the binaphthyl probes
are incorporated in a matrix with a higher Tg, the thermal
racemization rate will be increased in the region of the glass
transition. In this manner by studying the racemization in a
higher temperature glass forming polymer, we gain the informa-
tion yielded by the photochemical process (Figure 2c) but in a
purely thermal racemization.
The results of this experiment for a copolycarbonate with a
Tg near 200 °C are consistent with this picture as shown in
Figure 3. Relative to Tx, determined by the intersection of the
segmental and racemization time scales,19,25 the results from
this high-Tg polymer are identical to those shown in Figure 2.
However, in this case, Tg and Tx are nearly the same since the
racemization and segmental rates cross close to the Tg (Figure
3). Again the smallest probe is oblivious to both Tg and Tx while
the larger probes exhibit a steep deviation from both the
Arrhenius dependence and first-order kinetics below Tx.
(21) (a) Kohlrausch, R. Ann. Phys. (Leipzig) 1847, 12, 393. (b) Williams,
G.; Watts, D. C. Trans. Faraday Soc. 1970, 66, 80. See also Analysis of
Exponential and Nonexponential Kinetics Data in the Experimental Section
for information on how the nonexponential kinetic data were treated.
(22) Ngai, K. L. J. Phys. Chem. B 1999, 103, 10684.
(23) (a) Struik, L. C. E. Physical Aging in Amorphous Polymers and
Other Materials; Elsevier: Amsterdam, 1978. Probe studies have been used
to study physical aging: (b) Sung, C. S. P.; Lamarre, L.; Chung, K. H.
Macromolecules 1981, 14, 1839. (c) Lamarre, L.; Sung, C. S. P. Macro-
molecules 1983, 16, 1729. (d) Hwang, Y.; Inoue, T.; Wagner, P. A.; Ediger,
M. D. J. Polym. Sci., Part B: Polym. Phys. 2000, 38, 68.
(24) (a) Irie, M.; Yoshida, K.; Hayashi, K. J. Phys. Chem. 1977, 81,
969. (b) Zhang, M.; Schuster, G. B. J. Phys. Chem. 1992, 96, 3063. (c)
Zhang, M.; Schuster, G. B. J. Am. Chem. Soc. 1994, 116, 4852.
(25) The segmental motions of the higher temperature copolycarbonate
were assigned using the WLF equation with the same parameters as for the
bisphenol A polycarbonate adjusted for the higher Tg (473 K). See also ref
19 for details.
There is, however, an alternative view of the nonexponential
kinetics at low temperature (Figure 2b). The long half-life for
(19) The parameters for bisphenol A polycarbonate are C1 ) 22.9, C2
) 78.6, and Tg ) 418 K in the WLF equation: log[τ(T)/τ(Tg)] ) -[C1(T
- Tg)]/[C2 + (T - Tg)], where τ(T) is the segmental relaxation time at
temperature T and the glass transition temperature (Tg). The τ(Tg) was
assumed as 100 s for the construction of the log[1/τ(T)] in Figure 2. For
more details about the WLF equation and its parameters, see: (a) Ngai, K.
L.; Plazek, D. J. In Physical Properties of Polymers Handbook; Mark, J.
E., Ed.; AIP Press: Melville, NY, 1996; p 341. (b) Ferry, J. D. Viscoelastic
Properties of Polymers; 3rd ed.; John Wiley & Sons: New York, 1980.
(20) (a) Plazek, D. J.; Ngai, K. L. Macromolecules 1991, 24, 1222. (b)
Frick, B.; Richter, D. Science 1995, 267, 1939. (c) Dejean de la Batie, R.;
Laupreˆtre, F.; Monnerie, L. Macromolecules 1989, 22, 2617.

