低密度聚乙烯光引发交联机理Ⅵ.模型化合物光交联点的13C NMR研究

用溶液高分辨¹³C NMR谱系统地研究了二本甲酮光引发低密度聚乙烯各种模型化合物(正烷烃,含有文化结构以及末端双键的化合物等)交联产生的H型和Y型交联点的结构和数目.定量研究结果表明:形成的交联点对模型化合物的种类有较大的依赖性;在正十二烷光交联过程中,H型和Y型交联点均可形成,且二者的产率相当;而在含有文化结构的模型化合物的文联过程中,形成H型和Y型交联点的产率与文化结构的空间位阻有关;对合末端双键的模型化合物,则在交联过程中双键被打开而形成Y型交联点.这些结果与低密度聚乙烯光引发交联体系中得到的结果相一致,为进一步阐明聚乙烯光交联点的结构及其形成机制提供了新的实验证据.

MECHANISM OF PHOTOINITIATED CROSS LINKING OF LOW DENSITY POLYETHYLENE Ⅵ.13C NMR Studies on the Crosslinks of LDPE Model Compounds

H-and Y-crosslinks formed by photoinitiated crosslinking of dodecane,squalane,isooctane and 1-hexene as the model compounds of low density polyethylene in the presence of benzophenone as photoinitiator have been studied for the first time by solution state ¹³C NMR spectroscopy. The quantitative studies show that the types of crosslinks depend on the sorts of the model compounds.H-and Y-links are both formed for photo crosslinked dodecane and isooctane samples Whereas only H-links were detected for the crosslinked squalane.On the other hand,the double bond of unsaturated hydrocarbons such as 1-hexene can be opened to form Y-link by the reaction between a terminal vinyl group and an alkyl radical.These results are in good agreement with those obtained from low density polyethylene and give new evidence for elucidating the formation of the crosslinks in the photo cosslinked polyethylene.