Two-Stage in Situ Intercalation Polymerization of Acrylic Copolymer

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Two-Stage in Situ Intercalation Polymerization of Acrylic Copolymer/Montmorillonite Nanocomposites Ming Gao, Dong-Liang Zhou, Xiao Hu, and Pu-Xin Zhu* Textile Institute, Sichuan University, Chengdu 610065, People's Republic of China ABSTRACT: An amphiphilic acrylic copolymer/montmorillonite nanocomposite was synthesized by way of a two-stage radical copolymerization of emulsion intercalation and solution intercalation, using acrylates, methacrylic acid, and acrylamide as monomers. The water-based product was designed with a structure of a hydrophobic copolymer dispersed in an aqueous copolymer solution to meet the needs of warp sizing agents on adhesiveness to hydrophobic and/or hydrophilic fibers, appropriate glass transition temperature, as well as water-solubility. XRD patterns and TEM observation for the product films showed an exfoliated structure of montmorillonite (MMT) in the part of soluble acrylic copolymer as the MMT content equal to or less than 7%, while in the part of emulsion copolymer alone or the product as a whole, the MMT showed an intercalated structure. Determination of DSC indicated that chemical bondings occurred between the hydrophobic and hydrophilic components, which guaranteed storage stability of the system and water-solubility of the sizing film, and that there were three Tgs corresponding to the emulsion copolymer, solution copolymer and the interfacial copolymer between the two phases. All of the Tgs increased with increasing content of the MMT in the composites. The elongation at break of the composite films increased with increasing MMT contents up to 3 wt % and then dropped down, and the tensile strength and abrasive resistance of the acrylic copolymer increased with content of the MMT.

’ INTRODUCTION Polymer/layered silicate nanocomposites are a new class of composites which are compounded by two phases of a polymer matrix and dispersed layered silicate with the thickness in the nanometer range.1 During the past decade, polymer-based nanocomposites have received significant attention both in industry and in academia,2 for their enhanced properties compared with unfilled polymers or conventional composites, including tensile properties,36 impermeability to gas,710 thermal stability,1113 flame retardancy,1416 and biodegradability as the layered silicates are integrated into biodegradable polymers in nanoscale.17 With the purpose of applying polymer-based nanocomposites in textile industry, in our previous study,18 a water-soluble acrylic copolymer/montmorillonite nanocomposite for warp sizing was synthesized by way of in situ intercalative polymerization of acrylic acid, acrylamide, and methyl acrylate in water with varied contents of the clay, and the warp size showed an improvement in mechanical properties and weaving quality for sized cotton yarns. For synthetic fibers, especially polyethylene terephthalate (PET) staple fiber and its blends with cotton, more hydrophobicity is needed for a warp size to adhere to the PET yarn as well as PET/cotton blended yarns than the soluble size agent that we previously prepared.18 It is clear from the adhesion demand that acrylate copolymers with certain hydrophobicity will be attractive candidates for textile sizes applied to PET yarns and their blends, if there is no problem with solubility or dispersibility in water for the sizes in favor of sizing and desizing. On the basis of these considerations mentioned above, we designed a new amphiphilic acrylic size with a hydrophobic acrylate copolymer latex dispersed in a continuous phase of a hydrophilic acrylic copolymer solution. A two-stage radical copolymerization of an emulsion intercalation followed by a r 2011 American Chemical Society

solution intercalation was employed in the presence of montmorillonite (MMT) and using acrylates, methacrylic acid, and acrylamide as monomers. The hydrophobic latex part was expected to provide the size with adhesion to hydrophobic fibers, and the hydrophilic part was to guarantee such the necessary properties of the size as good water-solubility, moderate moisture absorption, and good affinity to hydrophilic fibers. The amphiphilic acrylic size could be used together with starches or modified starches for sizing PET yarns and PET/cotton yarns, which may be possible to resolve the contradiction between hydrophobicity and water-solubility for textile sizes. The microstructure of the size was evaluated and the application performance was tested.

