Covalent Functionalization Of Silica And Carbon Nanotubes With Polyamide 6

In this paper, toluene 2, 4-diisocyanate (TDI) was utilized as a surface modifier for silica nanoparticles and hydroxyl functionalized multiwalled carbon nanotubes (MWNT-OH). The TDI modified silica particles and MWNT-OH were used as initiator precursor to conduct ring-opening anionic polymerization ofε-caprolactam in the presence of a sodium caprolactamate catalyst. The main contents were as follows:Preparation of silica graft polyamide 6 from silica surface initiated ring-opening anionic polymerization. Firstly, the silica was treated with excess toluene 2, 4-diisocyanate (TDI), after which the residual isocyanate groups were reacted withε-caprolactam to form the acyl caprolactam initiator (SiO₂-CL). Silica graft polyamide 6 (PA6) was synthesized by in situ ring-opening anionic polymerization ofε-caprolactam in the presence of sodium caprolactamate as a catalyst and caprolactam-functionalized silica (SiO₂-CL) as an initiator. The effects of reaction time and the feed ratio of monomer to silica initiator (Rfeed) on the monomer conversion and the polymer molecular weight were investigated. It was found that the grafted polymer molecular weight could be adjusted by the feed ratios of monomer to silica initiator. In addition, FTIR spectrum, TGA analysis and the differential scanning calorimetry (DSC) were employed to characterize the graft materials. Transmission electron microscopy was utilized to image polymer-functionalized silica, showing fine dispersion of silica particles and their size ranging from 20 to 40 nm.Functionalization of multiwalled carbon nanotubes with polyamide 6 through ring-opening anionic polymerization. Firstly, hydroxyl functionalized multiwalled carbon nanotubes was treated with excess toluene 2, 4-diisocyanate (TDI), after which the residual isocyanate groups were reacted withε-caprolactam to form the acyl caprolactam initiator (MWNT-CL). Covalent functionalization of multiwalled carbon nanotubes (MWNTs) with polyamide 6 was accomplished by ring-opening anionic polymerization ofε-caprolactam in the presence of sodium caprolactamate as a catalyst and caprolactam functionalized MWNTs as an initiator. The effects of reaction time and the feed ratio of monomer to MWNT initiator (Rfeed) on the grafted polymer content as well as the solubility of the resulting polymer-functionalized MWNTs have also been investigated. It was found that the grafted polymer weight proportion could be roughly adjusted by the feed ratios of monomer to MWCNT initiator. In addition, the MWNT-PA6 conjugates were characterized by FTIR, TGA, UV-Vis and TEM techniques. The results indicated that polyamide 6 was covalently bounded to the carbon nanotubes, not by adsorption. TEM showed that polyamide 6 was attached to the carbon nanotubes unevenly. The polymer-functionalized tubes exhibited high solubility in organic solvents, such as formic acid and m-cresol, and the solutions remained stable for at least 6 months.