Generation of Microcellular Materials via Polymerization in Carbon Dioxide

通过二氧化碳聚合生成微孔材料

• 批准号: 9870925
• 负责人: Eric Beckman
• 金额: $ 26.24万
• 依托单位: University of Pittsburgh
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1998
• 资助国家: 美国
• 起止时间: 1998-09-01 至 2001-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9870925&HistoricalAwards=false
• 关键词: Generation; Microcellular; Materials; via; Polymerization

Abstract - Beckman - 9870925 Aerogels are crosslinked materials which exhibit both very low bulk density (less than 100 kg/m3) and very small average pore size (less than 1 nanometer). They have been proposed for use as a catalyst supports (specific surface area can top 1000 m2/g), highly efficient insulation, and as membranes. While they exhibit fascinating physical and chemical properties, aerogels are relatively time-consuming to produce and the silica-based versions (the most prevalent type) are quite brittle. In summary, aerogels are of interest because the small pore size and high pore density gives very high specific surface area, while the low bulk density allows for efficient use of materials. It would be interesting and useful to explore more efficient means by which aerogels can be produced, and to expand the range of physical properties available to them. A number of researchers have explored generation of microcellular organic polymers via phase separation (induced by temperature, non-solvent addition, crosslinking, etc.) in both liquids and supercritical fluids, yet production of materials with both small pores and low foam density (reduction of over 90% compared to the bulk polymer) has not been achieved. Given this background, the PI's plan to generate low density, microcellular materials via a non-linear polymerization in a dilute carbon dioxide (CO2) solution where premature precipitation of the polymer is prevented via the use of the highly CO2 -soluble reactive precursors. To overvcome the low rate of reaction inherent to dilute reactant concentration, they plan to generate precursors where the reactive end groups tend to aggregate in carbon dioxide, thus generating local concentrations significantly higher than the nominal, mean field composition. They plan to synthesize and characterize CO2-philic reactive oligomers with CO2-phobic end groups, confirm that the model reactive oligomers are miscible with carbon dioxide, generate porous materials via reaction of model oligomers in CO2 followed by solvent removal above 31C, and explore changes in cellular microstructure as the molecular weight between crosslinks, and the identity of the CO2-philic and CO2-phobic groups is varied. Preliminary work with crosslinked polyurethanes in carbon dioxide has shown that they can indeed design a crosslinked polymer system that exhibits a single phase (swollen network without without an excess CO2 phase) in the presence of high pressure CO2. Further, using reactive polymer systems in liquids, they have shown that use of precursors with solvent-philic repeat units and solvent-phobic reactive end groups enhances the rate of reaction in dilute solution through aggregation of end groups.

摘要 - Beckman - 9870925 气凝胶是交联材料，具有非常低的堆积密度（小于 100 kg/m3）和非常小的平均孔径（小于 1 纳米）。 它们被建议用作催化剂载体（比表面积可达 1000 m2/g）、高效绝缘体和膜。 虽然气凝胶表现出令人着迷的物理和化学特性，但气凝胶的生产相对耗时，而且基于二氧化硅的版本（最普遍的类型）非常脆。 总之，气凝胶之所以令人感兴趣，是因为其小孔径和高孔密度提供了非常高的比表面积，而低堆积密度允许材料的有效利用。 探索更有效的气凝胶生产方法并扩大其可用的物理性能范围将是有趣且有用的。 许多研究人员探索了在液体和超临界流体中通过相分离（由温度、非溶剂添加、交联等引起）生成微孔有机聚合物，但尚未实现同时具有小孔和低泡沫密度（与本体聚合物相比减少90％以上）的材料。 鉴于此背景，PI 计划通过在稀二氧化碳 (CO2) 溶液中进行非线性聚合来生成低密度微孔材料，其中通过使用高度溶解 CO2 的反应前体来防止聚合物过早沉淀。 为了克服稀释反应物浓度所固有的低反应速率，他们计划生成反应性端基倾向于在二氧化碳中聚集的前体，从而产生显着高于标称平均场组成的局部浓度。 他们计划合成和表征具有疏CO2端基的亲CO2反应性低聚物，确认模型反应性低聚物与二氧化碳混溶，通过模型低聚物在CO2中反应生成多孔材料，然后在31℃以上除去溶剂，并探索细胞微观结构作为交联之间的分子量的变化，以及亲CO2和亲CO2的特性。 厌恶二氧化碳的群体多种多样。 对二氧化碳中交联聚氨酯的初步研究表明，他们确实可以设计出一种交联聚合物体系，该体系在高压二氧化碳存在下表现出单相（膨胀网络，没有过量的二氧化碳相）。 此外，通过在液体中使用反应性聚合物体系，他们发现使用具有亲溶剂重复单元和疏溶剂反应性端基的前体可以通过端基聚集来提高稀溶液中的反应速率。