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Macromolecular Research, Vol. 18, No. 2, pp 120-128 (2010) www.springer.com/13233

The Polymer Society of Korea

Preparation and Characterization of Polyimide/Modified β-CyclodextrinNanocomposite Films

Taesung Lee, Jihan Lim, Ildoo Chung, Il Kim, and Chang-Sik Ha*Department of Polymer Science and Engineering, Pusan National University, Busan 609-735, Korea

Received May 27, 2009; Revised July 2, 2009; Accepted July 15, 2009

Abstract: A series of pyromellitic dianhydrides (PMDAs)- 4,4'-oxydianiline (ODA) polyimide nanocompositefilms with modified β-cyclodextrin (CD) were prepared via in situ polymerization and subsequent thermal imidiza-tion. The effect of CD modified with the functional group of -NH2 on the mechanical properties and dielectric con-stant of the nanocomposite films were investigated. The tensile strength and modulus of the nanocomposite filmscontaining modified CD were higher than the neat PI. The dielectric constant decreased with increasing content ofthe modified CD up to 10 wt% from 3.34 for neat PI to 2.56.

Keywords: modified cyclodextrin, dielectric properties, nanocomposite, polyimide.

Introduction

Polyimides (PIs) are widely used as dielectric and pack-aging materials in microelectronic products because of theirexcellent thermal, mechanical, dielectric and chemical resis-tance properties.1-6 Conventional PIs have dielectric con-stant (k) in the range of 3.2-3.9. This value will not fulfillthe requirements of future microelectronic applications.Recently, many works have studied on polyimides withlower dielectric constant, including new PIs such as fluori-nated PIs7 and porous PI films.8-11 Fluorination generallyincreases chain flexibility and reduces the glass transitiontemperature of a PI. Therefore, the upper temperature limiton the use of fluorinated PI is also reduced. Approaches forpreparing porous PIs include the incorporation of foamingagents9 and the formation of nanofoams8,10 or embedded hol-low spheres.11 Additionally, nanoporous PI films have alsobeen prepared by the thermal decomposition of the labilecomponents of block copolymers.12 PIs manufactured bythe aforementioned approaches contain large pores, a broadpore size distribution and open pore structures. Furthermore,nano- or micro-porous structures commonly detrimentallyaffect the mechanical properties of PIs and thus limit their use.

Polyimide/layered-silicates (clay) nanocomposites13 haverecently attracted substantial research interest because incorpo-rating only a few (by weight percent) layered-silicates, dis-persed on the nanometer scale, markedly improves thermal,mechanical, and gas barrier properties over those of the pristinepolyimide. However, the dielectric constant still exceeds3.0, because the clay structure is not hollow and the leakage

current associated with the metal ions in clay is another issueof concern. Additionally, there have been a few approachesto PI/mesoporous silica nanocomposites recently. Based onthe low-dielectric constant of the mesoporous silica (k<2.5),addition of the mesoporous silica into the PIs for the appli-cations in the microelectronics and the insulations would beexpected to reduce the dielectric constant of the PIs. How-ever, they have experienced some difficulties in removal oftoxic solvents or surface modification of mesoporous silicaand phase separation.14-16 The technical challenge is todevelop PIs with lower dielectric constant without compro-mising other key characteristics, such as the elastic modulusor the coefficient of thermal expansion (CTE).β-Cyclodextrin (CD), a cyclic oligosaccharide consisting

of at least seven glucopyranose residues that are joinedtogether by α,1→4 linkages, can form inclusion complexeswith a variety of organic and inorganic molecules.17 On thebasis of this quite unique property, CDs have been singledout for studies involving supramolecular chemistry.17-19 Fur-thermore, CDs and their derivatives have been widely usedin the food, cosmetic, and pharmaceutical industries as hostcompounds to increase the solubility of drugs, to stabilizesensitive compounds, and to fix volatile aromas.19 Addition-ally, CDs have been used to create supramolecular templatesor as porogen for the synthesis of functional porous materi-als.20-22 Although several studies have addressed the inclu-sion complex and microporous cabons based on polyimide/cyclodextrin composites, very little attention has been paidto its dielectric constant, thermal and mechanical character-istic of PI/CD composite films.23,24

We dispersed the homogeneously nanoscale cyclodextrininto polyimide matrix to form novel polyimide/modified*Corresponding Author. E-mail: csha@pnu.edu

