دانلود رایگان مقاله سینتیک وزن مولکولی و مدل بریدگی زنجیره برای پلیمر دکستران

ABSTRACT

Ultrasonic degradation of six dextran samples with different initial molecular weights (IMW) has been performedto investigate thedegradationbehavior andchainscissionmechanismofdextrans. The weightaverage molecular weight (Mw) and polydispersity index (D value) were monitored by High Performance Gel Permeation Chromatography (HPGPC). Results showed that Mw and D value decreased with increasing ultrasonic time, resulting in a more homologous dextran solution with lower molecular weight. A significant degradation occurred in dextrans with higher IMW, particularly atthe initial stage ofthe ultrasonic treatment. The Malhotra model was found to well describe the molecular weight kinetics for all dextran samples. Experimental data was fitted into two chain scission models to study dextran chain scission mechanism and the model performance was compared. Results indicated that the midpoint scission model agreed well with experimental results, with a linear regression factor of R2 > 0.99.

4. Conclusions

The current study showed that ultrasonic treatment reduces molecular weight and polydispersity of six dextran samples, yielding a more homogenous dextran solution with a narrower molecular weight distribution. Significant degradation was observed at the initial degradation stage, particularly for samples with a larger IMW. A kinetic model proposed by Malhotra elucidates the time dependence of molecular weight during the degradation process, with a lack of the limiting molecular weight of dextran. A midpoint scission model, based on a central cleavage assumption, appears to be suitable to describe the results obtained in this study, suggesting that dextran chain scission proceeds in a non-random way. Ultrasonic treatment is capable of yielding dextran with a lower molecular weight and in the meanwhile improving the homogeneity of molecular weight distribution. As a simple, rapid and controllable method, ultrasonic degradation has a good industrial application prospect for further preparation of lower molecular weight clinical dextran.