Rational Design of Polyhedral Oligomeric Silsesquioxane Fillers for Simultaneous Improvements of Thermomechanical Properties and Lowering Refractive Indices of Polymer Films

$Page 1: Rational Design of Polyhedral Oligomeric Silsesquioxane Fillers for Simultaneous Improvements of Thermomechanical Properties and Lowering Refractive Indices of Polymer Films$
Rational Design of Polyhedral Oligomeric Silsesquioxane Fillers for

Simultaneous Improvements of Thermomechanical Properties and

Lowering Refractive Indices of Polymer Films

Jong-Hwan Jeon, Kazuo Tanaka, Yoshiki Chujo

Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo-ku,

Kyoto 615-8510, Japan

Correspondence to: Y. Chujo (E-mail: [email protected])

Received 11 February 2013; accepted 2 May 2013; published online 5 June 2013

DOI: 10.1002/pola.26757

ABSTRACT: We describe here the design and synthesis of the

polyhedral oligomeric silsesquioxane (POSS)-based dual-func-

tional molecular fillers for simultaneously lowering refractive

indices and improving thermomechanical properties of conven-

tional polymers. We prepared the composite films with poly

(methyl methacrylate) and polystyrene containing the series of

the POSS derivatives with the single functional unit for inter-

acting with polymer chains and heptacyclopentyl substituents

for creating exclusive volumes around the POSS core. From

the measurements of refractive indices of polymer composites,

it was revealed that all POSS fillers can lower the refractive

index of the films. In addition, thermal stabilities and mechani-

cal properties were enhanced by adding POSS fillers. The filler

effect on the thermal properties can be explained by the struc-

tural features of POSS: The highly symmetrical structure of the

silica cube should suppress thermal motions, resulting in the

large enhancement of thermomechanical properties of polymer

matrices. VC 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A:

Polym. Chem. 2013, 51, 3583–3589

KEYWORDS: composites; filler; poly(methyl methacrylate); poly-

siloxanes; polystyrene; POSS; refractive index

INTRODUCTION Requirements of precise controls of opticalproperties in polymers have increased for improving theefficiency of conventional optoelectronic devices and gener-ating advanced materials. For example, polymer films thathave refractive index (RI)-gradients through the film con-tributes to improvements in luminescence efficiencies inelectroluminescent devices by suppressing undesired reflec-tion or scattering inevitably caused at the refraction gaps.1

The use of molecular fillers is a simple and feasible tech-nique for fabricating these functionally gradient materialsbecause it is easy to control the local concentrations andmodulate functions based on the preprogrammeddesigns.2,3 Thus, the development of effective molecularfillers should be potentially of great significance.

There are two categories of molecular fillers for the loweringRIs of the materials; molecules with low dielectric constantssuch as perfluorinated compounds, and large exclusion vol-umes as found with rigid-caged compounds.4–6 However, theintroduction of these fillers into polymers often induces criti-cal decreases in the thermal stabilities and mechanical prop-erties of the polymer matrices. Because of poor compatibilityof fluorine groups with polymer chains, phase separation can

occur readily, leading to significant decreases in thermal du-rability. Although void spaces can efficiently reduce RIs, me-chanical properties are also likely to be reduced. Thus, themaintenance of the balance between decreasing RIs whileincreasing thermomechanical properties is the criticalrequirement to the development of effective molecular fillersthat lower RIs.

Polyhedral oligomeric silsesquioxanes (POSSs) are wellknown as molecular building blocks to construct functionalmaterials as well as to improve the thermomechanical prop-erties of polymers.7–20 The rigid POSS structure can suppressthe molecular motions of polymer chains, thereby enhancingthe thermal and=or mechanical properties of the matrices.Particularly, we observed the significant enhancements tothe thermal stabilities of the polymers by adding octa-substi-tuted POSS derivative with vinyl and phenyl groups. In addi-tion, it is implied that the symmetrical structure of the silicacube could contribute to reducing entropy differences inphase transitions.21 Therefore, the molecular motion couldbe suppressed, resulting in the improvements of the thermalstabilities of POSS-containing composites. Furthermore, ithas been reported that POSS is a suitable nanobuilding block

Additional Supporting Information may be found in the online version of this article.