54 J. Am. Chem. Soc., Vol. 123, No. 1, 2001
Park et al.
length scales for motion in the glassy state. In the many
variations of this approach, in which a wide range of chiral
molecules subject to atropisomeric racemization may be con-
sidered,28 new kinds of experiments can be designed to explore
other important aspects of the glassy state such as aging29 and
as well to use the glassy properties of polymers to allow new
kinds of variations of the kinetic properties of atropisomeric
motion that are not possible in conventional solutions. Moreover,
irradiation-induced racemization in glasses also has potential
technological applications. A holographic image could be
produced since an appropriate paddle allows the same wave-
length of light to write an image above Tx and read the
information at lower temperatures without further racemization.
In addition, since the enantiomers have identical relationships
to the matrix, volume change on racemization and therefore
undesirable distortions in the matrix will be avoided. This is a
severe problem limiting other systems that have been proposed
for this mode of information storage.30
Figure 3. Arrhenius plot of the racemization data of the four paddled
bridged binaphthyls in the high-Tg copolycarbonate films (top). KWW
â parameters plotted against inverse temperature (bottom).
Experimental Section
General Procedures. 1H and 13C NMR spectra were recorded on a
Bruker DPX-300 and Varian Unity 200 or 600 as noted. The shifts are
reported in δ (ppm) relative to tetramethylsilane as internal standard.
CD and UV-vis spectra were recorded on a JASCO J-710 spectropo-
larimeter. A homemade CD sample holder connected to a Cole Parmer
temperature controller model 89000 was placed in the JASCO J-710
for high-temperature measurements (150-215 °C). Optical rotation was
measured on a Perkin-Elmer 141 polarimeter. Glass transition temper-
atures were recorded on a Perkin-Elmer DSC7 series with a heating
rate of 10 °C/min under nitrogen flow. Melting points were measured
either on the Perkin-Elmer DSC7 or on a capillary melting point
apparatus (Thomas-Hoover). Elemental analysis was performed by
Schwarzkopf Microanalytical Laboratory (Woodside, NY). MALDI data
were obtained on the PerSeptive Biosystems Voyager DE-STR. A
Fisher Scientific dry bath incubator connected to the Cole Parmer
temperature controller was used to maintain a constant temperature for
kinetic studies in the range of 100-150 °C. Gel permeation chromato-
graphs (GPC) were recorded on a system with a Waters 510 pump in
line with TSK gel HMXL and H5000 columns and dual detectors of a
Waters 440 UV absorbance detector and a Waters R401 differential
refractometer, in which chloroform was eluted with a flow rate of 1
mL/min at 30 °C. The molecular weights of the polymers were
calculated using Waters Millennium software calibrated relative to
polystyrene standards (from Polysciences). A medium-pressure mercury
arc lamp (UVP, 100 W) was used for the photoracemization.
Although the above conclusions concerning time scale are
based on quantitative considerations, the interpretation of the
length scale information in these experiments is subject to
speculation. The data show that BNO differs from all the other
probes in racemizing without restriction from the surrounding
matrix over the entire temperature range studied. While the
length and arc length swept out by this smallest racemizing
probe in the necessary twisting of the two naphthalene rings is
precisely known (5.3 and 8.8 Å), it is not clear what this
information means with regard to the surrounding matrix. For
example, how should these distances be interpreted in com-
parison with recent NMR measurements26 of the length scale
of heterogeneous dynamics in a polymer just above Tg? Our
results suggest that the critical racemization motion for BNO
is sufficiently small that the necessary adjustments in the matrix
are not motions associated with the glass transition, that is, those
of the polymer segments, but rather this smallest of the probes
may be in contact with polymeric moieties that relax far more
quickly. Alternatively there may be sufficient free volume27 to
essentially eliminate contact between the polymer and the BNO.
Experiments are in progress to attempt to discriminate between
these possibilities.
Materials. All solvents and reagents were obtained from commercial
sources and used without further purification, unless otherwise noted.
THF was distilled under N2 from Na/benzophenone. Acetone was dried
over CaCl2. Silica (70-230 mesh ASTM) and TLC plates were
purchased from Merck. Decalin (cis/trans mixture, Aldrich) was distilled
under reduced pressure. All polymers were purified by precipitation
into methanol from the solutions in chloroform followed by drying
under high vacuum at 80 °C for 3 days. Bisphenol A polycarbonate
(GE Lexan LS2) was a kind gift from Prof. G. McKenna of Texas
Tech University. The copolycarbonate with a 65/35 ratio of bisphenol
A and 3,3,5-trimethylhexylidenediphenol was purchased from Aldrich.