’ EXPERIMENTAL SECTION Materials. Na-montmorillonite (Na-MMT) was supplied by Santai Mineral Clay Co., Ltd. (Mianyang, China) with a cationexchange capacity of 128 mequiv./100 g. Acrylamide (AM), methyl acrylate (MA), ethyl acrylate (EA) and methacrylic acid (MAA) were chemical reagents available from Kelong Chemical Reagent Co., Ltd. (Chengdu, China). Sodium alcohol ether sulfate (AES) and polyoxyethylene nonylphenyl ether (NP-10) were obtained from Jilin Chemical Reagent Co., Ltd. (Jilin, China). Aqueous ammonia, potassium persulfate, and 1-dodecanethiol were chemical reagents purchased from Niansha Chemical Received: February 4, 2011 Accepted: May 11, 2011 Revised: April 21, 2011 Published: May 13, 2011 7784

dx.doi.org/10.1021/ie200236x | Ind. Eng. Chem. Res. 2011, 50, 7784–7790

Industrial & Engineering Chemistry Research Reagent Co., Ltd. (Kunshan, China). Freshly redistilled water was used in all of the experiments. Preparation of the Amphiphilic Nanocomposites. Emulsion Intercalation Polymerization. A certain amount of Na-MMT was dispersed in water by agitation, and was allowed to stand overnight to swell the Na-MMT adequately. Then it was sonicated with a KQ-250 sonicator (Kunshan Ultranic Instrument Co., Ltd., Jiangsu, China) for 30 min before use. The monomers, with a MA/EA/MAA molar ratio of 8.5/9.1/1, were mixed with blended emulsifiers of NP-10/AES (weight ratio 3/7) in 3.0 wt % on the basis of the monomers, and then the clay slurry was poured in. The system was sonicated again for 30 min at room temperature with the purpose of pre-emulsification. The nanocomposite latex was synthesized by a seeded semibatch emulsion polymerization using potassium persulfate (0.5 wt %, relative to mass of monomers) as initiator. The typical procedure for the synthesis of these nanocomposite latexes was as follows: A 500-mL three-necked flask was fitted with a stirrer, a reflex condenser, a nitrogen inlet, two dropping funnels, and a Backman thermometer in a thermostatic water bath. One-fifth of the pre-emulsion, along with one-third of the initiator solution of ammonium persulfate, was added into the flask under stirring and nitrogen purging. The mixture was heated to 80 °C. After initiation of the emulsion polymerization for 1 h, the remaining pre-emulsion and aqueous solution of potassium persulfate from two different dropping funnels were then fed continuously into the reactor over 1.5 h. The reaction was allowed to maintain at 82 °C for 2 h followed by another hour at 90 °C to ensure the complete polymerization. The solid content of the resultant was about 30% with varied Na-MMT loading of 1%, 3%, 5%, 7%, or 9% on dry basis of the solid mass. Solution Intercalation Polymerization. The monomers of MA and AM were chosen for the solution intercalation with a molar ratio of 1.2/1, and 1-dodecanethiol was used as a chain-transfer agent in 0.4 wt % on the basis of the monomers. The monomers and chain-transfer agent were mixed with the clay slurry in a glass bottle and sonicated for 30 min at room temperature, in which the Na-MMT loading was 1%, 3%, 5%, 7%, or 9% based on the weight of monomers used. After that, one-fifth of the mixture was placed into a 500-mL three-necked flask fitted with a stirrer, a reflex condenser, nitrogen inlet, two dropping funnels, and a thermostatic water bath, and then one-third of the aqueous solution of potassium persulfate, 0.5 wt % based on the total mass of monomers, was introduced in the flask. The reaction mixture was filled with nitrogen and heated to 80 °C with stirring. After initiation for 10 min, the remaining amounts of the monomer mixture and the initiation solution were added separately and continuously into the reactor in 2.5 h until complete addition, and then the reactants were allowed to polymerize at 82 °C for 3 h. The reaction system was cooled to 50 °C, and certain amount of the aqueous ammonia was added with vigorous stirring to neutralize the resultant. The solid content was about 30 wt %. Stage Intercalative Polymerization of the Amphiphilic Size. The in situ intercalative emulsion polymerization was first carried out in the same way as the emulsion intercalation. Second, the system at 82 °C was fed with the solution of water-soluble monomers, chain-transfer agent and Na-MMT according to the step of the solution intercalation, separately and continuously in 2.5 h. The HP part was equal to the LP part in mass ratio in the composition of amphiphilic polymer. The reactants were allowed to polymerize in nitrogen atmosphere for 3 h at 82 °C. After that, the resultant was cooled to 50 °C, and some ammonia was added

