Improvement of Carbon Nanotubes Dispersivity in Poly(Styrene/Methacrylate) Composites by Chemical Functionalization

In this work composite materials of improved properties based on styrene and methacrylate copolymers with differently functionalized multiwalled carbon nanotubes (CNT) were prepared. In order to obtain a fine dispersion and to enhance the interfacial interaction of CNT with surrounding polimer matrix a chemical modification of the surface of carbon nanotubes was performed. Various types of functionalized multiwall carbon nanotubes were used: oxidized (CNT-COOH) and their ester analogues (methyl, dodecyl and ethylbenzene). The reaction of covalent functionalization of CNT-COOH with NaOH and further with (2-bromethyl)-benzene and hexadecyl-trimethylammonium bromide into CNT-COOEtBz was successfully performed. Also, oxidized multiwall carbon nanotubes were reacted with thionyl chloride and further in esterification reaction with given alcohols transformed into corresponding methyl or n-dodecyl ester. Functionalization of CNTs was confirmed by FTIR, Raman and X-ray photoelectron spectroscopy as well as by thermogravimetric analysis. Dodecyl and ethylbenzene ester modified carbon nanotubes showed contact angle for water 150 and 141 degrees, while the oxidized and methyl ester modified carbon nanotubes displayed seepage. Dispersibility of all modified carbon nanotubes in methanol and toluene was quantified by UV-Vis spectroscopy and differs considerably in both solvents for all systems, due to the significant change in chemistry of surface of CNTs. Mixtures of styrene / methacrylate monomer with up to 1 wt. % of CNT in toluene were reacted in a radical in-situ polymerization reaction. The synthesized composites were characterized by the SEC, TGA, DSC, DMA, SEM and contact angle method. The improvement of the properties of polymer/CNT composite can be attributed to better interaction between nanotubes and the polymer matrix.