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

提出了聚合物体积模量的基础研究，目的是确定它如何依赖于化学结构。体积模量主要来自分子内弛豫，而剪切模量取决于分子间（或节段间）弛豫的假设将使用模型系统进行测试，其中b弛豫的强度可以通过改变，例如，弹性、交联密度或转换来系统地改变。还将比较随时间变化的体积模量与随时间变化的剪切模量，以解决这些粘弹性特性中的色散是否涉及相似的弛豫时间谱并来自相同的分子起源的问题。将研究三种模型系统，包括i)聚甲基丙烯酸甲酯（聚甲基丙烯酸甲酯）作为弹性函数，ii)基于六亚乙烯二异氰酸酯和异氰酸己酯的杂环网络作为交联密度的函数，以及iii)二氰酸酯/聚氰尿酸酯热固性材料作为交联密度和转化的函数。测量将使用可加压汞膨胀计进行，该膨胀计是专门为确定应力和应变控制模式下随时间变化的体积模量和体积顺应性而建造的。仪器中的温度控制稳定到优于0.01 K，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，并按照常规方案在玻璃中进行测量。时间-温度叠加将用于构造主曲线，从中可以得到弛豫或延迟时间谱。模型化合物的主曲线和弛豫（或延迟）时间谱将在给定的族中进行比较，以确定弹性、交联密度和转换对体积模量的影响，此外还将与剪切模量的数据进行比较。热固性系统的结果还将用于测试基于时间-温度和时间-转换叠加概念的一般模型是否能够定量描述反应系统中体积模量的时间、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良好的培训，也将包括一名本科生研究员。将通过在德克萨斯州和西南地区的女子和少数民族学院的特别招生工作，努力将妇女和代表性不足的少数民族纳入其中。将尝试包括参加TTU麦克奈尔学者计划的第一代大学生（通常是少数民族）的本科生。除了为参与该项目的学生提供优秀的培训外，这项工作还将通过在国家论坛上发表和在会议和档案期刊上发表的方式在科学界广泛传播。项目的成果也将在可行的范围内纳入PI教授的本科和研究生课程。

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.