VC 2013 Wiley Periodicals, Inc.

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for lowering RIs.22,23 We have reported the significant effectof octa-substituted POSS derivatives with ethyl, vinyl, andcyclopentyl groups to lower RIs of the conventional polymermatrices (20.0040, 20.0027, and 20.0010 with 1.5 mol %filler concentrations, respectively).24 Because of the largeexclusion volumes created around POSS cores, the RIs ofpolymer films decreased by adding these octa-substitutedPOSS derivatives. However, there is still a critical issue forsimultaneously lowering a RI while enhancing the thermo-mechanical properties of the polymers by using designedmolecular fillers.

Herein, we report a series of dual-functional POSS fillers forsimultaneously increasing the thermomechanical propertiesand decreasing the RIs of polymer matrices. To solve theproblem on the reduction of thermal stability induced byreducing packing density of the matrices for reducing RIs, wedesigned the POSS fillers with two kinds of the substituentsfor enhancing the affinity of the POSS core to polymer chainsand for creating exclusive volumes around filler molecules.The design concept, synthesis of the POSS fillers using incom-plete cages of POSS, and the results are described here.

EXPERIMENTAL

General1H NMR spectra were measured with a JEOL EX-400 (400MHz) spectrometer. Coupling constants (J-value) are reportedin Hertz. MASS spectra were obtained on a JEOL JMS-SX102A. Scanning electron microscopy (SEM) images wereperformed using a JEOL JSM-5600 operated at an accelerat-ing voltage of 15 kV. UV–vis absorption spectra wererecorded with a SHIMADZU UV-3600UV-vis-NIR spectropho-tometer. The RIs were determined with an Abbe refractome-ter DR-M4 (accuracy, 60.0002; ATAGO, Tokyo, Japan) at 580nm at 25 �C. Dynamic mechanical analysis (DMA) was per-formed on a SDM5600=DMS210, Seiko Instrument, with theheating rate of 2 �C=min at 1 Hz with 1% of strain under air.Differential scanning calorimetry (DSC) thermograms werecarried out on a SII DSC 6220 instrument by using �10 mgof exactly weighed samples at a heating rate of 10 �C=min.The glass transition temperatures (Tg) were evaluated fromthe second monitoring curves after annealing at 100 �C for10 min, followed by cooling to 30 �C. Thermogravimetricanalysis (TGA) was performed on an EXSTAR TG=DTA 6220,Seiko Instrument, with the heating rate of 10 �C=min up to500 �C under nitrogen atmosphere. Residual chloroform wasremoved by keeping in a vacuum oven at 100 �C for 1 hbefore the TGA measurements. The van der Waals volumesof POSS derivatives and the monomer unit of poly(methylmethacylate) (PMMA) were calculated after the modelingusing a semi-empirical AM1 method.

MaterialsTrichlorocyclopentylsilane (Aldrich), trichlorophenylsilane(Aldrich), trichlorododecylsilane (Aldrich), trichloro(3,3,3-tri-fluoropropyl)silane (Aldrich), and allyltrichlorosilane (TCI)were purchased and used for the assays without further

purification. PMMA (Mw 5 350,000, cat# 445746) and poly-styrene (PS) (Mw 5 35,000, cat# 32775) were purchasedfrom Aldrich and used as received. Tetrahydrofuran (THF)and triethylamine were distilled over sodium and calciumhydride, respectively.