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to neutralize the product, in which the solid content was about 30 wt % and the Na-MMT loadings were 1, 3, 5, 7, and 9 wt %, respectively, on a dry basis of the amphiphilic size. Characterization of the Sizes. Film Formation. Each of the amphiphilic sizes with different contents of Na-MMT was diluted with water to a solid content of 10 wt %, and the viscous fluid was stirred vigorously for 30 min at 50 °C. The fluid of 50 mL was put with a syringe onto a glass flat-bottomed shallow dish (210 150 mm2) paved with a polyester sheet of the same size. The dish was kept on a leveled surface in ambient condition until the casting film was dried, and then the film was separated carefully from the polyester sheet. X-ray Diffraction. Cast films of the sizes with different NaMMT contents were equilibrated at room temperature and constant relative humidity (RH) 68% for 2 days. XRD data of the films were measured with an X-ray diffractometer (D/maxIIIA; Rigaku Co., Japan) with Cu radiation (λ = 0.1542 nm) at a voltage of 40 kV and an electric current 35 mA. The samples were scanned between 2θ = 2°∼10° with a scan rate of 0.03°/s. According to the peak position on the XRD pattern and the Bragg equation: 2dsin θ ¼ λ

ð1Þ

the d001 spacing of Na-MMT in the polymer matrix can be calculated. TEM Characterization. A TEM sample was prepared by casting the sample dilute solution onto copper microgrids and naturally dried, and the morphology was examined by a JEM100CX transmission electron microscope (JEOL Ltd., Tokyo, Japan) with an acceleration voltage of 80 kV. FTIR Spectroscopy Measurement. Cast film samples were cut into strips (10 100 mm2) and dried further under vacuum at 60 °C for 24 h before use. Infrared spectra for film samples, on both surfaces contacted with the polyester sheet and exposed to the air, were measured by the attenuated total reflection (ATR) with a FTS3000 FTIR Spectrum Scanner (Hercules, U.S.). The spectral data were collected over 32 consecutive scans with a resolution of 4 cm1 at room temperature. DSC Analysis. Film samples with different amounts of NaMMT were allowed to dry over P2O5 in a desiccator at room temperature for one week. DSC measurements were carried out for 4 mg of samples sealed in aluminum pans under a nitrogen atmosphere at a heating rate of 10 °C/min from 40 to 180 °C with a Netzsch 200PC Differential Scanning Calorimeter (Netzsch Group, Selb, Germany). Evaluation of the Nanocomposite Sizes. Storage Stability of the Compounded Sizes. The stability of the warp sizes was estimated using the sedimentation method. The mechanical mixture of the emulsion intercalated product and the solution intercalated one in a volume ratio of 1:1 were violently agitated, then the blends of 15 mL were taken into a glass test tube with stopper and set aside for 4 weeks in a temperature-controlled environment. The amphiphilic nanocomposite size was used for comparison. Resolubility. Cast film samples were cut in strips in a size of 10 50 mm2 and the exact thickness of the films was measured using a CH-10-AT Centesimal Thickness Testing Instrument (Shanghai Liuling Instrument Co., Ltd., Shanghai, China). For every sample, 10 data points were tested and the average value was taken as the thickness H (μm) of the film. Two-thirds of each individual strip was immersed into an aqueous solution of NaOH 7785

dx.doi.org/10.1021/ie200236x |Ind. Eng. Chem. Res. 2011, 50, 7784–7790

Industrial & Engineering Chemistry Research

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Figure 1. XRD patterns for nanocomposites with various Na-MMT contents.

