Copolymers with Cyanoterphenyl Moieties by Atom
Transfer Radical Polymerization
KUAN-WEI LEE, KUNG-HWA WEI, HONG-CHEU LIN
Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu, Taiwan, Republic of China
Received 11 April 2006; accepted 18 May 2006 DOI: 10.1002/pola.21556
Published online in Wiley InterScience (www.interscience.wiley.com).
ABSTRACT: A series of new mesomorphic block copolymers composed of different macro-initiators, including poly(ethylene oxide), polystyrene, and poly(ethylene oxide)-b-polystyrene, and polymethacrylate with a pendent cyanoterphenyl group were syn-thesized through atom transfer radical polymerization. The number-average molecu-lar weights of the three diblock copolymers, determined by gel permeation chromatog-raphy, were 10,254, 9,772, and 15,632 g mol1, and their polydispersity indices were 1.17, 1.28, and 1.34. The mesomorphic and optical properties of all the block copoly-mers were investigated, and they possessed a smectic A phase with mesophasic ranges wider than 1008C. Moreover, X-ray diffraction patterns provided evidence of the smectic A phase and the corresponding interdigitated packing of all the polymers.
V
VC 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4593–4602, 2006
Keywords: atom transfer radical polymerization (ATRP); block copolymers; liquid-crystalline and photoluminescence properties; X-ray
INTRODUCTION
In recent years, many research groups have con-centrated on the synthesis of liquid-crystalline (LC) block copolymers and the characterization
of their phase behavior and morphology.1–6
These kinds of LC block copolymers are synthe-sized via different types of living free-radical
polymerizations.7–10 The interest in these types
of materials resides in the combined properties of two (or more than two) completely different polymers that are chemically bonded to each other. Macrophase separation takes place be-cause of the segregation of different polymer chains. Regarding LC properties, the combina-tion of rigid cores and flexible chains is required for the LC molecular design. In general, there
are two kinds of LC block copolymers: main-chain and side-main-chain LC block copolymers. Mesogenic groups are connected along the poly-mer backbones as main-chain copolypoly-mers, and pendent mesogenic groups are attached to the polymer backbones via flexible spacers as side-chain copolymers.
Side-chain LC polymers are often used in electro-optical applications; different kinds of
rigid cores, including azobenzene11–13 and
biph-enyl units,14–19are used in the mesogenic
mono-mers. In previous studies, aromatic cores in con-jugation with a terminal cyano group had high values of birefringence and reasonable viscosities. Moreover, they were chemically and photochemi-cally stable. Cyanoterphenyl derivatives have been used in a wide range of nematic mixtures possessing high thermal, chemical, and photo-chemical stabilities.20Therefore, a series of novel side-chain LC block copolymers consisting of dif-ferent flexible macroinitiators, including poly(eth-Correspondence to: H.-C. Lin (E-mail: [email protected].
edu.tw)
Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 44, 4593–4602 (2006)
V
ylene oxide) (PEO), polystyrene (PS), and PEO-b-PS, and polymethacrylate with a pendent cyano-terphenyl group were synthesized through atom transfer radical polymerization (ATRP). Further-more, the thermal, mesomorphic, and PL proper-ties of all the polymers were investigated in this study.
EXPERIMENTAL
Measurements 1
H NMR spectra were recorded on a Varian
Unity 300-MHz spectrometer with CDCl3 and
dimethyl sulfoxide-d6 (DMSO-d6) as solvents.
