Metallocene-catalyzed synthesis of polyethylenes with side-chain triarylamines: Effects of catalyst structure and triarylamine functionality

Article abstract of DOI:10.1016/j.polymer.2010.08.033

The copolymerization of ethylene with 8-triarylamine (TAA) substituted 1-octene monomers (TAA = triphenylamine (M1), N,N-diphenyl-m-tolylamine (M2), N,N-diphenyl-1-naphthylamine (M3)) using various types of group 4 single-site catalytic systems (Cp₂ZrCl₂ (C1), rac-EBIZrCl₂ (C2), rac-SBIZrCl₂ (C3), i-PrCpFluZrCl₂ (C4), Me₂Si(η⁵-C₅Me₄)(η¹-N-^tBu)TiCl₂ (C5)) was investigated to prepare functionalized polyethylene with side-chain TAA groups. The metallocene/methylaluminoxane (MAO) catalytic systems (C1-C4) efficiently lead to the production of high-molecular-weight poly(ethylene-co-M1). While the C4/MAO catalytic system shows the highest comonomer response, the C5/MAO system exhibits the poor compatibility with the M1 comonomer. Copolymerization results of ethylene with M1-M3 using C4/MAO indicate that M1-M3 are well tolerated by both the cationic active species of C4 and MAO cocatalyst, giving rise to the copolymers with high levels of activity and molecular weight. Inspection of the aliphatic region of the ¹³C NMR spectra of the copolymers (P1-P3) having ca. 11 mol% of M1-M3, respectively, reveals the presence of isolated comonomer units with prevailing [EEMEE] monomer sequences in the polymer chain. UV-vis absorption and PL spectra exhibit an apparent low-energy band broadening for P1 and P2 indicative of intrachain aggregate formation. Whereas P2 and P3 undergo completely reversible one-electron oxidation process, P1 shows relatively poor oxidational stability.

Full text of DOI:10.1016/j.polymer.2010.08.033

Polymer 51 (2010) 4735e4743
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Metallocene-catalyzed synthesis of polyethylenes with side-chain triarylamines:
Effects of catalyst structure and triarylamine functionality
,
,
,
b,
Myung Hwan Park a 1, Jun Ha Park a 1, Youngkyu Do a , Min Hyung Lee
**
*
a Department of Chemistry, KAIST, Daejeon 305-701, Republic of Korea
b Department of Chemistry and Energy Harvest-Storage Research Center, University of Ulsan, Ulsan 680-749, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
The copolymerization of ethylene with 8-triarylamine (TAA) substituted 1-octene monomers
Received 29 June 2010
Received in revised form
13 August 2010
Accepted 14 August 2010
Available online 21 August 2010
(TAA
(M3)) using various types of group 4 single-site catalytic systems (Cp2ZrCl2 (C1), rac-EBIZrCl2 (C2),
rac-SBIZrCl2 (C3), i-PrCpFluZrCl2 (C4), Me2Si(
5-C5Me4)( 1-N-tBu)TiCl2 (C5)) was investigated to
¼
triphenylamine (M1), N,N-diphenyl-m-tolylamine (M2), N,N-diphenyl-1-naphthylamine
h
h
prepare functionalized polyethylene with side-chain TAA groups. The metallocene/methyl-
aluminoxane (MAO) catalytic systems (C1eC4) efficiently lead to the production of high-molecular-
weight poly(ethylene-co-M1). While the C4/MAO catalytic system shows the highest comonomer
response, the C5/MAO system exhibits the poor compatibility with the M1 comonomer. Copoly-
merization results of ethylene with M1eM3 using C4/MAO indicate that M1eM3 are well tolerated
by both the cationic active species of C4 and MAO cocatalyst, giving rise to the copolymers with high
levels of activity and molecular weight. Inspection of the aliphatic region of the 13C NMR spectra of
the copolymers (P1eP3) having ca. 11 mol% of M1eM3, respectively, reveals the presence of isolated
comonomer units with prevailing [EEMEE] monomer sequences in the polymer chain. UVevis
absorption and PL spectra exhibit an apparent low-energy band broadening for P1 and P2 indicative
of intrachain aggregate formation. Whereas P2 and P3 undergo completely reversible one-electron
oxidation process, P1 shows relatively poor oxidational stability.
Keywords:
Metallocene catalysts
Polyethylene
Triarylamine
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
polyolefins with amine groups could be useful for lubricant appli-
cations [12]. Recently, arylamine-functionalized polyolefins find
Functionalized polyolefins have attracted great interest in
a wide range of polyolefin applications since they can endow
polyolefins with improved properties such as adhesion, dyeability,
paintability, and compatibility with polar substrates. In addition to
the chemical or free-radical modification of preformed polyolefins
[1,2], a direct copolymerization of a functionalized olefin monomer
using group 4 single-site catalytic systems has also proven to be
a viable approach although the compatibility of a catalytic system
with Lewis basic monomers is required for high catalyst perfor-
mance [3e11]. Among the various functionalized polyolefins,
amine-functionalized polyolefins may be particularly intriguing
due to their applicability. For example, polyolefins with hindered
aliphatic amines are reported to be effective light stabilizer of
polyolefins [5,9]. It was also suggested that the end-functionalized
their potential use as hole-transporting layer (HTL) materials in the
optoelectronic device applications such as organic light-emitting
diodes (OLEDs) due to their facile formation of stable radical cation
of triarylamine, a proper HOMO level, and high thermal stability
[3,6,13e18]. Since polyolefins generally possess excellent physical/
mechanical properties as well as high chemical and thermal
stability [19], the use of triarylamine (TAA)-functionalized poly-
olefin as HTL materials may be highly desired for the improvements
in solution processability which is suitable for the fabrication of
large-area and flexible OLEDs based on spin-coating and inkjet
printing [20,21]. It was also previously demonstrated that the
nonpolar polymer backbone is advantageous for the retention of
hole mobility of the attached hole-transporting groups [22,23].
