Properties of post‐cured siloxane networks
Properties of post‐cured siloxane networks
复制标题
后固化硅氧烷网络的特性
DOI：
--
复制
发表时间：
1989
期刊：
影响因子：
--
通讯作者：
X. Quan
中科院分区：
文献类型：
--
作者：
X. Quan
乙烯基加成固化的硅氧烷网络的后固化可由于过量氢化硅的存在而发生。这些基团的反应导致交联密度增加，特别是在升高的温度下，可以通过用氨气处理来延迟或通过暴露于乙烯气体来消除。在后固化行为和凝胶化过程之间存在有趣的对应关系。在这两种情况下，观察到两种固化方案。对于低程度的反应，链的流动性是高的，即使后固化实验是在已经胶凝的样品上进行的，并且固化是由反应动力学控制的，而不是由反应物的扩散控制的。在高度固化或后固化时，两种情况都表现为交联网络以降低反应物之间相互作用的可能性，并且固化是扩散控制的。然而，后固化凝胶不表现出理想的网络行为，因为在后固化期间形成的最后交联对物理性质的影响比最初形成的交联大得多。这可能是由于在后固化期间形成的交联之间的链长的双峰分布。
Post-curing of vinyl-addition cured siloxane networks can take place due to the presence of excess silicon hydride. The reaction of these groups, which leads to increased crosslink density especially at elevated temperatures, can be retarded by treatment with ammonia gas or eliminated by exposure to ethylene gas. There is an interesting correspondence between post-curing behavior and the gelation process. In both cases, two curing regimes are observed. For low extents of reaction, the mobility of chains is high, even though the post-curing experiment is performed on samples which have already gelled, and the cure is controlled by reaction kinetics, not by the diffusion of the reactants. At high degrees of cure or post-cure, both cases behave as crosslinked networks to reduce the probability of interaction between reactants, and the cure is diffusion-controlled. However, the post-cured gels do not exhibit ideal network behavior since the last crosslinks formed during post-curing have a much greater effect on the physical properties than those formed initially. This may be due to the bimodal distribution of chain lengths between crosslinks that is formed during post-curing.