Synthesis of Silsesquioxane Partial Cage[(c-C5H9)7Si7O9(OH)3]Incompletely condensed trisilanol (c-C5H9)7Si7O9(OH)3 wasprepared in 29% of yield by the hydrolytic condensationreaction of trichlorocyclopentylsilane in reflux aqueous ace-tone, according to the procedure reported earlier.25

Synthesis of POSS fillersThe trisilanol (0.5 g, 0.6 mmol) and triethylamine (0.33 mL,2.3 mmol) were cooled in an ice bath, and trichlorosilane(phenyl-, 93 lL, 0.6 mmol; allyl-, 84 lL, 0.6 mmol; dodecyl-,0.17 mL, 0.6 mmol; trifluoropropyl-, 95 lL, 0.6 mmol) inTHF was added slowly to the mixture. The resulting solutionwas stirred overnight at room temperature. After removinginsoluble salts by filtration, the filtrate was concentrated to5 mL and poured into excess acetonitrile. The white precipi-tate was collected by filtration and dried in vacuo to producea white solid (Cp POSS-P, 71%; Cp POSS-A, 70%; Cp POSS-D,67%; Cp POSS-F, 60%).

Cp POSS-P: 1H NMR (CDCl3, 400 MHz) d 5 7.67 (m, 2 H), d5 7.36–7.42 (m, 3 H), d 5 1.79 (m, 20 H), d 5 1.56 (m, 36H), d 5 0.97 (m, 7 H); 13C NMR (CDCl3, 400 MHz) d 5

139.8, 134.1, 129.7, 137.6, 26.7, 26.6, 26.5, 26.3, 26.2; 29SiNMR (CDCl3, 400 MHz) d 5 266.09, 266.43; LRMS (NBA)[(M1H)1] calcd. 977, found 977; HRMS (NBA) [(M1H)1]calcd. 977.6554, found 976.2865. Cp POSS-A: 1H NMR(CDCl3, 400 MHz) d 5 5.76 (m, 1 H), d 5 4.92 (m, 2 H), d 5

1.79 (m, 20 H), d 5 1.56 (m, 38 H), d 5 0.97 (m, 7 H); 13CNMR (CDCl3, 400 MHz) d 5 132.6, 114.6, 26.7, 26.6, 26.5,26.3, 26.2, 19.7; 29Si NMR (CDCl3, 400 MHz) d 5 266.47,266.53; LRMS (NBA) [(M1H)1] calcd. 941, found 941;HRMS (NBA) [(M1H)1] calcd. 941.6233, found 940.2865. CpPOSS-D: 1H NMR (CDCl3, 400 MHz) d 5 1.79 (m, 20 H), d 5

1.56 (m, 36 H), d 5 1.39 (m, 4 H), d 5 1.26 (m, 16 H), d 5

0.97 (m, 7 H), d 5 0.88 (t, 3 H), d 5 0.59 (t, 2 H); 13C NMR(CDCl3, 400 MHz) d 5 77.3, 76.6, 32.5, 26.7, 26.6, 26.5, 26.3,26.2, 22.8, 22.7, 22.3, 14.1, 11.9; 29Si NMR (CDCl3, 400 MHz)d 5 266.54, 266.69; LRMS (NBA) [(M1H)1] calcd. 1069,found 1069; HRMS (NBA) [(M1H)1] calcd. 1069.8784, found1068.4430. Cp POSS-F: 1H NMR (CDCl3, 400 MHz) d 5 2.12(t, 2 H), d 5 1.79 (m, 20 H), d 5 1.56 (m, 36 H), d 5 0.97(m, 7 H), d 5 0.83 (t, 2 H); 13C NMR (CDCl3, 400 MHz) d 5

130.1, 26.7, 26.6, 26.5, 26.3, 26.2, 24.1, 2.2; 29Si NMR (CDCl3,400 MHz) d 5 265.68, 265.93; LRMS (NBA) [(M1H)1]calcd. 997, found 997; HRMS (NBA) [(M1H)1] calcd.997.6106, found 996.2739.

Preparation of Polymer CompositesThe mixtures (20 mL) containing 1 g of polymers (PMMA orPS) and various amounts of POSS fillers in chloroform werestirred at room temperature for 3 h and then poured intothe bottom of vessels (7 cm 3 4.5 cm). After drying at room

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temperature for 2 days, the film samples were dried again ina vacuum oven at 60 �C for 2 h. The resulting films wereused for subsequent measurements.

