IntroductionGood thermal stability and high optical transpar-

ency combined with high refractive index (high-n) or low refractive index (low-n) are the basic con-cerns in designing the optical coatings for the mi-cro-lens in CCD image sensors (Fig. 1) and the anti-reflection coatings for various types of displays.1,2 Conventional optical polymers such as epoxy, poly(methyl methacrylate) (PMMA), and polyure-thane modified with sulfur (for high-n) and fluo-rine (for low-n) can meet most of the requirements. However, their relatively poor thermal stability often limits their wide applications. Further, the conventional polymers usually exhibit refractive indices of 1.5–1.7, which are not enough for high performance applications (the initial targets: n > 1.8 for high-n and n < 1.45 for low-n).3 Wholly aromatic polyimides (PIs), a well-known class of thermal-resistant polymers, have been increasingly applied in advanced optical fabrications after several decades of technologi-cal evaluations.4-6 PIs possess good combined properties, including high thermal and radiation stability, high mechanical and insulating properties, and in particular, inherent high refractive index; hence, they are considered as one of the best candidates as high-n polymers.7 Although the conventional PIs exhibited considerably higher refractive indices due to the high contents

Organic/Inorganic-Polyimide Nano-Hybrids withHigh / Low Refractive Indices for Optical Applications

Shinji ANDO*, Atsuhisa SUZUKI, Yasuhiro NAKAMURA, Jin-gang LIU, and Mitsuru UEDA

Department of Chemistry & Materials Science, Tokyo Institute of Technology, Ookayama 2-12-1, Meguro-ku, Tokyo 152-8552, JAPAN

Tel: +81-3-5734-2137, Fax: +81-3-5734-2889, E-mail: sando@polymer.titech.ac.jp

Fig.1 Schematic view of C-MOS image sen-sors including micro-lens array. High-n poly-mers (n>1.8) are required for the lens.

Abstract : The refractive indices (n) and their wavelength dispersion of a series of sulfur-containing aromatic polyimides (PIs) were analyzed, and organic/inorganic-polyimide (PI) nanohybrid materials were prepared by combining inorganic nanopar-ticles with highly refractive sulfur-containing PIs and a lowly refractive fluorinated semi-alicyclic PI. The PI films were hybridized by thermal curing of the correspond-ing poly(amic acid)s which contain high refractive nanoparticles (SiO2-modified TiO2) or low refractive soluble precursor (Mg(CF3COO)2). Inorganic nanoparticles were homogeneously dispersed and fixed in the PI films by thermal curing at 250~350ºC. Colorless and transparent PI nanohybrid films exhibiting high or low refractive indi-ces were obtained, and their structures and properties were characterized by UV/Vis, FT–IR/FarIR absorption spectra and 19F solid state NMR. PI nanohybrid materials that demonstrate high thermal stability, good mechanical properties, and functional optical properties are promising for the future optical devices and applications.

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of aromatic rings and imide structures than the common optical polymers, their poor transpar-ency in the visible region might be a serious obstacle to their wide applications.8,9 The opti-cal absorption of PIs in the visible region are mainly caused by the intra- and intermolecular charge-transfer (CT) interactions between the electron-donating diamine and the electron-accepting dianhydride moieties. Considerable efforts have been made to modify the coloration of conventional PIs. However, according to the Lorentz-Lorenz equation, procedures that aim to decrease the polarizability of PI molecular chains, such as the introduction of electron-withdrawing fluorine atoms or fluorinated substituents,10,11 the incorporation of alicyclic moi-eties,12 and the modification of the molecular skeleton by meta-substituted structures,13 often decrease the refractive indices of PIs. Thus, it is an challenging project to develop novel high-n or low-n PI optical materials with colorlessness, high transparency, and high thermal stability.