1,1′-Bi-2-naphthol was synthesized and resolved by known methods31
Summary
The experiments discussed above demonstrate that spatially
heterogeneous dynamics strongly influence molecular motion
deep within the glass state of a conventional polycarbonate. This
heterogeneity is not sensed until the time scales for segmental
motions and probe racemization overlap and then only above a
particular probe length scale. Below the temperature corre-
sponding to this overlap, racemization is dramatically slowed
by segmental relaxation of the polymer. Under these conditions,
different dynamic environments give rise to different racem-
ization rates. This picture is confirmed by the ability to vary
the relationship between the two time scales by photochemical
racemization in the conventional polycarbonate and by changing
to a copolycarbonate with a higher Tg.
(28) Eliel, E. L.; Wilen, S. H. Stereochemistry of Organic Compounds;
Wiley-Interscience Publishers: New York, 1994.
(29) In lower Tg polymers than the polycarbonates studied here, it is
possible, because of the high thermal barrier, to maintain the polymer at a
temperature below Tg for long periods of time without significant racem-
ization. Kinetic measurements of the photochemical racemization of the
binaphthyl probes as a function of aging time would yield information on
the aging process at the maintained temperature.
We have created, in the work reported here, a new tool based
on optical activity that is applicable for exploration of time and
(26) Tracht, U.; Wilhelm, M.; Heuer, A.; Feng, H.; Schmidt-Rohr, K.;
Spiess, H. W. Phys. ReV. Lett. 1998, 81, 2727.
(27) (a) Eyring, H.; Hirschfelder, J. O. J. Phys. Chem. 1937, 41, 249.
(b) Frenkel, J. Kinetic Theory of Liquids; Oxford University Press: Oxford,
1946. (c) Doolittle, A. K. J. Appl. Phys. 1951, 22, 1471. See also ref 19b.
(30) Hellemans, A. Science 1999, 286, 1502.
(31) (a) Hu, Q.-S.; Vitharana, D.; Pu, L. Teterahedron: Asymmetry 1995,
6, 2123. (b) Tanaka, K.; Okada, T.; Toda, F. Angew. Chem., Int. Ed. Engl.
1993, 32, 1147. (c) Toda, F.; Tanaka, K.; Stein, S.; Goldberg, I. J. Org.
Chem. 1994, 59, 5748.

Chiral Studies in Amorphous Solids
J. Am. Chem. Soc., Vol. 123, No. 1, 2001 55
to yield (R)-1,1′-bi-2-naphthol (1) (93% enantiomeric excess), which
was used as the starting compound for all the probe molecules. (R)-
1,1′-Binaphthyl-2,2′-diyloxymethane (BNO, 2), (R)-6,6′-dibromo-1,1′-
bi-2-naphthol (3), and (R)-6,6′-dibromo-1,1′-binaphthyl-2,2′-diyloxy-
methane (4) were synthesized from the (R)-1,1′-bi-2-naphthol (93%
ee) following known methods.32 1,4-Dibromo-2,5-di-n-hexylbenzene
(9) was synthesized as reported.33 Phenylboronic acid and 4-biphenyl-
boronic acid were obtained by the reaction of the corresponding
Grignard reagents with trimethyl borate followed by acid hydrolysis.34
Tetrakis(triphenylphosphine)palladium (Pd(PPh3)4) was purchased from
Aldrich.
126.87, 127.08, 127.42, 127.57, 127.66, 128.86, 130.68, 131.43, 132.20,
137.19,138.19, 139.61, 140.33, 140.69, 151.47. MS/EI: m/z ) 602
(M+), Mw(calcd) ) 602.7. Anal. Calcd for C45H30O2: C, 89.67; H, 5.02.
Found: C, 88.69; H, 5.05.