Elemental analyses were performed on a Her-aeus CHN-OS Rapid elemental analyzer. The transition temperatures were determined by dif-ferential scanning calorimetry (DSC; Diamond model, PerkinElmer) with a heating and cooling
rate of 5 8C/min. The mesophases were studied
with a polarizing optical microscope (DMLP mo-del, Leica) equipped with a hot stage. Thermog-ravimetric analysis (TGA) was conducted on a DuPont Thermal Analyst 2100 system with a TGA 2950 thermogravimetric analyzer at a
heat-ing rate of 108C/min under nitrogen. Gel
permea-tion chromatography (GPC) analysis was con-ducted on a Waters 1515 separation module with chloroform as the eluant against a PS calibration curve. Ultraviolet–visible (UV–vis) absorption spectra were recorded in dilute chloroform
solu-tions (106M) on an HP G1103A
spectrophotom-eter. Photoluminescence (PL) spectra were ob-tained on a Hitachi F-4500 spectrophotometer. Polymer solid films were spin-coated on quartz substrates from chloroform solutions with a con-centration of 1 mg/mL.
Materials
The chemicals and solvents were reagent-grade and were purchased from Aldrich, Acros, TCI, and Lancaster Chemical Co. Dichloromethane and tetrahydrofuran (THF) were distilled to keep them anhydrous before use. Pyridine was dried via refluxing over calcium hydride. The other chemicals were used without further purification.
Synthesis
Scheme 1 summarizes the steps involved in the synthesis, with the details of each step given next.
4-Bromo-40-octoxybiphenyl (2)
1-Bromooctane (11.6 g, 60 mmol), 4-bromo-40
-hydroxybiphenyl (10 g, 40 mmol), and potassium carbonate (16.6 g, 120 mmol) were dissolved in butan-2-one (100 mL) and reacted under reflux for 24 h. After the mixture cooled to room tem-perature, the potassium salt was filtered off. The solvent was removed by a rotavapor, and the crude product was recrystallized from
petro-leum ether (bp ¼ 35–60 8C) to yield a white
solid (13.5 g, 93%). 1 H NMR (ppm, CDCl3, d): 0.89 (t, J ¼ 6.9 Hz, 3H), 1.29–1.47 (m, 10 H), 1.80 (quintet, J ¼ 6.6 Hz, 2H), 3.98 (t, J ¼ 8.6 Hz, 2H), 6.99 (d, J ¼ 8.8 Hz, 2H), 7.40–7.54 (m, 6H).21 40-Octoxybiphenyl-4-ylboronic Acid (3)
2 (5 g, 13.8 mmol) was dissolved in THF (200 mL), and then n-butyllithium (8.9 mL, 2.5 M, 22.1
mmol) was added dropwise at 78 8C to react.
The reaction mixture was maintained under these conditions for 1 h more. Furthermore, it was added dropwise to a trimethyl borate
solu-tion (3.5 g, 33.2 mmol) at 78 8C. The solution
was allowed to cool to room temperature over-night. The final solution was acidified with a 10% HCl solution (100 mL) and stirred for 45 min at room temperature. The solution was washed with a saturated sodium carbonate solution and water, and THF was removed. The crude product was extracted by diethyl ether, and the organic layer was dried over magnesium sulfate. After the solvent was removed by a rotavapor, the resulting solid was washed with petroleum ether and briefly dried on a filter to obtain a white solid (6.0 g, 80%). 1 H NMR (ppm, DMSO-d6, d): 0.85 (t, J ¼ 7.2 Hz, 3H), 1.24–1.41 (m, 10H), 1.71 (quintet, J ¼ 6.6 Hz, 2H), 3.98 (t, J ¼ 6.6 Hz, 2H), 6.99 (d, J ¼ 8.8 Hz, 2H), 7.56–7.62 (m, 4H), 7.83 (d, J ¼ 8.8 Hz, 2H), 8.03 (s, 2H).21 4-Octoxy-400-cyanoterphenyl (5)
Compound 4 (2.3 g, 12.8 mmol), compound 3 (5.0 g, 15.3 mmol), and tetrakis(triphenylphos-phine)palladium(0) (740 mg, 0.64 mmol) were reacted in THF (100 mL) for 10 min, and then
