Bulk and suspension polymerization of styrene in the presence of n‐pentane. An evaluation of monofunctional and bifunctional initiation

Abstract

SYNOPSISThe plasticizing effect of n-pentane on the rate of bulk free radical polymerization of styrene and molecular weight distribution development has been modeled on the basis of the free volume theory for both monofunctional and bifunctional initiation. A strong decrease in the reaction rate in the late stages of the polymerization, due to the displacement of the onset of the gel effect, has been observed for both types of initiation. This decrease in the polymerization rate limited the terminal conversion to values well below 100% for monofunctional initiation. However, in bifunctionally initiated polymerization, terminal conversions close to 100% were obtained in spite of the decrease in reaction rate. Contrary to what was expected, the molecular weight distribution obtained at terminal conversion was almost completely insensitive to these changes in polymerization rate. This phenomenon is explained in terms of limited transfer to monomer reactions when n-pentane is present in the system. In suspension polymerization, the limiting conversion and plasticizing effects of n -pentane in monofunctionally initiated systems, caused enhanced coalescence leading to suspension set-up. In bifunctionally initiated systems this enhanced coalescence was completely overcome by the short duration of the particle growth stage, owing to high polymerization rates, and stable suspensions were achieved. For these systems the particle size distributions obtained were similar to that of suspension polystyrene without n-pentane.

Kinetic modeling of free radical polymerization of styrene initiated by the bifunctional initiator 2,5-dimethyl-2,5-bis(2-ethyl hexanoyl peroxy)hexane

“…• The concentration of polymeric diradical species S n is three orders of magnitude smaller than the polymeric monoradicals P n and Q n [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. The diradical species S n could then be neglected [3,4,6,8,10] (Fig.…”

“…The diradical species S n could then be neglected [3,4,6,8,10] (Fig. 3) leading to the simplified model used for all our simulations.…”

“…The problem can be overcome by using multifunctional initiators and by controlling the decomposition rate of the labile groups [2]. Comparison of monofunctional systems with bifunctional can be found in the literature [3][4][5][6][7][8]. The presence of a second radical generating function distributed in the growing and dead polymer can be engaged in further initiation, propagation, chain transfer and termination reaction during the course of polymerization.…”

Optimal policies for BMA polymerization in nonisothermal batch reactor

“…Based on the approach of Villalobos et al, 13 and Dhib et al, 14 the following free-radical polymerization mechanism is used in this study.…”

“…The model comprises the equations of change of the volume (V) and temperature (T) of reactants, and the concentrations of monomer (m), initiator (i), inhibitor (z), and of the first three moments of radicals and dead polymer radicals. The equations are based on a free-radical polymerization reaction mechanism of Villalobos et al, 13 and Dhib et al 14 (Appendix). The symbols in following expressions are defined in Nomenclature.…”