1-Bromo-2,5-di-n-hexyl-p-terphenyl (10). To a stirred mixture of
1,4-dibromo-2,5-di-n-hexylbenzene (42 g, 104 mmol) and Pd(PPh3)4
(80 mg) in toluene (70 mL) were added 4-biphenylboronic acid (4.0 g,
20.8 mmol) and 1 M Na2CO3 (70 mL) under an argon atmosphere.
The solution was stirred near 100 °C overnight. After the mixture was
cooled, the organic layer was extracted with diethyl ether, dried with
magnesium sulfate, and evaporated to dryness. About 20 g of excess
1,4-dibromo-2,5-di-n-hexylbenzene was removed by crystallization in
hexanes in a freezer (-20 °C). The residual mother liquor was
concentrated and purified by flash chromatography eluting with hexanes.
(R)-1,1′-Binaphthyl-2,2′-diyloxymethane-6,6′-bisboronic Acid (5).
(R)-6,6′-Dibromo-BNO (4) (3 g, 6.6 mmol) was dissolved in 50 mL
of THF. To the solution was slowly added 1.6 M n-BuLi in n-hexane
(16 mL) at dry ice temperature under an argon atmosphere. The
temperature was maintained so as not to exceed -70 °C. The mixture
was stirred for 5 h at this temperature. Trimethyl borate (4.5 mL, 39.6
mmol) was syringed into the reaction mixture. The resulting solid mass
was shaken several times and stirred overnight while the temperature
was increased to room temperature. The reaction was terminated by
addition of 1 N HCl (50 mL). Diethyl ether (50 mL) was added, and
the organic layer was separated and washed with water twice. The
solution was slowly added to hexanes (200 mL) with vigorous stirring.
White precipitates were collected by filtration and dried under vacuum
at room temperature (1.6 g). This was used for the coupling reaction
without further purification. 1H NMR (300 MHz, DMSO-d6): 5.67 (d,
2H), 7.15 (d, 2H), 7.51 (d, 2H), 7.67 (d, 2H), 8.1 (d, 2H), 8.48 (s, 2H).
1
Yield: 6.5 g (65%). H NMR (300 MHz, CDCl3): 0.82 (t, 3H), 0.89
(t, 3H), 1.08-1.69 (m, 16H), 2.54 (t, J ) 7.8 Hz, 2H), 2.71 (t, J ) 7.7
Hz, 2H), 7.08 (s, 1H), 7.3-7.69 (m, 10H).
2,5-Di-n-hexyl-p-terphenyl-1-boronic Acid (11). n-BuLi (1.6 M
in n-hexane, 17 mL) was added to the solution of 1-bromo-2,5-di-n-
hexyl-p-terphenyl (6.5 g, 13.6 mmol) in dry diethyl ether (30 mL) at
dry ice temperature. The mixture was stirred overnight, being allowed
to warm to room temperature. The mixture was cooled again to -78
°C. Triethyl borate (7.2 mL) was added to the mixture and stirred
overnight at room temperature. HCl (1 N) (20 mL) was added to finish
the reaction, and the product mixture was extracted with diethyl ether
followed by washing with water. After evaporation of solvents, the
solids were dissolved in a minimum amount of hexanes. HCl (1 N)
was added dropwise until the formation of white solids started. The
mixture was kept overnight, and the product was collected by filtration
followed by vacuum-drying. Yield: 2.5 g (42%). 1H NMR (300 MHz,
DMSO-d6): 0.76 (t, 3H), 0.85 (t, 3H), 1.41 (m, 2H), 1.53 (m, 2H),
1.04-1.34 (m, 12H), 2.54 (t, J ) 7.7 Hz, 2H), 2.73 (t, 2H). Anal.
Calcd for C30H39BO2: C, 81.44; H, 8.88; B, 2.44. Found: C, 80.93;
H. 8.92; B, 2.72.
(R)-6,6′-Diphenyl-1,1′-binaphthyl-2,2′-diyloxymethane (PBNO, 6).
