Time-Lapse and Cure-On-Demand Polymerizations for Adhesives, Wood Repair and Art

The goal of cure-on-demand polymerization is to create one-pot systems that have a long shelf live but will react rapidly when curing is desired. We use two approaches: coupling polymerizations with clock reactions and an approach called frontal polymerization in which a localized reaction zone propagates from the coupling of thermal transport and the Arrhenius dependence of the reaction rate of an exothermic polymerization. We demonstrate that frontal polymerization can be used to create a cure-on-demand putty for filling holes in wood, marble, and sheet rock. The putty has a months-to-years shelf life, is a one-pot formulation, can be applied leisurely and then cured rapidly with a flat heat source. Finally, we will explore current efforts to commercialize “3P QuickCure Clay” for the arts and crafts market

Immobilization adjusted clock reaction in the urea-urease-H+ reaction system

The bell-shaped reactivity-pH curve is the fundamental reason that the temporal programmable kinetic switch in clock reactions can be obtained in bio-competitive enzymatic reactions. In this work, urease was loaded on small resin particles through ionic binding. Experimental results reveal that the immobilization not only increased the stability of the enzyme and the reproducibility of the clock reaction, but also shifted the bell-shaped activity curve to lower pHs. The latter change enables the clock reaction to occur from an initial pH of 2.3, where the free enzyme had already lost its activity. Two mechanisms explain the influence of the immobilization on the clock reaction. Immobilization modified the pH sensitive functional groups on the enzyme, shifting the activity curve to a more acidic region, and reduced diffusion alters the enzyme dynamics

Deindividuation of Drivers: Is Everyone Else a Bad Driver?

Deindividuation is a psychological phenomenon that occurs when a given environment reduces the individuality or identifiability of a person. These environments may cause a psychological reduction in self-consciousness, potentially leading to violations of sociocultural norms (Festinger, Pepitone, & Newcomb, 1952; Singer, Brush, & Lublin, 1965). The present research sought to empirically test deindividuation theory among automobile drivers utilizing the anonymizing factor of observation. Participants (N = 31) used a driving simulator and were either in the observed condition or an unobserved condition. Analysis of driving data did not reveal significant results, however self-report data had some interesting trends. Though limited in scope, this research begins to shed light on deindividuation of drivers and may provide a foundation for future research

Effect of Interfacial Tension on Propagating Polymerization Fronts

This paper is devoted to the investigation of polymerization fronts converting a liquid monomer into a liquid polymer. We assume that the monomer and the polymer are immiscible and study the influence of the interfacial tension on the front stability. The mathematical model consists of the reaction-diffusion equations coupled with the Navier-Stokes equations through the convection terms. The jump conditions at the interface take into account the interfacial tension. Simple physical arguments show that the same temperature distribution could not lead to Marangoni instability for a nonreacting system. We fulfill a linear stability analysis and show that interaction of the chemical reaction and of the interfacial tension can lead to an instability that has another mechanism: the heat produced by the reaction decreases the interfacial tension and initiates the liquid motion. It brings more monomer to the reaction zone and increases even more the heat production. This feedback mechanism can lead to the instability if the frontal Marangoni number exceeds a critical value. (C) 2000 American Institute of Physics. [S1054-1500(00)01701-8]

Binary Frontal Polymerization: Velocity Dependence on Initial Composition

Frontal polymerization is a mode of polymerization in which a localized zone of reaction propagates through the coupling of thermal diffusion and the Arrhenius dependence of the reaction rate. The dependence of the front propagation velocity on the initial composition has been determined in initially miscible binary systems of a free-radically cured diacrylate and an amine- or cationically cured epoxy resin. A minimum of the velocity as a function of the monomer mole fraction is observed if the two polymerizations occur independently. Excellent agreement with an analytical description was found with the diacrylate and an amine-cured epoxy but not for a diacrylate and a cationically cured one because of the effect of HCl impurities on the peroxide

The Effect of Convection on a Propagating Front with a Liquid Product: Comparison of Theory and Experiments