100 mL of a 2 M aqueous Na2CO3 solution was
added. The mixture was reacted and refluxed for 48 h. After the reaction, the cooled solution was washed with dilute hydrochloric acid (10%)
and water and dried over magnesium sulfate. The final solution was purified by column
chro-matography (silica gel, 1:1 CH2Cl2/hexane) to
yield a white solid (4.7 g, 83%). 1 H NMR (ppm, CDCl3, d): 0.87 (t, J ¼ 6.6 Hz, 3H), 1.26–1.46 (m, 10 H), 1.80 (quintet, J ¼ 6.9 Hz, 2H), 3.99 (t, J ¼ 6.6 Hz, 2H), 6.98 (d, J ¼ 9.0 Hz, 2H), 7.54 (d, J ¼ 9.0 Hz, 2H), 7.62 (m, 4H), 7.71 (m, 4H). 4-Hydroxyl-400-cyanoterphenyl (6)
5 (3.7 g, 9.5 mmol) was dissolved in dry chloro-form (150 mL) under nitrogen, and then boron
tribromide (4.8 g, 19.1 mmol) was added
drop-wise and reacted at 78 8C. The mixture was
allowed to warm to room temperature and reacted for 24 h. The solution was washed with sodium hydroxide (1 M, 50 mL). Then, the solu-tion was acidified with 10% HCl and stirred for 4 h. Finally, the suspension was filtered off and purified by column chromatography (silica gel, ethyl acetate) to yield a white solid (2.37 g, 92%). 1 H NMR (ppm, DMSO-d6, d): 6.86 (d, J ¼ 8.4 Hz, 2H), 7.55 (d, J ¼ 8.7 Hz, 2H), 7.71 (d, J ¼ 8.4 Hz, 2H), 7.79 (d, J ¼ 8.7 Hz, 2H), 7.91 (m, 4H), 9.63 (s, 1H).
4-(6-Hydroxyhexyloxy)-400-cyanoterphenyl (7) 6 (2.4 g, 8.7 mmol), 6-chloro-1-hexanol (2.1 g,
11.3 mmol), K2CO3 (3.6 g, 26.1 mmol), and less
KI (20 mg) were dissolved in 200 mL of DMF and refluxed overnight. The reaction mixture was then cooled and poured into 200 mL of water and was stirred for 2 h. The crude prod-uct was extracted with ethyl acetate, and the or-ganic layers were washed with a saturated aqueous solution of NaCl and water; then, the organic layer was dried over magnesium sulfate. After the solvent was removed by a rotavapor, the residue was recrystallized from absolute ethanol to give a colorless solid (2.6 g, 80%).
1 H NMR (ppm, DMSO-d6, d): 1.28–1.70 (m, 8H), 3.44 (m, 2H), 3.99 (t, J ¼ 6.6 Hz, 2H), 4.32 (t, J ¼ 5.0 Hz, 1H), 7.00 (d, J ¼ 8.6 Hz, 2H), 7.62 (d, J ¼ 8.6 Hz, 2H), 7.71(d, J ¼ 8.4 Hz, 2H), 7.80 (d, J ¼ 8.4 Hz, 2H), 7.90 (m, 4H). 4-(6-Methacryloyloxyhexyloxy)-400 -cyanoterphenyl (8)
7 (2.6 g, 7.0 mmol), triethylamine (2.1 g, 21 mmol), and 2,6-di-tertbutyl-4-methylphenol (200 mg; used as a thermal inhibitor) were dissolved in 150 mL of anhydrous THF under a nitrogen atmosphere, and then methacryloyl chloride (2.2 g, 21 mmol) was added dropwise. The reaction mixture was heated under reflux overnight and then was cooled and poured into 200 mL of an aqueous
solution of NH4Cl (10%). The crude product was
extracted with CH2Cl2. The resulting organic
layer was washed with a saturated solution of NaCl and water, and the organic layer was dried over magnesium sulfate. After the solvent was removed by a rotavapor, the resulting solid was purified by column chromatography with hex-ane/ethyl acetate (7:3) as an eluant to yield a colorless solid (2.3 g, 75%). 1 H NMR (ppm, CDCl3, d): 1.46–1.53 (m, 4H), 1.62–1.74 (m, 2H), 1.82 (m, 2H), 1.93 (s, 3H), 4.00 (t, J ¼ 6.3 Hz, 2H), 4.15 (t, J ¼ 6.6 Hz, 2H), 5.53 (m, 1H), 6.09 (m, 1H), 6.97 (d, J ¼ 8.7 Hz, 2H), 7.55 (d, J ¼ 8.7 Hz, 2H), 7.64 (m, 4H), 7.71 (m, 4H). ELEM. ANAL. Calcd. for C29H29NO3: C, 79.24%; H, 6.65%; N, 3.19%. Found: C, 79.30%; H, 6.71%; N, 3.05%.
