The Research On Multi-walled Carbon Nanotubes Functionalized With Living Polymers And Its Composite With Liquid Crystals

Carbon nanotubes (CNTs) have attracted great research interest due to their unique structures and outstanding mechanical properties, which have been investigated for numerous applications such as composites. However, the application progress of CNTs has been largely impeded by their insolubility in most solvents and poor compatibility with other matrix materials. Therefore, the research on CNTs surface modification has important scientific significance to improve not only their solubility but also the interactions between matrix and modified nanotubes for taking full advantage of CNTs in composites. In the research, the polymer of 4-chloromethylstyrene functionalized multi-walled carbon nanotubes (MWNTs) were synthesized by“graft to”method based on the molecular design. The influencing factors of this functionalization and possible grafting mechanism model had been studied. Subsequently, a novel nanocomposite of liquid crystals functionalized MWNTs was prepared by solution synthesis. The main contributions are as follows:(1) Poly(4-chloromethylstyrene) (PCMS) with functional groups was synthesized by free radical polymerization, then it was covalently grafted onto the surfaces of oxidized MWNTs by esterification with the aid of a phase transfer catalyst. The effects of reaction time, feed ratio of MWNTs to PCMS and molecular weight of PCMS on the functionalization of MWNTs were discussed. FT-IR, Raman, 1HNMR and UV-vis results reveal that PCMS has been attached to MWNTs via covalent bonding, with a thickness of PCMS layer in the range of 3 to 6 nm. The weight percentage of grafted PCMS is about 45.8%. The experiments of solubility and dispersion suggest that the optimum reaction time is 7h. The increasing feed ratio of PCMS to MWNTs has little effects on the micromorphology of MWNT-PCMS. And increasing the molecular weigh of PCMS is unfavorable to PCMS grafting.(2) Hexamethylene bis(4-hydroxybenzoate) (HMBH) was synthesized by melting transesterification reaction. Subsequently, liquid crystalline polymer terminated with phenolic hydroxyl groups (LCP-OH) was prepared by the polycondensation of HMBH with terephthalyl chloride through controlling their mole ratio. The molecular structure of HMBH and LCP-OH was confirmed by FT-IR and 1HNMR spectroscopy. POM results indicated that LCP-OH is thermotropic liquid crystalline with typical nematic mesophase. (3) Using the phase transfer catalyst, a novel liquid crystals functionazied MWNTs nanocomposite (MWNT-PCMS-LCP) was prepared by solution synthesis reaction of LCP-OH with living MWNT-PCMS. FT-IR and Raman spectroscopy demonstrate that LCP-OH has been reacted with grafted PCMS on the surface of MWNT-PCMS, forming a covalent linkage. Compared with MWNT-PCMS, resultant nanotubes with a thicker diameter are observed in SEM and TEM images, the wrapped thickness is about 6-10 nm. According to TGA results, the loss-weight fraction of the grafted layers for the MWNT-PCMS-LCP is 63.5%. This functional material can be dispersed stably in CHCl3/phenol mixture.