10 g/L at 70 °C. The dissolution time t (s) needed to break off the film was recorded with a stopwatch. For each sample, the test was repeated five times. The dissolution rate (v, μm/s) was calculated to represent the resolubility of the size: v¼

H t

ð2Þ

Mechanical Properties. The films (10 200 mm2) were conditioned at 20 °C and 68% RH for 48 h, the exact thickness of the strip was measured. The tensile strength and elongation at break of each strip were determined with a YG061 tensile testing instrument (Laizhou Electron Instrument Co., Ltd., Laizhou, P. R. China) with a clamping distance of 100 mm and a stretching speed of 100 mm/min. For each data point, 10 samples were tested, and the average values with corresponding standard deviations were taken. Abrasion Resistance. Cast film samples (50 200 mm2) were equilibrated at constant RH 68% and 18 °C for 48 h before abrasion testing. The test was performed in the same conditions above with a Y571L fabric rubbing apparatus (Laizhou Electron Instrument Co., Ltd., Laizhou, China). The film was abraded 600 times with a grinding head covered with 800-mesh sand paper, and after every 100 cycles, the sand paper was replaced to renew another 100 cycles. The load of the test head were 9 N/19 25 mm2, and the abrasing stroke was 100 mm. Before and after the test, the weight of the sample was examined by an electronic balance with precision (0.0001 g. Three samples were tested for each data point and the average abraded mass, together with the standard deviation, was calculated.

’ RESULTS AND DISCUSSION X-ray Diffraction Patterns. The film of the amphiphilic nanocomposite sizes consisted of lipophilic phase (LP) from the emulsion intercalation polymerization and hydrophilic phase (HP) from the solution intercalation polymerization, and both phases contained Na-MMT clay. The interlayer spacing of the clay layers in the original and in the intercalated polymer/MMT nanocomposites can be determined by XRD. The XRD patterns for Na-MMT and the nanocomposites with various Na-MMT contents were shown in Figure 1. In the inset in Figure 1, the d001 reflection for the Na-MMT clay precursor was found at

Figure 2. TEM micrographs of the composites: (a) HP, (b)LP, and (c) LP/HP copolymer.

2θ = 6.82° corresponding to the basal space of an interlayer distance of 1.29 nm according to eq 1. For the LP with 5 wt % NaMMT loadings, a peak was observed at 2θ = 5.20° (d = 1.70 nm), which indicated that the dispersed silicate layers still retained an ordered structure after emulsion intercalation polymerization. While in the case of the HP with 5 wt % Na-MMT, the curve showed no characteristic Na-MMT peaks in the range of the 2θ = 210°, which means an exfoliated structure of the dispersed MMT layers in the matrix. As for the amphiphilic size, peaks were observed at about 2θ = 5.20°, at which the peak intensity became stronger with increasing the clay content. So we can reasonably infer that the intercalated structure found in the amphiphilic composites was from the LP. Because the Na-MMT used for emulsion polymerization was not treated by organic modification with cations,1,19 there was lack of sufficient affinity between the hydrophilic Na-MMT layer and the lipophilic polymer. TEM Characterization. It is well-known that TEM allows a qualitative understanding of the aggregated structure, spatial 7786



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Figure 3. FTIR spectra of the nanocomposites with changes in the Na-MMT content: (a) on the side exposed to the air, and (b) the side separated from the polyester sheet.

