Styrene polymerization kinetic parameters

Fig. 9. Increase of the radical concentration in a conventional AIBN-initiated bulk polymerization of styrene. For kinetic parameters see text.

In conclusion, we have reviewed how our kinetic model did simulate the experiments for the thermally-initiated styrene polymerization. The results of our kinetic model compared closely with some published isothermal experiments on thermally-initiated styrene and on styrene and MMA using initiators. These experiments and other modeling efforts have provided us with useful guidelines in analyzing more complex systems. With such modeling efforts, we can assess the hazards of a polymer reaction system at various tempera-atures and initiator concentrations by knowing certain physical, chemical and kinetic parameters. 

Since this reaction is not affected by hydroquinone and galvinoxyl and does not initiate polymerization of styrene, it obviously occurs without the formation of free radicals. The kinetic parameters of the reactions of three hydroperoxides with triphenyl phosphite in different solvents are given in Table 17.2 [21]. 

TABLE 5-1 Kinetic Parameters in CF3SO3H Polymerization of Styrene at 20°C in CICILCILCI ... 

Table 5-1 shows the various kinetic parameters, including k+ and kp, in the polymerization of styrene initiated by triflic acid in 1,2-dichloroethane at 20°C. Data for the polymerization of isobutyl vinyl ether initiated by trityl hexachloroantimonate in methylene chloride at 0°C are shown in Table 5-2. Table 5-3 shows values for several polymerizations initiated... 

Table 1 [1] summarizes the relevant kinetic parameters. Clearly, the polymerization of macromonomers, 23-25, is characterized by very low kt values and by less reduced kp values, compared to those of the corresponding conventional monomers such as styrene and MMA. This means that the propagation involving the macromonomer and the multibranched radical is slightly less favored... 

At present, the kinetic parameters for prediction of copolymerization rates are scanty, except for a few low conversion copolymerizations of styrene and some acrylic comonomers. Engineering models of high conversion eopolymerizations are, however, overdetermined, in the sense that the number of input parameters (kinetie rate constants, activation energies, enthalpies of polymerization, and soon)... 

Hamielec et al.93 continue to develop the approach based on calculating the kinetic parameters from experimental data obtained by the GPC method. As with styrene polymerization, the dependence of the values of kinetic constants on conversion is sought as a complex function... 

Polymerization of methyl methacrylate (MMA) and styrene in bulk via ruthenacarboranes and carbon tetrachloride was investigated first, ft was found that proposed ruthenium complexes were able to efficiently catalyze polymerization of MMA in conjunction with carbon tetrachloride as an initiator. Moreover, as follows from the data obtained (Table I), high conversion of the monomer is achieved in a number of cases. The structure of ruthenium carborane complexes closo or exo-nido) has a substantial effect on the kinetic parameters of MMA and styrene polymerization, as well as on the molecular-weight characteristics of synthesized polymers. 

Equation (2.26) leads to a solution for from available knowledge of the rate R, the concentration of monomer in the monomer-polymer particles [M], and the number of particles, N. This method has been applied to several monomers and has been especially useful in the case of the dienes, where the classical method of photoinitiation poses difficulties. Some of these results are shown in Table 2.4 in the form of the usual kinetic parameters. The results obtained for styrene by photoinitiation techniques are included for comparison. It can be seen that the agreement is remarkably good, considering the widely different experimental methods used. Recent studies of the emulsion polymerization of butadiene have shown that the rate constant for propagation is even higher than previously estimated (see Table 2.1) (Weerts et al., 1991). 

Non-catalytic thermal decarbonylation of quinones proceeded for 9,10-anthraquinone (ANQ), 9,10-phenanthrenequinone (PHQ), 1,4-and 1,2-naphthoquinone(NPQ) and p-benzoquinone (BNQ) in the presence of atmospheric hydrogen at 500- 600 C. ANQ or PHQ decar-bonylated in the presence of hydrogen to form fluorenone (FLR) at the first step, followed by successive hydrodecarbonylation and hydrocracking to form biphenyl and benzene. In the case of 1,4-NPQ, the reaction did not proceed in any obvious stoichiometric relation. Only 60- 70 % of 1,4-NPQ decarbonylated and was hydrogenated yielding styrene, ethylbenzene, toluene, benzene and lower hydrocarbons the remainder polymerized or partly polycondensed. Similar, or less selective results were obtained for 1,2-NPQ and p-BNQ. Analyses of kinetic treatments are reported for the consecutive reaction schemes of ANQ or PHQ as well as of FLR. The kinetic parameters for decarbonylation, polymerization, polycondensation reactions of quinones are discussed. 