Determination of RIs of the Polymer CompositesAccording to the Lorentz–Lorenz equation, the refractiveindex (n) of the polymer (Element 1) composites containingfillers (Element 2) can be described using the molar frac-tions (a), molar refractions (R), and molar volumes (V).26

n221

n2 þ 2¼ a1

n2121

n21 þ 2þ a2

n2221

n22 þ 2¼ a1

R1

V1þ a2

R2

V2(1)

The degree of packing can be described by the molecularpacking coefficient Kp that is defined as

Kp ¼VVDW

Vint(2)

where Vint and VVDE are the intrinsic and van der Waals vol-umes of the molecules, respectively. Therefore, moleculesthat have significant abilities to lower the interactionsbetween polymer chains would show a smaller Kp value. Inaddition, according to Vuks equation, eq 1 can be trans-formed into eq 3.27

n221

n2 þ 2¼ a1

n2121

n21 þ 2þ a2

n2221

n22 þ 2¼ a1

Kp1R1

VVDW;1þ a2

Kp2R2

VVDW;2(3)

In the case of amorphous polymers, the Kp values (Kp1) weredetermined to be 0.68.28 Therefore, we can simply calculate Kp2values by measuring the RIs of the composite (n) using eq 3.

RESULTS AND DISCUSSION

We designed the POSS fillers with two kinds of substituentsat the vertices of the silica cube. In the previous report, itwas found that cyclopentyl groups can create large exclusivevolumes around filler molecules, lowering the RIs of the mat-rices.24 Thus, we introduced the seven cyclopentyl groups inthe POSS fillers. To reinforce the thermomechanical proper-ties of the polymeric materials, the introduction of the func-tional units to enhance intermolecular interactions amongpolymer chains or symmetries of the chemical structure ofthe components to reduce the transition entropy is the typi-cal manner.24 However, the former strategy negative affectedattempts to lower RIs. Thus, we sought to apply symmetricPOSS for the reinforcement of polymers.29,30 In other words,we envisioned a scenario that by interacting POSS fillersonly with a single polymer chain, molecular motions shouldbe suppressed. Then, thermal and mechanical propertiescould be improved. According to the previous report, phenyl-and vinyl-POSS showed large enhancements to the thermalstability of PS.20 Long alkyl chain-substituted POSS canimprove the thermal stability of PMMA. Based on theseresults, we selected the phenyl-, allyl-, dodecyl-, and trifluor-opropyl groups to obtain high affinity to the polymer chains.

The chemical structures and thermal decomposition tempera-tures with 20 wt % weight loss (Td20) of the POSS fillers used

in this study as filler are listed in Table 1. These POSS deriva-tives are composed of heptacyclopentyl groups for lowering RIsand a one-functional unit for improving the durability of thepolymers using PMMA and PS. The composites containing POSSfillers were prepared by blending POSS fillers and polymers insolution. The mixtures of polymers (1.0 g) in chloroform (20mL) were added to the POSS fillers with various concentrations(from 0.5 to 2 mol % to the monomer unit of the polymers)and stirred until the mixtures turned clear. Then, the resultingmixtures were poured into the polypropylene vessels (7 cm 3

4.5 cm), and the sample films for measurements were obtainedafter drying in a vacuum oven at 60 �C for 2 h.

Initially, we investigated the surface morphologies of thecomposite films using SEM. Significant phase separation oraggregation of POSS fillers was hardly observed in thePMMA composites (Supporting Information Figs. S1 and S2).These results suggest that homogeneous dispersions of thePOSS fillers were realized in PMMA.

