Period-doubling behavior in frontal polymerization of multifunctional acrylates

Front dynamics in the frontal polymerization of two multifunctional acrylat e monomers, 1,6-hexanediol diacrylate (HDDA) and trimethylolpropane ethoxyl ate triacrylate (TMPTA), with Lupersol 231 [1,1-di(t-butylperoxy)-3,3,5-tri methylcyclohexane] as the initiator, are studied. In most frontal polymeriz ation 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 mod es and pulsations. To determine how these periodic and aperiodic modes aris e, reactant solutions consisting of HDDA diluted with diethyl phthalate (DE P) 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 chaot ic mode. Also, a pulsating symmetric mode has been observed. These observat ions have a striking similarity to observations made in studies of self-pro pagating 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 a ctivation of multifunctional acrylate polymerization is a strong function o f 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. (C) 1999 American Institute of Phys ics. [S1054-1500(99)01202-1].