Recently, with the rapid development of nano-technology, an effective method to provide high-n polymers is revealed, i.e., to combine high-n inorganic nanoparticles such as TiO2 (anatase, n=2.45; rutile, n=2.70), ZrO2 (n=2.1), amorphous silicon (n=4.23), PbS (n=4.2), or ZnS (n=2.4) with a polymer matrix in order to develop an organic-inorganic nanohybrid sys-tem Whereas, no attempt was made to develop low-n materials by nanohybridization. When the sizes of nanoparticles are below 40 nm (~1/10 of the visible wavelengths), the nanohybrid films are often optically transparent.14,15 In addition, their refractive indices can be estimated by nhyb=fpar·npar+fpol·npol,15,16 where nhyb, npar, and npol are the refractive indices of the nano-hybrid, particle, and polymer matrix, respectively. fpar and fpol are the volume fractions of the nanoparticles and matrix. For instance, in order to achieve a higher nhyb by nanohybridization, the higher the npol value, the lower the fpar value. This is important for the design of high-n or low-n nanohybrids for optical applications because an overload of nanoparticles frequently in-creases the optical loss and deteriorates the processability of polymer matrix.17

Experimental4,4’-[p-Thiobis(phenylenesulfanyl)]diphthalic anhydride (3SDEA) and 4,4’-[m-sulfonylbis

(phenylenesulfanyl)]diphthalic anhydride (mDPSDA) were synthesized according to the meth-ods described in our previous studies.18,19 1,2,3,4-Cyclobutanetetracarboxylic dianhydride (CBDA) and 1,2,4,5-cyclohexanetetracarboxy-lic dianhydride (CHDA) were kindly supplied by Japan Synthetic Rubber and New Japan Chemical Co.,Ltd, respectively. The other dianhydrides listed in Scheme 1 were pur-chased from Wako Chemical Co.Ltd. 4,4’-(p-Phenylene-disulfanyl)dianiline (2SPDA), 4,4’-thiobis[(p-phenylenesulfanyl)aniline] (3SDA), 2,8-bis(4-aminophenylenesulfanyl) dibenzothiophene (APDBT), 2,7-bis(4-amino- phenylenesulfanyl)thianthrene (APTT), and 4,4’-sulfonylbis[(p-phenylenesulfanyl)aniline] (BADPS) were synthesized according to the methods described in our previous stud-ies.20-25 All the source materials were dried in vacuo at 120~180°C for 24 h prior to use. The PI films were prepared by a two-step

n

NO

ON

O

OR'R

R=s-BPDA

,

O

,ODPA

S

S

S

3SDEA

R'=S

SDAS

S

S

3SDA

, S

S

2SPDAS

S SAPDBT

S

S

S

SAPTT

S S

mDPSDA

SO2

CHDA,,CBDA

,

S

SO2 SBADPS

,

,

C

6FDA

F3C CF3

C

DCHM

H H

Scheme 1 Molecular structures of sulfur-contain-ing high-n PIs and fluorinated low-n PIs .

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polymerization procedure via poly(amic acid) (PAA) precursors soluble in DMAc. PAA solu-tions were spin-coated onto Si wafers or fused-silica substrates followed by drying at 70°C for 1h and thermal curing in nitrogen or in vacuo at 200, 250, and 300°C for 1h. The thicknesses of the PI films were 8~12 mm. They were kept in a vacuum desiccator to avoid moisture sorp-tion. TGA and DSC thermograms were recorded on a Seiko TG/DSC-6300 at a heating rate of 10°C/min in nitrogen. DMA analysis was performed for film specimens (30 x 10 mm) on a Seiko DMS-6300 at a heating rate of 2°C/min with a load frequency of 1 Hz in air. The glass transition temperature (Tg) was determined as the peak temperature of the loss modulus (E”). UV-Vis and FT-Far IR absorption spectra were measured on a Hitachi U-3500 and JASCO 6100-FF spectrometer, respectively. The in-plane (nTE) and out-of-plane (nTM) refractive indi-ces of PI films were measured with a prism coupler (Metricon, PC-2010, l=632.8, 845, 1324, and 1515 nm). The average refractive index (nav) and the in-plane/out-of-plane birefringence (Dn) were calculated as nav2=(2nTE2+nTM2)/3 and nTE–nTM, respectively. The nTE of a very thin PI film was measured with a spectroscopic n&k analyzer (n&k Tech. model-1280). Solid state 19F NMR spectra were measure on a JEOL GSX-300 spectrometer with a 19F{1H} MAS probe.Calculations