Macroinitiator I1
A solution of 1.8 g (7.7 mmol) of 2-bromo-2-methylpropionyl chloride in 10 mL of dry THF
was added to a mixture of 1.1 g (10 mmol) of triethylamine and 10 g (5 mmol) of poly(ethyl-ene glycol) methyl ether with a number-average
molecular weight (Mn) of 2000 g mol1 in 30 mL
of THF at 0 8C, and then the mixture was
stirred for 18 h. After the mixture was filtered, half of the solvent was evaporated, and the poly (ethylene glycol) macroinitiator was precipitated into cold ether. After dissolution in ethanol, the solution was stored in a refrigerator to recrystal-lize to yield a white solid.
Yield: 55%.1H NMR (ppm, CDCl
3, d): 1.94 (s, 6H), 3.38 (s, 3H), 3.54–3.76 (m, 174H), 4.33 (dd, 2H).
Preparation of Macroinitiators I2, I3, and I4
Polymerization of Macroinitiator I3. To a
Schlenk flask, 3.46 mg of N,N,N0,N0,N00 -pentame-thyldiethylenetriamine (PMDETA; 0.02 mmol), 14.3 mg of CuBr (0.1 mmol), and 5.5 g of styrene (52.8 mmol) were added, and they were stirred for 30 min. 1-(1-Bromoethyl)benzene (74 mg, 0.4 mmol) was added, and the mixture was im-mediately frozen in liquid nitrogen in vacuo. Af-ter several freeze–thaw cycles, the flask was sealed in vacuo and put in an oil bath at 100 8C for 20 h. After the reaction, the content was dis-solved in chloroform. After being concentrated, the chloroform solution was precipitated into methanol. The precipitation was repeated three
times. The final product was dried at 50 8C
in vacuo. Mn was 10,337 g mol1, and the
poly-dispersity index [PDI; i.e., weight-average
molecu-lar weight/number-average molecular weight
(Mw/Mn)] was 1.28 (by GPC).
The macroinitiators (I2 and I4) were synthe-sized with analogous procedures via ATRP, and
the Mn and PDI values for I2 and I4 are given
next.
Macroinitiator I2. Mn was 1016 g mol1, and
PDI (Mw/Mn) was 1.11 (by GPC).
Macroinitiator I4. Mn was 27,474 g mol1, and
PDI (Mw/Mn) was 1.35 (by GPC).
Preparation of the Homopolymer and Block Copolymers
The block copolymers (P1–P4) and homopoly-mer (P5) were synthesized with an analogous procedure, except for the utilization of different initiators (see Scheme 2).
Preparation of Polymer P1 (Polymerization of Monomer 8 with Macroinitiator I1). CuCl (4 mg, 0.04 mmol), 20 mg (0.01 mmol) of I1, and 440 mg (1 mmol) of monomer 8 were mixed
under nitrogen.
