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用DSC研究了预期为聚丙烯-聚乙烯两嵌段共聚物(PP-PE)和相应共混物(PP+PE)在热学性能上的差异。经用不同分子量的PP和PE及其共混物进行试验后发现,由于PP和PE在结晶时出现过冷的难易不同。在共混物降温热分析曲线上,当降温速率较快时仅出现一个放热峰,而降温速率较慢时出现PP和PE各自的结晶放热峰,从而解释了文献中的不同结果。并发现共混物的PP和PE熔融、结晶温度均较组分相同的嵌段共聚物的相应温度为高;嵌段共聚物中PP和PE的△H_f值均低于均聚物的△H_f值,而PE的值降低尤甚。我们认为这与嵌段间的共价键限制嵌段活动和结晶过程有关,从而确认DSC热分析可以作为识别是否为嵌段共聚物的一种方法. 本工作的结果表明,所研究的PP-PE试样具有嵌段结构。
Differences in thermal properties between the polypropylene-polyethylene diblock copolymer (PP-PE) and the corresponding blend (PP + PE) were investigated by DSC. The experiments with PP and PE with different molecular weights and their blends showed that due to the difficulty of subcooling PP and PE during crystallization, On the thermal analysis curve of the blend cooling, only one exothermic peak appears when the cooling rate is faster, while the respective crystallization exothermic peaks of PP and PE appear when the cooling rate is slow, thus explaining the different results in the literature. The results showed that the corresponding temperature of the block copolymer with the same composition and crystallization temperature was higher. The △ H_f values of PP and PE in the block copolymers were all lower than that of the homopolymer Value, while the value of PE decreases especially. We consider this to be due to covalent bonding between the blocks limiting the activity of the block and the crystallization process, confirming that DSC thermal analysis can be used as a means of identifying whether a block copolymer is present or not.Results of this work indicate that the PP- PE samples have a block structure.