This work is devoted to the investigation of propagating polymerization fronts converting a liquid monomer into a liquid polymer. We consider a simplified mathematical model which consists of the heat equation and equation for the depth of conversion for one-step chemical reaction and of the Navier-Stokes equations under the Boussinesq approximation. We fulfill the linear stability analysis of the stationary propagating front and find conditions of convective and thermal instabilities. We show that convection can occur not only for ascending fronts but also for descending fronts. Though in the latter case the exothermic chemical reaction heats the cold monomer from above, the instability appears and can be explained by the interaction of chemical reaction with hydrodynamics. Hydrodynamics changes also conditions of the thermal instability. The front propagating upwards becomes less stable than without convection, the front propagating downwards more stable. The theoretical results are compared with experiments. The experimentally measured stability boundary for polymerization of benzyl acrylate in dimethyl formamide is well approximated by the theoretical stability boundary. (C) 1998 American Institute of Physics

Numerical Modeling of Self-Propagating Polymerization Fronts: The Role of Kinetics on Front Stability

Frontal propagation of a highly exothermic polymerization reaction in a liquid is studied with the goal of developing a mathematical model of the process. As a model case we consider monomers such as methacrylic acid and n-butyl acrylate with peroxide initiators, although the model is not limited to these reactants and can be applied to any system with the similar basic polymerization mechanism. A three-step reaction mechanism, including initiation, propagation and termination steps, as well as a more simple one-step mechanism, were considered. For the one-step mechanism the loss of stability of propagating front was observed as a sequence of period doubling bifurcations of the front velocity. It was shown that the one-step model cannot account for less than 100% conversion and product inhomogeneities as a result of front instability, therefore the three-step mechanism was exploited. The phenomenon of superadiabatic combustion temperature was observed beyond the Hopf bifurcation point for both kinetic schemes and supported by the experimental measurements. One- and two-dimensional numerical simulations were performed to observe various planar and nonplanar periodic modes, and the results for different kinetic schemes were compared. It was found that stability of the frontal mode for a one-step reaction mechanism does not differ for 1-D and 2-D cases. For the three-step reaction mechanism 2-D solutions turned out to be more stable with respect to the appearance of nonplanar periodic modes than corresponding 1-D solutions. Higher Zeldovich numbers (i.e., higher effective activation energies or lower initial temperatures) are necessary for the existence of planar and nonplanar periodic modes in the 2-D reactor with walls than in the 1-D case

Period-doubling behavior in frontal polymerization of multifunctional acrylates

Front dynamics in the frontal polymerization of two multifunctional acrylate monomers, 1,6-hexanediol diacrylate (HDDA) and trimethylolpropane ethoxylate triacrylate (TMPTA), with Lupersol 231 [1,1-di(t-butylperoxy)-3,3,5-trimethylcyclohexane] as the initiator, are studied. In most frontal polymerization systems, the dynamics are associated with a planar front propagating through the sample. However, in some cases, front behavior can be altered: the front becomes nonplanar characterized by complex patterns like spin modes and pulsations. To determine how these periodic and aperiodic modes arise, reactant solutions consisting of HDDA diluted with diethyl phthalate (DEP) and TMPTA diluted with dimethyl sulfoxide (DMSO) were used in the study. In the study we reveal frontal behavior characteristic of period-doubling behavior, a doubling of spin heads that degenerate into an apparently chaotic mode. Also, a pulsating symmetric mode has been observed. These observations have a striking similarity to observations made in studies of self-propagating high-temperature synthesis (SHS) in which the addition of an inert diluent afforded a rich variety of dynamical behavior. The degree of cross-linking has also been found to be a bifurcation parameter. The energy of activation of multifunctional acrylate polymerization is a strong function of the degree of polymerization. By adding a monoacrylate (benzyl acrylate: BzAc), such that the front temperature was invariant, we observed a period-doubling bifurcation sequence through changes in the energy of activation, which has not been previously reported. © 1999 American Institute of Physics

Thermal frontal polymerization with a thermally released redox catalyst

We studied thermal frontal polymerization using a redox system in an attempt to lower the temperature of the frontally polymerizable system while increasing the front velocity so as to obtain a self-sustaining front in a thinner layer than without the redox components. A cobalt-containing polymer with a melting point of 63 °C (Intelimer 6050X11) and cumene hydroperoxide were used with a triacrylate. The use of the Intelimer decreased the front velocity but allowed fronts to propagate in thinner layers and with more filler while still having a pot life of days. Nonplanar modes of propagation occurred. Fronts propagated faster when 6-O-palmitoyl-L-ascorbic acid was used as a reductant. Interestingly, fronts were also faster with the reductant even without the Intelimer if kaolin clay was the filler; however, the pot life was significantly reduced. © 2012 Wiley Periodicals, Inc