Controlled Crystallization in Novel Block Copolymers

该奖项将研究嵌段共聚物直接结晶聚合物的能力。具有无缺陷结晶嵌段的两嵌段和三嵌段共聚物将检验晶态-非晶态嵌段共聚物中链折叠的平衡度的预测，这与均聚物通常表现出的动力学诱导的链折叠形成鲜明对比。通过晶态和非晶态熔块长度或添加非挥发性稀释剂来控制微晶厚度将产生熔融范围窄且可调的材料。具有可结晶端块的稀释三块将代表一种新型的热塑性弹性体凝胶，具有低模数和良好的尺寸稳定性，是大变形执行器的理想候选者。在这项工作的第二个方面，通过开环歧化和阴离子聚合合成的新型嵌段共聚物将解决线型和短支化聚乙烯之间长期存在的共晶问题。这些聚合物将包含线性聚乙烯、PE和聚(乙烯-共丁烯)PEB的嵌段，由可变长度的无定形嵌段隔开。当这种“连接物”运行时间很短时，聚合物本质上是PE-PEB双嵌段，有望显示出有趣的晶体异质性。当连接体的长度为中等长度(足够长到与其他嵌段微相分离)时，PE和PEB嵌段被拴在无定形结构域上，有利于PE/PEB共结晶。最后，当连接体是主要成分时，混合的PE+PEB链将在离散的微区内分离，在那里它们只有在深度过冷和广泛的共晶时才会结晶。这为制备PE/PEB共晶体提供了一条途径，以便系统地研究其结构和性能。聚合物的结晶对其性能有着深远的影响，并为其许多应用奠定了基础。在从纳米到微米的尺寸范围内，典型聚合物的结晶结构在很大程度上取决于结晶方法的细节。在这项工作中，我们建议通过在合成过程中内置到聚合物中的分子特征--所谓的“嵌段结构”--来强有力地控制结晶过程，从而控制结构。拟议的工作将为两名研究生和大约六名本科生提供综合研究和教育经验，他们将能够在内部和外部传播他们的工作成果。国际和平研究所和研究生将继续积极工作，通过开发新的教材和教师培训，支持默瑟县的K-6科学教育。

This award will investigate the ability of block copolymers to direct polymer crystallization. Diblock and triblock copolymers with defect-free crystallizable blocks will test the prediction of an equilibrium degree of chain folding in crystalline-amorphous block copolymers, which contrasts sharply with the kinetically-induced chain folding typically exhibited by homopolymers. Control of crystallite thickness through crystalline and amorphous block lengths or the addition of a nonvolatile diluent will yield materials with narrow and tunable melting ranges. Diluted triblocks having crystallizable endblocks will represent a new type of thermoplastic elastomer gel with low modulus and good dimensional stability-desirable candidates for large-deformation actuators. In the second aspect of this work, novel block copolymers synthesized by combining ring-opening metathesis and anionic polymerizations will address the long-standing issue of cocrystallization between linear and short-branched polyethylenes. These polymers will contain blocks of linear polyethylene, PE, and poly(ethylene-co-butene), PEB, separated by an amorphous block of variable length. When this "linker" run is short, the polymers are essentially PE-PEB diblocks, which are expected to show an interesting crystal heterogeneity. When the linker run is of medium length (long enough to microphase-separate from the other blocks), then the PE and PEB blocks are tethered to amorphous domains, favoring PE/PEB cocrystallization. Finally, when the linker run is the majority component, the mixed PE + PEB chains will be segregated within discrete microdomains, where they will crystallize only at deep undercoolings and with extensive cocrystallization. This provides a route to the preparation of PE/PEB cocrystals for systematic examination of their structure and properties. Crystallization of polymers has a profound impact on their properties, and underpins many of their applications. At size scales ranging from nanometers to microns, a typical polymer's crystalline structure depends strongly upon details of method used to crystallize it. In this work, we propose to robustly control the crystallization process, and hence the structure, through molecular features built into the polymers-the so-called "block architecture"-during synthesis. The proposed work will provide an integrated research and educational experience for two graduate students and approximately six undergraduates, who will be able to disseminate results from their work both internally and externally. The PI and the graduate students will continue their active work in support of K-6 science education in Mercer County, both through the development of new educational materials and through teacher training.