双烯类聚合物的热分析——I.间规1,2-聚丁二烯的熔融-结晶与热氧化

由钴催化体系合成的间规1,2-聚丁二烯是结晶性的,熔点205—210℃,与1,2-链节含量无关。低1,2-含量(12—20mol％)时,热氧化峰温为185℃左右,高1,2-含量(95—100mol％)时,200到240℃。换言之,与主链双键相比,侧链乙烯基的热氧化反应发生在更高的温度,即在熔融后的较窄的温度范围表现出较大的热效应。高1,2-含量间规聚丁二烯热氧化的热效应和活化能值,似与合成转化率有一定联系,当达到一定转化率时,热效应急剧增高,而活化能降低,估计这与残留在试样中催化剂的量及存在形式有关。

THERMAL ANALYSIS OF POLYDIENES I. The Melting-Crystallization and Thermo-Oxidation of Hight 1,2-Syndiotactic Polytbutadiene

The syndiotactic 1,2-polybutadiene-1,4-polybutadiene copolymer is crystalline with a m.p. of 205-210℃, independent of the content of 1,2-unit. It is considered that the copolymer is block in nature.The DSC peak temperatures (Tp) for thermo-oxidation of a low 1,2-content (12-20%) sample and a high one (95-100%) are 185 and 200-240℃, respectively. It is believed that the double bond in side group is more stable than that in the main chain. The difference in stability between the two kinds of double bond can be explained by the facts that: 1) the inner double bond has four a-hydrogens, but the outer one has only one; 2) the block of 1,2-unit is crystalline below 203℃, whereas that of 1,4-unit is amorphous even at room temperature.The activation energy, exothermal effect of thermo-oxidation for high 1,2-content polybutadiene of various conversion is also described.