distribution of the various phases, and views of the defect structure through direct visualization.1 Both TEM and XRD are essential tools for evaluating nanocomposite structure, and they are regarded as complementary to each other for the characterization of the polymer/clay nanocomposites.20 The TEM micrographs for the composites with 5 wt % Na-MMT were showed in Figure 2, where the darker part represents the clay and the lighter part the polymer matrix. For the HP from solution intercalative polymerization (Figure 2a), individual layers dispersed in the polymer matrix could be observed and few stacks of clay platelets (the dark zones) could be distinguished. Combining with the XRD pattern, the HP showed an exfoliated structure as a whole. While for the LP (Figure 2b) and LP/HP copolymer (Figure 2c), darker zones with compact arrangement clay layers could be distinguished. In a very real sense, the LP and LP/HP copolymers did not belong to nanocomposites. However, the copolymer via the in situ polymerization enlarged the basal spacing of MMT layers, destroyed the original crystalline structure of the clay, and formed a physically cross-linked structure with MMT layers, which might be beneficial to the mechanical properties of the acrylic sizes. The XRD and TEM results indicated that water-soluble monomers, especially monomers with high dipole moments

and strong hydrogen-bonding groups (polyacrylamide, for example), were apt to react with hydrophilic Na-MMT to form intercalated or exfoliated nanocomposite.21 However, acrylate monomers, such as MA and EA in our experiment, have partial polarity and could intercalate Na-MMT by in situ emulsion intercalated polymerization to form an intercalated polymer/ MMT nanocomposite.22 FTIR Spectroscopy. Figure 3 shows the FTIR spectrum of both sides of the acrylic copolymer/MMT nanocomposite films with different Na-MMT contents in the wavenumber range 500 to 4000 cm1. A typical SiO stretching vibration23 is observed at 1023 cm1 in all the spectra of the nanocomposites containing MMT. Characteristic absorbance bands of the nanocomposites occurred in the following assignments: CH symmetrical stretching vibration around 2930 cm1, CH asymmetrical stretching vibration around 2850 cm1, CdO stretching vibration around 1730 cm1, NH in amide groups around 1655 cm1, OH flexural vibration around 1450 cm1, and CO in COH stretching vibration around 1160 cm1. For the FTIR spectra of the film side exposed to the air (Figure 3a), the intensity as well as the sharpness of the peaks representing CH stretching vibration were found to be enhanced with increasing Na-MMT contents, which indicated an increase of hydrocarbon chains on the polymer surface. However, 7787



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Table 1. Glass Transition Temperatures (Tg's) of the Nanocomposites Tg (°C) MMT (wt%)

emulsion copolymer

interfacial copolymer

solution copolymer

0

8.5

24.1

107.0

1

6.8

39.2

102.2

3

5.4

43.6

105.0

5

3.8

34.3

109.0

7

6.3

41.3

119.8

9

6.0

52.9

155.1

Figure 4. DSC thermogram of the amphiphilic nanocomposite with 3 wt % Na-MMT.

the absorbance peak at 1655 cm1 became smaller with the increment of Na-MMT loadings, implying that amide groups might be partially captured by silicate layers. Both the increase of hydrocarbon chains and the decrease of amide groups made the film surface on the air side more hydrophobic. For the side of the film separated from the polyester sheet (Figure 3b), like the air side (Figure 3a), once the Na-MMT was composited with the acrylic copolymer, there were big changes at about 2930, 2850, 1655, and 1023 cm1 in the FTIR spectra. More hydrophobicity happened on the both sides of the film upon addition of the Na-MMT. This will be in favor of the size adhesion to synthetic fibers and of less sensitivity to environment humidity. The spectra of the side separated from the polyester sheet, however, showed little changes of the peaks at around 2930, 2850, and 1655 cm1 with the increase of Na-MMT loading, in comparison of the air side. The reason might be explained by the interactions between the size film and the polyester sheet at the interface. DSC Analysis. In general, the glass transition temperature, Tg, of a random copolymer can be analyzed on the basis of its homopolymer composition by using the GordonTaylor equation.24 For the discussed copolymers without Na-MMT via the two-stage radical copolymerization, Tg values calculated by the GordonTaylor equation are 8.0 °C for the emulsion copolymer (LP), 86.7 °C for the solution copolymer (HP), and 20.9 °C for the two-stage copolymer (LP-HP), respectively. The Tg values can be observed during DSC thermo-scan as shown in Figure 4. Tg's for all of the nanocomposites were displayed in Table 1. For the LP-HP without Na-MMT, there were three Tg's, 8.5, 107.0, and 24.1 °C, which may be regarded as corresponding to the parts of LP, the HP, and the LP-HP that existed as the interface between the two components, respectively. The appearance of the Tg for the interface part suggested a chemical combination between the LP and the HP. From the DSC data in Table 1, it can be seen that almost all of the Tg's increased with increasing content of the Na-MMT in the nanocomposites, and the increment rate was more for HP, and less for LP. This is because dominating structures of exfoliated or intercalated layered silicates in the solution copolymer and the emulsion copolymer, respectively, as shown in XRD patterns (Figure 1), restricted the segmental motion of the polymer more or less.25,26 Stability of the Sizes. In the stability test, the mixture of the emulsion copolymer and solution copolymer by mechanical

