Rheology and photo-cross-linking of thiol-ene polymers
Rheology and photo-cross-linking of thiol-ene polymers
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DOI：
10.1021/ma960383e
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发表时间：
1996-07-29
期刊：
影响因子：
5.5
通讯作者：
Khan, SA
中科院分区：
文献类型：
--
作者：
Chiou, BS;English, RJ;Khan, SA
动态流变学技术，傅里叶变换力学光谱（FTMS），被用来监测在真实的时间演变的流变学性质在两个硫醇-烯系统的紫外交联。这些体系包含三官能硫醇（正丙烷三（2-巯基乙酸酯））与三官能烯丙基单体（异氰脲酸三烯丙酯）和四官能硫醇（季戊四醇四（2-巯基乙酸酯））与相同的烯丙基单体。FTMS，结合专门设计的石英板，提供了一种原位方法来阐明这些系统的光引发聚合反应的温度和单体功能的影响。发现在所研究的温度范围（25-50 ° C）内，四官能硫醇体系以比三官能硫醇体系更快的速率交联。此外，提高温度增加了两个系统的交联速率。应用Winter-Chambon标准来确定凝胶点和表征材料在其凝胶点的两个参数，即凝胶刚度S和松弛指数n。发现三官能硫醇体系的凝胶刚度更大，这与从凝胶化的Flory-Stockmayer理论计算的更高的转化率值一致。松弛指数为0.80和0.81-0.82的三和四官能硫醇系统，分别确定，表明类似的分形结构在凝胶点。这些弛豫指数也是不变的温度范围内研究，表明交联机制保持不变的温度。从凝胶时间的温度依赖性，分别为6.6和14千卡/摩尔的表观活化能计算为三和四官能硫醇系统。
A dynamic rheological technique, Fourier transform mechanical spectroscopy (FTMS), was used to monitor in real time the evolving rheological properties during UV cross-linking of two thiol-ene systems. These systems comprised a trifunctional thiol (trimethylolpropane tris(2-mercaptoacetate)) together with a trifunctional allyl monomer (triallyl isocyanurate) and a tetrafunctional thiol (pentaerythritol tetrakis(2-mercaptoacetate)) with the same allyl monomer. FTMS, in conjunction with specially designed quartz plates, provided an in situ method to elucidate the effects of temperature and monomer functionality on the photoinitiated polymerization of these systems. It was found that the tetrafunctional thiol system cross-linked at a faster rate than the trifunctional thiol system over the temperature range (25-50 degrees C) studied. Moreover, increasing the temperature increased the cross-linking rates for both systems. The Winter-Chambon criterion was applied to determine the gel point and the two parameters which characterize the material at its gel point, the gel stiffness, S, and the relaxation exponent, n. The gel stiffness was found to be greater for the trifunctional thiol system, which was consistent with the higher value of conversion calculated fi om the Flory-Stockmayer theory of gelation. Relaxation exponents of 0.80 and 0.81-0.82 were determined for the tri- and tetrafunctional thiol systems, respectively, indicating similar fractal structures at the gel point. These relaxation exponents were also invariant over the temperature ranges studied, suggesting that the cross-linking mechanisms remained unchanged with temperature. From the temperature dependence of the gel times, apparent activation energies of 6.6 and 14 kcal/mol were calculated for the tri- and tetrafunctional thiol systems, respectively.