聚二硫化物的光降解行为研究

Photodegradation of Poly(disulfide)s

系统地研究了不同结构聚二硫化物的光降解行为,并探索了溶剂、聚二硫化物的分子量、浓度以及光照波长对其降解行为的影响.研究结果显示,不同起始分子量的聚二硫化物以不同的速率降解,最终形成相同分子量的线形或者环状聚二硫化物;起始浓度越高,到达光降解平衡时聚二硫化物的分子量越高;辐射波长越短,降解速率越小,到达平衡所需的时间越长.结合降解产物的核磁共振氢谱以及质谱的分析结果,提出了聚二硫化物光降解机理:在紫外-近紫外光照射下,聚二硫化物断裂生成自由基碎片,不同自由基碎片通过分子间或者分子内的重组,形成低分子量的线形或者环状聚二硫化物.

Poly(disulfide)s,a typical dynamic polymer,could be degraded by light,heat or chemical reductant due to its disulfide bonds in main chain.The degradation methods of poly(disulfide)s reported mainly include in the reductive or thermal degradation.However,the photodegradation of the poly(disulfide)s behavior,as well as the degrading mechanism is less involved.In this work,a systemic investigation on the photodegradation of poly-(disulfide)s is presented.Under the irradiation of near UV-Vis light,the linear poly(disulfide)s are degraded into cyclic or linear poly(disulfide)s with low molecular weight.In addition,the effects of light wavelength,molecular weight and concentration of poly(disulfide)s on degradation rate were explored.Under the same conditions,poly-(disulfide)s with different initial molecular weights are degraded into linear or cyclic poly(disulfide)s with the approximate molecular weight in different degradation rates;the higher the initial concentration,the higher molecular weight of poly(disulfide)is at the equilibrium state;the shorter the radiation wavelength,the longer the time is needed to reach the photodegradation equilibrium.In addition,based on the analysis of degradation products,the corresponding degradation mechanism is proposed,that is,with the irradiation of UV-Vis light,the disulfide bonds in the poly(disulfide)s homo-cleaved into corresponding sulfur free radical fragments,and different free radical fragments form linear or cyclic poly(disulfide)s with low molecular weight through intermolecular or intramolecular recombination.The photodegradation gives a new idea on the further degradation of poly-(disulfide)s or other polymers with disulfide bonds.