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

PI：Pojman，JohnProposal#：1510612按需固化聚合就是“在你想要的时候得到你想要的东西。”换句话说，只有当您选择开始聚合时，聚合才会进行。氰基丙烯酸酯有一种“按需固化”的特性，即聚合反应在受潮时发生。异氰酸酯胶粘剂也是如此，如大猩猩胶水或硅酮密封胶。这些系统的问题是，反应并不完全在用户的控制之下。最理想的情况是，在提供外部刺激之前，材料不会发生反应。光聚合反应表现出这一特征，但它们仅限于光线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曲面投射阴影导致区域未固化时没有用处。一种可能是通过使用正面聚合(FP)来实现按需固化，FP是一种聚合过程，其中聚合在局部反应区进行定向聚合。热锋聚合是放热聚合过程中热传递和反应速率的耦合作用的结果。FP的基本标准是，系统在初始温度下必须具有极低的反应速率，但在前沿温度必须具有高的反应速率，以使产热速率超过热损失速率。换句话说，体系必须在室温下反应缓慢或根本不反应，具有较大的热释放和较高的活化能。大多数胶粘剂和修复配方需要混合两种成分，然后开始反应，或需要很长时间才能完成固化。PI将研究尿素酶催化的尿素水解，尿素产生氨和二氧化碳。如果初始pH设置为4，则反应以自动催化方式进行，因为尿素酶在pH为7时具有最佳的反应活性。该反应可以是时钟反应，在可编程的一段时间后，pH突然上升，或者可以支持一个不断增长的碱性pH前沿。PI计划使用这个系统触发Michael在丙烯酸酯中加成硫醇。他可以创造延时聚合和等温正面聚合。在尿素浓度较高的情况下，较高的最终pH值会导致延迟的水解，从而允许可编程的临时粘合剂或聚合物颗粒的程序化降解。他计划利用自动催化生产哌啶的有机系统，创造非水的延时聚合系统和正面聚合系统。这项研究可能会导致消费者使用的商业粘合剂。尿素-尿素酶-硫醇-丙烯酸酯体系可以用来创造一种按需固化的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创建可编程粘合剂，而可降解特征可用于创建将在确定时间后停止粘合的程序化粘合剂。使用瓜尔胶和硼酸盐，人们可能能够创造出一种用于水力压裂的添加剂，这种添加剂只有在流体被泵入油层深处后才能增加粘度。

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.