Study On Preparation Of Functionalized CdS Nanocrystal And Its Assembly With Polymers

Molecular assembly technologies of inorganic nanoparticles and organic polymers, and associated nanoscience for the synthesis of revolutionary polymer nanocomposites have aroused increasing interest among scientists. These technologies and science are engaged in improving compatibility between inorganic nanoparticles and organic polymers and bringing novel performances for the hybrid nanocomposites such as mechanical, electrical, optical, magnetic and catalytic properties. Of these inorganic nanoparticles, CdS semiconductor nanocrystal has been attracting much attention due to its remarkable quantum confinement effect, ultrafast nonlinear optic response, ultraviolet absorption and photoluminescence properties. CdS nanocrystal can be fabricated by sol, reverse micelle and other techniques, however, active functional groups on the surface of those nanocrystals are unavailable to be obtained by these methods, and also it will make nanocrystals difficult to be modified chemically furthermore. In this study, much work was performed on the preparations of CdS nanocrystals. The CdS nanocrystals coated with active hydroxyl group were size-tunable, and well dispersed in solvents in the presence of organic ligand.Recent progress in new polymer synthesis techniques makes it possible to design and synthesize well-defined polymer hybrid nanocomposites with novel properties and controlled architectures in the molecular scale. There are many methods for attaching polymer chains onto nanoparticle surfaces, including chemisorption, synthesis in situ, "grafting to", "grafting from". In this paper, methods of "physic blending" and "polymerizing in situ" were employed to synthesize CdS/PU hybrid nanocomposites. In addition, "grafting to" was performed on the assembly of polyether and CdS nanocrystal.Different raw materials were employed for preparing the hydroxyl coated CdS nanocrystal in the presence of mercaptoethanol (ME) as a stabilizer. The effects on the size of CdS nanocrystal, such as recipes and solvents, organic ligand content, and the technological conditions were investigated in detail. The structure morphology,particle size, and optic properties of CdS nanocrystal prepared were characterized by Fourier transform infrared spectroscopy (FT-IR), transmission electron microscope (TEM), UV-vis spectrometer (UV-vis), fluorescence spectrometer (FL), thermal gravimetric analysis (TGA), and X-ray diffraction (XRD).In order to assemble CdS nanocrystal with various polymer matrixes, isocyanate and silane coupling agents with active functional groups were employed to modify the surface of CdS nanocrystal. Amino group, double bond and isocyanate group were confirmed to be coated on the surface of CdS nanocrystals by the characterization of FT-IR respectively.The main work is focused on the polymerization in situ to obtain CdS/PU hybrid nanocomposites via inorganic nanoparticles chemically bounded with organic polymers matrix. The CdS nanocrystal modified with ME ligand can be mixed with waterborne polyurethane by physical blending method to achieve hybrid as compared with the above method. The structure and properties of the hybrid nanocomposites were characterized with FT-IR, TEM, UV-vis, FL, TGA, scanning electron microscope (SEM) and other measurements. It was found that the hydroxyl group on the surface of CdS nanocrystal reacted with isocyanate firstly and then the grafted isocyanate group polymerized with the monomers of PU in situ. Finally, the shell-core structure of the hybrid based on designing was achieved. The star-like CdS nanocrystals/PU hybrids were well dispersed in PU matrix and novel optic properties were obtained also, which strong ultraviolet absorption was visible between 350-450 nm as well as obvious blue light and weak red light emissions were presented with 325 nm laser beams as light source.Silane coupling agent containing epoxy group was also used to copolymerize with propylene oxide monomer under double metal cyanide complex (DMC) catalyst to form functional polyether with active silicon alkoxyl group. Preliminary research on assembly of the functional polyether and CdS nanocrystal was performed.