1,1,4,7,10,10-Hexamethyltrie-thylenetetramine (HMTETA; 11 lL, 23 mg, 0.1 mmol) in 6 mL of anisole was added through a syringe. The mixture was degassed three times with the freeze–pump–thaw procedure and sealed in vacuo. After stirring for 30 min at room temperature, the mixture was reacted in a
preheated 80 8C oil bath for 12 h. The solution
was passed through a neutral Al2O3 column
with THF as an eluant to remove the catalyst. The white filtrate was concentrated under re-duced pressure and reprecipitated twice into methanol. The white product of the polymer was collected by filtration and dried in vacuo. The
yield was 150 mg (34%). Mnwas 10,258 g mol1,
and PDI (Mw/Mn) was 1.17 (by GPC).
P2. The yield was 158 mg (33%). Mnwas 9772 g
mol1, and PDI (Mw/Mn) was 1.28 (by GPC; the
soluble part of the polymer).
P3. The yield was 206 mg (32%). Mnwas 15,632
g mol1, and PDI (Mw/Mn) was 1.34 (by GPC;
the soluble part of the polymer).
P4 and P5. No data were obtained because of the poor solubilities of the longer cyanoter-phenyl blocks.
RESULTS AND DISCUSSION
Synthesis and Characterization
ATRP has proven to be a very powerful polymer-ization technique for the preparation of block
copolymers from a wide variety of
mono-mers.22,23 In this work, macroinitiators,
includ-ing PEO (I1),11PSs (I2 and I3),6 and PEO-b-PS
(I4), were used to copolymerize cyanoterphenyl methacrylate monomers to produce LC cyanoter-phenyl block copolymers. GPC measurements
Figure 1. 1H NMR spectra of block copolymers P1, P3, and P4. 4598 LEE, WEI, AND LIN
indicated that all macroinitiators (I1–I4) and the diblock copolymers (P1–P3) with extended molecular weights had narrow polydispersities. Because of the poor solubilities of the longer cyanoterphenyl blocks in P4 and P5, no GPC
data were obtained for these polymers. The Mn
values of the macroinitiators (I2, I3, and I4) determined by GPC were 1016, 10,337, and
27,474 g mol1 with PDIs of 1.11, 1.28, and
1.35, respectively. The precursor of I1 was
procured from commercially available PEO (Mn
¼ 2000 g mol1) with PDI ¼ 1.04. The
cyanoter-phenyl homopolymer (P5) exhibited poor solubil-ity in conventional organic solvents and so was
not characterized and processed into films.24
Figure 1 shows the NMR spectra of block copoly-mers P1, P3, and P4; the NMR spectrum of P2 is omitted because of its similarity to that of P3.
Table 1 shows the Mn values of the diblock
copolymers containing LC cyanoterphenyl blocks (P1–P3) as determined by GPC, for which chlo-roform was used as an eluant. Triblock copoly-mer P4 also exhibited poor solubility in conven-tional organic solvents. Although the flexible chains of the PEO and PS blocks were longest in P4, this suggested that the molecular weight of the LC cyanoterphenyl block might be poly-merized to such a high degree of polymerization as to induce poor solubility.
Thermal Properties and X-Ray Investigation
The average molecular weights and PDIs of these macroinitiators (I1–I4) and block copoly-mers (P1–P3) were obtained by GPC. The ther-mal stability of the polymers (P1–P4) under an atmosphere of nitrogen was evaluated by TGA, which indicated that the degradation
tempera-ture of 5% weight loss (Td) in nitrogen was
greater than or equal to 325 8C for all the
poly-mers (shown in Table 1). The mesomorphism was characterized with polarizing optical mi-croscopy (POM) and DSC. The phase-transition temperatures and enthalpies of all the polymers are summarized in Table 2. Regarding these results, all block copolymers (P1–P4) possessed a smectic A phase, which also existed in the cya-noterphenyl homopolymer (the same structure
as P5) in a previous study.24 The DSC
thermo-grams are displayed in Figure 2. To avoid ther-mal decomposition, these polymers were heated
to about 250 8C (at a heating rate of 5 8C/min),
and their melting temperatures were not
ob-served even over 250 8C. All the block
copoly-mers revealed clearing (isotropization)
tempera-Table 1. Molecular Weights and Thermal Properties of Block Copolymers P1–P4 Sample Mn(g mol1) Mw(g mol1) PDI (Mw/Mn) Td(8C)a Tg(8C)b
P1 10,258 11,996 1.17 325.0 162.9
P2 9,772 11,308 1.28 347.5 111.7
P3 15,632 18,110 1.34 341.6 98.4
P4 — — — 326.3 82.7 and 153.7
aMeasured by TGA under nitrogen. b
Determined by DSC (with a heating and cooling rate of 58C/min).