DOI 10.1007/s13233-009-0120-1

Preparation and Characterization of Polyimide/Modified β-Cyclodextrin Nanocomposite Films

Macromol. Res., Vol. 18, No. 2, 2010 121

CD (M-CD) nanocomposites via covalent bonding. A seriesof the novel pyromellitic dianhydride (PMDA)-4,4'-oxydi-aniline (ODA) polyimide nanocomposite films with modi-fied β-CD were synthesized via in situ polymerization andfollowing thermal imidization. The bonding between poly-imide main chain and reactive amino functional group ofmodified CD significantly improves tensile strength, modu-lus and dielectric constant of the novel composite.

Experimental

Materials. Pyromellitic dianhydride (PMDA), 4,4'-oxy-dianiline (ODA), β-cyclodextrin (CD), dimethylacetamide(DMAc), N,N-dimethylformamide (DMF, 99.9%) werepurchased from Aldrich and used as received. Sodium hydrox-ide (NaOH), sodium chloride (NaCl), and hydrochloric acid(HCl) (37%) were reagent grade and used without furtherpurification.

Synthesis of Mono-6-deoxy-6-p-toluenesulfonyl β-CD(β-CD-OTs). The procedure for monofunctionalization ofβ-CD is given in Scheme I. The mixure of p-toluenesulfo-nylchloride (2.5 g, 13.1 mmol) and β-cyclodextrin (10 g,8.68 mmol) in water (220 mL) was stirred at ambient tem-perature for 2 h under the inert atmosphere. Aqueous NaOH(2.5 M, 40 mL) was added and the solution was stirred andthe solution was stirred for 10 min before unreacted p-tolue-nesulfonylchloride was filtered off. Ammonium chloride(11.6 g) was added to the solution for pH 8. The solutionwas cooled and the resultant white precipitate was collectedby filtration. The white powder was washed with acetoneand dried under vacuum to afford 3.55 g (31%) of the titlecompound.25,26

FTIR (KBr): 3385 m-1(OH), 1030 cm-1(C-O-C), 1H NMR(300 MHz, DMSO-d6): 4.83(1H), 3.65-3.37(3H, 5H, 6H),3.35-3.21 (2H, 4H), Yield: 31%.

Synthesis of Mono-6-deoxy-6-azido β-CD (β-CD-N3).β-CD-OTs (1 g, 0.776 mmol) was suspended in dry DMF(10 mL), after warming to 63 oC, the mixture becamehomogeneous. Crystalline KI (0.062 g, 0.388 mmol) andNaN3 (0.504 g, 3.8 mmol) were added, and the reactionmixture was stirred at 60-65 oC for 24 h. The reaction mix-ture was cooled to room temperature and acetone (200 mL)was added. The product of mono-6-deoxy-6-azido β-CD wasrecrystallized form chloroform (200 mL).26,27

FTIR (KBr): 3385 m-1(OH), 2106 m-1(N3), 1030 cm-1(C-O-C), 1H NMR(300 MHz, DMSO-d6): 4.83(1H), 3.65-3.37(3H, 5H, 6H), 3.35-3.21 (2H, 4H), Yield: 89%.

Synthesis of Mono-6-deoxy-6-amino β-CD (β-CD-NH2

viz. Modified CD (M-CD)). The mono-6-deoxy-6-azido β-CD (2.01 g, 1.53 mmol) was dissolved in DMF (40 mL),and Ph3P (6.36 g, 24.2 mmol) was added. The evolution ofN2 can be observed by the formation of bubbles in the reac-tion vessel. After 1 h, during which time the evolution of N2

ceased, concentrated aqueous NH3 (6 mL, approximately 35%)were dropped to the solution. Shortly after the addition ofthe NH3 solution was complete, the reaction mixture turnedinto an off-white suspension. It was stirred at room tempera-ture for 18 h before the resulting suspension was concen-trated under reduced pressured to approximately 10 mL.The product was then precipitated by the addition of EtOH(100 mL). The precipitate was washed with EtOH and driedunder high vacuum to yield a white solid.26,28

FTIR (KBr): 3385 m-1(OH), 1030 cm-1(C-O-C), 1H NMR(300 MHz, DMSO-d6): 4.83(1H), 3.65-3.37(3H, 5H, 6H),3.35-3.21 (2H, 4H), Yield: 98%.

