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

Nonlinear chemical dynamics: Competition and convection effects in reaction-diffusion fronts and controlling chaos.

Competition and convection effects in reaction-diffusion fronts and controlling chaos are studied. In Chapter 3 we report theoretical studies of competition in which two self-replicating organic molecules compete for a common reactant. We found that the self-replicating organic molecule can give sustained reaction-diffusion fronts. This phenomenon is investigated by numerical solutions of partial differential equations that couple local nonlinear kinetics and diffusion. Reaction-diffusion fronts involving competing species are then initiated and the concentration profiles of the autocatalysts monitored. The results show that the more reactive species totally predominates over the less reactive species as its front moves ahead into the fresh reactant solution and consuming all of the common resource. Observations of steady nonaxisymmetric chemical reaction-reaction diffusion fronts in an upward propagation in iodate-arsenous acid solutions within vertical tubes are reported in Chapter 4. These observations confirm theoretical predictions of hydrodynamic stability theory that the onset of convection in such fronts should be nonaxisymmetrical. The nonaxisymmetric waveform reflects the presence of a single convective roll in the vicinity of the moving front. The Belousov-Zhabotinsky reaction exhibits deterministic chaos which is characterized by long term unpredictability arising from extreme sensitivity to initial conditions. Feedback algorithms have been used to stabilize periodic oscillations in chaotic systems like laser, diodes and myocardial tissue. In chapter 5 we report the stabilization of periodic behavior in the BZ reaction, the first example of controlling chaos in a chemical system. Unstable periodic orbits are stabilized by supplying small, controlled perturbations to a system constraint according to a map-based, proportional-feedback algorithm

Free Radical-Scavenging Dyes as Indicators of Frontal Polymerization Dynamics

A novel method of monitoring frontal polymerization propagation has been presented. Using commercially available dyes that change color upon coupling with free radicals, the propagating fronts of free radical polymerization reactions can be visualized and recorded using conventional digital imaging techniques. To demonstrate the utility of this method, we have applied it in the frontal polymerization reactions of trimethylene glycol dimethacrylate (TGDMA) and 1,6-hexanediol diacrylate (HDDA), with Lupersol 231 [1,l-di(tert-butylperoxy)-3,3,5-trimethylcylohexane] as the initiator

Optical Gradient Materials Produced via Low-Temperature Isothermal Frontal Polymerization

Using a newly developed low‐temperature frontal polymerization technique, poly(methyl methacrylate) (PMMA) matrices were prepared with nonuniform distributions of organic nonlinear optical dyes, with potential use as optical limiters. This technique affords lower temperature conditions than have been used before. A PMMA tube was filled with a dye, the initiator tert‐butyl peroxide, and methyl methacrylate (MMA). Curing at 4°C resulted in a radial gradient of dye. An axial dye gradient was observed when MMA was overlaid and polymerization effected from a dye‐doped PMMA seed using tricaprylmethyl ammonium persulfate as the initiator. In both cases, polymerization reactions were observed as a result of isothermal frontal polymerization with the subsequent formation of a nonlinear concentration distribution of the optical dye dopants. Low temperatures are desirable to eliminate thermal and photothermal degradation of temperature‐sensitive dyes during the polymerization. The preparation of long polymer rods with organic dye gradients on the scale of several centimeters can also be realized with the use of low‐temperature polymerization and the gradients controlled by the concentration of initiator. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 686–691, 200

Synthesis and characterization of cationic copolymers of butylacrylate and [3-(methacryloylamino)-propyl]trimethylammonium chloride

Cationic copolymers of butylacrylate (BA) and [3-(methacryloylamino)-propyl]trimethylammonium chloride (MAPTAC) were synthesized by free-radical-solution polymerization in methanol and ethanol. An FT-Raman Spectrometer and NMR were used to monitor the polymerization process. The copolymers were characterized by light scattering, NMR, DSC, and thermogravimetric analysis. It was found that random copolymers could be prepared, and the molar fractions of BA and cationic monomers in the copolymers were close to the feed ratios. The copolymer prepared in methanol had a higher molecular weight than that prepared in ethanol. As the cationic monomer content increased, the glass-transition temperature (Tg) of the copolymer also increased, whereas the thermal stability decreased. The reactivity ratios for the monomers were evaluated. The copolymerization of BA (M1) with MAPTAC (M2) gave reactivity ratios such as r1 = 0.92 and r2 = 2.61 in ethanol as well as r1 = 0.79 and r2 = 0.90 in methanol. This study indicated that a random copolymer containing a hydrophobic monomer (BA) and a cationic hydrophilic monomer (MAPTAC) could be prepared in a proper polar solvent such as methanol or ethanol. © 2001 John Wiley & Sons, Inc