The time-dependent density functional theory (TD-DFT) with the three-parameter Becke-style hybrid functional (B3LYP) was adopted for the calculations of one-electron transition energies (De) and the corresponding oscillator strengths ( f ), and the molecular polarizability (a) of PI models in conjunction with the Gaussian basis sets. The 6-311G(d) basis set was used for geometry optimizations under no constraints, and the 6-311++G(d,p) was used for the calcula-tions of De, f, and a.26,27 All the computations were performed using the Gaussian-03 software (Rev.D01). Further, refractive indices of PIs were estimated using the Lorentz-Lorenz equation (1) as shown below, where n is the refractive index; r the density; NA, the Avogadro number; Mw, the molecular weight; a, the linear molecular polarizability; and Vmol, the molecular vol-ume. To predict refractive index, a typical packing coefficient (Kp) of 0.60 was used to evaluate the Vmol of PI models from their van der Waals volumes (Vvdw).28

Results and DiscussionSulfur-containing High-n PIs

Scheme 2 shows the structures of PIs derived from mDPSDA and 3SDEA dianhydrides.19,25 The weight fractions of sulfur (Sc), and the thermal and optical properties of these PIs are listed in Table 1.19 The nav of all PIs (1.716~1.748) are significantly higher than conventional optical polymers (PMMA:1.489, polycar-bonate:1.577, polystyrene:1.586) due to their high Sc val-ues (19~22 wt%). In addition, the in-plane/out-of-plane orientation of PI chains in the films was effectively sup-pressed by the sequential flexible linkages (–S–, –SO2– ) in the main chains, leading to the small birefringence (Dn< 0.007). These properties are preferable for most of the op-tical applications. In addition, the Tgs and the 5% weight loss temperatures of these PIs are higher than 178°C and 474°C, respectively. However, since the absorption edges of these PIs represented by the cut-off wavelengths (lcutoff) are close to the visible limit (~400 nm), all the

(1)

S

S

S

O O

S

S

S

S

S

SS

NS X S

N

O

O

O

O

Ar

m-DPSDA-BADPS, PI-1

m-DPSDA-APTT, PI-4

m-DPSDA-APDBT, PI-3

S

S

Sm-DPSDA-3SDA, PI-2

S

S

S3SDEA-3SDA, ref-PI

X= −SO2−, Ar =

X= −SO2−, Ar =

X= −SO2−, Ar =

X= −S−, Ar =

X= −SO2−, Ar =

Scheme 2 Sulfur-containing PIs ex-hibiting high refractive indices.

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films show pale-yellow to deep-yellow color. Figures 2 and 3 show the calculated absorption spectra with calculated refractive indices (inset) and the experimental absorption spectra with the wavelengths dispersion of refractive index of the PI films derived from sBPDA dianhydride and APTT diamine. Note that the refractive indices and the absorption spectra calculated by the TD-DFT reproduce well the experimental values and spectra. The calculated absorption spectra demonstrate that the absorption tailings extended to the visible region are inherent in the fully aromatic PIs, and colorless PIs can be obtained only when alicyclic dianhydrides (CBDA, CHDA) or BADPS diamine were used. However, PI-1 (mDPSDA-BADPS) shows pale-yellow color, which originates from the inter-molecular CT interactions (the calculations did not include the intermolecular interactions). As shown in Figs. 2(b) and 3(b), the wavelength dispersion of the refractive indices are well fitted by the simplified Cauchy’s formula (nl=n∞+D/

Table 1 Thermal and optical properties of the sulfur-containing PIs listed in Scheme 2.19