Preparation of Polyimide/Modified β-Cyclodextrin (M-CD) Composite Films. A typical procedure for preparingthe polyimide/modified CD nanocomposites by thermal imi-dization is as follows. PMDA was put into a three-neckflask with continuous stirring for 2 h under nitrogen gaspurge in DMAc. An appropriate amount of M-CD, i.e., 1, 3,5, 7, or 10 wt% of polyimide, was introduced into the flaskunder stirring for 12 h at room temperature. After 0.4005 g(2 mmol) of ODA was added to the above solution with vig-orous stirring for 2 h, 0.4362 g (2 mmol) of PMDA was dis-solved in previous solution for 12 h at room temperature toform a viscous and homogeneous polyamic acid (PAA)solution. The solid content of the solution was 10 wt%. ThePAA/modified CD solution was spread onto a glass plate,which was soft-baked at 60 oC for overnight. The semidriedPAA film was heated for 1 h at each of 80, 140, 200, and250 oC sequentially under nitrogen atmosphere. A flexiblepolyimide/modified CD composite film was self-strippedfrom the glass surface by soaking in water. Some sampleswere kept at 300 oC for 2 h in the atmosphere for the removalof CD in the composite films. These samples were preparedto observe the changes of dielectric constants caused byannealing CD contents, which were denoted as A-x wt% (x=1, 3, 5, 7, and 10, ex. A-10 wt%). The composite filmsbased on CD (i.e. non-modified CD) were also prepared forcomparison by the same procedure described above exceptthat pure CD (i.e. non-modified CD) was used instead of M-CD. The composite films with CD loading of 2, 5, and 10%were denoted as CD2, CD5, and CD10, respectively. Table Isummarizes the detailed specifications for the preparationof the composite precursor films and the correspondingnames of the samples. The PMDA-ODA PI was also pre-pared from their corresponding PAA in DMAc by similarScheme I. Synthesis of modified CD.

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122 Macromol. Res., Vol. 18, No. 2, 2010

methods as mentioned above (in the absence of the modi-fied CD). This PI was designated as “neat PI”.

Measurements. FTIR spectrometer (React IRTM 1000,Applied System) was used to identify the chemical structureof polyimides and their composites. UV-Vis spectra weremeasured using a Hitachi U-2010 spectrometer. Materialswere characterized by 1H NMR (300 MHz, DMSO, 293 K,Varian Unity Plus-300) spectrometer. X-ray photoelectronspectroscopy (XPS) was performed using a VG-ScientificESCA lab 250 spectrometer and AlKα radiation (1486.6eV); the peak positions were referenced internally to theC1s peak at 284.6 eV. Gel permeation chromatography (GPC)was carried out using a Waters GPC system (a 410 control-ler, a 515 pump, a 717 Plus autosampler and a 410 differen-tial refractometer) using Ultra styragel columns (HR-3)with N,N-dimethylformamide (DMF) as an eluent. LiquidChromatograph-Mass Spectroscopy (LC-MS) spectra wereobtained using Agilent 1100 LC/MSD SL model spectro-meter. Wide-angle X-ray diffraction (XRD) data were col-lected on a Rigaku Miniflex X-ray diffractometer, operatedat 40 kV and 30 mA, using CuKα (λ=1.5401 Å) radiation.The morphology of the fractured surfaces of the compositefilms was measured using a field emission-scanning electronmicroscopy (FE-SEM, JSM-6700F, Korea Basic ScienceInstitute) with an acceleration voltage of 20 kV. The thermaldecomposition of composite films was measured using athermogravimetric analyzer (TGA, Q50, TA Instrument).The glass transition temperature (Tg) was taken from differen-tial scanning calorimeter (DSC, Q100, TA Instrument). Theheating rate was 20 oC/min in the temperature range between30 and 900 oC. The thermal transition temperature of com-posite films was measured using a dynamic mechanicalthermal analyzer (DMTA Q800, TA Instrument) by employingthe sample (gauge) length of 2.5 cm, the sample width of 0.5cm, the heating rate of 5 oC/min from room temperature to400 oC, and the head oscillation frequency of 3 Hz. Themechanical (tensile) properties of composite films were

measured using a universal testing machine (UTM, KoreaApparel Testing & Research Institute) by employing a strainrate of 10 mm/min at room temperature: The reported val-ues are averaged of five specimens in each case. Before themeasurement of dielectric constant, the composite filmswere dried for 1 h at 200 oC in order to remove water. Mea-surements were done under the ambient atmosphere withRH (relative humidity) <20%. The dielectric constant wasmeasured by LCR meter (4284A. Agilent) with dielectrickit (16451B, Agilent) at 1 kHz. Surface morphology of thecomposite films was obtained by an atomic force micros-copy (AFM) (Nanoscope IIIaR_Digital Instruments Co.). Allsamples for the measurement of morphology were coatedonto glass, followed by thermal imidization. And then, itwas kept at 300 oC for 2 h in the atmosphere for the removalof CD in the composite films.

