Yulai Zhao

Chemical Modifications of Chitosan and Its Applications

Chitosan is considered as a promising material in the pharmaceutical and biomedical fields based on its unique biological properties. This review presents chemical modifications of chitosan via using photosensitizers, dendrimers, sugars, cyclodextrins and crown ethers as modifiers and places an emphasis on the applications of chitosan derivatives as carriers in drug delivery systems, as supporting materials for tissue engineering, as dye removing agents and as metal ion adsorbents. Recently, the progress on chemical modifications of chitosan is quite rapid and we are confident that a more extensive range of applications of chitosan derivatives could be expected in the near future.

Modulation of the Microstructure of Polyethylene from Ethylene Polymerization Mediated by α-Diimine Ni Complex/MAO via Chain Transfer to ZnEt2 and Temperature

Temperature and chain transfer agents (CTA) are two primary factors that influence the microstructure of the resultant polymer. This contribution mainly studied the effects of polymerization temperature and concentration of diethyl zinc (ZnEt2) on ethylene polymerization and chain microstructure of resultant polyethylene (PE). The polymerization temperature showed a notable influence on the catalytic activity and the molecular weight of PE. It was observed that raising polymerization temperature from 4°C to 36°C resulted in a gradual decrease of the catalytic activity and a dramatic reduction of the molecular weight. The molecular weight of the prepared PE also decreased regularly with the increase of the concentration of ZnEt2 while the polydispersity did not broaden. The branching structure of PE prepared in the presence of varying concentrations of ZnEt2 was investigated via 13C-NMR spectroscopy. The addition of ZnEt2 had a moderate influence on the total branching degree and the branching distribution of PE. A possible mechanism is proposed for the influence of ZnEt2 on the microstructure of resultant PE.