Proposal #: 1510612 Cure-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.