Figure 5. Tensile properties of the amphiphilic nanocomposite films with various Na-MMT contents.

mixing was unstable, and the system was separated into two liquid phases with the emulsion down and the solution up after a few hours. The real mechanism of the phase separation needs to be investigated further. As for the amphiphilic acrylic copolymer/ MMT nanocomposite, no phase separation can be observed during the test. The results illustrated that there existed chemical combination between the LP and HP in the amphiphilic nanocomposite, also indicated by the DSC analysis. Solubility of the Cast Films. The solubility of the products was tested by immersing the cast films with 5 wt % Na-MMT into an alkali solution containing 10 g/L of NaOH at 70 °C. For the emulsion copolymer, and the physical mixture of the emulsion copolymer with solution copolymer, the strips of the films could not be broken off by dissolution into the alkali solution within 10 min, so that these composites could not be applied to the textile sizing because of their poor desizing abilities. In contrast, the dissolving rates of the films of solution copolymer and amphiphilic nanocomposite were 2.44 and 1.82 μm/s, respectively. Both of them could be used as textile sizes for their favorable solubility. Mechanical Properties. In a conventional sizing, warps are immersed in a sizing solution up to seventeen percent and passed under an immersion roll in a slasher box. Then, a pair of impression rolls is applied to the warps to remove superfluous sizing solution. The warps are passed through a drying section where hot air and/or heated dry cans are utilized. After drying, the warp sheets are separated into individual sized yarns by a leasing apparatus for weaving. Sizing of a warp yarn is essential to reduce breakage of the yarn during weaving. The warp yarns are subjected to various kinds of actions such as cyclic strain, flexing, 7788



Figure 6. Abrasion loss of the nanocomposite films with various Na-MMT contents.

abrasion by loom parts of the weaving machine and friction between yarns. After sizing, the strength and abrasion resistance of the yarn should be improved, so size films used to protect the warp yarns should have higher tensile strength and elongation at break. Figure 5 shows tensile properties of the nanocomposite films with various Na-MMT contents. The tensile strength of the amphiphilic nanocomposite increased with increasing Na-MMT contents, and the elongation at break of the composite films increased as the Na-MMT increased up to 3 wt % and then dropped down as Na-MMT increased. The results indicated that addition of 35 wt % Na-MMT had good strength and toughness effect for the amphiphilic nanocomposites. As Ray and Okamato1 has revealed, the structure and surface characteristics of MMT platelets are probably the main reason for the enhanced tensile strength and improved elongation at break of the polymer-based nanocomposites. The exfoliated nanocomposite has more enhanced interactions between the layered silicates and the matrix to withstand external forces compared to the intercalated nanocomposite. Above 5 wt % Na-MMT in our experiment, the elongation at break of the composites significantly decreased with Na-MMT concentration, because of the formation of nonexfoliated aggregates at higher filler content. Abrasion Resistance. Abrasion resistance is a property that allows a material to resist mechanical actions such as rubbing, scraping, or erosion, and the actions would progressively remove material from the surface. Therefore, abrasion loss is the measure of the abrasion resistance of a size agent.18 Soluble polymers with abrasion resistance are useful for textile sizing. As shown in Figure 6, the abrasion performance of the amphiphilic acrylic copolymer/MMT nanocomposites was significantly improved when Na-MMT content was increased. It could be explained by the fact that in the nanocomposite the MMT layers were either intercalated or exfoliated, so that MMT nanoparticles with great amount of active centers and large specific area could enhance the interfacial combination strength of the filler/matrix.