Another synthetic method for submicrometer fluorescence CdSe/ZnS/PS nanocomposite particles was developed by Joumaa et al. [205]. Submicrometersized particles were synthesized via a mini-emulsion PS process and CdSe/ZnS was coated by PS. Styrene emulsion and mini-emulsion polymerizations were performed in the presence of either TOPO-coated or vinyl-fimctionalized CdSe/ZnS nanocrystals. Both emulsion and mini-emulsion processes were first applied to the incorporation of TOPO-coated CdSe/ZnS nanoparticles. Then, the concentration and type of QD as well as the surfactant concentration were varied in order to investigate the influence of these parameters on the mini-emulsion polymerization kinetics and PL properties of the final particles. The final particle size could be tuned between 100 and 350 nm by varying the initial surfactant concentration. The intensity of luminescence properties increased with the number of incorporated TOPO-coated CdSe/ZnS nanoparticles, and the slight red shift of the emission maximum, induced by the polymerization, was correlated with modification of the medium surrounding the nanoparticles. TOPO-coated CdSe/ZnS nanoparticles showed higher fluorescence intensity than those with a vinyl moiety [205]. 

Butte et al. [1999] carried out experiments for both types of free radical polymerization of styrene and simulated the results using kinetic parameters obtained from the literature after adaptation accounting for their own observations. 

Deady M, Mau AWH, Moad G, Spurling TH. Evaluation of the kinetic-parameters for styrene polymerization and their chain-length dependence by kinetic simulation and pulsed-laser photolysis. Makromol Chem-Macromol Chem Phys 1993 194 1691-1705. 

The curing reactions of UPRs based on glycolyzed PET and maleic anhydride were studied by differential scanning calorimetry and various kinetic parameters were obtained from dynamic data using the Kissinger expression [59]. It was demonstrated that the polymerization heat, associated with styrene and polyester double bonds, can be calculated by extrapolating the heat of reaction obtained from different styrene contents. 

The Instantaneous values for the initiator efficiencies and the rate constants associated with the suspension polymerization of styrene using benzoyl peroxide have been determined from explicit equations based on the instantaneous polymer properties. The explicit equations for the rate parameters have been derived based on accepted reaction schemes and the standard kinetic assumptions (SSH and LCA). The instantaneous polymer properties have been obtained from the cummulative experimental values by proposing empirical models for the instantaneous properties and then fitting them to the cummulative experimental values. This has circumvented some of the problems associated with differenciating experimental data. The results obtained show that ... 

The nature of the active species in the anionic polymerization of non-polar monomers, e. g. styrene, has been disclosed to a high degree. The kinetic measurements showed, that the polymerization proceeds in an ideal way, without side-reactions, and that the active species exist in the form of free ions, solvent-sparated and contact ion pairs, which are in a dynamic equilibrium (l -4). For these three species the rate constants and activation parameters (including the activation volumes), as well as the rate constants and equilibrium constants of interconversion have been determined (4-7.) Moreover, it could be shown by many different methods (e. g. conductivity and spectroscopic methods) that the concept of solvent-separated ion pairs can be applied to many ionic compounds in non-aqueous polar solvents (8). 

Several methodologies for preparation of monodisperse polymer particles are known [1]. Among them, dispersion polymerization in polar media has often been used because of the versatility and simplicity of the process. So far, the dispersion polymerizations and copolymerizations of hydrophobic classical monomers such as styrene (St), methyl methacrylate (MMA), etc., have been extensively investigated, in which the kinetic, molecular weight and colloidal parameters could be controlled by reaction conditions [6]. The preparation of monodisperse polymer particles in the range 1-20 pm is particularly challenging because it is just between the limits of particle size of conventional emulsion polymerization (100-700 nm) and suspension polymerization (20-1000 pm). 

Equation 4 was foimd to explain particle size data fairly well, with reasonable kinetic and coverage parameter values (k s and Sent), in the dispersion polymerization of styrene in ethanol with PVP dispersant [24]. Many other dispersion polymerization systems with homopolymer dispersants appear to be explained by Eq. 4, except for the frequently observed direct particle size dependence on initiator concentration [27]. 

The free-radical kinetics described in Chapter 6 hold for homogeneous systems. They will prevail in well-stirred bulk or solution polymerizations or in suspension polymerizations if the polymer is soluble in its monomer. Polystyrene suspension polymerization is an important commercial example of this reaction type. Suspension polymerizations of vinyl ehloride and of acrylonitrile are described by somewhat different kinetic schemes because the polymers precipitate in these cases. Emulsion polymerizations aie controlled by still different reaetion parameters because the growing macroradicals are isolated in small volume elements and because the free radieals which initiate the polymerization process are generated in the aqueous phase. The emulsion process is now used to make large tonnages of styrene-butadiene rubber (SBR), latex paints and adhesives, PVC paste polymers, and other produets. 

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