0

1

2

300 350 400 450 500

3SDEA-APTT (ncal=1.7860)sBPDA-APTT (ncal=1.7703)mDPSDA-APTT (ncal=1.7537)aBPDA-APTT (ncal=1.7487)ODPA-APTT (ncal=1.7622)CBDA-APTT (ncal=1.7096)CHDA-APTT (ncal=1.6871)

Wavelength (nm)

Cal

cula

ted

Abs

orpt

ion

(arb

.uni

t)

a)

0

0.5

1

1.5

1.65

1.70

1.75

1.80

400 600 800 1000 1200 1400

sBPDA-APTTaBPDA-APTTODPA-APTT3SDEA-APTTCHDA-APTTCBDA-APTTmDPSDA-APTT

Wavelength (nm)

Absorption spectrumWavelength dispersion

Ref

ract

ive

Inde

x

Abs

orba

nce

b)

0

1

2

300 350 400 450 500

sBPDA-APTT (ncal=1.7703)sBPDA-APDBT (ncal=1.7705)sBPDA-APST (ncal=1.7317)sBPDA-3SDA (ncal=1.7327)sBPDA-SDA (ncal=1.7089)sBPDA-2SDPA (ncal=1.7260)sBPDA-BADPS (ncal=1.7086)

Wavelength (nm)

Cal

cula

ted

Abs

orpt

ion

(arb

.uni

t)

0

0.5

1

1.5

1.65

1.70

1.75

1.80

400 600 800 1000 1200 1400

sBPDA-APTTsBPDA-APDBTsBPDA-3SDAsBPDA-2SPDAsBPDA-SDAsBPDA-BADPSsBPDA-APST

Wavelength (nm)

Ref

ract

ive

Inde

x

Abs

orba

nce

Absorption spectrum

Wavelength dispersion

Fig.2 a) Calculated absorption spectra with calcu-lated refractive indices (inset), and b) experimen-tal absorption spectra and wavelengths dispersion of refractive indices of the PI films derived from sBPDA dianhydride.

Fig.3 a) Calculated absorption spectra with calcu-lated refractive indices (inset), and b) experimen-tal absorption spectra and wavelengths dispersion of refractive indices of the PI films derived from APTT diamine.

a)

b)

a)

b)

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l2).29 The n∞ reflects the inherent refractive index of a PI, which is free from the influence optical absorption. As shown in Fig. 4, two different linear relationships are observed between Sc and n∞ for the aromatic PIs and the semi-alicyclic PIs, which clearly indicates the effect of alicyclic structures in the dianhydride moi-ety. These positive slopes indicates that an increase in a/Vmol due to the incorporation of –S– and –SO2– leads to an effective increase in n. Although the n∞s of the semi-alicyclic PIs are significantly lower than those of the aromatic PIs, it should be noted that the linear relation for the former possesses a larger slope than that for the latter, indicating that the incorporation of –S– and –SO2– is more effective in the semi-alicyclic PIs. As a result, PI (3SDEA-APTT) having the highest Sc of 23.2 % shows the highest n of 1.761 at 632.8 nm.22 This is one of the top values in high-n polymers. Figure 5 shows the relations between the values of n∞ and D. In the same manner as Fig. 4, two dif-ferent linear relationhips are observed for the semi-alicyclic and the aromatic PIs, which agree well with the relation that we have reported previously.29 The higher the n∞, the larger the D, which straightforwardly indicates that a high-n rarely exists with a low D. Among various di-anhydrides, ODPA and mDPSDA, which have lower electron affinities, can provide PIs with higher transparency and lower dispersion.

