Polyamide Nanocomposites by In-situ Polymerization

In clay-polyamide nanocomposites, effective exfoliation and dispersion of clay can be obtained by in-situ polymerization technique. In this process, layered silicate particles are dispersed in the monomer and then polymerized. It is done by ring-opening polymerization of e-caprolactum in the presence of organically modified clay [7-8,40-41]. 

Method for preparation of polyamide nanocomposite compositions by in situ polymerization. WO Patent 0,009,571. 

Kim, J., Hong, S. M., Kwak, S. and Seo, Y., Physical properties of nanocomposites prepared by in situ polymerization of high-density polyethylene on multiwaUed carbon nanotubes , Physical Chemistry Chemical Physics, 2009,11, 10851-10859. Yang, R, Ou, Y. and Yu, Z., Polyamide 6/shca nanocomposites prepared by in situ polymerization . Journal of Applied Polymer Science, 1997, 69, 355-361. 

M. Tarameshlou, S. H. Jafari, H. A. Khonakdar, M. Farmahini-Farahani, and S. Ahmadian, Synthesis of exfoliated polyamide 6,6/organically modifled montmorillonite nanocomposites by in situ interfacial polymerization. Polymer Composites, 28 (2007), 733-8. 

Yang, F., Ou, Y. and Yu, Z. (1998) Polyamide 6 silica nanocomposites prepared by in situ polymerization. Journal of Applied Polymer Science, 69, 355-361. 

The dispersion of clay platelets (exfoliation and intercalation level of the silicate layers) and surface area of silicate platelets have the potential to alter the rheological behavior of the nanocomposites. In-situ polymerized nano composites exhibit more exfoliated structure than the composites prepared by the melt blending technique. Irrespective of the processing parameter, the nanocomposites show shear thinning behavior at high shear rate (Figure 9.14), whereas the pristine polyamide exhibits Newtonian behavior (i.e., the viscosity remains almost the same). It has also been reported that the polymer nanocomposite possesses higher steady shear viscosity than pristine polyamide at low shear rates. 

The in-situ polymerization technique has received much attention since the successful preparation of exfoUated nanocomposite structures from polyamides [16-18] by promoting polymerization from initiators located on the clay surfaces. 

For other polyamide/clay nanocomposites, PA 11/OMMT nanocomposites were prepared by Zhang, Yu, and Fu [30] via in situ intercalative polymerization. The polymerization involved two steps first the cation exchange of MMT with 11-aminolauric acid, and then the polymerization of 11-aminolauric acid in the presence of OMMT. The crystallization rate of the PA 11 matrix was obviously improved by the nanoscale-dispersed MMT clay. A similar in situ polymerization of exfoliated PAll/MMT nanocomposites containing different amounts of MMT was performed by Yang and co-workers [31]. First, 11-aminoundecanoic acid was mixed with organoclay in a vessel, and then the mixtures were heated to 100-150 °C to drive off the water and heated again to 230-260 °C for 4 h to achieve polymerization. 

In situ polymerization was the first method used to synthesize polymer-clay nanocomposites based on polyamide (PA) 6. In this technique, the modified layered silicate is swollen by a liquid monomer or a monomer solution. The monomer migrates into the galleries of the layered silicate, so that the polymerization reaction can occur between the intercalated sheets. The reaction can be initiated either by heat or radiation, by the diffusion of a suitable initiator or by an organic initiator or catalyst fixed through cationic exchange inside the interlayer before the swelling step by... 

Unlike melt intercalation, a layered silicate is mixed with monomer before polymerization takes place with in situ polymerization. This method was developed by Toyota researchers [27,28], in which electrostatically held 1-nm thick layers of layered alumina silicates were dispersed in a polyamide matrix on a nanometer level, which led to an exponential growth in the research endeavors, in layered silicate nanocomposites. These nanocomposites were based on the in situ synthesis approach in which a monomer or monomer solution was used to swell the filler interlayers, followed by polymerization. With this process, one can control the nanocomposite morphology through the combination of reaction conditions and clay surface modification. The in situ polymerization method is especially important for insoluble and thermally unstable polymers, which solution blending or melt blending technique cannot process. 

---