Molecular Design of Novel Polymer Materials Based onBottlebrush Macromolecules

聚合技术的重大进步使得合成具有精确控制的分子尺寸和明确形状的超支化结构成为可能。高支化大分子的一个最独特的例子是分子瓶刷，它由许多聚合物侧链稠密地接枝到线性链(主链)上组成。浓密接枝的分支之间强烈的空间排斥会影响硬度，确保单个瓶刷的高度延伸构象，并减少浓缩液和熔体中分子之间的重叠。这些显著的特点为制造瓶刷型材料提供了途径，这些材料具有不同于由线性聚合物组成的传统材料的物理性能。该项目的目标是开发瓶刷聚合物的分析和数值模型，为设计新型超软和超韧材料提供指导。通过分子的解缠可以大大提高聚合物的柔软性。在熔体中，瓶刷结构促进解缠，导致异常的流变性，即平台模数比通常在线性链状熔体中观察到的低2-3个数量级。我们建议研究交联瓶刷的结构与所得弹性体的柔软度之间的关系。研究表明，通过合成不同刚性的网络可以改善聚合物凝胶的性能。瓶刷的硬度可以通过改变其厚度来控制。我们建议研究由不同刚度的交联瓶刷组成的互穿网络的性质。我们的方法是使用分子动力学和蒙特卡罗模拟技术以及标度和平均场概念的组合研究，以发展对瓶刷熔体和网络的理论理解。

Significant progress in polymerization techniques allows synthesis of hyperbranched architectures with precisely controlled molecular dimensions and well-defined shapes. One of the most distinctive examples of highly-branched macromolecules are molecular bottlebrushes composed of many polymer sidechains densely grafted to a linear chain (backbone). Strong steric repulsion between densely grafted branches affects stiffness and ensures highly extended conformations of individual bottlebrushes and reduces overlap between molecules in concentrated solutions and melts. These remarkable features provide access to fabrication of bottlebrush based materials with physical properties that are distinct from conventional materials composed of linear polymers. The goal of this project is to develop analytical and numerical models of bottlebrush polymers that will provide guidelines for designing novel super-soft and super-tough materials. Softness of polymers can be greatly enhanced by disentanglement of molecules. In melts, bottlebrush architecture promotes disentanglement resulting in unusual rheological properties, i.e. plateau modulus is 2-3 orders of magnitude lower than typically observed in linear chain melts. We propose to study the relationship between architecture of cross-linked bottlebrushes and softness of the resulting elastomer. It has been demonstrated that properties of polymer gels can be improved by synthesizing networks with different stiffness. Stiffness of bottlebrushes can be controlled by varying their thickness. We propose to study properties of interpenetrating networks composed of cross-linked bottlebrushes with different stiffness. Our approach is a combined study using molecular dynamics and Monte-Carlo simulation techniques as well as scaling and mean-field concepts to develop a theoretical understanding of bottlebrush melts and networks.