Experimental .1. Materials

Sodium montmorillonite (Na⁺-MMT) with 1.45 mequiv/g cationic exchange capacity (CEC) was purchased from Nanocor Co. Most chemicals used in this study, including monomeric styrene, chemically pure acetone, methanol, tetrahydrofuran, acetonitrile, potassium hydroxide (KOH), triethylamine, and trichloro [4-(chloromethyl)phenyl] silane were acquired from the Aldrich Chemical Co., Inc.

The styrene monomer was purified by removing the inhibitor with the aid of an inhibitor-removal column. Sodium dodecyl sulfate (SDS) and hydrochloric acid were both obtained from Curtin Matheson Scientific, Inc. Potassium persulfate (K2S2O8) and aluminum sulfate [Al2(SO4)3] were acquired from Fisher Scientific Co., USA.

N,N-Dimethyloctadecylamine (C20), and 4-Vinylbenzyl chloride (4VB) were obtained from Acros Organics, USA. Trisilanolisobutyl polyhedral oligomeric silsesquioxane (POSS) was obtained from Hybrid Plastics, Inc.

2.2.2. Preparation of POSS-Cl compound.

The corner-capping reaction was employed to prepare POSS-Cl compound as shown in Scheme 2-2. Trisilanolisobutyl polyhedral oligomeric silsesquioxane (1, 3 g) and Et3N (1.26 g) were added into a 100 mL two-neck round bottom flask and stirred continuously 3 h under nitrogen, then 20 mL THF was added into the flask at 0 °C for 1 h. After stirring at 0 °C under nitrogen, triethylamine and trichloro[4-(chloromethyl)phenyl]silane(2, 1.28 g) in THF (10 mL) were added dropwisely into the solution and stirred at 0 °C . The cooling bath was removed and stirring continuously for additional 7.5 h under nitrogen. The POSS type compound and HNEt3-Cl byproduct were separated by filtration. The clear THF solution was

dropped into a beaker of acetonitrile and rapidly stirred. The resulting product (3) was collected and dried in a vacuum oven for 24 h. ¹H NMR (CDCl3),δ: 7.59 (d, 2H), 7.33 (d, 2H), 4.52 (s, 2H), 1.92-1.62 (m, 7H), 1.09-0.85 (m, 42H), 0.75-0.48 (m, 14H).

2.2.3. Preparation of C20-4VB intercalated agent.

The intercalated agent of C20-4VB was prepared according to the pathway shown in Scheme 2-3(a). N,N-dimethyloctadecylamine (C20, 4.2 mL) and 4-vinylbenzyl chloride (4VB, 1.87 g) in acetone (10 mL) were refluxed at 60 ˚C under nitrogen for 5 h. After cooling, the mixture was washed with cold acetone and the volatiles were removed in vacuum oven for 24h at 65 C. 　 ¹H NMR (CDCl3), δ: 7.56 (d, 2H), 7.38 (d, 2H), 6.65 (q, 1H), 5.75 (d, 1H), 5.31 (d, 1H), 4.96 (s, 2H), 3.39 (t, 2H), 3.23 (s, 6H), 1.72 (m, 2H), 1.23 (m, 30H), 0.82 (t, 3H).

2.2.4. Preparation of C20-POSS intercalated agent.

The intercalated agent of C20-POSS was prepared according to the pathway shown in Scheme 2-3(b). N,N-dimethyloctadecylamine (C20, 1.49 g), POSS-Cl compound (5.68 g) in acetone (15 mL) was refluxed at 60 °C under nitrogen for 24 h.

After cooling, the mixture was evaporated by a rotatory evaporator and then added Et2O (20 mL). The solution was extracted with deionized water three times (150 mL × 3). The organic phase was dried with MgSO4 and evaporated by a rotatory evaporator to obtain the C20-POSS intercalated agent. ¹H NMR (CDCl3), δ: 7.68 (d, 2H), 7.58 (d, 2H), 5.03 (s, 2H), 3.42 (t, 2H), 3.30 (s, 6H), 1.81 (m, 7H), 1.41 (m, 2H), 1.26 (m, 30H), 0.90 (m, 42H), 0.82 (t, 3H), 0.59 (m, 14H).

