UNS: Time-lapse and Cure-on-Demand Polymerization using Autocatalytic Reactions

UNS：使用自催化反应进行延时和按需固化聚合

• 批准号: 1511653
• 负责人: John Pojman
• 金额: $ 30.95万
• 依托单位: Louisiana State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-08-01 至 2019-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1511653&HistoricalAwards=false
• 关键词: UNS; Time; lapse; Cure; Demand

PI: Pojman, JohnProposal #: 1510612Cure-on-demand polymerization is "getting what you want, when you want it." In other words, the polymerization only proceeds when you choose it to commence. Cyanoacrylates have a "cure-on-demand" property in that the polymerization occurs when exposed to moisture. This is also true for isocyanate adhesives such as Gorilla glue or silicone sealants. The problem with these systems is that the reaction is not completely under the control of the user. The ideal case is that the material does not react until an external stimulus is provided. Photopolymerizations exhibit this feature but they are limited to situations in which the light can penetrate the system. Therefore, photopolymerization is not useful for highly-filled systems or when a surface casts shadows that leave areas uncured. One possible was to accomplish cure-on-demand is by using frontal polymerization (FP), a polymerization process in which polymerization occurs directionally in a localized reaction zone. Thermal Frontal Polymerization results from the coupling of thermal transport and the dependence of the reaction rate of an exothermic polymerization. The essential criteria for FP is that the system must have an extremely low rate at the initial temperature but a high rate of reaction at the front temperature such that the rate of heat production exceeds the rate of heat loss. In other words, the system must react slowly or not at all at room temperature, have a large heat release and have a high energy of activation.Most adhesive and repair formulations require mixing two components, which then begin reacting, or require a lengthy time to complete the curing. The PI will study the urease-catalyzed hydrolysis of urea, which produces ammonia and carbon dioxide. If the initial pH is set to 4, the reaction proceeds autocatalytically because urease has optimal reactivity at pH 7. The reaction can be a clock reaction, with the pH abruptly rising after a programmable period of time or can support a propagating basic pH front. The PI plans to use this system to trigger the Michael addition of a thiol to an acrylate. He can create time-lapse polymerizations and isothermal frontal polymerization. With high concentration of urea, the high final pH results in a delayed hydrolysis that allows a programmable temporary adhesive or programmed degradation of a polymer particle. Using an organic system that autocatalytically produces piperidine, he plans to create nonaqueous time-lapse and frontal polymerization systems. This research could lead to commercial adhesives for consumer use. The urea-urease-thiol-acrylate systems could be used to create a "cure-on demand" bone repair material or a programmed drug release system. The time-lapse character of the system could be used to create a programmable adhesive and the degradable feature to create a programmed adhesive that will stop adhering after a determined time. Using Guar gum and borate, one may be able to create an additive for fracking that will allow the viscosity to increase only after the fluid is pumped deep into the reservoir.

按需聚合是“在你想要的时候得到你想要的”。换句话说，聚合只有在你选择开始时才会进行。氰基丙烯酸酯具有“按需固化”的特性，因为当暴露于潮湿时发生聚合。这也适用于异氰酸酯粘合剂，如大猩猩胶或硅酮密封剂。这些系统的问题在于，反应并不完全在用户的控制之下。理想的情况是，在提供外部刺激之前，材料不会发生反应。光聚合表现出这种特征，但它们仅限于光可以穿透系统的情况。因此，光聚合对于高度填充的系统或当表面产生阴影而留下未固化区域时是无用的。一种可能实现按需固化的方法是使用正面聚合（FP），这是一种聚合过程，聚合在局部反应区定向发生。热正面聚合是热传递耦合和放热聚合反应速率依赖的结果。FP的基本标准是，系统在初始温度下必须具有极低的速率，但在前端温度下必须具有高的反应速率，使得产热速率超过热损失率。换句话说，系统必须在室温下反应缓慢或根本不反应，有大的放热和高的活化能。大多数粘合剂和修复配方需要混合两种成分，然后开始反应，或者需要很长时间才能完成固化。PI将研究脲酶催化的尿素水解，这将产生氨和二氧化碳。如果初始pH设置为4，则反应进行自催化，因为脲酶在pH为7时具有最佳反应活性。反应可以是一个时钟反应，pH值在可编程的一段时间后突然上升，或者可以支持一个传播的碱性pH前沿。PI计划使用该系统触发Michael将硫醇添加到丙烯酸酯中。他可以制造延时聚合和等温正面聚合。在高浓度尿素的情况下，高最终pH值导致水解延迟，从而允许可编程的临时粘合剂或聚合物颗粒的可编程降解。利用一种能自动催化产生哌啶的有机系统，他计划创建非水延时聚合和正面聚合系统。这项研究可能会导致消费者使用的商业粘合剂。尿素-脲酶-巯基丙烯酸酯系统可用于制造“按需治疗”骨修复材料或程序化药物释放系统。该系统的延时特性可用于制造可编程粘合剂，而可降解特性可用于制造在确定时间后停止粘附的可编程粘合剂。利用瓜尔胶和硼酸盐，人们可以制造出一种用于压裂的添加剂，只有当流体被泵入储层深处时，才能增加粘度。