The Synthesis And Application Of Low-polydispersity Hyperbranched Polyphenylene Sulfide

In this work, the hyperbranched poly（phenylene sulfide） with the narrow molecular weight distribution had been prepared by a modified polycondensation of AB₂ monomer with a core molecule, in which 2,4-Dichlorobenzenethiol and 3,5-Dichlorothiophenol were used as the starting monomer respectively. Stabilized by LD-HPPS, Pd nanoparticles with the narrow particle size distribution were prepared in situ reduction through the two-phase synthetic method. The effect of PdCl₂: HPPS mass ratios on the formation and stabilization of Pd nanoparticles was discussed. The catalytic performance for Heck reaction catalyzed by palladium nanoparticles with near-uniform was also studied. In addition, for detection of cyanide ions, the reaction-based hyperbranched polymer fluorescence chemosensor had been designed and synthesized, their structure and fluorescence property were characterized. The sensor performance including detection limit, linear region and selectivity were also investigated. 1. The synthesis and characterization of low-polydispersity hyperbranched poly（phenylene sulfide）A low-polydispersity（Mw/Mn=1.009） hyperbranched poly（phenylene sulfide）（LD-HPPS） was successfully prepared by modified polycondensation of an AB₂ monomer 3,5-Dichlorothiophenol with a core molecule 1,3,5-tribromobenzene in a slow addition manner. To explore the effect of modified approach and monomer structure on the molecular weight and molecular weight distribution of products, the asymmetric 2,4-Dichlorobenzenethiol and symmetric 3,5-Dichlorothiophenol respectively was chosen as the starting monomer for the traditional and modified polycondensation of AB₂ monomer and the resultant four polymers were marked as H1- H4. The resulting polymers were soluble in common solvents such as dichloromethane, trichloromethane, toluene and tetrahydrofuran. The Elementar, FT-IR Spectrometer, nuclear magnetic resonance spectrometer（¹H NMR） were used to investigate the structure of the polymers. The Size Exclusion Chromatography-Multi-Angle Laser Light Scattering（SEC-MALLS） analysis was carried out to determine the molecular weight and molecular weight distribution（MWD） of the HPPSs. In these results, especially the MWD（1.009） of H4 displayed most uniform similar to those of the dendrimer analogue. The thermal stability of the products was also investigated by thermogravimetric analysis（TGA）. It was found that H4 possessed the most outstanding thermostability, which endowed it with potential to be used in high temperature environment. 2. Low-polydispersity hyperbranched polyphenylene sulfide-supported palladium nanoparticles: synthesis, characterization and catalytic applicationsWith LD-HPPS as the stabilizer, the Pd nanoparticles with small average particle size（2.0 nm） and the narrow distribution（σ=0.4 nm） were prepared in situ reduction through the two-phase synthetic method, which were employed as the catalysts in Heck reaction. HPPS-stabilized Pd NPs were prepared in a two-step process: complexation of Pd（II） ions with thioether moieties of HPPS in the presence of phase transfer agent followed by chemical reduction with the excess of NaBH₄ relative to Pd（II） ions. The effect of PdCl₂: HPPS mass ratios on the formation and stabilization of Pd NPs was discussed in the experiment. The results of transmission electon microscopy（TEM） characterization implied that size of the nanoparticle increased gradually with the increase in the mass ratio of PdCl₂:H4. The resulting Pd nanoparticles with small average particle size had a narrow distribution when the mass ratios of PdCl₂:H4 was 0.018. The stabilization mechanism and thermal stability of Pd NPs were discussed. The results of TGA analysis revealed that the nanocomposites were quite thermally stable, which allowed HPPS-stabilized Pd NPs to be used at high temperature. In addition, the successful use, separation and easy recycling of the resulting Pd NPs in a model Heck cross-coupling reaction were presented. 3. The reaction-based single-molecule fluorescence nanosensor for detection of cyanide ionsIn this work, based on a specific nucleophilic addition reaction with cyanide, a single-molecule nanosensor（HPPS-NHCOCF₃） for cyanide anion had been synthesized, which was taken advantage of hyperbranched polyphenylene sulfide（HPPS） as the single molecule nano-matrix. The structures of the resulting hyperbranched polymers were supported by elemental analysis, IR and NMR. The effect of solvents on the fluorescence properties of HPPS-NHCOCF₃ was discussed. Moreover, its sensing performance was studied by Fluorescence spectrophotometer. Taking advantage of the “amplified molecular wire effect” and specific nucleophilic addition reaction, the nanoprobe displayed a limit of detection down to 0.35μM with a wide linear region.