In contrast, inhomogeneity implying the aggregation orphase separation was observed in the PS film. In the PS com-posites containing 0.5 mol % of POSS fillers, aggregatedmasses of POSS fillers were hardly observed on the surfacemorphologies as shown in Supporting Information Figure S1.They become easily visible in PS composites containing1.0 mol % of POSS fillers. However, the sizes of these inho-mogeneities in PS composites were below 100 nm except forthe sample containing Cp POSS-F. Therefore, we concludethat sufficient transparency for measuring refractivity withgood reproducibility occurs at < 1 mol % concentrations ofthe POSS fillers. Most samples showed turbidity with 1.5mol % of POSS fillers, and the transparency of the compositefilms decreased drastically as shown in Supporting Informa-tion Figure S2. The phase separation of POSS fillers was sig-nificant in most of the composite films containing 2 mol %of POSS fillers. The processability of the film and reproduci-bility for the refraction measurements were reduced. Thus,we discuss the filler effects with data sets obtained fromsamples containing POSS fillers (0.5 and 1.0 mol %).

TABLE 1 Chemical Structures and Decomposition Tempera-

tures with 20 wt % Weight Loss of POSS Fillers Used in This

Study

Framework Description

Chemical

Structure

(R)

Td20

(�C)a

Cp POSS-P 391

Cp POSS-A 376

Cp POSS-D 375

Cp POSS-F 380

a Determined from TGA.



RIs of the composite films with variable concentrations ofPOSS fillers were measured using an Abbe refractometer.The averages of the values at five distinct points in the com-posite films are listed in Table 2. The RIs of polymer filmswith POSS fillers were lower than that of pure polymers.Moreover, the RIs of the polymers decreased correspondingwith increases in POSS filler concentrations (Fig. 1). Fromthese results, as we expected, the POSS fillers described herehave the ability to lower RIs of polymer films. The mecha-nism of the lowering of refractivity can be explained by thefindings in the previous report.24 The cyclopentyl groups onPOSS can effectively create the exclusion volumes. Conse-quently, the reduction of the packing of the polymer chainslikely occurs, resulting in the lowering refractivity. Accordingto the recent reports, the degree of decreases in RIs by thepresent POSS fillers is large enough for the application of theoptical fibers.31,32 Thus, our concept for the design of molec-ular fillers could be applicable in the practical materials.

The degree of the packing of polymer chains and filler mole-cules can be estimated by the packing coefficients, Kp1 andKp2, respectively, according to the equations shown in the“Experimental” section. We have obtained the Kp1 value as0.677 with the pure polymer films corresponded to other

reports (ca. 0.68).24 From these data, we can claim that airbubbles or the residual solvents inside the polymer films didnot influence the RIs in our experiments. To evaluate thedegree of packing of the POSS fillers, we determined the Kp2values according to eq 3 (Table 2). It was found that all POSSfillers used in this experiment showed lower values than thatof Kp1. These results indicate that the POSS filler shouldreduce the packing of polymer chains in the materials. There-fore, polymer composites with POSS fillers showed the lowerRIs than those of the polymer films in the absence of POSS.

Next, the thermal properties of the composites were exam-ined. Table 3 summarizes the results of DSC for polymercomposites containing POSS fillers. The values were deter-mined from the second heating curves to eliminate the heathistory in the samples. The glass transition temperatures(Tg) of composites gradually shifted to higher temperaturesby increasing the POSS fillers concentrations. These resultswere attributed to a reduction in the segmental mobility ofpolymer chains in the composites. Although the packing ofthe polymer chains should be reduced by adding POSS fillers,the POSS fillers were responsible for the suppression of mo-lecular motions. In particular, the substituent effect at thesingle group on POSS on the Tg values was obtained. This

FIGURE 1 RIs (n) of the (A) PMMA and (B) PS composites containing various concentrations of POSS fillers.

