Qingquan Liu

Morphology, Molecular Mass Changes, and Degradation Mechanism of Poly-L-Lactide in Phosphate-Buffered Solution

The hydrolytic degradation of poly-L-lactide (PLLA) material was investigated in order to elucidate the effects of degradation on the morphology and molecular mass changes. The degradation mechanism and kinetics of PLLA were also studied. Molecular mass decreases and molecular weight distribution becomes broader continuously with an increase in the degradation time. After 20 weeks of degradation, there were a large number of diagonal striations on the surface and many erosive holes in the interior of the PLLA materials. The degradation mechanism of PLLA is indicative of an autocatalysis process and simple bulk hydrolysis at the same time, and the terminal hydroxyl group of the oligomer plays an important role. The degradation of PLLA complies with first-order kinetics, and the rate constant of the biodegradation process of PLLA is 9.2 × 10−3 day−1.

Mechanical and Antibacterial Properties of Polypropylene/Polyamide 6 Blends-TiO2 Nanocomposites

Polypropylene/Polyamide 6 (PP/PA6) blends-TiO2 nanocomposites have been prepared via melt blending PP/PA6 with TiO2 nanoparticles, which were pretreated with toluene-2,4-di-isocyanate. The functionalized-TiO2 can react with the terminal amino and carboxyl groups at PA6, interfacial interaction and compatibility between TiO2 and matrix have been greatly improved resulted in higher tensile and impact strength than that of those filled with pristine TiO2 or pure PP/PA6 blends, and they have strong antimicrobial abilities against Bacillus subtilis, Staphylococcus aureus and Escherichia coli. The average efficiency of antibacterial is over 90% within 2.0 h. Mechanical and antibacterial properties can achieve their maximum with 3.0 wt%TiO2.

Preparation of Monodisperse Cationic Microspheres by Dispersion Polymerization of Styrene and a Cation-Charged Monomer in the Absence of a Stabilizer

Cationic polystyrene (PS) microspheres with monodispersity were prepared by dispersion polymerization of styrene and [2-(methacyrloyloxy) ethyl] trimethylammonium chloride (METMAC) in methanol/water system. The effects of METMAC, styrene, and initiator concentration as well as solvent composition on the diameters and size distribution of PS microspheres were systematically investigated. The results indicated that monodisperse cationic PS microspheres could be generated at METMAC concentration less than 2 mol% relative to styrene amount, and too high or low styrene amount was unfavorable to produce cationic PS microspheres. Moreover, it was found that with initiator concentration increasing, the average diameter and the size distribution of cationic PS microspheres also markedly increased. Solvent composition played a significantly important role in the preparation of cationic PS microspheres by dispersion polymerization of styrene and METMAC. Finally, the possible growth and stabilization mechanism of cationic PS microspheres was proposed. The electrostatic repulsion derived from positive charge on the surface of PS microspheres was responsible for the stabilization during dispersion polymerization in the absence of a stabilizer.

Preparation and Characterization of Poly (vinylbenzyl chloride)-b-poly (lactide) Copolymers via Nitroxide-Mediated Controlled Radical and Ring-Opening Polymerization

Hydroxyl-terminated poly(vinylbenzyl chloride) (PVBCOH) were synthesized using nitroxide-mediated controlled radical polymerization. Then, PVBCOH was used as a macro-initiator for ring-opening polymerization of lactide (LA) in the presence of stannous octanoate (Sn(Oct)2) as a catalyst. The structures, molecular weights and polydispersity index (PDI) of PVBCOH and PVBC-b-PLA were characterized by 1H-NMR, and GPC, respectively. The results indicated that PDI of PVBCOH and PVBC-b-PLA was 1.63 and 1.27, respectively. Moreover, the molecular weight and PDI of PVBCOH and PVBC-b-PLA could be well tuned by changing monomer-to-initiator ratio.

Hybrid Catalysts Compose of Mono-Substituted Keggin-Polyoxometalate and Different Aminopyridine Derivatives as Catalysts for Oxidation of Benzyl Alcohol with Hydrogen Peroxide

amino- pyridinium salts of mono-substiuted Keggin-polyoxometalate were synthesized and the catalytic performance the oxidation of benzyl alcohol to benzaldehyde under solvent-free conditions with hydrogen peroxide was examined. The influences of the composition of hybrid catalyst and mole ratio of H2O2 to benzyl alcohol were discussed, under the testing conditions of 70 oC, catalyst load 0.3 g, benzyl alcohol 2 mL, 30% H2O2 6mL, 5 h, 2-N-(2-pyrindinemethyl) -aminopyridinium salt of FeII substituted phosphotungstate (5b)4HPW11FeO39 exhibited the best activity, the conversion of benzyl of 95.4% with high selectivity of 98% was achieved, aminopyridine component in hybrid catalyst act as a counterion of polyoxometalate anion as well as a ancillary ligand, the interactions between organic counterion and polyoxometalate anion involve the electrostatic bond NH3+…Fe-POM as well as dative bond pyridine-N→Fe-POM, both affect the redox reactivity of mono-substituted polyoxometalte.