As shown in Fig. 3, CHDA-APTT exhibits the highest optical transparency with n=1.680 and Dn=0.0048.23 Thus, it was combined with SiO2-modified TiO2 nanoparticles. The PAA solution showed good affinity with nanoparticles up to the proportion of PAA: TiO2=55:45 (w/w), and a homogeneous mixture was readily achieved using a mechanical stirrer. The nanohy-brid PI film cured at 300°C exhibits good uniformity as evidenced in Fig. 6. The homogeneous and transparent film has a very high refractive index of 1.810 at 632.8 nm, which achieves the initial target (n>1.80). This value could be evaluated from the equation; nhyb=fpar·npar+fpol·npol with the parameters of rpar=3.11, npar= 2.00, rpol = 1.45, and npol=1.68. The estimated nhyb value (~1.78) is slightly lower than that of the experimental nhyb, which might be attributable to the densification of PI nanohybrid films due to the interactions between the PI chains and the modified TiO2 surfaces.

1.2

1.4

1.6

1.8

2.0

2.2

2.4

1.60 1.65 1.70

3SDEAsBPDAaBPDAODPADPSDACBDACHDA

Dis

pers

ion

Coe

f, D

(104 nm

2 )

Refractive Index at the infinite wavelength, n∞

1.60

1.65

1.70

0 5 10 15 20 25

3SDEAsBPDAaBPDAODPACBDACHDA

Sulfur content in repeating unit (wt%)

Ref

ract

ive

Inde

x at

the

infin

ite w

avel

engt

h, n

∞

Fig.4 Relations between the sulfur content (Sc) and the refractive indices at infinite wavelength of the PIs derived from 6 kinds of dianhydrides.

Fig.5 Relations between the n∞ values and the dispersion coefficients (D) for the PIs derived from 7 kinds of dianhydrides.

Fig.6 SEM micrograph of PI (CHDA-APTT) thin film containing TiO2 nano-particles (55:45 w/w). The highest n of 1.81 at 632.8 nm was obtained.23

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Low-n PI nanohybrids containing MgTfAc and MgF2

As mentioned in Introduction, low-n materials have a high demand for anti reflection coatings and waveguide applications. We have been develop-ing PIs exhibiting high transparency with shorter absorption edges and low refractive indices by in-troducing fluorines and alicyclic structures in the main chain (Scheme 2).5,10,11 The PI (6FDA-DCHM) show a low n of 1.509 and a low Dn of 0.001 at the wavelength of 1324 nm. Since organic/inorganic PI nanohybrids can be versatile optical materials, we attempted to decrease the refractive indices of PIs by incorporating nanopar-ticles of magnesium fluoride (MgF2). MgF2 is known as a representative low-n inorganic glass with a refractive index of 1.38 at 632.8 nm. Recently, it was reported that Mg(CF3COO)2·nH2O (MgTfAc) is thermally converted to MgF2 under nitrogen at ca.300°C.30 Figure 7 shows the solid state 19F magic-angle spinning (MAS) NMR and the Fourier-transformed (FT) Far-in-frared (Far-IR) absorption spectra of polycrystalline MgTfAc annealed at 200, 250, and 300°C for 1 h. These spectra demonstrate that MgTfAc was transformed to MgF2 by 94.5% at 250°C and 99.5 % at 300°C, whereas it was unchanged after curing at 200°C. Accordingly, MgTfAc was dissolved in a DMAc solution of poly(amic acid) (PAA) of 6FDA-DCHM to afford a pre-cursor for PI nanohybrid film. Figure 8 shows the 19F MAS NMR and FT-Far-IR spectra of the hybrid films thus obtained, which demonstrate that 93.3% of MgTfAc was converted to MgF2 by curing at 300°C, but MgTfAc was unchanged at 200 and 250°C despite the almost com-

-250-200-150-100-500δ

F/ppm

∗

∗

∗

∗

∗ ∗

∗250ºC

200ºC

300ºC

Mg(CF3COO)

2

MgF2

0

1

2

200300400500600

200°C250°C300°C

Abs

orba

nce

Wavenumber (cm-1)

Mg-Fbending

-CF3

-250-200-150-100-500

250ºC

200ºC

300ºC

Mg(CF3COO)2

PI(6FDA-DCHM)

MgF2

∗ ∗

∗ ∗

δF/ppm

∗

∗

∗

N

CN

O

O

O

O

F3C CF3

CH H

PI (6FDA-DCHM) : n=1.509 at 1324 nm

Scheme 2 Structure of a semi-alicyclic fluori-nated PI exhibiting low n and low Dn.

