Research Initiation Award: Intermolecular Reactions in Flexible Polymer Solutions

大量的工业过程涉及连接到高相对分子质量柔性聚合物上的反应基团之间的化学反应。例子包括：(1)通过自由基聚合和缩合聚合生产直链；(2)通过化学或通过高能辐射作用使长聚合物链交联来制造橡胶弹性体和凝胶；以及(3)生产高强度复合材料的反应加工方法。虽然在这些情况下也会发生小分子反应，但主要的困难在于大分子反应，因为活性物种满足的能力取决于它们所连接的聚合物的动态和静态性质。这项研究的目的是通过计算两个长的未支化的聚合物的反应速率来确定这些过程的基本机制，当两个长的未支化的聚合物各自携带一个活性基团位于它们各自的主链上的某个地方时，如果这两个基团被带到彼此之间的一定距离(捕获半径)内，它们将在单位时间内以一定的概率进行反应。两个聚合物线圈必须在空间中扩散，然后显著地相互穿透，然后才能进行反应(典型的聚合物线圈和捕获半径尺寸分别为300埃和10埃)。PI正在计划发展一个关于高分子量聚合物在溶液中反应速率的分子理论，并预测聚合物在稀溶液、半稀溶液(其中聚合物强烈重叠，导致一些浓度效应)和稠密溶液(熔体)中的反应速率作为聚合物相对分子质量和浓度的函数。反应速率取决于浓度，因为如果聚合物在单体背景中稀释，线圈在空间中扩散相对较快，但在近距离相遇时相互强烈排斥，而如果链密集(在熔体中)和长，这种排斥被屏蔽，但扩散因缠结而急剧减慢。这项研究的另一个预期结果是，它将增加对加入不可逆反应的平衡体系的性质的了解(聚合物反应是非平衡热体系的一个例子)。

A large number of industrial processes involve chemical reactions between reactive groups which are attached to high molecular weight flexible polymers. Examples includes: (1) the production of linear chains by radical and condensation polymerization; (2) the manufacture of rubber elastomers and gels by cross-linking long polymer chains either chemically or through the action of high energy radiation; and (3) reactive processing methods producing high strength composites. While small molecule reactions also occur in these situations, the main difficulty concerns the macromolecular reactions since the ability of reactive species to meet is determined by the dynamical and static properties of the polymers to which they are attached. The objective of this research is to determine a fundamental mechanism for these processes by calculating reaction rates for the case when two long unbranched polymers each carrying one active group located somewhere along their respective backbones, such that if ever the two groups are brought to within a certain distance of one another ( the "capture radius") they will react with certain probability per unit time. The two polymer coils must diffuse through space and then penetrate one another significantly before reaction may proceed (typical polymer coil and capture radius dimensions are 300 Angstroms and 10 Angstroms respectively). The PI is planning to develop a molecular theory of reaction rates between high molecular weight polymers in solution and to predict reactions rates as a function of polymer molecular weight and concentration for polymers in dilute, semi-dilute (where polymers overlap strongly giving rise to some concentration effects) and dense solutions (melt). The reaction rates are dependent on concentration because if the polymers are dilute in a monomeric background, the coils diffuse relatively quickly through space but strongly repel one another on close encounter, while if the chains are dense (in a melt) and long, such repulsions are screened but diffusion is drastically slowed down by entanglements. An additional outcome expected of this research is that it will increase knowledge about the nature of an equilibrium system to which irreversible reactions are added (polymer reactions are an example of a non-equilibrium thermal system).