To a solution of (R)-6,6′-dibromo-BNO (500 mg, 1.1 mmol) and a
catalytic amount of Pd(PPh3)4 in toluene(5 mL) were added phenyl-
boronic acid (330 mg, 2.74 mmol) and 1 M sodium carbonate (5 mL),
successively. The solution was heated overnight at 100 °C and cooled
to room temperature. Water and enough chloroform were added to
separate the phase. The chloroform layer was washed with water three
times and dried over calcium chloride. After evaporation of the solvents,
the resulting solids were dissolved in a mixture of hexanes and
chloroform. The solution was filtered through silica gel and evaporated
to dryness. The resulting solids were dissolved in a mixture of
chloroform (minimum amount) and acetone with heating. White
crystalline solids were obtained on cooling in the freezer. Yield: 260
1-Bromo-2′′′,5′′′-di-n-hexyl-p-quinquephenyl (12). To a mixture
of 2,5-di-n-hexyl-p-terphenyl-1-boronic acid (11) (1.5 g, 3.39 mmol)
and 4,4′-dibromobiphenyl (5 g, 16.0 mmol) in toluene/THF (1/1
mixture, 30 mL) were added Pd(PPh3)4 (30 mg) and 1 M Na2CO3 (10
mL). The mixture was refluxed for 3 days. After being cooled to room
temperature, the mixture was extracted with chloroform, dried over
magnesium sulfate, and evaporated to dryness. The remaining excess
4,4′-dibromobiphenyl was removed by sublimation (130 °C, 0.05
mmHg) overnight. The residual mass was chromatographed in a silica
gel column eluting with hexanes. The product was recrystallized in
mg (52%). [R]25 ) -795° (chloroform). 1H NMR (300 MHz,
D
CDCl3): 5.72 (s, 2H), 7.37 (t, 2H), 7.44-7.55 (dd, 6H), 7.57-7.68
(m, 4H), 7.73 (d, 4H), 8.05 (d, 2H), 8.15 (s, 2H). 13C NMR (75 MHz,
CDCl3): 103.5, 121.45, 125.83, 126.05, 126.18, 127.34,127.44, 127.50,-
128.91, 130.65, 131.37, 132.15, 137.73, 140.75, 151.41. MS/EI: m/z
) 450 (M+), Mw(calcd) ) 450.5. Anal. Calcd for C33H22O2: C, 87.98;
H, 4.92. Found: C, 86.52; H, 4.80.
1
hexane. Mp: 135-136 °C. Yield: 1.18 g (55%). H NMR (CDCl3,
600 MHz): 0.82 (t, 6H), 1.15-1.25 (m, 12H), 1.55 (m, 4H), 2.6 (t,
4H), 7.19 (s, 1H), 7.21 (s, 1H), 7.37 (t, 1H), 7.44-7.5 (m, 6H), 7.53
(d, 2H), 7.59 (d, 2H), 7.63 (d, 2H), 7.67 (d, 2H), 7.68 (d, 2H). Anal.
Calcd for C42H45Br: C, 80.11; H, 7.20; Br, 12.69. Found: C, 80.24;
H, 7.18; Br, 12.62.
(R)-6,6′-Bis(4-biphenylyl)-1,1′-binaphthyl-2,2′-diyloxymethane
(BPBNO, 7). To a mixture of 4-biphenylboronic acid (350 mg, 1.77
mmol) and (R)-6,6′-dibromo-BNO (4) (280 mg, 0.61 mmol)0 in THF/
toluene(1/2 mixture) (10 mL) were added a catalytic amount of Pd-
(PPh3)4 and 5 mL of 1 M sodium carbonate, successively. The resulting
solution was heated at 80 °C for 5 days. The reaction mixture was
extracted with a large amount of chloroform and washed with water
several times followed by drying over magnesium sulfate. After
filtration, the solvent was evaporated to dryness and the solids were
dissolved in a minimum amount of hot chloroform. Cooling the solution
yielded the product as a white crystalline powder. Yield: 295 mg (80%).
