聚氯乙烯结构缺陷和热不稳定性之间关系的研究 2.各种结构缺陷含量和热脱氯化氢速率之间的关系

本工作采用溴加成法、酚解法、FTIR法及臭氧裂解法分别测定了五种不饱和蒸气压下聚合的PVC样品(u-PVC)和五种商品PVC样品(s-PVC)的总双键、总不稳定氯、孤立双键和内部双键的含量.通过研究结构缺陷和PVC的平均分子量及脱HCl速率的相互关系,揭示了不饱和总双键值,总不稳定氯和孤立双键含量彼此的相关性是建立在它们分别与1/M_n的相关性基础之上,从而得出了这三种定量值测得的主要都是端基烯丙基氯结构.根据三者对脱HCl速率的良好线性相关性,首次提出了端基烯丙基氯结构在HCl催化作用下异构化成内部烯丙基氯从而成为脱HCl速率主要原因的机理.

STUDIES ON THE RELATION BETWEEN THE STRUCTURAL DEFECTS AND THERMAL INSTABILITY OF POLY (VINYL CHLORIDE) 2. THE RELATION BETWEEN THE CONTENTS OF DIFFERENT STRUCTURAL DEFECTS AND DEHYDROCHLORINATION RATES OF PVC

The contents of diferent structural deffects of five PVC samples, obtained by polymerization at monomer unsaturation vapor pressure, and five commercial PVC samples were determined. The total number of double bonds(C = GT) and labile chlorine atoms(ClL) were determined by bromine addition and phenolysis methods, respectively. The determination of internal double bonds (C = Cint) and isolated doubl bonds(C=Ciso) was carried out by means of ozonlysis and FTIR methods. It was found that the dehydrochlorination rates of PVC samples depended linearly on the content of ClL, C=CT and (C=C)1so, respectively. In addition, the contents of these three structural defects were all correlated linearly with 1/Mn, so most parts of themwould be the same defect-terminal allyl chlorine. Therefore, the main source of thermaldehydrochlorination of PVC could be attributed to the presence of terminal allyl chlorine groups. A mechanism, that in the presence of HC1 as catalyst the terminal allyl chlorine can be isomerized into internal allyl chlorine, was proposed to explain the main role of termina1 allyl chlorine in the thermal dehydrochlcrination of PVC.