Table 2. Phase Behavior of Block Copolymers P1–P4a Sample Temperature (8C)b Tc(8C)c P1 K 173.8 (9.8) SA *300 P2 K 152.5 (4.1) SA *300 P3 K 181.6 (7.0) SA *275 P4 K 191.1 (4.7) SA *300 a
The transition temperatures and enthalpies (shown in parentheses; kJ/mol) were determined by DSC (at a heating rate of 58C/min).
bK
¼ crystalline; SA¼ smectic A. c
Observed by POM.
Figure 2. DSC thermograms of block copolymers P1–P4 during the first heating scan at 58C/min.
ture (Tc) values around 275–300 8C at which thermal decomposition occurred. Figure 3 shows a fan-shaped texture of the corresponding
smec-tic A phase of P1 observed by POM at 270 8C
(cooling).
Because it was not easy to observe the
glass-transition temperatures (Tg’s) of these block
copolymers, the Tgvalues were detectable by
liq-uid nitrogen quenching of the polymers in the first heating scans of DSC measurements (at a
heating rate of 58C/min). At this rate, the DSC
results indicated Tg values of all the block
copolymers more clearly, and the Tg values were
in the range of 82–163 8C (see Table 1). As
shown in Figure 2, Tg for P3 and P4 was easily
revealed, but the Tg values of P1 and P2 could
not be observed because of the low Tg value of
the PEO block in P1 and the short block of PS
in P2. Tg of P3 (at 98 8C) was mostly
contrib-uted by the PS block with PS repeating units of 98.25,26 However, two Tg values (at 83 and
154 8C) were present in P4, which were
attrib-uted to the immiscibility between the more extended PS block (with PS repeating units of
244 and Tg¼ 83 8C) and the LC cyanoterphenyl
block (with Tg ¼ 154 8C). The lower Tg value of
the more extended PS block (with PS repeating
units of 244 and Tg ¼ 83 8C) in P4 in
compari-son with the higher Tg value of the shorter
PS block (with PS repeating units of 98 and Tg
¼ 98 8C) in P3 was due to the plasticizer effect of the PEO block in triblock copolymer P4. Hence, this situation may serve as evidence for the microphase-separation morphology of
tri-block copolymer P4.27
To elucidate the structures of the mesophases, X-ray diffraction (XRD) measurements were carried out at the temperature ranges of the mesopha-ses for polymers P1–P5. As shown in Figure 4, the XRD patterns of polymers P1–P5 are almost identical, and their layer d-spacing values are around 37 A˚ . In addition, the layer d-spacing val-ues in the ratio of 1:1/2 indicate a lamellar order in the mesophases, and the XRD data are sum-marized in Table 3. Furthermore, a fan-shaped texture can be clearly observed by POM, as shown in Figure 3, which is a characteristic texture of the smectic A phase. According to the molecular modeling calculation, the layer d-spacing value of the coplanar structure in monomer 8 is around 35.6 A˚ (the layer d-spacing value is ca. 37 A˚ by XRD patterns). Therefore, a possible layer struc-ture of block copolymers P1–P5 is suggested to be interdigitated packing of rods. From this evidence,
Figure 3. Optical texture of the mesophase (smectic A) of P1 observed by POM at 2708C (cooling).
