杂多酸引发四氢呋喃聚合反应Ⅴ.生长链浓度与链生长速率常数的测定

TETRAHYDROFURAN POLYMERIZATION INITIATED WITH HETEROPOLYACID Ⅴ. DETERMINATION OF CONCENTRATION OF PROPAGATING SPECIES AND CHAIN PROPAGATION RATE CONSTANT

采用改进的酚钠法及端羟基测定法对环氧乙烷促进的低浓度磷钨杂多酸引发的四氢呋喃聚合反应过程中生长链浓度的测定表明 ,杂多酸分子中的三个质子均参与了引发反应 ,各引发一个聚合链 .采用醋酸酐为促进剂时杂多酸引发四氢呋喃聚合反应生长链浓度测定的结果也证明了这一点 .由此测得在 0℃和 2 0℃时四氢呋喃聚合反应链增长表观速率常数分别为 3 78× 10 -3 和 1 98× 10 -2 L·mol-1·s-1,这与四氢呋喃按离子型生长链增长时的反应速率常数相近 .说明PW12

Kinetic studies of tetrahydrofuran polymerization intiated by heteropolyacid showed that the concentration of propagating species maintained unchanged in the main period of the polymerization,indicating the absence of chain termination.The concentration of propagating species was measured by using a modified sodium phenoxide method and hydroxyl end\|group analysis method,and it showed that each of the three protons in heteropolyacid initiated one chain.The same result was also verified for the acetic anhydride promoted system by the hydroxy end\|group analysis method.The values of the chain propagation rate constant of THF polymerization at 0℃ and 20℃ were found to be 3 78×10 -3 and 1.98×10 -2 L·mol·s 1 , respectively,which are in correspondence with the chain propagation rate constant of THF on ionic active species.