In present work, the comparative study on annealing-induced high-impact toughness of linear and grafted polypropylene random copolymer (PPR and MPP) was performed. The changes of microstructure and mechanical properties of PPR and MPP upon annealing were investigated in detail. The results showed that maleic anhydride was grafted onto the backbone of PPR to form long-chain branched structure. During the melt grafting process, the degradation reaction is dominant, giving rise to the decrease in molecular weight and degree of chain entanglement, and hence PPR demonstrates higher flexural modulus and impact strength, as well as lower elongation at break than MPP. The long-branched chains perform the function of heterogeneous nucleation. The depressed chain entanglement facilitates the diffusion of polymer chains during the crystallization process, followed by higher total crystallization rate and crystallinity of MPP in contrast to those of PPR. Thermal annealing treatment promotes the secondary crystallization, and hence the crystallinity and crystal perfection of the polymer is elevated, resulting in enhanced mobility of the chain segments in the amorphous region. After annealing at 100°C for 3 h, the impact strength of MPP is 71% higher than that of its unannealed counterpart, while this value is increased remarkably by 153% for PPR. The existence of long-branched chains may not be conducive to sufficient rearrangement of chain segments of MPP during the annealing treatment. As a consequence, the crystallinity and impact strength of PPR are elevated more pronouncedly in comparison with those of MPP after annealing treatment.

中文翻译：

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线性和接枝聚丙烯无规共聚物退火诱导高冲击韧性的比较研究

在目前的工作中，对线性和接枝聚丙烯无规共聚物（PPR 和 MPP）的退火诱导的高冲击韧性进行了比较研究。详细研究了退火后PPR和MPP的微观结构和力学性能的变化。结果表明，马来酸酐接枝到PPR的主链上，形成长链支化结构。在熔融接枝过程中，降解反应占主导地位，导致分子量和链缠结度降低，因此 PPR 表现出比 MPP 更高的弯曲模量和冲击强度，以及更低的断裂伸长率。长支链执行异质成核的功能。降低的链缠结促进了聚合物链在结晶过程中的扩散，其次是与 PPR 相比，MPP 的总结晶速率和结晶度更高。热退火处理促进了二次结晶，从而提高了聚合物的结晶度和结晶完整性，导致非晶区链段的流动性增强。在 100°C 下退火 3 小时后，MPP 的冲击强度比未退火的对应物高 71%，而 PPR 的冲击强度显着提高了 153%。长支链的存在可能不利于退火处理过程中MPP链段的充分重排。结果，与退火处理后的 MPP 相比，PPR 的结晶度和冲击强度提高得更明显。