Figure 4. X-ray diagrams of polymers P1–P5.
Table 3. XRD Diffraction Data of Polymers P1–P5 at 1908C
Sample d-Spacing (A˚)a
P1 d001¼ 37.45 d002¼ 18.82 P2 d001¼ 36.70 d002¼ 18.45 P3 d001¼ 37.27 d002¼ 18.73 P4 d001¼ 38.03 d002¼ 18.91 P5 d001¼ 36.90 d002¼ 18.45 a
The theoretical d-spacing was 35.6 A˚ for polymers P1– P5.
the layer structures of all the polymers, P1–P5, have little relationship with respect to the flexible blocks, such as the PS and PEO blocks.
Optical Properties
The photophysical properties of block polymers P1–P4 containing luminescent cyanoterphenyl blocks were studied by photoluminescence (PL) and UV–vis absorption spectra in dilute chloro-form solutions and solid films. The optical prop-erties of all the polymers are summarized in Ta-ble 4. Because of the identical rigid cores of the luminescent cyanoterphenyl blocks, all the syn-thesized polymers in solutions had almost the same maximum absorption wavelength around 310 nm and emitted blue light at approximately kmax,PL (the maximum photoluminescence
wave-length)¼ 435 nm in solid films.
Figure 5 shows an example of UV–vis and PL spectra of diblock copolymer P1. In comparison
with the maximum PL wavelength in solutions, the materials in solid films exhibited a red-shifted PL emission because of the p–p* aggre-gation of the rigid cores (luminescent cyanoter-phenyl blocks). In terms of the PL wavelengths of all the block copolymers in dilute solutions, Figure 6 indicates that P2 and P4 were more redshifted than P1 and P3. The redshifted PL emission in P4 might have resulted from a large molecular weight of the LC cyanoterphenyl block with higher aggregation of emitting cyano-terphenyl moieties. In contrast to P1and P3, P2 had shorter flexible PS chains resulting in a stronger p–p* aggregation effect of the cyanoter-phenyl blocks.
CONCLUSIONS
ATRP was employed to fabricate block copoly-mers composed of different macroinitiators and LC cyanoterphenyl-based polymethacrylate blo-cks. Thermal and XRD investigations indicated that all the polymers exhibited the interdigi-tated packing smectic A phase and had little relationship with respect to the flexible PS and PEO blocks. In terms of the PL wavelengths of all the block copolymers in dilute solutions, P2 and P4 were more redshifted than P1 and P3, and this might have been due to the p–p* aggre-gation effect of the cyanoterphenyl blocks in block copolymers.
The powder X-ray diffraction measurements were supplied by the BL17A beam line (charged by Jey-Jau Lee) of the National Synchrotron Radiation Research Table 4. Absorption and PL Spectral Data of Block
Copolymers P1–P4
Sample
kmax,Abs(nm)a kmax,PL(nm)a
Solutionb Film Solutionb Film
P1 310 309 403 427
P2 312 314 416 435
P3 310 308 404 434
P4 312 310 431 438
a
kmax,Abs: the maximum absorption wavelength. kmax,PL:
the maximum photoluminescence wavelength.
bAbsorption and PL emission spectra were recorded in
dilute CHCl3solutions at room temperature.
Figure 5. (—) Absorption and (- - -) PL spectra of P1 in solutions (CHCl3as the solvent) and solid films.
Figure 6. PL spectra of block copolymers P1–P4 in solution (CHCl3as the solvent).
Center in Taiwan. The instruments for the gel perme-ation chromatography measurements were provided by Prof. Yun Chen (Department of Chemical Engi-neering, National Cheng Kung University).
