Elastomeric Networks with Bimodal Chain-Length Distributions
Elastomeric Networks with Bimodal Chain-Length Distributions
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DOI：
10.1021/ar00045a003
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发表时间：
1994-09
影响因子：
18.3
通讯作者：
J. E. Mark
中科院分区：
文献类型：
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作者：
J. E. Mark
类似橡胶的弹性意味着极高的变形能力和基本上完全的可恢复性，并且材料必须具有几个分子特征才能表现出它。它首先必须由长链分子组成，长链分子具有足够的灵活性和流动性，可以在响应施加的压力时从紧凑的空间安排切换到更扩展的空间安排。然而，这些聚合物链也必须通过交联连接成网络结构，以实现弹性可恢复性。然而，这种交联过程也带来了严重的缺点，最明显的是所产生的网络结构的不稳定性。例如，它们不溶于所有溶剂，因此需要放弃所有其他有用的表征技术，这些技术依赖于将材料放入溶液中。因此，在获取建立结构-属性关系所需的结构信息方面存在严重问题。由于已知弹性体的模量与交联密度直接相关，因此获得结构信息的最早尝试集中在交联密度上。这些方法在很大程度上依赖于监测交联反应，例如测量天然橡胶等二烯弹性体在经典硫化过程中所消耗的硫量。得到的结果不是很可靠，主要是因为副反应和缺乏交联中硫原子数量的信息。随着制造网络结构的更仔细控制的方法的出现，可以获得更可靠的信息。其中最重要的是使用只在末端有反应性的链，例如末端有羟基
Rubberlike elasticity implies extremely high de-formability with essentially complete recoverability, and there are several molecular features a material must have in order to exhibit it. 1-3 It must first consist of long-chain molecules, which have sufficient flexibility and mobility to switch from compact spatial arrangements to more extended ones in response to an imposed strain. These polymer chains, however, must also be interconnected with cross-links into a network structure, in order to achieve the elastic recoverability. This cross-linking procedure also brings about serious disadvantages, however, most notably the intractability of the resulting network structures. For example, they are insoluble in all solvents, thus requiring forfeiting all ofthe otherwise-useful characterization techniques which rely on putting a mate-rial into solution. As a result, there are serious problems ingetting the structural information re-quired in establishing structure—property relation-ships.The earliest attempts to obtain structural information focused on the cross-link density since the modu-lus of the elastomer was known to be directly related to it. The methods relied largely on trying to monitor the cross-linking reaction, for example by measuring the amount of sulfur used up in the classic vulcanization process of diene elastomers such as natural rubber. Results obtained were not very reliable, primarily because of side reactions and lack of information on the number of sulfur atoms in a cross-link. More reliable information became available with the advent of more carefully controlled ways to make network structures. The most important of these involves using chains that are reactive only at their ends, for example by having terminal hydroxyl