Regarding the optoelectronic device application, our group
recently demonstrated that polyethylenes with pendant triphe-
nylamine (TPA) groups can be efficiently produced by copolymer-
ization of ethylene with 8-TPA substituted 1-octene monomer
using rac-Et(Ind)2ZrCl2/MAO catalytic system and moreover such
polymers can function as HTL materials in OLEDs [13]. It was also
* Corresponding author. Tel.: þ82 52 259 2335; fax: þ82 52 259 2348.
** Corresponding author. Tel.: þ82 42 350 2829; fax: þ82 42 350 2810.
E-mail addresses: ykdo@kaist.ac.kr (Y. Do), lmh74@ulsan.ac.kr (M.H. Lee).
1
Tel.: þ82 42 350 2869; fax: þ82 42 350 2810.
0032-3861/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.polymer.2010.08.033

4736
M.H. Park et al. / Polymer 51 (2010) 4735e4743
found that the polymerization behavior such as catalytic activity
and comonomer enchainment is largely affected by the steric
bulkiness of TPA moiety rather than possible Lewis acidebase
interactions between cationic active species and triarylamine
groups. Taking into account that the single-site catalytic systems
can lead to the tailored polymer architecture via a highly controlled
manner in terms of molecular weight, functionalities, and degree of
incorporation of functional groups from varying the catalyst
structure [2,24e26], a proper choice of the catalytic system may
provide an efficient route to control the amount of TAA moieties in
the polymer chain, as well as to investigate the occurrence of Lewis
acidebase interactions between cationic active species and triar-
ylamine groups that would detrimentally affect catalyst perfor-
mance. Furthermore, since the properties of polymers are primarily
related to the pendant triarylamine functionality, the variation of
side-chain TAA group could also be useful in attaining novel poly-
mer properties.
a Spex Fluorog-3 Luminescence spectrophotometer, respectively, in
TCE solvent with a 1-cm quartz cuvette. Cyclic voltammetry
experiment was performed using an AUTOLAB/PGSTAT12 system.
2.3. Synthesis of monomers, M2 and M3
An analogous method for M1 [13] was employed using N-
(4-bromophenyl)arylphenylamine (aryl ¼ m-tolyl for M2 and
1-naphthyl for M3) as a starting material. A solution of N-(4-bro-
mophenyl)arylphenylamine (30.6 mmol) in THF (50 mL) was
treated with 2 equiv of t-BuLi (36.0 mL) at ꢀ78 ꢁC. After stirring for
1 h, the reaction mixture was allowed to warm to room tempera-
ture and stirred briefly at this temperature. The reaction vessel was
cooled to 0 ꢁC and the solution of 8-bromo-1-octene (6.30 g,
33.0 mmol) in THF (50 mL) was added dropwise into the cooled
solution. The reaction mixture was slowly allowed to warm to room
temperature and stirred overnight. The resulting solution was
treated with 50 mL of a saturated aqueous solution of NH4Cl and
the organic portion was separated. The aqueous layer was further
extracted with diethyl ether (2 ꢂ 30 mL). The combined organic
portions were dried over MgSO4, filtered, and evaporated to
dryness. The dark oily crude product was sequentially purified by
flash column chromatography on silica (eluent: n-hexane) and
vacuum sublimation to remove unreacted 8-bromo-1-octene and
triarylamine side product, respectively, affording the monomers as
pale yellow oil. 4-(7-Octen-1-yl)-N-phenyl-N-m-tolylaniline (M2):
In a continuous effort to this area [13,27], the various kinds of
group 4 single-site catalysts were examined to optimize the
copolymerization reactions of ethylene with TAA-containing
a
-olefin monomers, which would thus allow for the efficient
preparation of the TAA-functionalized polyethylene. The selected
catalyst was further investigated to produce the polyethylenes
bearing different TAA functionality. Details of synthesis and char-
acterization of polymers are described in this contribution.
2. Experimental
Yield ¼ 10.4 g (92%). 1H NMR (CDCl3) [ppm]
d 1.37 (m, 6H, 3,4,5-
CH2), 1.63 (m, 2H, 2-CH2), 2.05 (m, 2H, 6-CH2), 2.25 (s, 3H, 9-CH3),
2.57 (t, J ¼ 7.8 Hz, 2H, 1-CH2), 4.95 (dd, J ¼ 10.2/1.6 Hz, 1H, CH2]
CH), 5.01 (dd, J ¼ 17.2/1.6 Hz, 1H, CH2]CH), 5.82 (ddt, J ¼ 17.2/10.2/
6.6 Hz, 1H, CH2]CH), 6.80 (d, J ¼ 7.4 Hz, 1H), 6.87 (d, J ¼ 8.0 Hz, 1H),
6.92e6.97 (m, 2H), 6.99e7.13 (m, 7H), 7.20 (t, J ¼ 8.0 Hz, 2H). 13C
2.1. Materials
All operations were performed under an inert nitrogen atmo-
sphere using standard Schlenk and glovebox techniques. Anhydrous
grade solvents (Aldrich) were dried by passing through an activated
NMR (CDCl3) [ppm] d 21.39 (9-CH3), 28.82, 28.95, 29.18 (3,4,5-CH2),
ꢀ
alumina column and stored over activated molecular sieves (5 A).
31.40 (2-CH2), 33.74 (6-CH2), 35.32 (1-CH2), 114.20 (CH2]CH),
121.09, 122.01, 123.25, 123.55, 124.48, 124.55, 128.90, 129.00,
129.06, 137.41, 138.83, 139.01 (CH2]CH), 145.44, 147.92, 148.11. HR
EI-MS: m/z calcd for C27H31N, 369.2457; found, 369.2459.