REFERENCES AND NOTES
1. Hao, X.; Heuts, J. P. A.; Barner-Kowollik, C.; Davis, T. P.; Evans, E. J Polym Sci Part A: Polym Chem 2003, 41, 2949.
2. Lee, K. M.; Han, C. D. Macromolecules 2002, 35, 3145.
3. Poser, S.; Fischer, H.; Arnold, M. J Polym Sci Part A: Polym Chem 1996, 34, 1733.
4. Moriya, K.; Seki, T.; Nakagawa, M.; Mao, G.; Ober, C. K. M. Macromol Rapid Commun 2000, 21, 1309. 5. Yu, H.; Shishido, A.; Ikeda, T.; Iyoda, T. Macromol
Rapid Commun 2005, 26, 1594.
6. (a) Cui, L.; Zhao, Y.; Yavrian, A.; Galstian, T. Macromolecules 2003, 36, 8246. (b) Lin, H. C.; Lee, K. W.; Tsai, C. M.; Wei, K. H. Macromole-cules 2006, 39, 3808.
7. Gopalan, P.; Li, X.; Li, M.; Ober, C. K.; Gonzales, C. P.; Hawker, C. J. J Polym Sci Part A: Polym Chem 2003, 41, 3640.
8. Hawker, C. J.; Wooley, K. L. Science 2005, 309, 1200. 9. Shunmugam, R.; Tew, G. N. J Polym Sci Part A:
Polym Chem 2005, 43, 5831.
10. Denizli, B. K.; Lutz, J. F.; Okrasa, L.; Pakula, T.; Guner, A.; Matyjaszewski, K. J Polym Sci Part A: Polym Chem 2005, 43, 3440.
11. Tian, Y.; Watanabe, K.; Kong, X.; Abe, J.; Iyoda, T. Macromolecules 2002, 35, 3739.
12. Schneider, A.; Zanna, J. J.; Yamada, M.; Finkel-mann, H.; ThoFinkel-mann, R. Macromolecules 2000, 33, 649. 13. He, X.; Zhang, H.; Yan, D.; Wang, X. J Polym Sci
Part A: Polym Chem 2003, 41, 2854.
14. Figueiredo, P.; Gronski, W.; Bach, M. Macromol Rapid Commun 2002, 23, 38.
15. O¨ zbek, H.; Yıldız, S.; Pekcan, O¨.; Hepuzer, Y.; Yagci, Y.; Galli, G. Mater Chem Phys 2002, 78, 318.
16. Hepuzer, Y.; Serhatli, I. E.; Yagci, Y.; Galli, G.; Chiellini, E. Rapid Commun 2002, 202, 2247. 17. Anthamatten, M.; Wu, J. S.; Hammond, P. T.
Macromolecules 2001, 34, 8574.
18. Salnger, J.; Gronski, W.; Maas, S.; Stuhn, B.; Heck, B. Macromolecules 1997, 30, 6783.
19. Anthamatten, M.; Zheng, W. Y.; Hammond, P. T. Macromolecules 1999, 32, 4838.
20. Gray, G. W.; Harrison, K. J.; Nash, J. A. J Chem Soc Commun 1974, 431.
21. Kiryanov, A. A.; Sampson, K. S.; Seed, A. J. J Mater Chem 2001, 11, 3068.
22. Matyjaszewski, K.; Xia, J. Chem Rev 2001, 101, 2921.
23. Kamigaito, M.; Ando, T.; Sawamoto, M. Chem Rev 2001, 101, 3689.
24. Oriol, L.; Pinol, M.; Serrano, J. L.; Martinez, C.; Alcala, R.; Cases, R.; Sanchez, C. Polymer 2001, 42, 2737.
25. Wang, J.; Mao, G.; Ober, C. K.; Kramer, E. J. Macromolecules 1997, 30, 1906.
26. Schmalz, H.; Bolker, A.; Lange, R.; Krausch, G.; Abetz, V. Macromolecules 2001, 34, 8720.
27. Otmakhova, O. A.; Kuptsov, S. A.; Talroze, R. V.; Patten, T. E. Macromolecules 2003, 36, 3432. 4602 LEE, WEI, AND LIN