Mp: 332 °C (DSC). [R]25D ) -728° (chloroform). 1H NMR (300 MHz,
CDCl3): 5.74 (s, 2H, CH2), 7.36 (t, J ) 7.4 Hz, 2H), 7.46 (t, J ) 7.2
Hz, 4H), 7.53 (d, J ) 8.4 Hz, 2H), 7.64-7.67 (m, 8H), 7.72 (d, J )
8.5 Hz, 4H), 7.82 (d, J ) 8.5 Hz, 4H), 8.07 (d, J ) 8.9 Hz, 2H), 8.21
(s, 2H). 13C NMR (75 MHz, CDCl3): 103.5, 121.52, 125.70, 126.07,
6,6′-Bis(2′′′,5′′′-di-n-hexyl-p-quinquephenylyl)-1,1′-binaphthyl-
2,2′-diyloxymethane (PPBNO, 8). 1-Bromo-2′′′,5′′′-di-n-hexyl-p-quin-
quephenyl (12) (490 mg, 0.78 mmol) and Pd(PPh3)4 (20 mg) were
dissolved in toluene (10 mL). (R)-BNO-6,6′-bisboronic acid (5) (100
mg, 0.26 mmol) and 1 M Na2CO3 (10 mL) were successively added to
the mixture. The resulting solution was heated at 90 °C for 3 days.
The reaction mixture was extracted with chloroform and washed with
water several times followed by drying over magnesium sulfate. The
solution was evaporated to dryness. The product was obtained by
chromatography through silica gel in hexane/ethyl acetate (7/3).
Yield: 350 mg (97%). [R]25D ) -590° (toluene). 1H NMR (600 MHz,
CDCl3): 8.22 (s, 2H), 8.06 (d, 2H), 7.84 (d, 4H), 7.79 (d, 4H), 7.73 (d,
4H), 7.64-7.70 (m,12H), 7.53 (d, 2H), 7.48 (d, 4H), 7.45 (d, 8H),
7.36 (t, 2H), 7.2 (s, 4H), 5.55 (s, 2H), 2.61 (t, 8H), 1.5 (m, 8H), 1.1-
1.3 (m, 24H), 0.82 (t, 12H). 13C NMR (150 MHz, CDCl3): 14.0, 22.4,
29.3, 31.55, 31.6, 32.7, 103.37, 121.2, 125.38, 125.70, 126.22,126.4,
126.61, 126.8, 127.1, 127.25, 127.4, 128.4, 129.4, 129.5, 130.32, 130.6,
131.05, 131.8, 136.37,136.9,137.30, 138.0, 138.65, 139.21, 139.62,
140.03, 140.61, 140.80, 141.5, 151.5. MS/MALDI: m/z ) 1395 (MH+),
Mw(calcd) ) 1395.9. Anal. Calcd for C105H102O2: C, 90.34; H, 7.36.
Found: C, 90.27; H, 7.52.
(32) (a) Sogah, G. D. Y.; Cram, D. J. J. Am. Chem. Soc. 1979, 101,
3035. (b) Deussen, H.-J.; Hendrickx, E.; Boutton, C.; Krog, D.; Clays, K.;
Bechgaard, K.; Persoons, A.; Bjørnholm, T. J. Am. Chem. Soc. 1996, 118,
6841.
(33) Rehahn, M.; Schlu¨ter, A.-D.; Feast, W. J. Synthesis 1988, 386.
(34) (a) Washburn, R. M.; Levens, E.; Albright, C. F.; Billig, F. A.;
Cernak, E. S. AdV. Chem. Ser. 1959, 23, 102. (b) Coutts, I. G. C.;
Goldschmid, H. R.; Musgrave, O. C. J. Chem. Soc. C 1970, 488.

56 J. Am. Chem. Soc., Vol. 123, No. 1, 2001
Park et al.
Kinetics of Thermal Racemization in Decalin. The probes were
dissolved in decalin at dilute concentrations suitable for CD measure-
ments. The solutions of each probe were split into five glass ampules
and sealed under a slightly negative vacuum. All ampules were placed
in a temperature-controlled heating stage at the same time. The CD
spectrum of the solution was recorded one by one after every desired
interval.