’ CONCLUSIONS An amphiphilic acrylic copolymer/MMT nanocomposite has been developed by way of a two-step radical copolymerization of in situ emulsion intercalation and solution intercalation. The dispersed acrylate copolymer latex component was hydrophobic, and the continuous acrylic copolymer component was hydrophilic. DSC analysis indicated that there existed three glass

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transition temperatures, the lower Tg corresponding to the acrylate copolymer, the higher Tg to the acrylic copolymer and the moderate Tg to the interface component between the dispersed and the continuous components. XRD patterns and TEM observation revealed a dispersed state of the clay in the nanocomposite: an exfoliated structure of MMT in the acrylic copolymer and an intercalated structure of MMT in the acrylate copolymer latex. The amphiphilic acrylic copolymer/MMT nanocomposite can be used as a textile size for synthetic yarns, because of its good storage stability, solubility in a dilute alkali solution and more hydrophobicity on the both sides of the film upon addition of the Na-MMT. Moreover, when the Na-MMT content was increased, the tensile strength and abrasion resistance of the size films increased, but the elongation at break of the composites showed a tendency to ascend first and then to decrease. Addition of 35 wt % Na-MMT had good toughness and strength effects on the acrylic size. The two-step radical copolymerization can be used to resolve the contradiction between hydrophobicity and water-solubility of textile sizes needed for yarns of synthetic fibers and/or their blends with cotton. Compounds of Na-MMT by in situ stage intercalation polymerization can enhance mechanical properties of the acrylic size. The nonexfoliated structure of Na-MMT in the emulsion copolymer, which is the main deficiency of the work, may arise from hydrophilicity of Na-MMT. We are working on the organic modification of Na-MMT to be suited to the in situ emulsion polymerization, so as to enhance mechanical properties of the amphiphilic acrylic size.

’ AUTHOR INFORMATION Corresponding Author

*Phone: þ86-28-85405437. E-mail: [email protected].

’ ACKNOWLEDGMENT We thank the National High-tech R&D Program of China (Grant No. 2007AA03Z344) and the Chinese Natural Science Foundation (Grant No. 50673062) for their financial supports. ’ REFERENCES (1) Ray, S. S.; Okamoto, M. Polymer/layered silicate nanocomposites: a review from preparation to processing. Prog. Polym. Sci. 2003, 28, 1539. (2) Lepoittevin, B.; Pantoustier, N.; Devalckenaere, M.; Alexandre, M.; Calberg, C.; Jerôme, R.; Henrist, C.; Rulmont, A.; Dubois, P. Polymer/layered silicate nanocomposites by combined intercalative polymerization and melt intercalation: a masterbatch process. Polymer 2003, 44, 2033. (3) Usuki, A.; Koiwai, A; Kojima, Y.; Kawasumi, M.; Okada, A.; Kurauchi, T.; Kamigaito, O. Interaction of nylon 6-clay surface and mechanical properties of nylon 6-clay hybrid. J. Appl. Polym. Sci. 1995, 55, 119. (4) Pinnavaia, T. J.; Lan, T.; Wang, Z.; Shi, H. Z.; Kaviratna, P. D. Clay-reinforced epoxy nanocomposites: synthesis, properties, and mechanism of formation: Nanotechnology-molecularly designed materials; ACS Symposium Series 622; American Chemical Society: Washington, DC, 1996; Chapter 17. (5) Giannelis, E. P. Polymer layered silicate nanocomposites. Adv. Mater. 1996, 8, 29. (6) Biswas, M.; Ray, S. S. Recent progress in synthesis and evaluation of polymer-montmorillonite nanocomposites. Adv. Polym. Sci. 2001, 155, 167. 7789



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Two-Stage in Situ Intercalation Polymerization of Acrylic Copolymer

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