Results and Discussion

Characterization of Synthesized Modified CD. As shownin Figure 1, the broad band around 3200~3600 cm-1 and thebands around 2930~2980 cm-1 were attributed in -OH stretch-ing and aliphatic CH adsorption of CD. For the β-CD-N3,

the new peaks were appeared at 2108 cm-1 attributed to -N3

groups. After modification, the peaks were disappeared inthe β-CD-NH2. It indicates that the -N3 groups were changedto -NH2 groups successfully.

The 1H NMR spectra of β-CD, β-CD-OTs and β-CD-NH2

can show the chemical structure of these materials obtainedby modification of CD as shown in Figure 2. The peaks ataround 3 to 5 ppm are related to different kinds of H atomsfor the CD. The β-CD-OTs was confirmed from differentfour peaks at 6-8 ppm, which is associated with chemicalstructure of benzene. However, there are no peaks relatedwith benzene in case of β-CD-NH2 due to the functionaliza-tion of -OTs.

X-ray photoelectron spectra of N1s for β-CD-NH2 and β-

Table I. Preparation of PI /Modified CD Nanocomposite Films

Sample Code PMDA (g) ODA (g) CD or Modified CD (g) Mn (×104) Mw (× 104) PDI** Film State***

Neat PI 0.4362 0.4005 0 7.98 9.69 1.21 T

1 wt% 0.4362 (0.0016)* 0.4005 0.008 7.99 9.61 1.20 T

3 wt% 0.4362 (0.005)* 0.4005 0.026 7.07 9.11 1.28 T

5 wt% 0.4362 (0.0086)* 0.4005 0.045 7.21 9.19 1.27 T

7 wt% 0.4362 (0.0123)* 0.4005 0.064 7.33 9.04 1.23 T

10 wt% 0.4362 (0.018)* 0.4005 0.094 7.23 8.82 1.21 T

CD2 0.4362 0.4005 0.018 7.98 9.81 1.73 O

CD5 0.4362 0.4005 0.047 5.82 6.68 1.62 O

CD10 0.4362 0.4005 0.099 5.85 6.68 1.61 O*Mole ratio to PMDA, **PDI: Mw/Mn, ***T: Transparent, O: Opaque.

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Macromol. Res., Vol. 18, No. 2, 2010 123

CD-N3 are shown in Figure 3. The spectrum of β-CD-N3 isfitted by a Gaussian function. The two components due tothe -N3 (azide) bonding at 397.4 eV (N*NN*) and 401.9 eV(NN*N*) can be separated as in Figure 3. We find a weakpeak (at about 393.8 eV) which corresponds to calcinationsof the sample by the strong X-ray beam. The three peaks atabout 397.1 eV (-N), 399.49 eV (-NH2) and 403.8 eV (-NO2)were found in the N1s binding energy region. The thirdpeak at 403.8 eV was the result of surface oxidation from-NH2 to -NO2 at the atmosphere. The LC-MS spectrashowed that the molecular weights of β-CD (C42H70O35) andβ-CD-NH2 (C42H71O34N1) are 1,135 and 1,134, respectively,meaning that the only one -OH group of CD was substitutedby -NH2 group.29 Thus, we can conclude that modified CDwas prepared successfully.

FTIR and UV-vis Spectroscopy. Figure 4 shows FTIRspectra of the neat polyimide and its nanocomposite films.

