Development of a reaction injection molding encapsulant system. 2. Chemorheology of the anionic bulk polymerization of styrene

Abstract

463Greek Symbols t = rate of dissipation of turbulent energy, m2/s3 p = viscosity, Pa s p = specific density, kg/m3 @ = (fuel-air ratio)/ (stoichiometric fuel-air ratio) = equiva-Subscripts 0 = initial (at flamefront) 1 = region ahead of flamefront 2 = zone of combustion 3 = region after flamefront i = index LFR = laminar-flow reactor PFR = plug-flow reactor r = radial component R = reactant TSB = thermally stabilized burner z = axial component Superscript -= mixed-mean value lence ratio

Anionic Polymerization of Styrene in a Tubular Reactor

“…The initiation and propagation rates have been experimentally verified to be ,− As in the ideal reaction system, the initiation reaction is sufficiently fast to neglect. The equilibrium reactions, eqs 10 and 13, are also fast.…”

An improved general kinetic analysis of non-linear irreversible polymerisations

“…After a few fundamental studies on its chemical kinetics (Worsfold, 1970;Eschwey and Burchard, 1975) have been carried out, this system was later found to be useful as a model for RIM encapsulation of electronic parts (Your et al, 1989;Christiansen et al, 1990;Karles et al, 1991).…”

Development of a reaction injection molding encapsulant system. 3. Gel times for the anionic bulk polymerization of styrene with divinylbenzene

“…Prior to polymerization, oxygen, water, and carbon dioxide were stripped from the monomer by bubbling either argon or oxygen-free nitrogen at 40-80 mL/min through no more than 25 mL of monomer for at least 30 min. Stripping is necessary to prevent preferential reaction of these materials with the BuLi initiator, as detailed in previous studies (Your et al, 1989; Christiansen et al, 1990). Typically, stripping of styrene lowered the active contaminant level to (2-5) X 10-3 M, as determined by titration with BuLi, using an end point defined by the persistence of the orange styryllithium complex (Morton et al, 1970; Worsfold and Bywater, 1972).…”

“…Attempts to measure the viscosity rise preceding and accompanying gelation with the torque rheometer, described previously (Christiansen et al, 1990), were not successful. The initially formed gel has very low mechanical strength and is easily disintegrated by the shear fields in this apparatus at torque or shear stress levels that are too low to be accurately detected by the instrument.…”

“…The motivation for this approach and kinetics information for the anionic polymerization of styrene are presented in part 1 of this series (Your et al, 1989). In part 2 (Christiansen et al, 1990) an experimental protocol and fundamentally based model for predicting the viscosity rise during the bulk linear polymerization of styrene, anionically initiated by butyllithium, is presented. This paper, part 3, considers the potentially more difficult to predict case of nonlinear polymerization where the viscosity rise results from the formation of a three-dimensional network due to the presence of divinylbenzene (DVB) in the reacting mixture.…”