A new approach for the kinetic modeling of free radical bulk polymerization of styrene

Abstract

The kinetics of styrene-free radical bulk polymerization was studied by differential scanning calorimetry (DSC). The data obtained from DSC thermograms were used to model and predict the autoacceleration during styrene polymerization and to understand how it is influenced by temperature. The experimental data were well described by the estimated kinetic model. The model included two processes (the first-order reaction and autoacceleration), because they occur simultaneously as two parallel reactions rather than being strictly separated. It was found that the autoacceleration activation energy is approximately four times lower than the energy of the first-order reaction. In addition, the first-order reaction followed by the autoacceleration of the styrene-free radical bulk polymerization occurs simultaneously only between 41.7 and 110.5 1C. Keywords: autoacceleration; differential scanning calorimetry; polymerization kinetics; polystyrene; styrene-free radical bulk polymerization INTRODUCTION It is well known that the free radical bulk polymerization of vinyl monomers (derivates of acrylic and methacrylic acids, vinyl acetate, styrene, ethylene and so on) is characterized by the autoacceleration phenomenon. 1-3 The free radical polymerization of these monomers can be explained by classical theory up to definite conversion. After that conversion, autoacceleration of polymerization occurs. The onset of autoacceleration is the moment when the polymerization rate departs from the value anticipated by the classical theory of free radical polymerization. [3][4][5][6][7] The onset and the intensity of autoacceleration are determined by the type of monomer, initiator concentration, temperature and other reaction conditions. Ebdon and Hunt 3 used differential scanning calorimetry (DSC) to follow the course of free radical bulk polymerization of styrene and concluded that autoacceleration is less pronounced at 90 1C than at 80 1C and is absent at 100 1C and above. Autoacceleration appeared at about 2% conversion of styrene polymerized at 20 1C for 252 days in the presence of 2,2¢-azobisisobutyronitrile. 8 To explain this autoacceleration, an equation was applied to the kinetic data obtained under the condition of predominant transfer to the monomer. It was concluded that polymer molecules may move by repetition and the mobility of segments decreases with decrease of free volume. 8 Comparisons of the results obtained for styrene-free radical bulk polymerization with model predictions have quantified the dependence of the gel effect strength on the predominance of chain transfer events. 9 Cioffi et al. 10 performed a rheokinetic study of the bulk-free radical polymerization of styrene with a helical barrel rheometer. The rheokinetic measurements show that autoacceleration in the free radical polymerization of styrene can be reduced when the polymer-

Kinetic modeling of bulk free-radical polymerization of methyl methacrylate

“…The polymerization of MMA exhibits the same characteristic points as the polymerization of other lower alkylmethacrylates 2,3 and styrene: 28 the onset of acceleration (M), the maximum acceleration (P), and the maximum polymerization rate (S), proceeded by a deceleration stage with a minimum (R) and a final conversion (K). A kinetic model that has been tested earlier on styrene polymerization 28 was adjusted and applied to describe MMA free-radical bulk polymerization. The model is composed of two contributions, one from the first-order reaction and the other from the autoacceleration reaction.…”

“…18,19 This possibility fits into the description of the model discussed previously. 2,28,30 Figure 7 Conversion (X), rate of polymerization (dX/dt) and acceleration (d 2 X/dt) vs time (t) curves obtained by our mathematical model (equation 6 using parameters from Table 2, describing MMA polymerization at 60 1C).…”

“…In the current paper, we have focused on determining the existence of these characteristic points, as well as on testing a mathematical model of the free-radical bulk polymerization developed earlier by our research group and successfully tested on the polymerization of styrene. 28 Experimental data were obtained by using DSC to follow the bulk free-radical polymerization of MMA at different temperatures.…”

Radical bulk polymerization of styrene in the presence of rubber particles from recycled tires: a kinetic study using DSC

“…The main purpose of this study is to investigate the effects of the presence of GTR particles on the free-radical polymerization kinetics of styrene by using differential scanning calorimetry (DSC). DSC is a sensitive and precise thermal analysis technique that has proven to be a useful tool in the measuring of polymerization kinetics [9][10][11]13]. In this technique, the heat flow, which is assumed to be proportional to the reaction rate evolution, is recorded during the course of the reaction.…”

Surface functionalization of poly(vinylidene fluoride) membrane by radiation‐induced emulsion polymerization of hydroxyethyl acrylates in an aqueous medium

“…The micelle is most‐likely are the entanglement of poly‐HEA, which is known as bulk polymerization. Bulk polymerization occurred due to the high kinetic polymerization, and it is proved by the high degree of grafting 18,19 …”