Upon curing, the characteristic adsorption peaks of imidegroups are present near at 1780, 1711, 1368, and 730 cm-1 inthe composite samples as well as PI. In particular, the peaksat 1711 cm-1, due to an imide group and 1780 cm-1, indicat-ing a cyclic five-membered ring, confirmed imide forma-tion. The bands at 1368 and 730 cm-1 are attributed to the C-N-C bond and the imide ring deformation, respectively. Theband at 1173 cm-1 is attributed to the C6H4 or C6H2. The peakat 677 cm-1 is assumed due to C-C=O in plane swing vibra-tion. FTIR spectra were used to verify imidization of thePAA by observing the disappearance of the band at 1650 cm-1

and the growth of the imide group at 1711 cm-1. This obser-vation showed a good agreement with the earlier studies.30-35

The extremely broad band near 3386 cm-1, caused by theOH stretching and the bands around 2930~2980 cm-1, attrib-uted to the aliphatic CH adsorption, were indicative of somechemical bonding or hydrogen bonding between M-CD andpolyimide in the nanocomposites, as can be explained in

Figure 1. FTIR spectra of CD, CD-OTs, CD-N3, and CD-NH2.

Figure 2. NMR spectra of CD, CD-OTs, CD-N3, and CD-NH2.

Figure 3. X-ray photoelectron spectra of CD-N3 and CD-NH2.

Figure 4. FTIR spectra of PI/modified CD nanocomposite filmswith various modified CD loadings. Inset shows the magnifiedIR spectra in the wavenumber region from 2000-4200 cm-1.

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Scheme II. It became much stronger and increased withincreasing contents of the M-CD, as can be seen in the selectedwavelength ranges in the inset.

Figure 5 displays the optical properties of PI as a functionof the weight percentage of M-CD. The transparency wasdecreased with increasing contents of M-CD and their col-ors were changed from yellow to brown. Though the con-tent of M-CD was 10 wt%, the composite film was stilltransparent comparing with CD10 in Figure 5(a) and (b). Itwas attributed to the chemical interaction of M-CD withpolyimide matrix. It was already found from Figure 4 thatthe M-CD was much more compatible with PI comparingwith pure CD, suggesting chemical bonding between M-CDand PI.

Periodicity of PI in Nanocomposite Films. Figure 6

shows the XRD patterns of the neat PI and nanocompositefilms. The conventional PMDA-ODA PI is characterizedwith a major diffraction peak at 2θ=10o-40o. There were nopeaks of pure CD in the composite films and no significantdifferences in the XRD patterns between PI and compositefilms were observed. This result indicates that all the sam-ples using the M-CD exhibit almost same crystalline struc-ture as for the neat PI’s amorphous structure due to denselinkage between the carboxylic groups of poly(amic acid)and the amino groups of CD-NH2. Therefore, it was consid-ered that the addition of M-CD to polyimides does not affecton the crystalline structure of PI, regardless of the stronginteraction.

Thermal Properties of Nanocomposite Films. Thermo-gravimetric curves of the PMDA-ODA PI and its nanocom-posites are shown in Figure 7. Even though the inset showsthat the pure CD and M-CD were decomposed around300 oC and 200 oC, it is shown that the initial loss of weightsof composites was appeared around 300 oC due to the M-CDin the composite films. The reason may be due to the factthat the M-CD bonded to the PI matrix in the compositefilm is more stable than ones in the atmosphere, since themain functionality of the M-CD has been changed to amide

Scheme II. Possible mechanism of chemical bonding betweenPMDA-OPDA PI and modified CD.

Figure 5. UV-vis spectra of PI/modified CD nanocomposite filmswith various modified CD loadings. Inset shows photographs ofcomposite materials containing (a) 10 wt% of M-CD and (b) CD10.

Figure 6. XRD patterns of PI/modified CD nanocomposite filmswith various modified CD loadings; (A) before and (B) afterannealing at 300 oC for 2 h (scan speed 2o/min).

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Macromol. Res., Vol. 18, No. 2, 2010 125

linkage in the composite films, where the amide linkage isin between PMDA and ODA. Thus, the TGA results are notsurprising if one considers that an amide linkage is morestable than amine functionalized one. Therefore, the initialloss of the composite films was appeared around 300 oCinstead of 200 oC. The weight loss was, however, increasedby increasing contents of M-CD and, thus the thermal sta-bility of the composite films was decreased with incrasingM-CD contents.

