Propagation polymerization front

J. Szalay, I. Nagy, I. Barkai, and M. Zsuga, Conductive composites prepared via a propagating polymerization front. Die Ang. Makr. Chem., 236 (1996), pp. 97-109. 

Figure 1. Schematic diagram showing changes in properties across a propagating polymerization front. (Courtesy of Paul Ronney.)...

Since not all RNA molecules replicate equally well, faster mutants gradually take over. At each mutation, the front propagates faster. Evolution can be directly observed in a test tube. Propagating polymerization fronts of synthetic polymers may be useful for making new materials, and they are interesting because of the rich array of nonlinear phenomena they show, with pulsations, convection, and spinning fronts. Finally, we will consider photopolymerization systems that exhibit spatial pattern formation on the micron scale, which can be used to control the macroscopic properties. 

Nagy, I. P. Sike, L. Pojman, J. A. 1995b. Thermochromic Composite Prepared via a Propagating Polymerization Front, J. Am. Chem. Soc. 117, 3611-3612. 

Figure 4 shows the propagating polymerization front with the liquid motion caused by the hydrodynamical instability under the front. 

Texier-Picard, R., Pojman, ).A., and Volpert, V.A. (2000) Effect of interfacial tension on propagating polymerization fronts. Chaos, 10, 224 230. 

Masere, J., Stewart, F., Meehan, T., and Pojman, J.A. (1999) Period-doubling behavior in propagating polymerization fronts of multifunctional acrylates. Chaos, 9, 315-322. 

Within the framework of this approach, a series of studies conducted by Eniko-lopian, Davtyan et al.132-139 dealt with the laws underlying radical polymerization and poly condensation in adiabatic conditions and in conditions favoring a propagating reaction front. 

Finally, we derive an expression for the propagation velocity of the polymerization front analogous to formula (3.58) derived for the gasless combustion wave. We substitute (4.126) into (4.123) to obtain... 

As was the case with gasless combustion, the uniformly propagating polymerization wave may become unstable as parameters are varied. We perform a linear stability analysis of the uniformly propagating polymerization wave by employing the reaction front approximation. 

Here, a is the thermal difiusivity of the reactive mass, T, is the combustion temperature (the maximum temperature of the front), K(TJ is the reaction constant at T = T. If this condition is met, the process becomes stabilized. In the experiment [71], the stabilization stage (constant position of the front) amounted to tens of minutes. All these stages are siniilar to the corresponding development of the combustion process [19] and if the viscosity of a substance were not increasing, the development of the process would be completed at this stage. It is obvious that the analysis of the polymerization front propagating in a stationary medium [66-69] does not yield any qualitatively new results as compared to combustion. 

If the front propagates downwards, the convective motion decreases the heat loss from the high-temperature spot to the unreacted monomer. The heat is conserved near the reaction front, and the perturbation of the temperature has better conditions to increase. Hence the critical value of the Zeldovich number decreases. We note that the influence of convection on the spinning modes for polymerization fronts with a liquid polymer is different in comparison with the case of a solid polymer 31),... 

What about ascending fronts If a front were to propagate upward, then the hot polymer-monomer solution in the reaction zone could rise because of buoyancy, removing enough heat at the polymer-monomer interface to quench the front. With a front that produces a solid product, the onset of convection is more complicated than the cases that we considered in Chapter 9, because the critical Rayleigh number is a function of the velocity (Volpert et al., 1996). Bowden et al. (1997) studied ascending fronts of acrylamide polymerization in dimethyl sulfoxide. As in the iodate-arsenous acid fronts, the first unstable mode is an antisymmetric one followed by an axisymmetric one. Unlike that system, in the polymerization front the stability of the front depends on both the solution viscosity and the front velocity. The faster the front, the lower the viscosity necessary to sustain a stable front. 

Begishev et al. (1985) studied anionic polymerization fronts with e-caprolactam. There were two interesting aspects to this system. First, the polymer crystallizes as it cools, which releases heat. Thus, a front of crystallization follows behind the main front. Volpert et al. (1986) investigated this two-wave system. Second, a hot spot moved around the front as it propagated down the tube, leaving a spiral pattern in the product. The entire front propagated with a velocity on the order of 0.5 cm min which was a function of the concentrations of activator and catalyst. The hot spot circulated around the outside of the 6-cm (i.d.) front sixteen times as rapidly as the front propagated. 

Applications of Propagating Fronts Polymerization fronts may be useful in three practical respects ... 

Heat losses in a propagating front have a significant effect on the front velocity. This is related to two factors the size of the tube that affects the surface-to-volmne ratio, and the medium outside the tube that affects the rate of heat conduction. If the tube diameter is decreased, the front travels slower. In tubes of the size we have used, the polymerization front stops when the vessel is placed in room-temperature water, because water conducts heat more effectively than air. 

S., and Pojman, J.A. (2006) Spherically propagating thermal polymerization fronts. J. Polym. Sci., Part A Polym. Chem., 44, 1387-1395. 

It is evident from Figure 7, that within the experimental error the behavior of relationship d = f(t) is well described by the logarithmic law d/do = A Int + B, where do is the cuvette dimension in the Erection of initiation, and A and B are constants. This equation was proposed by the authors based on the phenomenological model of polymerization front propagation in the absence of convective heat/mass transfer. Similar equations were obtained analytically in (24). Solution of the analytical equation gives... 

For example, epichlorohydrin can be rapidly cooled to 77 K and then irradiated with 680 kGy dose of gamma radiation.A polymerization front with a velocity of 1.3cms propagated after fracturing a small region of the sample. Cations formed by the irradiation were released by the cracking and a wave of polymerization resulted. 

Thermal polymerization fronts can exhibit a wide range of interesting dynamical behavior. Fronts do not have to propagate with a constant velocity or constant shape but can be affected by buoyancy-driven convection and/or intrinsic... 

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