Commercial reagents were used without any further purification
after purchasing from Aldrich (4-Bromotriphenylamine, t-BuLi
(1.7 M solution in n-pentanes), 1-octene, triphenylamine (TPA)) and
Strem (zirconocene dichloride (Cp2ZrCl2, C1), rac-ethylenebis
(indenyl)zirconium dichloride (rac-EBIZrCl2, C2), rac-dimethylsi-
lylbis(indenyl)zirconium dichloride (rac-SBIZrCl2, C3)). Iso-
propylidene(cyclopentadienyl)(fluorenyl)zirconium dichloride (i-
PrCpFluZrCl2, C4) [28], dimethylsilyl(tetramethylcyclopentadienyl)
4-(7-Octen-1-yl)-N-1-naphthyl-N-phenylaniline
(M3):
Yield ¼ 11.2 g (90%). 1H NMR (CDCl3) [ppm]
d 1.38 (m, 6H, 3,4,5-
CH2), 1.62 (m, 2H, 2-CH2), 2.07 (m, 2H, 6-CH2), 2.56 (t, J ¼ 7.8 Hz, 2H,
1-CH2), 4.97 (dd, J ¼ 10.2/1.6 Hz, 1H, CH2]CH), 5.03 (dd, J ¼ 17.0/
1.6 Hz, 1H, CH2]CH), 5.84 (ddt, J ¼ 17.0/10.2/6.7 Hz, 1H, CH2]CH),
6.91 (t, J ¼ 7.3 Hz, 1H), 6.99e7.08 (m, 6H), 7.17e7.21 (m, 2H),
7.33e7.38 (m, 2H), 7.44e7.49 (m, 2H), 7.77 (d, J ¼ 8.0 Hz, 1H), 7.89
(d, J ¼ 8.2 Hz, 1H), 7.99 (d, J ¼ 8.4 Hz, 1H). 13C NMR (CDCl3) [ppm]
(tert-butylamido)titanium dichloride (Me2Si(h h
5-C5Me4)( 1-N-tBu)
TiCl2, C5) [29e31], 8-bromo-1-octene [32], N-(4-bromophenyl)
phenyl-m-tolylamine [33], N-(4-bromophenyl)-1-naphthylphenyl-
amine [34], and 4-(7-octen-1-yl)-N,N-diphenylaniline (M1) [13]
were synthesized by the published procedures. 1,1,2,2-Tetrachloro-
ethane (TCE) was used as received from TCI. Polymerization-grade
ethylene monomer from Honam Petrochemical Co. was used after
purification by passing through LabclearÔ and OxiclearÔ filters. 1-
Octene was dried by passing through an activated alumina column.
Methylaluminoxane (MAO) was used as a solid MAO obtained by
evaporation of the solvent from a toluene solution of PMAO
(Chemtura, 30 T). CDCl3 and 1,1,2,2,-tetrachloroethane-d2 (C2D2Cl4)
from Cambridge Isotope Laboratories were used after drying over
d
28.83, 28.96, 29.16 (3,4,5-CH2), 31.42 (2-CH2), 33.76 (6-CH2), 35.24
(1-CH2), 114.16 (CH2]CH), 120.93, 120.99, 121.81, 122.48, 124.35,
126.02, 126.18, 126.23, 126.31, 127.06, 128.30, 128.94, 128.98, 129.05,
131.27, 135.24, 136.61, 139.12 (CH2]CH), 143.76, 146.02, 148.79. HR
EI-MS: m/z calcd for C30H31N, 405.2457; found, 405.2459.
2.4. Polymerization procedure
Into the 250 mL-glass reactor charged with a pre-weighed MAO
([Al]/[Cat.] ¼ 1000 or 2000) was transferred a toluene solution of
a prescribed amount of comonomer (49.5 mL), and the temperature
was adjusted to 75 ꢁC using an external bath. Ethylene monomer
was then saturated at 1 bar with vigorous stirring for 10 min after
degassing several times. Polymerization was started by the injec-
ꢀ
activated molecular sieves (5 A).
2.2. Measurements
NMR spectra of compounds were recorded on a Bruker Avance
400 spectrometer (400.13 MHz for 1H, 100.62 MHz for 13C) at
ambient temperature. Chemical shifts are given in ppm, and are
referenced against external Me4Si (1H, 13C). HR EI-MS measurement
(JEOL JMS700) was carried out at Korea Basic Science Institute
(Daegu). UVevis and PL spectra were recorded on a Jasco V-530 and
tion of a toluene solution of catalyst (0.5 mL, 1.0 mmol of catalyst).
The polymerization time was varied to keep the comonomer
conversion low (typically below 20%). The reactions were quenched
by the injection of ca. 2 mL of 10% HCl solution of EtOH. The
resultant mixture was then poured into the large volume of acidi-
fied EtOH (2%, 500 mL) and stirred for 1 h. The precipitated polymer

M.H. Park et al. / Polymer 51 (2010) 4735e4743
4737
was subsequently collected by filtration and washed with EtOH
(3 ꢂ 50 mL). The resulting polymers were finally dried in a vacuum
oven at 70 ꢁC to constant weight.
2.5. Polymer analysis
1H NMR spectra of the polymers were recorded on a Bruker
Avance 400 spectrometer at 100 ꢁC. 13C NMR spectra were obtained
from a Bruker AMAX 500 (13C; 125.77 MHz) spectrometer at 120 ꢁC
with 90ꢁ pulse angle, 2 s acquisition time, and 8 s relaxation delay.