The glass transition temperature (Tg) of the nanocompos-ite films are presented in Figure 8. It was shown that therewas the phase transition of composite films around 300 oC,caused by adding M-CD. This result was in accordance withthat the CD moieties effect on the initial loss of compositefilms around 300 oC in TGA curves. The Tg of the polyim-ide nanocomposites measured by DMA (in Figure 9)slightly exceeds that determined by DSC, but the depen-dency of the transition temperature on the amount of M-CD

is consistently revealed by both sets of data. Even though itwas expected that the Tg would be increased due to chemicalinteraction between poly(amic acid) and the amino groupsof CD-NH2, the decrease in the Tg of PI/ M-CD nanocom-posite was observed. The phase transition of M-CD effec-tively constrains the polyimide main-chain motion, thusdecreasing the Tg of the composite.

Morphology of Nanocomposite Films. Figure 10 displaysthe FE-SEM images of cross section of nanocomposites.The roughness of surface morphology was increased withincreasing contents of M-CD comparing with neat PI. It wascaused by rigid structure of CD and aggregation. At a lowM-CD loading, modified β-CD molecules are distributeduniformly throughout the PI matrix. However, the compos-ite films tend to phase-separate and form β-CD-rich micro-domains when the M-CD loading is around 10 %, and this isevident from some visible CD agglomerates under opticalmicroscope observation. Additionally, some large pores (inmicrometers) in A-7 wt% and more in A-10 wt% are viewedin Figure 10. This can be explained by the decomposition ofthe β-CD agglomerates leaving pores after annealing at 300 oCfor 2 h and it was consistent with images of AFM in Figures11 and 12.

Mechanical and Dielectric Properties of Nanocompos-ite Films. Table II shows mechanical properties of nano-composite films and indicates that the contents of M-CDhave significant effects on the mechanical properties of PI.The tensile strength of the polyimide nanocomposites increasesfrom 106.4 (near polyimide) to 136.2 MPa as the amount ofM-CD materials is increased from 0 to 7 wt%. When theamount of M-CD materials in the polyimide composites is 7wt%, the tensile strength of the polyimide nanocompositesis 28% greater than that of the pure polyimide. Furthermore,it was higher than those of CD2, CD5 and CD10, which wasattributed to homogeneous dispersion and compatibilitybetween CD and PI matrix as shown in Figure 10. The con-tinuous increase in the tensile strength of these nanocompos-ites with the amount of M-CD suggests again the strong

Figure 7. TGA curves of the neat polyimide and PI nanocompos-ite films with various modified CD loadings (inset: CD and mod-ified CD).

Figure 8. DSC thermograms of the neat polyimide and PI nano-composite films with various modified CD loadings.

Figure 9. DMA thermograms of the neat polyimide and PI nano-composites with various modified CD loadings.

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126 Macromol. Res., Vol. 18, No. 2, 2010

interfacial interaction between CD-NH2 and polyimide. Thisresult may follow from the effective covalent bond throughthe pore channel and the homogeneous dispersion of M-CDin the polyimide matrix. In case of 10 wt%, however, theratio of M-CD contents in the composite films was too highto improve the tensile strength due to the phase separationof the CD from PI matrix. The elongation of polyimidenanocomposites decreased slightly with the amount of M-CD to a maximum of 34% comparing with neat polyimide.The tensile modulus was increased with increasing contentsof M-CD, caused by CD’s rigid structures. And also thesecomposite films have much better mechanical propertiesthan the pure PI/CD composite films. The enhancedmechanical properties of the polymer network follow fromthe dense linkage between the carboxylic groups of

poly(amic acid) and the amino groups of CD-NH2 andhydrogen bonding between PI matrix and -OH group ofcyclodextrin.

As shown in Table II, the dielectric constant was decreasedwith increasing contents of M-CD up to 10 wt% from 3.34of the neat PI to 3.12. The reduction of the dielectric con-stant is attributed to the addition of the air volumes (κ = 1)stored within CD and the air voids existing in the gaps onthe interfaces between the PI matrix and CD (as shown inFigure 10). Additionally, in case of films after annealing M-CD, the dielectric constant was decreased remarkably up to2.56 at the addition of 10 wt%. After the removal of M-CD,it has much lower low-k, caused by air voids. It was dis-played that there were many voids in the films in the inter-faces between the PI matrix and M-CD as shown in Figure

Figure 10. Fractured surface morphology of composite films before annealing CD at 300 oC for 2 h ((a) neat PI, (b) 1 wt%, (c) 3 wt%,(d) 5 wt%, (e) 7 wt%, and (f) 10 wt%) and after annealing CD at 300 oC for 2 h ((A) neat PI, (B) A-1 wt%, (C) A-3 wt%, (D) A-5 wt%,(E) A-7 wt%, and (F) A-10 wt%).