Fig.7 a) Solid state 19F MAS NMR and b) FT-FarIR absorption spectra of MgTfAc powder cured at 200, 250, and 300°C for 1h.

Fig.8 a) 19F MAS and b)FT-FarIR spectra of PI (6FDA-DCHM) films with MgTfAc (100 mol%) cured in vacuo at 200, 250, and 300°C.

0.01

0.02

0.03

0.04

200300400500600

200°C250°C300°C

Abs

orba

nce

Wavenumber (cm-1)

Mg-Fbending

-CF3(PI) imide(PI)

a)

b)

a)

b)

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1.47

1.48

1.49

1.50

1.51

0 50 100 150

200ºC250ºC300ºCCalc.(300deg)

Mg content (mol%)

Ref

ract

ive

inde

x at

132

4 nm

Fig.10 Refractive indices of PI (6FDA-DCHM) films with different amounts of MgTfAc cured at 200, 250, and 300°C. The open circles indicate the calculated refractive indices using the n of MgF2.

0

0.1

0.2

0.3

300 400 500 600 700 800

200°C250°C300°C

Abs

orba

nce

Wavelength (nm)

Fig.9 UV-Vis absorption spectra of PI (6FDA-DCHM) films with MgTfAc (100 mol%) cured at 200, 250, and 300°C.

plete imidization of PAA at 200°C. These facts suggest that some attractive interactions exist between MgTfAc and PI chains, possibly dipolar-dipolar interactions between their carbonyl (C=O) groups. As shown in Fig.9, the hybrid PI films cured at 200 and 250°C are perfectly colorless and transparent, which is same as the pristine PI film. In contrast, the hybrid film cured at 300°C show pale-yellow color with slight haze, which may due to the light scattering caused by MgF2 nanoparticles precipitated in the film. Since amorphous MgF2 crystallizes over 600°C,30 no diffraction peaks characteristic to MgF2 were observed in the WAXD pat-terns of all films. Figure 10 shows the curing temperature dependence of the refractive indices of the PI nanohybrid films prepared with different MgTfAc contents. The observed n values were successfully reduced by –1.5, –1.6, –0.75 % by the incorporation of MgTfAc to the PIs cured at 200, 250, and 300°C, respectively, with 100 mol% content of MgTfAc. In addition, the variations in n are consistent with the pyrolysis behavior. Since MgTfAc was not decomposed in the PI films at 200 and 250°C, the n values of these films are proportional to the MgTfAc content. Note that the n values of these films are significantly lower than those of the films cured at 300°C. MgTfAc was unchanged in the former but decomposed to MgF2 in the latter, which indicates that the inherent refractive index of MgTfAc is much lower than MgF2. This is explainable by the fact that the molar ratio of Mg to F is 1:6 for MgTfAc but 1:2 for MgF2.

As shown as the open circles in Fig.10, the estimated refractive indices of the hybrid films using the equation: nhyb=fpar·npar+fpol·npol, in which all the particles are assumed to be de-composed to MgF2, agree well with the observed n of the films cured at 300°C. This also sup-ports the pyrolytic decomposition to MgF2 in the film. In contrast, the lowest n value of 1.477 at 1324 nm was obtained for the nanohybrid film prepared by dissolving 150 mol% of MgTfAc to PAA solution and curing at 250°C for 1h. This low n value is close to that of Pyrex glass (1.472) and significantly lower than those of the polymers stated above and optical glasses (BK7: 1.515, SK2: 1.605). In addition, this value is approaching to that of silica (1.457). The calculat-ed Fresnel reflection at the air-surface of this PI hybrid is 3.7 %, which can effectively reduce the surface reflection for high-n inorganic glasses and sulfur-containing polymers. Further-more, the theoretical dielectric constant (e=n2) of the PI nanohybrid film is 2.18, which is close to the e of poly(tetrafluoroethylene) (e=2.1). As a result, the nanohybridization of PI films with MgTfAc or MgF2 using soluble precursor is a facile and effective method to reduce the refrac-tive indices and the dielectric constants of PI films with keeping their fundamental properties.

