发现，钛酸四丁酯或草酸亚锡作为缩聚催化剂时，在整个高真空阶段羧基含量并不是一直增加的。
It is found that in the presence of butyl titanate or stannous oxalate as a polycondensation catalyst the carboxyl content is not always on the increase in all high vacuum stage.
发现，钛酸四丁酯或草酸亚锡作为缩聚催化剂时，在整个高真空阶段羧基含量并不是一直增加的。
It is found that in the presence of butyl titanate or stannous oxalate as a polycondensation catalyst the carboxyl content is not always on the increase in all high vacuum stage.
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