2.2.5. Preparation of C₂₀-, C₂₀-4VB, and C₂₀-POSS modified clays.

Na⁺ MMT (0.3 g) was dispersed in 1L deionized water at 80°C and stirred continuously for 4 h. C20 (0.18 g), C20-4VB (0.22 g) or C20-POSS (0.63 g) in water (5 mL) was placed into another flask,10 % hydrochloric acid (1 mL) and ethanol (5 mL) were added and then stirred at 80 °C for 1 h. This intercalating agent solution was then poured into the clay suspension solution and stirred vigorously at 80 °C for 4h.

The white precipitate was filtered to remove water and washed thoroughly with warm water until no chloride could be detected by an aqueous AgNO3 solution, and then dried overnight in a vacuum oven at room temperature.

2.2.6. Preparation of polystyrene/clay nanocomposites.

Desired amounts of organic modified clay, KOH, SDS and styrene monomer were added in a two-neck round bottom flask equipped with a stirring bar. The mixture was heated to 80 °C and stirred under N2, desired quantity of K2S2O8 was added slowly to the mixture. Polymerization was carried out at 80 °C for 8 h and then cooled to room temperature. 2.5 % aqueous aluminum sulfate (10 mL) was added into the polymerized emulsion, followed by adding dilute hydrochloric acid (10 mL) with stirring. Finally, acetone was added to break down the emulsion completely, and the polymer product was washed several times with methanol and distilled water and then dried in a vacuum oven at 80 °C for 24h. Similar procedures were employed to prepare virgin polystyrene.

2.2.7. Instrumentations

Wide-angle X-Ray diffraction (WAXD) spectrum was recorded on powdered sample using a Rigaku D/max-2500 type X-ray diffraction instrument. The radiation source used was Ni-filtered, Cu Kα radiation (λ=1.54Å). The sample was mounted on

a circular sample holder, the scanning rate was 0.6°/min from 2θ= 1 to 20. A Hitachi H-7500 transmission electron microscopy (100 kV) was used to examine clay morphology and orientation. The sample was ultramicrotomed at room temperature using a diamond knife using a Leica Ultracut UCT Microtome to give 70 nm-thick sections. Thermogravimetric analysis (TGA) was performed on a TA Instruments Q50 apparatus. The sample (5-10)mg was placed in a Pt cell at a scan rate of 20 °C /min from 30 to 800 °C under nitrogen. The calorimetric measurement was performed use a TA Instruments Differential Scanning Calorimeter (DSC-2010) to measure the glass transition temperature (Tg). The sample was preheated at a scan rate of 20 °C /min from 30 to 150 °C. In DSC measurement of the sample was cooled to 10 °C quickly from the melt of the first scan and the second scan rate was 20 °C /min from 30 to 150

°C. The Tg value was taken as the midpoint of the heat capacity transition between the upper and lower points of deviation from the extrapolated liquid and glass lines.

Molecular weights and molecular weight distributions were determined by gel permeation chromatography (GPC) using a Waters 510 HPLC equipped with a 410 Differential Refractometer, a refractive index (UV) detector, and three Ultrastyragel columns (100, 500, and 10³ Å) connected in series in order of increasing pore size.

The molecular weight calibration curve was obtained using polystyrene standards. ¹H NMR spectroscopic analyses were performed using a Varian Uniytinova-500 NMR Spectrometers at 500 MHz. All spectra were recorded using CDCl3 as the solvent and TMS as the external standard. Coefficient of thermal expansion was obtained using a TA 2940 Thermomechanical Analyzer (TMA). The force applied was 0.005 N and it was heated at rated of 5 °C/min from 25 to 150 °C.