TABLE 2 Differences of RIs (Dn) Induced by Adding Variable Concentrations of POSS Fillers and Representative Molecular Packing

Coefficients (Kp2) of POSS Fillersa

PMMA PS

0.5 mol % 1.0 mol % 1.5 mol % 0.5 mol % 1.0 mol % 1.5 mol %

Filler Dnb Dnb Dnb Kp2c Dnd Dnd Dnd Kp2

c

Cp POSS-P 20.0012 20.0015 20.0020 0.442 20.0011 20.0014 20.0016 0.557

Cp POSS-A 20.0015 20.0024 20.0038 0.361 20.0028 20.0035 20.0040 0.364

Cp POSS-D 20.0017 20.0023 20.0027 0.375 20.0025 20.0029 20.0032 0.429

Cp POSS-F 20.0034 20.0050 20.0079 0.201 20.0040 20.0055 20.0072 0.279

a Measured at 25 �C with an Abbe refractometer. The values were calcu-

lated from the averages measured at five distinct points in the compos-

ite films.b Caculated from the subtraction from the RI of the PMMA films

(1.4886).

c Caculated from the RIs of composite films containing 1.0 mol % of

POSS fillers.d Caculated from the subtraction from the RI of the PS films (1.5821).


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fact suggests that the interaction between the single substit-uent on POSS and the polymer chains should play a crucialrole in changing the thermal properties.

Thermal stabilities of polymer composites containing POSS fill-ers were examined by TGA. Figure 2 shows the TGA curves ofcomposites containing POSS fillers (0.5 and 1.0 mol %), and Ta-ble 4 summarizes the Td20 using the polymer composites con-taining POSS fillers. As the significant thermal degradation wasobserved in the composites around the temperature with 20%weight loss assigned as the main-chain scissions, the thermal

stabilizing effects by POSS fillers were discussed by comparingthe Td20 values of the composites. Residual chloroform wasremoved by keeping in a vacuum oven at 100 �C for 1 h beforethe measurements. Thermal reinforcement of PMMA compositesby loading POSS fillers was observed as shown in Figure 2(A,C).The dodecyl group of Cp POSS-D shows the enhancement tothe thermal stability of PMMA. The Td20 value of PMMA com-posite containing 1.0 mol % of Cp POSS-D increased by 27 �C.

Similar tendency was observed in PS composites. Pure PSexhibits a Td20 at 390 �C. The Td20 value of PS increases by

TABLE 3 The Results of DSC with Polymer Composites Containing POSS Fillersa

PMMA PS

0.5 mol % 0.5 mol % 1.0 mol % 1.0 mol % 0.5 mol % 0.5 mol % 1.0 mol % 1.0 mol %

Filler Tg (�C) DTg (�C) Tg (�C) DTg (�C) Tg (�C) DTg (�C) Tg (�C) DTg (�C)

None 72 – 72 – 80 – 80 –

Cp POSS-P 75 13 87 115 81 11 82 12

Cp POSS-A 74 12 84 112 83 13 84 14

Cp POSS-D 75 13 78 16 82 12 84 14

Cp POSS-F 76 14 78 16 83 13 82,93 12,113

a Determined from the second heating curves.

FIGURE 2 TGA thermograms of PMMA (0.5 mol % (A) and 1.0 mol % (C)) and PS (0.5 mol % (B) and 1.0 mol % (D)) composites

containing POSS fillers with a heating rate of 10 �C=min under nitrogen atmosphere.



4 �C by adding the Cp POSS-D. In addition, the thermal sta-bility of polymer composites was gradually enhanced corre-sponding with increases in concentration of Cp POSS-D.Moreover, the Td20 values of the polymer composites contain-ing 1.0 mol % of Cp POSS-A significantly improved the ther-mal stability of PMMA: 140 �C and same for PS: 17 �C.Furthermore, the addition of 2.0 mol % of Cp POSS-A greatlyinduced to the improvements of the thermal stability ofPMMA (151 �C) and PS (110 �C) as summarized in Sup-porting Information Table S2. These effects were alsoobserved in composites containing Cp POSS-P. The Td20 valueof the PMMA composite containing 1.0 mol % of Cp POSS-Pincreased dramatically by 34 �C. The PMMA composite con-taining 2.0 mol % of Cp POSS-P showed higher Td20 value at318 �C. It is likely that a longer alkyl chain and an unsatu-rated group could interact with the polymer chains becauseof the strong hydrophobic interaction and tangle formation.

