Network dynamics in cationically polymerized, crosslinked epoxy resins and its influence on crystallinity and toughness
Network dynamics in cationically polymerized, crosslinked epoxy resins and its influence on crystallinity and toughness
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DOI：
10.1016/j.polymer.2016.03.052
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发表时间：
2016-05-17
期刊：
影响因子：
4.6
通讯作者：
Hartwig, A.
中科院分区：
文献类型：
--
作者：
Arnebold, A.;Wellmann, S.;Hartwig, A.
在交联环氧树脂中结晶是很少观察到的现象。如果适当调节结晶度，则可导致阳离子聚合环氧树脂的韧性增强。这项工作表明，控制结晶的部分结晶的聚（3-己内酯）（PCL）在模型系统的基础上的脂环族环氧树脂基体聚合的热潜伏性，阳离子引发剂。具有相同组成的样品在不同的条件下聚合，导致不同的结晶度，进而导致形态和机械行为的差异。温和的固化条件导致环氧树脂基体的充分柔性化，并且环氧树脂消耗主要由活化单体机理引起。另一方面，与温和条件相比，更强烈的聚合条件导致更高量的酯交换，这通过降低结晶度和更高的凝胶含量来证明，尽管聚合反应完全。PCL链通过酯交换被缩短，而较小的PCL链被整合到网络中。此外，用DMA和变形-固定-松弛实验测量的应力松弛实验揭示了由重排反应引起的交联聚合物的流动和应力降低的类型。SEM显微照片显示，增加结晶度导致断裂表面粗糙度升高。对机械性能的研究表明，提高的结晶度导致更高的刚度、机械强度以及上级韧性，即使网络密度没有显著变化。这项工作表明，环氧树脂的形态和性能可以通过在聚合条件下的微小变化进行调整。(C)2016爱思唯尔有限公司版权所有
Crystallinity in crosslinked epoxy resins is a rarely observed phenomenon. If crystallinity is properly adjusted, it can lead to enhanced toughness in cationically polymerized epoxy resins. This work demonstrates the controlled crystallization of partially crystalline poly(3-caprolactone) (PCL) in a model system based on a cycloaliphatic epoxy matrix polymerized with a thermo-latent, cationic initiator. Samples with the same composition were polymerized under varied conditions leading to different degrees of crystallinity and furthermore to differences in morphology and mechanical behavior. Mild curing conditions lead to a sufficient flexibilization of the epoxy matrix and the epoxide consumption is caused mainly by the activated monomer mechanism. On the other hand, more intense polymerization conditions result in a higher amount of transesterification compared to mild conditions which is evidenced by decreasing crystallinity and higher gel content despite a complete polymerization reaction. The PCL chains are shortened by transesterification while the smaller PCL chains are integrated into the network. Additionally, stress relaxation experiments measured with DMA and deformation-fixation-relaxation experiments reveal a type of flowing and stress reduction of the crosslinked polymers caused by rearrangement reactions. SEM micrographs show that increasing crystallinity leads to a raised roughness of fracture surfaces. Examination of the mechanical properties shows that enhanced crystallinity leads to higher stiffness, mechanical strength and also to superior toughness even if the network density does not significantly change. This work shows how the morphology and properties of the epoxy resin can be adjusted by just small variations in the polymerization conditions. (C) 2016 Elsevier Ltd. All rights reserved.