The samples were dissolved in C2D2Cl4 (for 1H, ca. 5 mg and for 13C,
ca. 90 mg in 0.5 mL) in 5-mm tubes. All the measurements were
performed after complete dissolution by pre-heating the samples
to about 110 ꢁC in an oil bath. The comonomer contents in the
polymers were determined from 1H NMR spectra. 13C NMR peak
assignments of the polymers in the aliphatic region were analo-
gously made according to the reported literatures [35,36]. The
molecular weight (Mn and Mw) and polydispersity (Mw/Mn) of the
polymers were analyzed by high temperature gel-permeation
chromatography (GPC) on a Polymer Laboratories PL 220 at 140 ꢁC
in 1,2,4-trichlorobenzene and calibrated using narrow polystyrene
standards as a reference. The melting transition and glass transition
temperatures (Tm and Tg) of the polymers were measured by
differential scanning calorimetry (DSC, TA Instrument Q100) at
a heating rate of 10 ꢁC/min. Any thermal history in the polymers
was eliminated by first heating the samples to 180 ꢁC, cooling
to ꢀ70 ꢁC at 20 ꢁC/min, and then recording the second DSC scan
from ꢀ70 ꢁC to 180 ꢁC at 10 ꢁC/min. Thermogravimetric analyses
(TGA) were performed under N2 atmosphere using a TA Instrument
Q500 at a heating rate of 20 ꢁC/min from 50 ꢁC to 800 ꢁC.
Chart 1.
controlling the level of incorporation of large comonomer such as
TAA-containing -olefin monomer and thereby leading to the
a
copolymer of a controlled amount of TAA moieties, it was found in
the previous reports that the incorporation of comonomer into the
polyethylene backbone may be inhibited by not only steric effect of
comonomer, but also Lewis acidebase interactions between the
cationic active species of catalyst and the amine functionalities
[5,7,13]. Since the steric openness of catalyst structure and the
extent of such Lewis acidebase interactions are expected to
correlate positively with each other, both factors should be
considered together in the catalyst selection. Thus, the copoly-
merization reactions between ethylene and TPA-containing
a-
olefin monomer using various types of catalyst structures having
different steric openness at the metal center were first investigated
to choose an optimal catalyst for the efficient copolymerization.
Among the single-site catalysts developed so far, the well-
known catalyst structures including the previously examined rac-Et
(Ind)2ZrCl2 (C2) were employed as catalyst (Chart 1). It is well
established in the copolymerization of ethylene or propylene with
higher a-olefins that the ability to incorporate a-olefins is in the
increasing order from C1 to C5 [38,39], which is closely related to
their steric openness at the metal center [40]. 4-(7-Octen-1-yl)-
N,N-diphenylaniline monomer (M1) was introduced as
a comonomer.
2.6. UVevis absorption and photoluminescence measurements
Due to high toxicity of TCE solvent, great caution should be exer-
cised when handling and preparing solutions. UVevisible absorption
and PL measurements were performed in TCE solvent with a 1-cm
quartz cuvette at ambient temperature. The TCE solvent was used
after purification by distillation. The polymer used for the
measurements was purified by precipitation from a TCE solution
into EtOH. The samples were first dissolved in hot TCE and then
diluted to the desired concentrations based on triarylamine groups
at ambient temperature. Quinine sulfate was used as the standard
for determination of the quantum yields (1 ꢂ 10ꢀ4 M in 0.5 M
H2SO4, FF ¼ 0.55) [37].
The copolymerization reactions of ethylene and M1 were ach-
ieved at 75 ꢁC under atmospheric ethylene pressure upon MAO
activation (Scheme 1). As can be seen in Table 1, all the catalytic
systems efficiently lead to the production of the copolymer (P1)
with a decreasing tendency of activity [(kg polymer)/((mol of cat.)$
h$bar)] from C1 to C5 (runs 1e5) although C1 and C2 show a similar
level of activity. The decrease of activity is most apparent for the C5
catalytic system. GPC results indicate the formation of high-
molecular-weight copolymers from ansa-type catalysts (C2eC5),
but the non-bridged C1 shows low molecular weight.
The unimodal and narrow molecular weight distribution with
a polydispersity of ca. 2 indicates the involvement of single active
species in the copolymerization. Estimation of the comonomer
content from the 1H NMR spectra reveals that the comonomer M1
is readily incorporated into the polyethylene backbone and the
extent of the incorporation increases upon varying the catalyst
structure from C1 to C5 at the given comonomer concentration.
While the decreasing melting transition (Tm) of the copolymers
correlates very well with the increasing content of M1, the addi-
tional weak high-melting peak at 119 ꢁC is unexpectedly observed
for the copolymer from the C5 catalytic system (run 5) as evidenced
2.7. Cyclic voltammetry
Cyclic voltammetry measurements were carried out with
a three-electrode cell configuration consisting of platinum working
and counter electrodes and a Ag/AgNO3 (0.1 M in acetonitrile)
reference electrode at room temperature. The coated polymer on
the platinum wire was used as the sample. The solvent was
acetonitrile and 0.1 M tetrabutylammonium hexafluorophosphate
was used as the supporting electrolyte. The oxidation potentials
were recorded at a scan rate of 50 mV/s and reported with refer-
ence to the ferrocene/ferrocenium (Fc/Fcþ) redox couple.
3. Results and discussion
3.1. Catalyst screening
It is highly desirable for catalyst to be able to readily produce
copolymer having a high content of TAA moieties for the facile
control of hole-transporting properties. Although the sterically
open catalyst structure would be definitely advantageous for
Scheme 1. Synthesis of P1 with C1eC5/MAO catalysts.

4738
M.H. Park et al. / Polymer 51 (2010) 4735e4743
Table 1
Copolymerization results of ethylene and M1 with C1eC5/MAO.a
Activityd
10ꢀ3Mw
Mw/Mn
Content of M1f
e
e
g
Tm (ꢁC)
h
Td5 (ꢁC)
Run
Cat.
[M1] (M)
[TPA]/[Cat.]
