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

Abstract

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 (CNTs_p) or (ii) purified and functionalized CNTs possessing an acyl chloride moiety (CNTs_OCl). In both cases, the nanocomposites synthesis was carried out by in situ polymerization of acrylic acid (AA) by SHP. When CNTs_OCl were used previously to the polymerization of AA, a series of specific amounts of CNTs_OCl and AA were mixed to induce a chemical reaction between the carboxyl group of AA and the acyl chloride group of the CNTs_OCl. The product, acrylic acid grafted to CNTs_OCl (CNTs_OCl-AA), was used to prepare the PAA-CNTs_OCl nanocomposites. The PAA-CNTs_OCl nanocomposites were characterized by HRSEM, Raman, FTIR and CPMAS ¹³C-NMR spectroscopies and also by thermogravimetric analysis (TGA). The results reveal that PAA-CNTs_OCl nanocomposites were formed by PAA macromolecules grafted to CNTs_OCl. The kinetic behavior observed for the synthesis of pure PAA or PAA-CNTs_OCl nanocomposites by SHP was similar. Latexes of PAA-CNTs_OCl nanocomposites were stable without formation of a precipitate of CNTs_OCl for over 1.5 years, while latex prepared with CNTs_p and PAA, was unstable and formation of a precipitate of CNTs_p was observed immediately after its preparation. PAA-CNTs_p nanocomposites were characterized only by TGA. Moreover, latex of the PAA-CNTs_p nanocomposite that did not precipitate immediately after its preparation, turned into a gel; this gelation never occurred with the PAA-CNTs_OCl nanocomposite latex.

Keywords:

• Nanocomposites
• carbon nanotubes
• poly(acrylic acid)
• semi-continuous heterophase polymerization

Funding

This work was performed with financial support from the Mexican Council of Science and Technology (CONACyT grant # CB-2008-101369). One of us (JMSJ) acknowledges a scholarship from CONACyT.