Molecular Design of Novel Polymer Materials Based onBottlebrush Macromolecules

聚合技术的重大进展使合成具有精确控制分子尺寸和良好定义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由许多聚合物侧链密集接枝到线性链（主链）上的分子瓶刷。密集接枝之间的强空间排斥力影响刚度，确保单个瓶刷的高度延伸构象，并减少浓缩溶液和熔体中分子之间的重叠。这些显著的特点为制造具有物理特性的瓶刷基材料提供了途径，这些材料与由线性聚合物组成的传统材料不同。该项目的目标是开发瓶刷聚合物的分析和数值模型，为设计新型超软超韧材料提供指导。聚合物的柔软度可以通过分子的解缠而大大提高。在熔体中，瓶刷结构促进解缠，导致不寻常的流变特性，即平台模量比线性链熔体中通常观察到的低2-3个数量级。我们建议研究交联瓶刷的结构与产生的弹性体的柔软度之间的关系。研究表明，通过合成不同刚度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。我们提出研究由不同刚度的交联瓶刷组成的互穿网络的性能。我们的方法是结合分子动力学和蒙特卡罗模拟技术以及缩放和平均场概念的研究，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.