【文章內(nèi)容簡介】 clay [20]. Emulsion polymerization is a relatively new approach to synthesize polymerclay nanoposites. PSclay and poly(methylmethacrylate) (PMMA)clay nanoposites were synthesized via emulsion polymerization using an anionic surfactant (sodium lauryl sulfate) as emulsifier [21, 22]. PS?reactive organoclay intercalated nanoposites were prepared by emulsion polymerization [23]. The reactive organoclay was synthesized by exchanging the inorganic cations (Na+) with aminomethylstyrene. Since the alkyl chain of aminomethylstyrene is short, it is not very effective in expanding the clay interlayer [23]. Most recently, PMMAclay nanoposites Were synthesized by Emulsion polymerization With decyltrimethylammonium Chloride and [2methacryloyloxy)ethyl] trimethylammonium chloride to modify the surface of dispersed clay [24]. The synthesis of PSclay nanoposites via emulsion polymerization using a reactive surfactant is reported in this munication. The advantage of the present approach over other procedures of emulsion polymerization [2123] is that it bines cationic exchange of clay and emulsion polymerization in one step by using a Reactive cationic surfactant, vinylbenzyl dimethyldodecylammonium chloride (VDAC). This method is called onestep emulsion polymerization. Exfoliation of clay nanolayers in the nanoposites was achieved as revealed by Xray diffraction and TEM.ExperimentalMaterialsSodium montmorillonite (NaMMT) (Trade name Mineral Colloid BP) which contains exchangeable primarily Na+ cations was supplied by Southern Clay Products Incorporation. It is a fine powder with an average particle size of 75 181。m in the dry state, and a cation exchange capacity (CEC) of 90 mEq/100g. Styrene was purchased from Aldrich Chemical Company and purified by distillation under reduced pressure at 30 0C. The free radical initiator, potassium persulfate (KPS), was purified by recrystallization twice from methanol. VDAC was synthesized by the quaternizationreaction of vinylbenzyl chloride with dimethyldodecylamine (one half stoichiometric excess) under the protection of inhibitors in diethyl ether, and purified by recrystallization from ethyl acetate, as described in a previous paper [15]. Synthesis of PolystyreneClay Nanoposites by Emulsion Polymerization PSclay nanoposites were prepared using the following procedure. VDAC was added to an aqueous clay suspension and stirred for several hours. The molar amount of added VDAC was one half of the added clay times the CEC/100. Next styrene was added to form an emulsion. Finally, KPS was added to initiate polymerization at 70 0C in an oil bath. The prepared PSclay nanoposites were precipitated in methanol, filtered and washed with hot water and acetone, then dried in a vacuum oven. The vacuum dried PSclay powder was pression molded to obtain samples for TEM and Dynamic Mechanical Analysis (DMA). Characterization of Nanoposites Xray diffraction (XRD) patterns were obtained by using a Phillips XRG 3100 X ray generator equipped with a Nifiltered CuKa () source that was connected to a Phillips APD 3520 type PW 1710 diffractometer controller. All samples were dried in a vacuum oven for at least 24 hours before XRD measurements. The morphology of the prepared emulsion latex was imaged using a JEOL 200 EX scanning electron microscopy (SEM). The microstructure of molded nanoposites was imaged using a JEOL 1200 EX transmission electron microscopy (TEM). Samples for TEM were cut to 60 nm thick sections with a diamond knife. The thermal properties of PSMMT nanoposites were measured by differential scanning calorimetry (DSC) on a PerkinElmer DSC 7 calorimeter. Samples of 10 mg masses were heated to 150 0C, then decreased to 0 0C and heated again to 150 0C at a heating or cooling rate of 10 0C/min under nitrogen atmosphere. The glass transition temperature, Tg, of the nanoposites was determined from the respective second heating history. Dynamic mechanical properties were measured using a dynamic mechanical analyzer (PerkinElmer DMA 7) with a threepoint bend fixture. The specimens (1mm mm 20 mm) were cut from the center of the samples. A temperature sweep at 50C min1 from 25 to 110 0C at a frequency of 1 Hz was used to determine the dynamic modulus.Results and discussionThe surface of pristine clay is hydrophilic. The small inorganic cations such as Na+ and Ca+2 can be exchanged by organic cations to make the clay surface hydrophobic [25]. There are two advantages of using VDAC as an emulsifier instead of non reactive surfactants. The first one is that VDACMMT organoclay has a cohesive energy density similar to that of styrene [15]. Similar cohesive energy densities between styrene and the organoclay can lead to extensive intercalation of styrene into clay gallery and expansion of the interlayer distance. The second advantage is the possibility of VDACMMT reacting with styrene to form covalent bonds, thus increasing the interfacial adhesion between polymer matrix and clay [15]. There is some evidence that clay dispersed in water at low concentration can be in a partially exfoliated state [26]. This provides an advantage of onestep emulsion polymerizationapproach to obtain exfoliated polymer nanoposites. The loading of MMT for the onestep emulsion polymerization was varied in the range from 3 to 20 wt.% by weight of total styrene and MMT mixture. Figure 1 pares XRD patterns of untreated NaMMT, VDAC functionalized MMT (VDACMMT) by cationic exchange process and polystyreneMMT nanoposite. The XRD pattern of NaMMT shows a broad peak centered at 2θ = . In contrast, VDACMMT, prepared by cationic exchange of NaMMT with VDAC in aqueous solution [15], exhibits a sharp peak at 2θ = . The d001 spacing of VDACMMT increased from nm of pristine NaMMT [24] to nm in dried state [15]. The d001 increment in VDACMMT corresponds to the distance between silicate layers separated by the insertion of VDAC cations. In the present study, VDA