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ConclusionFirstly, the refractive indices (n) and their wavelength dispersion of a series of sulfur-con-

taining aromatic polyimides (PIs) which have been developed by the authors were analyzed. The PIs show very high n of 1.716 –1.761 at 632.8 nm due to their high sulfur contents (19.2–23.2 wt%), whereas they exhibit pale-yellow to deep-yellow colors. In contrast, the colorless semi-alicyclic poly(amic acid) (PAA) derived from CHDA and 3SDA demonstrated high compat-ibility with silica-modified TiO2 nanoparticles, thereby resulting in a transparent PI nanohy-brid film with a high n of 1.810. Secondly, the semi-alicyclic PAA derived from 6FDA and DCHM which has low-n of 1.509 at 1324 nm also exhibited high compatibility with MgTfAc, a precursor of MgF2, resulting in a colorless and transparent PI film with a low n of 1.477. PI nanohybrid materials which demonstrate high thermal stability, good mechanical properties, and characteristic optical properties are promising for the future optical applications.Acknowledgement : The authors thank C.A. Terraza, Y. Suzuki and Y, Shibasaki for the synthesis of sulfur-containing PIs, and S. Sugawara at JSR Corp. for the preparation of TiO2/PI nano-hybrid. References 1) J. L. Regolini, D. Benoit, and P. Morin, Microelectronics Reliability, 47, 739 (2007). 2) C. Cox, C. Planjec, N. Brakensiek, Z.M. Zhu, and J. Mayo Proc. SPIE, 6153, 61534E (2006). 3) M. Suwa, H. Niwa, and M. Tomikawa, J. Photopolym. Sci. Tech., 19, 275 (2006). 4) R. Reuter, H. Franke, and C. Feger, Appl.Optics, 27, 4565 (1988). 5) S. Ando, T. Matsuura, and S. Sasaki, Macromolecules, 25, 5858 (1992). 6) S. Ando, J. Photopolym. Sci. Technol., 17, 219 (2004). 7) S. Ando, Y. Watanabe, and T. Matsuura, Jpn. J. Appl. Phys., Part 1, 41 5254 (2002). 8) R.A. Dine-Hart and W.W. Wright, Makromol. Chem., 143, 189 (1971). 9) S. Ando, T. Matsuura, and S. Sasaki, Polym. J., 29, 69 (1997).10) T. Matsuura, Y. Hasuda, S. Nishi, and N. Yamada, Macromolecules, 24, 5001 (1991).11) T. Matsuura, S. Ando, S. Sasaki, and F. Yamamoto, Macromolecules, 27, 6665 (1994).12) Q. Jin, T. Yamashita, K. Horie, I. Mita, and R. Yokota, J. Polym. Sci. Polym.Chem., 31, 2345 (1993).

ibid, 32, 503 (2004). 13) K. St.Clair, T.L. St.Clair, and W.P. Winfree, Proc. ACS Polym. Mater. Sci. Eng., 59, 28 (1988).14) L. Zimmermann, M. Weibel, W. Caseri, U. W. Suter, and P. Walther, Polym. Adv. Technol., 4, 1 (1993).15) M.Weibel, W. Caseri, U.W. Suter, H. Kiess, and E. Wehrli, Polym. Adv. Technol., 2, 1 (1991).16) H. Althues, J. Henle, and S. Kaskel, Chem. Soc. Rev., 9, 1454 (2007).17) C. Paquet, P.W. Cyr, E. Kumacheva, and I. Manners, Chem. Commu. 2004, 234 (2004).18) J.-G. Liu, Y. Nakamura, Y. Suzuki, Y. Shibasaki, S. Ando, and M. Ueda, J. Polym. Sci. Part A, Polym

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