Tp (sec)
Yield (g)
(mol %)
1
2
3
4
5
6
7
8
9b
C1
C2
C3
C4
C5
C4
C4
C5
C4
C4
0.0563
0.0563
0.0563
0.0563
0.0563
0.113
0.169
0.113
0.0563
0.0563
2815
2815
2815
2815
2815
5650
8450
5650
0
43
45
42
0.353
0.377
0.266
0.166
0.368
0.300
0.920
0.092
0.230
0.190
29.5 ꢂ 103
30.2 ꢂ 103
22.8 ꢂ 103
10.0 ꢂ 103
1.7 ꢂ 103
7.2 ꢂ 103
5.5 ꢂ 103
0.3 ꢂ 103
13.8 ꢂ 103
11.4 ꢂ 103
43
119
177
136
179
143
118
333
21.9
2.17
2.57
1.92
1.72
1.74
2.33
2.29
0.9
1.8
2.4
4.0
6.8
7.8
11.6
5.4
8.8
8.4
123.8
115.2
109.5
100.5
82.6/118.5
81.1
447
451
450
446
431
442
442
n/dj
n/d
n/d
60
780
150
600
1020
60
n/oi
111.7/127.7
n/oi
,c
10b
2815
60
79.7
a
Conditions: [Cat.] ¼ 1.0
m
mol; MAO ¼ methylaluminoxane; PE ¼ 1 bar; [Al]/[Cat.] ¼ 1000; Tp ¼ 75 ꢁC; solvent ¼ 50 mL of toluene.
b
c
d
e
f
1-Octene comonomer.
In the presence of molecular triphenylamine (TPA).
Activity given in units of (kg polymer)/((mol of cat.)$h$bar).
Determined by GPC.
Determined by 1H NMR.
Determined by DSC.
g
h
i
Determined by TGA at 5% weight loss.
Not observed.
j
Not determined.
from the DSC trace in Fig. 1. This result may indicate that the
copolymers from C5 consist of a mixture of polymers with different
lengths of ethylene sequence.
C4 catalytic system in the presence and absence of molecular TPA.
According to the results, the C4 catalytic system shows both the
slightly decreased activity and 1-octene incorporation in the
presence of TPA (run 9 vs run 10), indicating that TPA interferes
with the monomer insertions at the cationic active center of C4 via
Lewis acidebase interactions. In fact, this result is in parallel with
the previous observation in the C2 catalytic system [13]. None-
theless, the retention of high level of activity and 1-octene incor-
poration in the presence of TPA may imply that the comonomer M1
should be electronically well tolerated by the cationic active species
of C4 as shown from the high activity (run 4). To confirm the
compatibility of the C4 catalytic system with the M1 comonomer,
the copolymerization reactions at the increased concentration of
M1 in the feed were examined (runs 6 and 7). The results show the
high level of activity with the moderate decrease upon increasing
the concentration of M1. Particularly, the incorporation of M1
increases nearly in proportion to the concentration of M1 in the
feed. In agreement with this observation, the relatively high reac-
tivity ratio of M1 in the C4 catalyst (rM1 z 0.09 and rE z 19.6) in
comparison with the previously calculated value in the C2 catalyst
(rM1 z 0 and rE z 43) [13] was estimated from curve fitting of the
composition of the monomer feed to the copolymer compositions
(runs 4, 6, 7 in Table 1) using the copolymerization equation based
on the first-order Markov model [13,38] DSC and GPC results are
also well consistent with the formation of uniform copolymers
through single active species. All these results support the
To elucidate this feature, the copolymerization using the C5
catalytic system was examined at the higher M1 concentration in
the feed (run 8). Remarkably, the result shows not only the sharp
decrease of catalytic activity, but also the reduced comonomer
incorporation when compared to that obtained at the lower M1
concentration. Inspection of the DSC curve further reveals the
appearance of two high-melting peaks without any indication of
the formation of the copolymer corresponding to the expected
comonomer content, thus indicating that the comonomer M1 is
poorly compatible with the cationic active species of C5 in the
copolymerization in terms of both activity and comonomer incor-
poration. This finding suggests that the large steric openness at the
metal center of C5 allows the strong Lewis acidebase interactions
between the cationic metal center and the TPA group in M1, leading
to inhibition of the monomer insertion, particularly the sterically
bulky M1 comonomer and thereby giving rise to the formation of
polymer chains with longer ethylene sequences.
To gain insights into the copolymerization reactions of other
metallocene systems (C1eC4), control experiments of 1-octene
copolymerization were investigated using the highly incorporating
Fig. 1. DSC traces of P1s from C1eC5 in Table 1.
Scheme 2. Synthesis of P1eP3 with C4/MAO catalyst.

M.H. Park et al. / Polymer 51 (2010) 4735e4743
4739
Table 2
Copolymerization results of ethylene and M1eM3 with C4/MAO.a
Activityd
10ꢀ3Mw
Mw/Mn
Content of M1f
Tm/Tg (ꢁC)
e
e
g
h
Td5 (ꢁC)
Run
Comon.
[Comon.] (M)
[TAA]/[Cat.]
Tp (sec)
Yield (g)
(mol %)
1b
2
M1
M2
M3
M1
M2
M3
0.0563
0.0563
0.0563
0.158
0.168
0.173
2815
2815
2815
7900
8400
8650
60
60
60
300
390
450
0.166
0.350
0.240
0.470
1.075
0.880
10.0 ꢂ 103
21.0 ꢂ 103
14.4 ꢂ 103
5.6 ꢂ 103
9.9 ꢂ 103
7.0 ꢂ 103
136
164
163
92
122
123
1.92
2.48
1.94
1.74
1.83
1.51
4.0
5.1
3.5
11.4
12.6
11.3
100.5
92.5
103.7
445
449
438
441
443
445
3
4c
5c
6c
n.o.i/ꢀ6.1
n.o./ꢀ7.3
n.o./9.9
a
Conditions: [C4] ¼ 1.0
m
mol; MAO ¼ methylaluminoxane; PE ¼ 1 bar; [Al]/[C4] ¼ 1000; Tp ¼ 75 ꢁC; solvent ¼ 50 mL of toluene.
b
c
d
e
f
Data taken from run 4 in Table 1.