Table II. Mechanical and Dielectric Properties of PI/Modified CD Nanocomposite Films

Sample Name Elongation at Break (%) Tensile Strength (MPa) Young’s Modulus (MPa) Dielectric Constant (Before/After)*

Neat PI 40 106.4 1,047 3.34 (3.34)

1 wt% 40 110.3 1,305 3.34 (3.31)

3 wt% 31 130.1 1,912 3.25 (2.91)

5 wt% 31 132.4 1,948 3.22 (2.81)

7 wt% 27 136.2 1,940 3.21 (2.63)

10 wt% 14 119.7 2,097 3.12 (2.56)

CD2 10 79.6 2,766 3.33 (2.97)

CD5 19 78.4 2,844 3.26 (2.86)

CD10 19 81.5 2,744 3.17 (2.66)*Before: Before annealing CD at 300 oC for 2 h. After: After annealing CD at 300 oC for 2 h.

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Macromol. Res., Vol. 18, No. 2, 2010 127

Figure 11. 2-Dimensional AFM images of the PI nanocomposite films after annealing CD at 300 oC for 2 h (from the top-left to the bot-tom-right; neat PI, A-1 wt%, A-3 wt%, A-5 wt%, A-7 wt%, and A-10 wt%, respectively).

Figure 12. 3-Dimensional AFM images of the PI nanocomposite films after annealing CD at 300 oC for 2 h (from the top-left to the bot-tom-right; neat PI, A-1 wt%, A-3 wt%, A-5 wt%, A-7 wt%, and A-10 wt%, respectively).

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10 and spaces of the surface area were also shown in theAFM images of the composite films (Figures 11 and 12). Itshould be also noted, however, that there seems to be a pos-sibility of dewetting phenomena rather than only by remov-ing CDs in the film, considering the size of CD moleculesand the void volume appeared in the AFM images.

Conclusions

We have discussed preparation and characterization ofpolyimide/modified CD nanocomposite films. A series ofthe novel PI composite films with modified CD were pre-pared via in situ polymerization and following thermal imi-dization. The FTIR, NMR, XPS and LC-MS spectra confirmedthat the modified CD was successfully prepared. The XRDpatterns confirmed that there were no significant aggrega-tions of M-CD from PI or deformations of the crystallinestructure of PI in the nanocomposite films. The mechanicalproperties were increased up to 7 wt% due to the dense link-age between the carboxylic groups of poly(amic acid) andthe amino groups of CD-NH2 and hydrogen bonding betweenPI matrix and -OH group of cyclodextrin. The thermal sta-bilities were decreased due to the presence of organic CDmoieties. The dielectric constant can be reduced from 3.34of the neat PMDA-ODA PI to 2.56 for the 10 wt% M-CDcontaining PI nanocomposite, especially when the films areannealed at 300 oC for 2 h. The reduction of the dielectricconstant was attributed to the incorporation of air voids (κ =1) between PI matrix and CD, and the air volumes stored inwithin CD. The PI nanocomposite films with M-CD pre-pared may attract interest because of their potential applica-tions in the electronic and environment-friendly industries.

Acknowledgements. This work was supported by theNational Research Foundation of Korea (NRF) throughAcceleration Research Program (No. 2009-0078791) fromthe Ministry of Education, Science & Technology, Republicof Korea (MEST) and a grant from the Fundamental R&DProgram for Core Technology of Materials funded by theMinistry of Knowledge Economy, Republic of Korea, a grantfrom the Korea-China Joint Research Center Program onMesoporous Thin Films (K20807000001-09B1200-00110)of the NRF, a grant-in-aid for the World Class UniversityProgram (No. R32-2008-000-10174-0) from NRF, and theBrain Korea 21 Project of the MEST. The authors thank toDr. K.S.V. Krishna Rao of Yogi Vemana University, Indiafor his help to synthesize modified CD during his stay atPusan National University, Korea.

References

(1) C. H. Jung and Y. M. Lee, Macromol. Res., 16, 555 (2008).(2) Y. Ha, M. C. Choi, N. Jo, S. W. Han, D. H. Han, I. Kim, C. S.

Ha, and M. Han, Macromol. Res., 16, 725 (2008).

