A Fundamental Study of the Bulk Modulus in Polymers and its Dependence on Chemical Structure

对聚合物的体积弹性系数进行了基础性研究，目的是确定其与化学结构的关系。体弹性模量主要来自分子内松弛，而剪切弹性模量取决于分子间(或链段间)松弛的假设将使用模型系统进行验证，在该模型系统中，b松弛的强度可以通过改变例如规整性、交联剂密度或转化率来系统地改变。为了解决这些粘弹性性质中的色散是否包含相似的松弛时间谱和来自相同的分子起源的问题，还将对随时间变化的体积弹性系数和随时间变化的剪切弹性系数进行比较。三个模型体系将被研究，包括i)聚甲基丙烯酸甲酯作为规整度的函数，ii)基于六亚甲基二异氰酸酯和己基异氰酸酯的杂环网络作为交联度的函数，以及iii)二氰酸酯/多氰尿酸酯热固性材料作为交联度和转化率的函数。测量将使用可加压汞膨胀仪进行，该膨胀仪是专门为分别在应力控制和应变控制模式下确定随时间变化的体积弹性系数和体积柔量而建造的。仪器中的温度控制稳定在0.01K以上，测量温度将覆盖从远低于玻璃温度到高于玻璃温度的广泛温度范围，并按照传统协议在玻璃中进行测量。采用时间-温度叠加的方法构建主曲线，由主曲线可以得到松弛或延迟时间谱。模型化合物的主曲线和松弛(或延迟)时间谱将在给定的家族中进行比较，以确定规整性、交联度和转换率对体积弹性系数的影响，此外还将与剪切弹性系数的数据进行比较。热固性体系的结果也将被用来检验基于时间-温度和时间-转换叠加概念的一般模型是否能够定量地描述反应体系中体积弹性系数的时间、温度和转换依赖关系。拟议的研究计划将为参与该项目的研究生提供出色的培训，并将涉及一名本科生研究人员。将努力通过在得克萨斯州和西南部地区的妇女和少数族裔大学进行特别招生工作，吸纳妇女和代表性不足的少数族裔。将尝试将参加TTU McNair奖学金计划的本科生包括在内，该计划面向第一代大学生(通常是少数民族)。除了为参与该计划的学生提供出色的培训外，这项工作还将在科学界广泛传播，方法是在国家论坛上发表报告，并在会议记录和档案期刊上发表文章。该项目的成果也将在可行的范围内纳入国际学校教授的本科生和研究生课程。

A fundamental study of the bulk modulus of polymers is proposed with the aim of determining how it depends on chemical structure. The hypothesis that the bulk modulus arises primarily from intramolecular relaxations while the shear modulus depends on intermolecular (or intersegmental) relaxations will be tested using model systems in which the strength of the b-relaxation can be systematically varied by changing, for example, tacticity, crosslink density, or conversion. Comparison of the time-dependent bulk modulus with the time-dependent shear modulus will also be made in order to resolve the issue of whether or not the dispersions in these viscoelastic properties involve a similar spectrum of relaxation times and arise from the same molecular origins. Three model systems will be investigated, including i) poly(methyl methacrylate) as a function of tacticity, ii) a heterocyclic network based on hexamethylene diisocyanate and hexyl isocyanate as a function of crosslink density, and iii) a dicyanate ester/polycyanurate thermosetting material as a function of crosslink density and conversion. The measurements will be made using a pressurizable mercury dilatometer which has been built specifically for determination of the time-dependent bulk modulus and bulk compliance in stress- and strain-controlled modes, respectively. Temperature control in the instrument is stable to better than 0.01 K, and measurement temperatures will cover a broad temperature range from far below to above the glass temperature with measurements made in the glass following conventional protocol. Time-temperature superposition will be used to construct master curves from which the relaxation or retardation time spectra can be obtained. The master curves and relaxation (or retardation) time spectra for the model compounds will be compared in a given family to determine the effects of tacticity, crosslink density, and conversion on the bulk modulus, in addition to being compared to the data from the shear modulus. The results for the thermosetting system will also be used to test whether a general model based on concepts of time-temperature and time-conversion superposition is able to quantitatively describe the time, temperature, and conversion dependence of the bulk modulus in a reacting system. The proposed research program will provide excellent training for the graduate student involved in the project and will also involve an undergraduate researcher. Efforts will be made to include women and underrepresented minorities through special recruiting efforts at women's and minority colleges in the Texas and southwest region. An attempt will be made to include undergraduate students who participate in the TTU McNair Scholars Program for first generation college students (often minorities). In addition to providing excellent training for the students involved in the program, the work will also be broadly disseminated within the scientific community by presentation at national forums and publication in both proceedings conferences and archival journals. The results of the project will also be incorporated to the extent feasible in both undergraduate and graduate courses taught by the PI.