[Al]/[C4] ¼ 2000.
Activity given in units of (kg polymer)/((mol of cat.) h bar).
Determined by GPC.
Determined by 1H NMR.
g
h
i
Determined by DSC.
Determined by TGA at 5% weight loss.
Not observed.
compatibility of the C4 catalytic system with the M1 comonomer.
These findings thus suggest that the copolymerization reactions by
the metallocene structures (C1eC4) are less significantly affected
by the large degree of nitrogen functionality of the TPA groups
probably owing to the steric protection of the metal center by both
cyclopentadienyl ring fragments. In other words, it can be said that
the degree of incorporation of M1 is primarily governed by the
steric openness at the metal center of the metallocene-type cata-
lysts. From these preliminary studies, the C4 catalytic system which
shows the highest comonomer response was employed in the
subsequent copolymerization reactions of ethylene with various
containing a-olefin monomers. As the TAA moieties, the mono-
amine analogues of the well-known molecular HTL materials, TPD
(4,40-bis(phenyl-m-tolylamino)biphenyl) [41] and NPB (4,40-bis
(1-naphthylphenylamino)biphenyl) [42] were introduced for M2
and M3, respectively. The M2 and M3 monomers could also be
obtained in high yield (>90%) from the analogous method
employed in the preparation of M1 [13]. The copolymerization
reactions of ethylene and M1eM3 were first achieved using the C4
catalytic system under the conditions described in the catalyst
screening experiments (Scheme 2).
According to the polymerization results in Table 2, the high-
molecular-weight P2 and P3 copolymers are also readily produced
with high activity (runs 2 and 3). Interestingly, the activities are
higher than that of the P1 copolymer and the activity for the
copolymerization of M2 is highest among them. Furthermore, the
comonomer incorporation is also highest for the P2 copolymer
while that of the P3 is lowest. These results may indicate that the
TAA-containing a-olefin monomers.
3.2. Synthesis of polyethylenes with pendant triarylamines
The 8-TAA substituted 1-octene monomers (M1eM3) with
different triarylamine moieties were considered as the TAA-
Fig. 2. 1H NMR spectra of P1eP3 from runs 4, 5 and 6, respectively, in Table 2 (*from C2D2Cl4).

4740
M.H. Park et al. / Polymer 51 (2010) 4735e4743
Fig. 3. An aliphatic region of 13C NMR spectra of P1eP3 from runs 4, 5 and 6, respectively, in Table 2. Peak assignments were made on the carbon resonances associated with the
isolated comonomer units.
increase in the steric bulkiness of TAA group could lead to the
reduction or prevention of Lewis acidebase interactions between
the cationic metal center and the TAA group, rendering the copo-
lymerization facile. The lower activity for the M1 comonomer
bearing the smallest TAA group than those for the M2 and M3
supports the involvement of such interactions in the copolymeri-
zation as similarly observed in the ethylene/1-octene copolymeri-
zations in the presence of molecular TPA described above.
Comparison of the polymerization results for M2 and M3 shows the
dependence of the copolymerization on the steric effect of TAA
group, suggesting that the nitrogen functionalities in both como-
nomers almost do not compete with the monomer insertions at the
cationic metal center. The higher activity and comonomer incor-
poration observed for the M2 copolymerization than those for the
M1 might be explained by the suggestion that the slight increase in
steric bulkiness by the methyl substitution on the TAA group exert
a negligible influence on the vinyl insertion probably due to the
presence of a long carbon spacer between the vinyl and TAA groups
while such an increase in steric bulkiness apparently reduce the
extent of the direct Lewis acidebase interaction between the TAA
group and the metal center. The narrow molecular weight distri-
bution and single Tms further indicate the formation of uniform
copolymers, confirming that the M2 and M3 comonomers are well
Fig. 5. UVevis absorption (left) and PL (right) spectra of P1eP3 from runs 4, 5 and 6 in
Fig. 4. TGA thermograms of P1eP3 from runs 1e6 in Table 2.
Table 2.

M.H. Park et al. / Polymer 51 (2010) 4735e4743
4741
The 1H NMR spectra of all the copolymers exhibit essentially
identical resonances in the aliphatic region corresponding to the
protons of the side-chain methylenes and the polyethylene back-
Table 3
Optical and electrochemical data of P1eP3.
Polymer labs (nm) lem (FF)
(nm) Egc (eV) Eox (V) HOMOf/LUMOg (eV)
a
b
P1
P2
P3
303
303
294/342
444 (0.03)
438 (0.05)
468 (0.07)
3.48
3.47
3.08
0.601d ꢀ5.44/ꢀ1.96
0.564e ꢀ5.39/ꢀ1.92
0.568e ꢀ5.40/ꢀ2.32
bone except for the additional methyl proton peak at d 2.30 ppm for
the tolyl moiety of P2. The aryl proton resonances are also well-
differentiated between the TAA moieties. While the carbon reso-
nances in the aromatic region of the 13C NMR spectra indicate the
existence of the TAA moieties in the copolymers, inspection of the
aliphatic region of the 13C NMR spectra reveals the well-resolved
resonances from the side-chain and polyethylene backbone, as well
as the isolated comonomer units in the polymer chains with the
identical carbon resonance features for P1eP3. While the major
carbon peaks attributable to the monomer sequence of [EEMEE] are
clearly observed, there are no detectable carbon peaks associated
with sequential comonomer incorporations corresponding to the
[MMM] triad and [MM] dyads. Instead, the only observable are the
a
Absorption measured in TCE (2.0 ꢂ 10ꢀ5 M based on TAA groups).
b
Acquired using a 1.0 ꢂ 10ꢀ5 M solution. Quinine sulfate used as a standard
(
FF ¼ 0.55).
c
Estimated from the absorption edge.
d
e
f
The oxidation onset potential vs a Fc/Fcþ couple.
Taken from the E1/2 vs a Fc/Fcþ couple.
