Miniemulsioin-based Synthesis Of AIE Polymeric Nanoparticles And Their Luminescent Properties

Fluorescent polymer nanoparticles(NPs) have been widely used in the fields of cell imaging, disease diagnosis, chemical sensing, and optoelectronic materials. Fluorescent NPs using conventional aggregation-induced quenching(ACQ) fluorescent molecules as functional components often suffer from a low fluorescence quantum yield(Ф_F) and narrow regulation range of photoluminescence(PL) intensity. However, when fluorescent molecules with an aggregation-induced emission(AIE) property were introduced into the fluorescent NPs, they can emit strong fluorescence because of the serious restriction of the intramolecular rotation. Moreover, the PL intensity of AIE NPs can be significantly enhanced through the increase of the loading of AIE molecules, because the aggregation degree of AIE molecules is expected to be higher at an increased concentration. Therefore, in compared with ACQ molecules, AIE ones are more promising to be used as fluorescent moiety to prepare fluorescent NPs with a high PL intensity and high Ф_F. Although several innovative techniques have been designed to prepare AIE NPs, they more or less had some drawbacks, such as the low loading of AIE molecules, use of organic solvent, and complex and tedious preparation process. Therefore, it is highly desired to invent a novel, efficient, scalable, green, and reproducible technique to synthesize AIE NPs. The convenient preparation of AIE NPs may highly promote the development of various AIE NPs and broaden their applications.In this thesis, AIE polymer NPs were successfully prepared through a one-pot green water-borne miniemulsion copolymerization of a main monomer and a silole-based AIE luminogen, 1-allyl-1-methyl-2,3,4,5-tetraphenylsilole(AMTPS). Styrene(St) with a conjugated phenyl side group and methyl methacrylate(MMA) with a weakly conjugated carbonyl side group were selected as the main monomer, respectively. Meanwhile, the morphology and particle size of AIE NPs, microstructure and molecular weight of copolymers, luminescent properties of copolymers and AIE NPs, and the fluorescence coloring capability of AIE NPs to cells and fiber materials were systematically investigated.In the water-borne miniemulsion systems, poly(St-co-AMTPS) AIE NPs(named as SNPs) with various contents of AMTPS were synthesized through copolymerization of St and AMTPS. The influence of the AMTPS content on the particle morphology and particle size, polymerization kinetics, luminescent properties of AIE NPs and copolymers were systematically studied. According to the microscopic observation result, SNPs displayed a regular spherical morphology and had a narrow size distribution. The kinetic results showed that all the polymerization rates of the systems with various AMTPS loadings were fast, and the St conversion could exceed 80% within 60 min. With the increase of the AMTPS content, the molecular weight of poly(St-co-AMTPS) decreased due to the chain transfer reaction of the propagated radicals to AMTPS. SNPs could emit blue-green fluorescence under the irradiation of UV light, and the PL intensity of the AIE NPs could be precisely controlled by the loading of AMTPS. It should be pointed out that the Ф_F of SNPs was relatively low, for example Ф_F of the SNPs with 20wt% of AMTPS was only 22.6%. With the increase of the volume fraction of water in the tetrahydrofuran(THF)/water mixed solvent, the PL intensity of poly(St-co-AMTPS) gradually increased prior to 70%. Further increase of the water fraction, the PL intensity of the copolymer was significantly enhanced, displaying a typical AIE behavior. As the polymerization proceeded, more and more polymers were produced in the dispersed phase, leading to the increase of the viscosity of the dispersed phase. In addition, with the accumulation of copolymers in the dispersed phase, the dispersed phase gradually transferred from a liquid state to a solid one. Correspondingly, the PL intensity of the emulsion increased.In order to further improve the Ф_F and PL intensity of AIE polymer NPs, a monomer with a weakly conjugated side group, MMA, was chosen as main monomer to prepared AIE polymeric NPs through miniemulsion copolymerization with AMTPS. The poly(MMA-co-AMTPS) AIE NPs(named as MNPs) could emit a blue-green fluorescence under a UV excitation. The PL intensity of MNPs could be precisely regulated by the loading of AMTPS. Compared with SNPs with a same loading of AMTPS, both the PL intensity and Ф_F of MNPs were obviously higher. For instance, the PL intensities of SNPs and MNPs with 20 wt% of AMTPS at the maximum emission wavelength were 819 and 1215, respectively. Furthermore, the Ф_Fs of the SNPs and MNPs with 20 wt% of AMTPS were 22.6% and 60.8%, respectively. The obviously lower PL intensity and Ф_F could be reasonably ascribed to the promotion of the non-radiative energy consumption through formation of stronger π-π interactions between the poly(St-co-AMTPS) chains, compared with the poly(MMA-co-AMTPS) chains, because the poly(St-co-AMTPS) chains contain a large amount of phenyl. In addition, the influence of the AMTPS content on the particle morphology and particle size of MNPs, microstructure and molecular weight of poly(MMA-co-AMTPS), luminescent properties of the copolymer were also systematically studied.The applications of AIE polymer NPs in the labeling of cells and coloring of fibers were evaluated through the cell experiments and electrospinning experiments, respectively. The AIE polymer NPs displayed a low cytotoxicity. In comparison with SNPs, the MNPs showed a better labeling capability to the breast cancer MCF-7 cells to achieve a better imaging quality of cells. For preparing the spinning solution, the AIE NPs were dispersed in an aqueous solution of polyoxyethylene(PEO). The fluorescent micro/nanofibers were prepared through electrospinning. The results showed that AIE NPs had a good coloring capability to fiber materials.In conclusion, AIE polymer NPs can be conveniently prepared through copolymerization of a common monomer and an AIE functional monomer in green water-borne miniemulsions. The proposed technique in this thesis holds high versatility and flexibility to prepare AIE NPs with a high PL intensity, high fluorescence quantum yield, and good biocompatibility.