Dynamics of Highly Constrained Polymer Chains

9910386Fuller本研究旨在了解支化结构或部分结晶度限制的高分子链的静态和动态性质。一个具体的目标是研究长链支化和低结晶度如何影响聚合物的流变性和物理性质。这些材料的流变学要比线性无定形链复杂得多，在线性无定形链中，旋转是控制取向松弛的主要机制。该实验方法将结合合成、光学双折射和红外二向色性技术来研究约束和部分约束高分子链的组分弛豫动力学。对于长链支化聚合物，我们计划解决为什么以及如何长链支化对受应变影响的高分子链起到分子约束作用。进一步的目标是研究链受低结晶度限制的半晶嵌段聚合物的松弛动力学。在较窄的相对分子质量范围内，长链支化聚乙烯代表了一种既具有优异的物理性能又具有良好的加工特性的新的物质组成。这些材料最近作为一类新的聚乙烯薄膜大规模推向市场。这种优异的性能组合的分子起源尚不清楚；更好的理解可能会导致合理的策略，以改善这一重要类别的商品塑料的性能和加工特性。

9910386FullerThe studies in this seek to understand the static and dynamic properties of polymer chains constrained by branched architectures or partial crystallinity. A specific objective is to investigate how long-chain branching and low levels of crystallinity influence the rheological and physical properties of polymers. The rheology of these materials is much more complicated than exhibited by linear, amorphous chains where reptation is the principal mechanism governing the relaxation of orientation. The experimental approach will combine synthesis with optical birefringence and IR dichroism techniques to investigate the component relaxation dynamics of constrained and partially-constrained polymer chains. For long-chain branched polymers we plan to address why and how a long-chain branch acts as a molecular constraint on polymer chains subjected to strains. A further objective is to investigate the relaxation dynamics of semi-crystalline block polymers whose chains are constrained by low levels of crystallinity.Narrow molecular weight, long-chain branched polyethylenes represent a new composition of matter that have both excellent physical properties and good processing characteristics. These materials have recently been introduced into the market on a large scale as a new class of polyethylene films. The molecular origins of this excellent combination of properties are poorly understood; a better understanding might lead to rational strategies to improve the properties and processing characteristics of this important class of commodity plastics.