Calculated from the Eox
Estimated from the HOMO and band gap (Eg) energies.
.
g
tolerated by both the cationic active species of C4 and MAO
cocatalyst.
very slight carbon peaks assignable to the [MEM] (
d
24.46 ppm, bb),
34.95 ppm, ag)
[MEEM] ( 30.97 ppm, gg), and [MEME/EMEM] (
d
d
Based on the forgoing copolymerization results, the copolymers
having a moderate comonomer content were prepared for further
consideration in the utilization as HTL materials. For comparison
purpose, the copolymers having the similar comonomer content of
ca. 11 mol% (ꢃ1 mol%) by 1H NMR spectroscopy (vide infra) were
prepared from the controlled polymerization reactions with the
varied concentration of each comonomer in the feed (runs 4e6 in
Table 2). Although the comonomer content was not optimized for
the use in OLEDs, it is noted in the catalyst screening experiment
that the copolymer having such comonomer content showed no
apparent melting transition, pointing to the formation of an
amorphous polymer (run 7 in Table 1). As similar to the M1 copo-
lymerization in Table 1, it can be seen that the copolymerization
reactions at the large feed of the M2 and M3 comonomers also
proceed in a well controlled manner, leading to the production of
the P2 and P3 copolymers with high levels of activity and molec-
ular weight. The identity of the copolymers was analyzed by 1H and
13C NMR spectroscopy and the spectra were shown in Figs. 2 and 3,
respectively.
sequences [35,36]. In spite of the moderate comonomer contents of
ca. 11 mol%, these results are quite different from those found in the
ethylene and usual a-olefin copolymerizations where the carbon
peaks attributable to the sequential comonomer incorporations are
apparently shown at such a comonomer content. This finding could
be ascribed to the very low reactivity ratios of M1eM3 comono-
mers, as similarly noted in the copolymerization of M1 by C2
catalyst [13]. Estimates for the comonomer content from the 13C
NMR spectra [36] are also in good agreement with those from the
1H NMR spectra, only showing a slight difference within ca. 1 mol%.
Overall, these results indicate that the copolymers constitute
a well-defined structure.
While DSC measurements show no apparent melting transitions
for P1eP3 consistent with the increased comonomer incorpora-
tion, the glass transition is observed below an ambient tempera-
ture. Comparison of the Tg values for P1eP3 indicates that the Tg of
the naphthylamine-containing P3 (9.9 ꢁC) is higher than those of
P1 (ꢀ6.1 ꢁC) and P2 (ꢀ7.3 ꢁC) whose values are very similar.
Interestingly, this result is in parallel with the trend of Tgs found in
the molecular triarylamine analogues for P2 and P3, i.e. TPD
(60e65 ꢁC) and NPB (95e100 ꢁC), respectively. This finding thus
suggests that the pendant triarylamine moieties also contribute to
the glass transition behavior of P1eP3. TGA measurements show
high Td5 values (Td5 > 441 ꢁC) for all the P1eP3 (runs 4e6)
comparable to those of the copolymers having a lower comonomer
content (runs 1e3) and the 1-octene copolymers, indicating high
thermal stability of the copolymers irrespective of the nature and
the amount of TAAs (Fig. 4). Despite the poor solubility in common
organic solvents, the copolymers showed good solubility in the
chlorinated solvents such as 1,1,2,2,-tetrachloroethane (TCE) and
chlorobenzene at elevated temperature.
3.3. Optical and electrochemical properties
The optical properties of the copolymers were examined by
UVevis and PL measurements in TCE. As shown in Fig. 5 and
Table 3, P1eP3 (runs 4e6 in Table 2) exhibit a major absorption
band at 294e303 nm assignable to the
pep* transitions in the
triaylamine moieties. The additional low-energy absorption band
observed for P3 (labs ¼ 342 nm) could be ascribable to the transi-
tion to the lowest-lying p* orbital localized on the naphthyl group
[43]. The almost invariant absorption features for P1 and P2 indi-
cate that methyl substitution at the phenyl ring of the triphenyl-
amine moiety negligibly influences the electronic transition [44].
Although the absorption maximum wavelength for P1 and P2 is in
good agreement with those observed for the copolymers having
low M1 contents reported previously [13], the weak low-energy
Fig. 6. Cyclic voltammograms of P1eP3 measured at a scan rate of 50 mV/s in CH3CN.

4742
M.H. Park et al. / Polymer 51 (2010) 4735e4743
Table 4
Comparison of thermal, optical and electrochemical data of polyolefins with pendant triarylamines.
Entry
Polymer
TAA
Tg/Td5 (ꢁC)
Eg (eV)
Eox (V)
HOMO (eV)
LUMO (eV)
Ref.
1
2
3
4
5
6
P1 (run 4)a
P2 (run 5)a
P3 (run 6)a
ENO5
PNB Naph
PNB NPB
Ph3N
ꢀ6.1/441
ꢀ7.3/443
9.9/445
n/db
268/401
365/449
3.48
3.47
3.08
3.48
3.08
3.00
0.601c
ꢀ5.44
ꢀ5.39
ꢀ5.40
ꢀ5.45
ꢀ5.35
ꢀ5.11
ꢀ1.96
ꢀ1.92
ꢀ2.32
ꢀ1.97
ꢀ2.27
ꢀ2.11
this work
this work
this work
[13]
[27]
[27]
Ph2N(m-Tol)
Ph2N(1-Naph)
Ph3N
Ph2N(1-Naph)
4,40-[(1-Naph)PhN]2Biph
0.564d
0.568d
0.608c
0.55d
0.31/0.53d,e
a
In Table 2.
b
c
Not determined.
Quasi-reversible oxidation.
