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 Aerogels是交联的材料，其体积密度非常低（小于100 kg/m3）和非常小的平均孔径（小于1纳米计）。 已提出将它们用作催化剂支撑（特定的表面积可以顶部1000 m2/g），高效的绝缘层和膜。 尽管它们具有引人入胜的物理和化学特性，但气凝胶的产生相对耗时，基于二氧化硅的版本（最普遍的类型）非常脆弱。 总而言之，气凝胶引起了人们的关注，因为较小的孔径和较高的孔密度可提供很高的特异性表面积，而较低的散装密度可以有效使用材料。 探索可以生产气凝胶并扩大可用物理特性范围的更有效的手段将是有趣且有用的。 许多研究人员通过相分离（通过温度，非溶剂添加，交联等诱导的微细胞有机聚合物在探索了微细胞有机聚合物，均未达到液体和超临界流体中的产生，但尚未实现毛孔和低泡沫密度的材料的产生（与Buldk Poligym相比，毛孔较小和低90％）的产生尚未达到。 鉴于此背景，PI的计划通过在稀有二氧化碳（CO2）溶液中通过非线性聚合产生低密度，微细胞材料，在该溶液中，通过使用高度二氧化碳 - 溶质溶质反应性预防聚合物的过早沉淀。 为了过多地降低稀释反应物浓度固有的低反应速率，它们计划产生前体，而反应性终端基团倾向于在二氧化碳中聚集，从而产生局部浓度明显高于标称的平均田间组成。 他们计划合成并表征与CO2-恐惧端组的CO2-湿含反应性低聚物，确认模型反应性低聚物与二氧化碳可混合，通过在31C上溶剂去除的CO2中的模型寡聚产生多孔材料，并随后在31C上进行溶剂去除，并探索了COR的识别量和与细胞微生物的变化，并且是在细胞中的识别量，并且在细胞中的体重构成，并探索了微生物的变化。二氧化碳 - 恐怖基团有所不同。 在二氧化碳中的交联聚氨酯的初步工作表明，在存在高压二氧化碳的情况下，它们确实可以设计一个交联的聚合物系统，该系统表现出单相（没有过量CO2相的肿胀网络）。 此外，使用液体中的反应性聚合物系统，它们表明，使用具有溶剂 - 球重复单元和溶剂粒性反应性终端组的前体通过聚集末端组来增强稀释溶液中的反应速率。