Development of a reaction injection molding encapsulant system. 1. Kinetic studies of butyllithium-catalyzed styrene polymerization

Abstract

Differential scanning calorimetry (DSC) was used to study the isothermal bulk polymerization of styrene, initiated by either n-butyllithium or 2-butyllithium, over the temperature range 20-50 °C. At higher temperatures, the rates of polymerization initiated with either n-butyllithium and 2butyllithium were the same within experimental error. The polymerization reaction order with respect to initiator and monomer concentrations was found to be 0.5 and 1.0, respectively. The heat of reaction was found to be 16 ± 0.5 kcal/mol, and the activation energy for polymerization was determined to be 14.4 ± 0.6 kcal/mol, with the corresponding prefactor A = 4.5 X 108 s'1 (L/mol)1/2. Nearly adiabatic polymerizations were carried out using 2-butyllithium-initiated styrene to simulate the reaction injection molding (RIM) operation. The reactor system was found to have a time constant for heat transfer of 48 s. Numerical calculations based on these kinetic and heat-transfer parameters were found to agree well with experiment.

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).…”

“…A thermocouple was placed through the septum and extended into the liquid to measure temperature during the polymerization. Temperature was recorded with the computer-based data acquisition system described previously (Your et al, 1989). At thermal equilibrium, the butyllithium was rapidly injected into the mixture to initiate polymerization.…”

“…Our laboratory has been developing a reaction injection molding (RIM) process for encapsulation of electronic components with rapidly polymerizing, cross-linked, compositions that contain substituted styrene. 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.…”