Reversible oxidation.
d
e
The second half-oxidation potential.
tails developed in the region between 350 and 450 nm might be
suggestive of intrachain aggregate formation.
polymer backbone might result in the lower long-term device
stability than the devices based on the polynorbornene derivatives
(entries 5e6). It can be seen that the optical and electrochemical
properties of polymers are solely dependent upon TAA function-
ality. The high oxidation potentials which in turn lead to the deep
HOMO levels for the TPA-containing polymers (entries 1 and 4)
indicate the low stability of radical cations as shown from the
quasi-reversibility of cyclic voltammograms. It is interesting to note
that the content of TPA moiety in P1 (11.4 mol%) and ENO5 (6.1 mol
%) [13] almost does not affect the oxidation potential and HOMO
level, being consistent with the electronic isolation between the
side-chain TAA groups in the copolymers. While the m-tolyl
substituted P2 shows a comparable band gap due to the identical
electronic transition with that of P1, the lower oxidation potential
(higher HOMO level) with a reversible oxidation feature may lead
to better hole-transporting property than P1. On the other hand,
the naphthyl substituted TAA polymers (entries 3 and 5) including
the NPB derivative (entry 6) show completely reversible oxidation
and the high HOMO levels that are close to the work function of ITO
(ꢀ4.7 to ꢀ4.8 eV). It could be thus expected for P3 to exhibit a facile
hole-transporting property as observed in the polynorbornene-
based HTL materials (entries 5 and 6) [27]. Despite the similar
values, a slightly higher HOMO level of the naphthyl-containing
homopolymer (PNB Naph) by ca. 0.05 eV than that of the copol-
ymer (P3, 11.3 mol%) might be attributed to the increased electron
density in the homopolymer owing to the presence of a large
number of Lewis basic TAA groups.
On the other hand, the emission spectra of P1 and P2 exhibit
similar emission maximum wavelengths (lem) but the low-energy
band broadening is apparently observed for both copolymers. It is
noteworthy that such broadening was actually not observed for the
copolymers having low M1 contents up to 6.1 mol% and the lem of
P1 (444 nm) is also slightly red-shifted when compared to those of
low-content copolymers (lem ¼ 436 nm for 6.1 mol% of M1) [13]. As
noted in the absorption spectra, these results could be attributed to
the intrachain aggregation between the side-chain TAA groups
promoted by the flexible nature of the polymer backbone and the
increased amount of neighboring TAA groups [45]. Since the
broadening of the emission band is more pronounced in P1 and
hardly observable for P3, such aggregation appears to be quite
dependent upon the steric bulkiness of the TAA groups, as similarly
found in the luminescent borane polymers [46]. The very low
fluorescence quantum yields of the copolymers are also supportive
of aggregate formation that may lead to emission quenching.
The electrochemical behavior of the copolymers was investi-
gated by cyclic voltammetry (CV). According to the cyclic voltam-
mograms shown in Fig. 6, it can be seen that P1eP3 undergo
one-electron oxidation process. In contrast to the completely
reversible redox behavior observed for P2 and P3, however, the
oxidation wave of P1 is not reversible as previously observed for the
low-content M1 copolymer [13]. This result indicates that
the radical cations derived from P2 and P3 are stable due to the
substitution at the phenyl ring which may prevent dimerization of
triarylamine radicals to tetraarylbenzidine species after oxidation
[47]. Finally, the HOMO and LUMO energy levels of P1eP3 were
calculated from the optical band gap (Eg) and oxidation onset
potential (Eox) measured by the UVevis absorption and cyclic vol-
tammetry, respectively, and are given with respect to zero vacuum
level in Table 3 [48]. The HOMO and LUMO levels for P1eP3 are
calculated to be ca. ꢀ5.4 eV and ꢀ1.9 to ꢀ2.3 eV, respectively. These
levels fall in the typical range observed for triarylamine-based HTL
materials and thus is expected to show hole-transporting ability
when incorporated into HTL of OLED devices.
4. Conclusion
We have demonstrated that the copolymerization of ethylene
with 8-triarylamine substituted 1-octene monomers (M1eM3)
efficiently leads to the triarylamine-functionalized polyethylene by
use of various types of metallocene catalysts (C1eC4) in combina-
tion with MAO cocatalyst. These catalytic systems produced high-
molecular-weight copolymers with controlled incorporation of
comonomer although the sterically open catalyst (C5) suffered from
Lewis acidebase interaction between the cationic metal center and
the amine functionality, giving rise to poor catalytic performance.
Analysis of copolymers having a moderate comonomer content (ca.
11 mol%, P1eP3) by NMR spectroscopy revealed well-defined
polymer structure with the isolated comonomer units in the
polymer chain. While UVevis absorption and PL spectra of P1eP3
suggest intrachain aggregate formation in solution particularly for
phenyl and m-tolyl substituted triarylamine copolymers (P1 and
P2), high oxidational stability was observed for the P2 and P3
copolymers having m-tolyl and 1-naphthyl substituted triaryl-
amines. The copolymers described here may hold promise as hole-
transporting materials for optoelectronic device applications and
relevant studies will be ongoing.
3.4. Comparison of thermal, optical, and electrochemical properties
of polyolefins with pendant triarylamines
In order to see the feasibility of P1eP3 (runs 4e6 in Table 2) for
the use as HTL materials in OLED devices, we compared the
thermal, optical, and electrochemical properties of P1eP3 with
those of the relevant polyolefins with pendant TAAs reported
previously [13,27]. The comparative data given in Table 4 indicate
that while both the polymers based on polyethylene (entries 1e4)
and polynorbornene backbone (entries 5e6) show similar high
thermal stability from their high Td5 values (>400 ꢁC), the low Tgs of
polyethylene-based copolymers (entries 1e4) due to flexibility of

M.H. Park et al. / Polymer 51 (2010) 4735e4743
4743
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Financial supports from the Korea Science and Engineering
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Appendix. Supplementary data
Supplementary data associated with this article can be found in
the on-line version, at doi:10.1016/j.polymer.2010.08.033.
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