Preparation of Polymer Nanocomposites via Suspension Polymerization

Suspension polymerization is a polymerization process in which dispersed monomer droplets are stabilized by surfactant and mechanical agitation in a liquid phase such as water. As in emulsion polymerization, the monomers used for suspension polymerization are usually insoluble in water. Advantages of suspension polymerization compared with other polymerization methods include easy removal of reaction heat, effective temperature control, low viscosity of the reaetion system, simple polymerization mechanism, high purity of the produet, easy separation and purifieation of the produet and shaped product in particle form. Polymers prepared by suspension polymerization inelude 

Reproduced from reference 40 by the permission of the American Chemical Society. 

In most cases, in situ suspension polymerization is carried out with nanoparticles dispersed in monomers. The surface modification of nanoparticles is usually required in order to achieve a good dispersion. Since the mechanism of in situ suspension polymerization is similar to that of in situ bulk polymerization, the surface modification used in bulk polymerization, including ion-exchange reaction, surfactant and coupling agent, polymer grafting and acid treatment can also be applied here. 

As mentioned before, MMT can be easily surface modified by ion-exchange reaction. Xie et al. prepared PS-MMT nanocomposites via suspension polymerization. Four different quaternary ammonium salts were used to modify the surface of MMT which were later shown to be exfoliated in the PS matrix according to XRD results. Hwu et al. prepared surface-modified MMT in different solvents and compared the dispersion of MMT in nanocomposites which were synthesized by suspension polymerization. Jung et al. prepared PVAc/PVA-MMT nanocomposite microspheres by suspension 

Carbon nanotubes (CNTs) and carbon nanofibers (CNFs) have a chemically inert surface and it is difficult to carry out surface modification. Acid treatment is usually used to introduce carboxylic groups at the defects of the CNT and CNF surface, which can improve particle dispersion. However, the acid treatment may damage the nanoparticles causing a reduction of mechanical properties. Park et al. prepared PMMA-MWCNT nanocomposites via suspension polymerization. Acid-treated MWCNTs were dispersed in MMA by ultrasonication, then an initiator (AIBN) was dissolved in the MMA-MWCNT mixture which was later poured into a solution with a stabilizer (PVA) to carry out polymerization at 95 °C for 3.5 h. After polymerization, the PS-MWCNT nanocomposite particles were collected by filtration. 

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Preparation of Polymer Nanocomposites via Suspension Polymerization of Inverse Emulsion... 

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