The mechanical properties of the polymer composites con-taining POSS fillers were evaluated by DMA (temperaturescan at 1 Hz). Representative sets of DMA curves using thecomposites containing 0.5 and 1 mol % of POSS fillers areshown in Figure 3. The mechanical properties of the polymercomposites containing POSS fillers are summarized in Table5. The POSS fillers improved the storage modulus (E0) withthe resulting highest increase seen in adding Cp POSS-D

even at 1.0 mol %. The E0-value of composite was dramati-cally enhanced by fivefold. In addition, the E0-value with 1.0mol % of Cp POSS-P increased by 67%. The E0-value of thePMMA composite containing 1.0 mol % of Cp POSS-A was1.8 times larger than that of pure PMMA film. In the PS com-posites, similar effects were also observed. The E0-values ofPS composites were improved by adding POSS fillers. Theseresults suggest that the one-functional group as longer alkylchain or unsaturated groups of POSS fillers could make aninteraction with the polymer chains. As a result, POSS fillersshould suppress the motion of polymer chains. From thesedata involving DSC, TGA, and DMA, it is summarized that thePOSS fillers used in this study have significant abilities tosimultaneously improve thermomechanical properties andlower the RIs of polymers.

CONCLUSIONS

We describe here the molecular design for the dual-function-alized fillers based on POSS. According to the results withocta-substituted POSS fillers, the series of the heptacyclopen-tyl- and the single-heterogeneous substituent-containingPOSS was designed and synthesized. It was observed thatthe modified POSS can have the ability to enhance thermo-mechanical properties of conventional polymers with largeexclusion volumes around filler molecules. This effect can be

TABLE 4 The Decomposition Temperatures with 20 wt % Mass Loss of Polymer Composites Containing POSS Fillersa

PMMA PS

0.5 mol % 0.5 mol % 1.0 mol % 1.0 mol % 0.5 mol % 0.5 mol % 1.0 mol % 1.0 mol %

Filler Td20 (�C) DTd20 (�C) Td20 (�C) DTd20 (�C) Td20 (�C) DTd20 (�C) Td20 (�C) DTd20 (�C)

None 263 – 263 – 390 – 390 –

Cp POSS-P 283 120 297 134 394 14 397 17

Cp POSS-A 284 121 303 140 394 14 397 17

Cp POSS-D 282 119 290 127 392 12 394 14

Cp POSS-F 268 15 282 119 392 12 392 12

a Determined from TGA curves.

FIGURE 3 Dynamic mechanical curves (depicting E0) of (A) PMMA and (B) PS composites containing POSS fillers (0.5 and 1 mol %).


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explained by the structural feature of POSS: The highly sym-metrical structure of the silica cube should reduce entropychanges during the transition involving pyrolysis, resulting inthe large enhancement of thermomechanical properties ofpolymer matrices. Our findings and the design concept areapplicable not only for obtaining robust optical materials butalso for producing highly effective thermomechanical nanofil-lers based on the polymer composites.

ACKNOWLEDGMENT

This research was partially supported by the Suzuki Founda-tion (for K. Tanaka).

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TABLE 5 The Results of DMA with Polymer Composites Containing POSS Fillersa

PMMA PS

0.5 mol % 1.0 mol % 0.5 mol % 1.0 mol %

Filler E0

(GPa)aDE0

(GPa)atan d(�C)

E0

(GPa)adE0

(GPa)atan d(�C)

E0

(GPa)aDE0

(GPa)atan

d (�C)

E0

(GPa)aDE0

(GPa)atan

d (�C)

None 560 – 70 560 – 70 870 – 89 870 – 89

Cp POSS-P 770 1210 73 880 1320 74 1,380 1510 95 1,360 1490 93

Cp POSS-A 1,160 1600 74 1,460 1900 75 1,060 1190 94 910 140 95

Cp POSS-D 2,590 12,030 76 2,870 12,310 78 1,100 1230 92 1,270 1400 96

Cp POSS-F 1,050 1490 74 1,060 1500 75 1,040 1170 82 630 –240 80

a The values represented at 25 �C and the errors are within 5%.



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