(3) A. Mathews, I. Kim, and C. S. Ha, Macromol. Res., 15, 114(2007).

(4) B. S. Kim, S. H. Bae, and Y. H. Park, Macromol. Res., 15,357 (2007).

(5) H. S. Lee, A. Roy, and A. S. Badami, Macromol. Res., 15,160 (2007).

(6) J. Y. Lee, J. H. Kim, and B. K. Rhee, Macromol. Res., 15, 234(2007).

(7) R. H. Vora, P. S. Gopala Krishnan, S. H. Goh, and T. S.Chung, Adv. Funct. Mater., 11, 362 (2001).

(8) H. J. Cha, J. Hedrick, R. A. DiPietro, T. Blume, R. Beyers,and D. Y. Yoon, Appl. Phys. Lett., 68, 1930 (1996).

(9) J. L. Hedrick, C. K. Hawker, R. DiPietro, R. Jerome, and Y.Charlier, Polymer, 36, 4855 (1995).

(10) M. Narkis, M. Puterman, H. Boneh, and S. Kenig, Polym. Eng.Sci., 22, 417 (1982).

(11) A. Tiwari, M. K. Gupta, K. N. Pandey, G. N. Mathur, and S.K. Nema, Polym. Int., 53, 1744 (2004).

(12) W. C. Wang, R. H. Vora, E. T. Kang, K. G. Neoh, C. K. Ong,and L. F. Chen, Adv. Mater., 16, 54 (2004).

(13) L. Y. Jiang, C. M. Leu, and K. H. Wei, Adv. Mater., 14, 426(2002).

(14) J. J. Lin and X. D. Wang, Polymer, 48, 318 (2007).(15) T. Yonezawa, N. Toshima, C. Wakai, M. Nakahara, M. Nishi-

naka, T. Tominaga, and H. Nomura. Colloid Surf. A, 169, 35(2000).

(16) T. Lee, S. S. Park, Y. Jung, S. Han, D. Han, I. Kim, and C. S.Ha, Eur. Polym. J., 45, 19 (2009).

(17) M. L. Bender and M. Komiyama, Cyclodextrin Chemistry,Springer-Verlag, Berlin, 1978.

(18) J. M. Lehn, Supramolecular Chemistry: Concepts and Per-spectives, VCH, Weinheim, Germany, 1995.

(19) J. Szejtli, Chem. Rev., 98, 1743 (1998).(20) J. H. Yim, Y. Y. Lyu, H. D. Jeong, S. A. Song, I. S. Hwang,

and J. Hyeon-Lee, Adv. Funct. Mater., 13, 382 (2003).(21) S. Li, Z. J. Li, and Y. S. Yan, Adv. Mater., 15, 1528 (2003).(22) B. H. Han, B. Smarsly, C. Gruber, and G. Wenz, Micropor.

Mesopor. Mater., 66, 127 (2003).(23) J. Y. Yang, B. T. Jung, and D. H. Suh, Polymer, 42, 8349 (2001).(24) J. Liu and H. Wang, J. Non-cryst. Solids, 351, 936 (2005).(25) N. Zhong, H. S. Byun, and R. Bittman, Tetrahedron Lett., 39,

2919 (1998).(26) A. R. Khan, P. Forgo, K. J. Stine, and V. T. D’Souza, Chem.

Rev., 98, 1977 (1998).(27) S. Hanessian, A. Benalil, and C. Laferriere, J. Org. Chem.,

60, 4786 (1995).(28) J. M. Gracia Ferriandez, C. O. Mellet, S. Maciejewski, and J.

Defaye, J. Chem. Soc. Chem. Commun., 1996, 2741 (1996).(29) The LC-MS spectra of β-CD and β-CD-NH2 are available

from the corresponding author.(30) C. J. Cornelius and E. Marand, Polymer, 43, 2385 (2002).(31) Y. Chen and J. O. Iroh, Chem. Mater., 11, 1218 (1999).(32) M. H. Tsai and W. T. Whang, Polymer, 42, 4197 (2001).(33) C. Xenopoulos, L. Mascia, and S. J. Shaw, Mater. Chem., 12,

213 (2002).(34) L. L. Becroft, N. A. Johnen, and C. K. Ober, Polym. Adv.

Technol., 8, 289 (1997).(35) M. A. Wahab, I. Kim, and C. S. Ha, Polymer, 44, 4705 (2003).