Semi-Continuous Heterophase Polymerization to Synthesize Nanocomposites of Poly(acrylic acid)-Functionalized Carbon Nanotubes

摘要

Two materials, pure poly(acrylic acid) (PAA) and nanocomposites with a matrix of PAA and carbon nanotubes (CNTs) as reinforcing agent were synthesized by semi-continuous heterophase polymerization (SHP). CNTs were prepared by a chemical vapor deposition technique and purified by steam. CNTs were characterized by a high resolution scanning electron microscopy (HRSEM) and Raman and Fourier transform infrared spectroscopies. Nanocomposites were prepared with: (i) purified CNTs (CNTsp) or (ii) purified and functionalized CNTs possessing an acyl chloride moiety (CNTsOCl). In both cases, the nanocomposites synthesis was carried out by in situ polymerization of acrylic acid (AA) by SHP. When CNTsOCl were used previously to the polymerization of AA, a series of specific amounts of CNTsOCl and AA were mixed to induce a chemical reaction between the carboxyl group of AA and the acyl chloride group of the CNTsOCl. The product, acrylic acid grafted to CNTsOCl (CNTsOCl-AA), was used to prepare the PAA-CNTsOCl nanocomposites. The PAA-CNTsOCl nanocomposites were characterized by HRSEM, Raman, FTIR and CPMAS C-13-NMR spectroscopies and also by thermogravimetric analysis (TGA). The results reveal that PAA-CNTsOCl nanocomposites were formed by PAA macromolecules grafted to CNTsOCl. The kinetic behavior observed for the synthesis of pure PAA or PAA-CNTsOCl nanocomposites by SHP was similar. Latexes of PAA-CNTsOCl nanocomposites were stable without formation of a precipitate of CNTsOCl for over 1.5years, while latex prepared with CNTsp and PAA, was unstable and formation of a precipitate of CNTsp was observed immediately after its preparation. PAA-CNTsp nanocomposites were characterized only by TGA. Moreover, latex of the PAA-CNTsp nanocomposite that did not precipitate immediately after its preparation, turned into a gel; this gelation never occurred with the PAA-CNTsOCl nanocomposite latex.