Kinetics of Thermal Racemization in Polymer Films. The
binaphthyl probes of an amount of less than 1% of the polymers by
weight were dissolved in the solutions of the polymers in chloroform,
where the polymer concentration was about 2.5% w/v. The resulting
probe/polymer solutions were dropped on quartz disks. After the films
stood at room temperature overnight, they were dried under high
vacuum for 3 days at 40 °C or baked at 100 °C for 2-3 h.
Prior to kinetic measurements, the films were heated to above the
glass transition temperatures of the polymers. The probe/bisphenol A
polycarbonate films were heated at 160 °C for 15-20 min and cooled
to room temperature. The probe/copolycarbonate films were heated at
205 °C for 5 min and then cooled to room temperature.
For kinetic runs above temperatures of about 150 °C, the film was
placed in a homemade sample holder with a temperature controller
(stability (0.2 °C) attached. CD spectra were recorded at appropriate
intervals. For kinetic measurements at temperatures below about 150
°C, the initial circular dichroism of the film was recorded before the
films were heated. Then the films were heated in a temperature-
controlled heating stage (stability (0.5 °C) that is placed outside of
the CD instruments. After the desired interval, the CD measurements
were made at ambient temperatures. The samples were returned to the
heater for further measurements as soon as the measurements were
completed.
The extrema in the CD spectra of the probes were normally read
for the kinetic analysis. The intensity of the circular dichroism signal
of the films was directly utilized. PBNO, BPBNO, and PPBNO have
strong positive and negative signals in the wavelength range longer
than 240 nm, at which the polymer films prepared as above usually
exhibited a UV cutoff. The difference of the two extrema was used for
the analysis. The relatively weak CD signal of BNO in the range longer
than 240 nm could be overcome by using thicker films. The CD
maximum value near 325 nm was subtracted from that at 370 nm
(baseline).
Kinetics of Photoracemization in Bisphenol A Polycarbonate. The
probe/polymer films were prepared in the same way as for the samples
for thermal racemization. The films were placed in a black anodized
aluminum-based heating block with deep cylindrical holes with a
slightly larger diameter than that of the quartz disk on which the film
was coated. The films were irradiated vertically from right above at a
constant distance for all samples to be compared. The films were
blocked from the light until the sample was heated to the desired
temperature and the lamp was fully warmed. After a desired time, the
lamp was shut off and the CD spectrum of the film was measured.
Analysis of Exponential and Nonexponential Kinetic Data. For
first-order kinetics, the rate constant of the racemization was calculated
by a linear regression using the usual expression for a reversible first-
order racemization reaction: k1 + k-1 ) (1/t) ln(CD0/CDt), where t is
the elapsed time and CDt and CD0 are the circular dichroism signals at
times t and zero, respectively. Since the equilibrium constant K ) 1,
k1 ) k-1 and therefore k ) k1 ) k-1 ) (1/2t) ln(CD0/CDt). The decay
rate of the CD signal is twice the rate constant (k).
For nonexponential kinetics, the normalized circular dichroism signal,
CD0/CDt, was fitted to the KWW equation, exp[-(kKWW t)â], where
kKWW, the KWW fitted rate constant of racemization, was used instead
of the usual 1/τ (relaxation time) for this equation. The average rate
constant, k, was calculated using the equation (1/2)kKWWâ/Γ(1/â), where
Γ is a gamma function. For the exponential kinetics, the rate constant
(k) of the racemization is equal to (1/2)kKWW with â ) 1.
Acknowledgment. The work at the Polytechnic University
was supported by the Polymers and Organic Dynamics Programs
of the National Science Foundation (Grant CHE-9975471), by
the Office of Naval Research, and by the donors of the
Petroleum Research Fund, administered by the American
Chemical Society. The effort at the University of Wisconsin
was also supported by the National Science Foundation (Grant
CHE-9988629). This work is abstracted from the doctoral thesis
(2000) of J.-W.P. at the Polytechnic University.
JA0023231