Study On The Preparation And Properties Of CdS/PAEK Composites

The unique physical and chemical properties of nanocrystals, such as quantumsize effect, quantum tunnel effect, have drawn much attention of researchers, for theirpotential applications in the fields of optical displays, solar cells, sensors, biologicalimaging, biological labeling, etc. Due to the quantum size effect caused by the smallsizes of nanocrystals, we can regulate the fluorescence peak by changing the sizes ofthe nanocrystals only. Nanocrystals have the high surface energy owing to their smallsizes. They can be easily destroyed by the external environment, and weaken or losetheir unique properties. Thus it is required to stabilize the nanocrystals in inertmedium to achieve their real application in the fields of biological probes,photovoltaic conversion, et al. Polymers are the ideal matrix for the nanocrystals, dueto their low cost and good processing properties. On one hand, the stability of thenanocrystals can be significantly improved with the polymer coating. On the otherhand, the introduction of the polymer can achieve the integration of the materialproperties, and give the nanocomposites new properties such as mechanical properties.and chemical reactivity. In this thesis, we prepared the nanocomposites of CdS andpoly（aryl ether ketone） polymers based on the synthesis and modification of poly（arylether ketone） of our group. For the purpose of preparation of nanocomposites withhigh quantum yield and excellent performance, we investigated the effects ofmacromolecular chain structure and preparing conditions on the luminescentproperties of composite materials. Finally, we obtained the nanocomposites withexcellent properties.We firstly synthesized the carboxylic-functionalized poly（arylene ether ketone） bya typical nucleophilic substitution polycondensation from phenolphthalin and4,4’-difluorobenzophenone, which contained the benzene carboxylic acids （expressedas PCA-PAEK）. CdS/PCA-PAEK nanocomposites were then prepared usingPCA-PAEK as the ligand in DMF solution from Cd（Ac）2and thiourea. The resulting CdS/PCA-PAEK nanocomposites were characterized to confirm the structure andproperties. Furthermore, the effects of reaction time, CdS/PCA-PAEK ratio andCd²⁺/thiourea ratio on the photoluminescence of CdS/PCA-PAEK nanocompositeswere also investigated. The results of photoluminescence measurement showed thatthe nanocomposites exhibited distinct luminescence properties with yellow-greenfluorescence.In order to prepare the light emitting material with the better performance, weintroduced the flexible side chain containing the carboxylic groups into the PAEK（expressed as ACA-PAEK）. The introduction of flexible side chain improved thesurface coating of the nanocrystals and didn’t decrease the heat resistance of thepolymers. The results of photoluminescence measurement with CdS/ACA-PAEKshowed the better luminescence properties compared with CdS/PCA-PAEKnanocompsites.Hyperbranched PAEKs have a large amount of terminal functional groups withthree-dimensional topological structures. Due to their unique inner cavities, they cancomposite with inorganic salts or organic small molecules easily, which are propitiousto achieve the dispersion of nanocrystals. So we synthesized hyperbranched PAEK,which contained the flexible side chain with carboxylic group （expressed asACA-HPAEK）. But the quantum yield increased a little for the chain entanglement.For the purpose of decrease the chain entanglement of hyperbranched PAEK, andpreparation of high quality CdS/PAEK nanocomposites, we synthesizedhyperbranched PAEK, which contained the benzene carboxylic acid group （expressedas PCA-HPAEK）. The introduction of benzene ring decreased the chain entanglementefficiently. The photoluminescence measurement of CdS/PCA-HPAEK showed thatthe nanocomposites not only exhibited excellent luminescence properties with63%quantum yield but also had good heat resistance.In summary, based on carboxylic-functionalized PAEK, a series of CdS/PAEKnanocomposite hybrid materials were prepared. These hybrid materials not onlyprovide the basis for the research and application of the new electro-active materials,but also provide important information for broadening the applications of PAEK materials.