Bulk Polymerization of Styrene with

Bulk Polymerization of Styrene with 2,2 -Azobisisobutyronitrile in a Dilatometer... 

Figure 13.7 Performance of a laminar flow, tubular reactor for the bulk polymerization of styrene with Tm = 135° K and i = Ih (a) stability regions (b) monomer conversion in stable region.

Figure 20-3. Change in the polymerization rate Vp with conversion t/ for the bulk polymerization of styrene with AIBN as initiator at 50°C. Initiator concentrations (I) 1.83 X 10, (II)...

FIGURE 10.5 Decreases in ( ) and k (O) for the bulk polymerization of styrene with an increase in conversion. Reprinted (adapted) with permission from Yamada B, Kageoka M, Otsu T. Dependence of propagation and termination rate constants on conversion for the radical polymerization of styrene in bulk as studied by ESR spectroscopy. Macromolecules 1991 24 5234— 5236. 1991 American Chemical Society. 

Bulk polymerization of styrene with the organomontmorillonites occurred with a freshly distilled monomer (all of the inhibitor is removed). Azobisiosobutylnitrile (AIBN) was employed as the initiator. Thermal initiation occurred at 60°C for 72 h. 

One of the few attempts to examine a polymerization reactor in periodic operation experimentally is the work of Spitz, Laurence and Chappelear (X6)who reported the influence of periodicity in the initiator feed to the bulk polymerization of styrene in a CSTR. To induce periodicity the initiator feed was pulsed on-and-off and the reactor output compared with steady-state operation with the same time-averaged initiator input. 

There is an interior optimum. For this particular numerical example, it occurs when 40% of the reactor volume is in the initial CSTR and 60% is in the downstream PFR. The model reaction is chemically unrealistic but illustrates behavior that can arise with real reactions. An excellent process for the bulk polymerization of styrene consists of a CSTR followed by a tubular post-reactor. The model reaction also demonstrates a phenomenon known as washout which is important in continuous cell culture. If kt is too small, a steady-state reaction cannot be sustained even with initial spiking of component B. A continuous fermentation process will have a maximum flow rate beyond which the initial inoculum of cells will be washed out of the system. At lower flow rates, the cells reproduce fast enough to achieve and hold a steady state. 

Several references to the bulk polymerization of styrene are worth consulting [46-50], Most consider a continuous bulk polymerization apparatus with some using spraying of the monomer through a nozzle. The controlled evaporation of unreacted monomer is one method of removing the heat of reaction. 

Example 5.7 A CSTR is commonly used for the bulk polymerization of styrene. Assume a mean residence time of 2h, cold monomer feed (300 K), adiabatic operation (UAext = 0), and a pseudo-first-order reaction with rate constant... 

Hamielec, Hodgins, and Tebbins (25) justified and used the PSSA with the solution and bulk polymerization of styrene. They calculated that the steady state was approached in a few thousandths of a second. Their equations for dead polymer were numerically integrated for 5000 species and, as previously mentioned, experimentally confirmed. 

For the bulk polymerization of styrene using thermal initiation, the kinetic model of Hui and Hamielec (13) was used. The flow model (Harkness (1)) takes radial variations in temperature and concentration into account and the velocity profile was calculated at every axial point based on the radial viscosity at that point. The system equations were solved using the method of lines with a Gear routine for solving the resulting set of ordinary differential equations. 

Various methacrylic-styrene copolymers were prepared in which the reactivity of methacrylate monomers used in the first step decreases in the order MM A > BuMA > benzyl methacrylate. For instance, the bulk polymerization of MMA with such an aromatic azo compound proceeds via a living radical mechanism and the sterically crowded C-C(C6H5)3 terminal bond of polymethacrylate 37 can be cleaved thermally to produce a,co-diaromatic PMMA-h-PS block copolymers in 48-72% yield. 

In Figure 1 are shown experimental conversion histories from bulk polymerization of styrene, methyl methacrylate, and vinyl acetate. It appears that with any of these monomers the rate of polymerization increases substantially during reaction, i.e. gel-effect is important in bulk polymerization of these monomers. The effect is particularly pronoimced with methyl methacrylate. 

Crystal polystyrene is produced by thermally initiated (Section 6.5.4) bulk polymerization of styrene at temperature of I20°C or more. (The term crystal refers to the optical clarity of products made from this polymer, which is not crystalline.) The rate of polymerization would decrease with increasing conversion and decreasing monomer concentration if the reaction were carried out at constant temperature. For this reason, the polymerization is performed at progressively increasing temperatures as the reaction mixture moves through a series of reactors. The exothermic heat of polymerization is useful here in raising the reaction temperature to about 250°C as the process nears completion. 

Problem 7.16 Bulk polymerization of styrene in the presence of 1 g/L of AIBN initiator at 60°C gave a measured polymerization rate of 5.92 mol/L-s. Predict the rate of copolymerization at 60°C of a mixture of styrene (Mi) and methyl methacrylate (M2) with 0.579 mole fraction styrene and the same initial concentration of the initiator as in the homopolymerization case. Compare the rates predicted from chemical control, diffusion control, and combined models with the experimental value of 4.8x10 mol/L-s [25]. Use relevant kp and kt values for homopolymerization from Table 6.7 and assume 0 = 15. [Other data ri = 0.52, T2 = 0.46 monomer density = 0.90 g/cm .]... 

In the study113) an attempt was made to model the whole process of thermal bulk copolymerization of styrene with polybutadiene up to high degrees of conversion. The calculations were based on the previously developed model of thermal bulk polymerization of styrene and supplemented with the reactions of chain transfer to rubber. 

There is an interior optimum. In this numerical example it occurs when 40% of the reactor volume is in the initial CSTR and 60% is in the downstream PFR. The model reaction is chemically unrealistic but illustrates behavior that can arise with real reactions. An excellent process for the bulk polymerization of styrene consists of a CSTR followed by a tubular postreactor. 

Figure 6.24 Molecular weight, M , dependence on monomer conversion for bulk polymerization of styrene at 114°C with only PS-TEMPO adduct initiator (System I) and with both PS-TEMPO and t--butyl hydroperoxide initiators (System n). The theoretical line represents molecular weight calculated on the assumption of a constant number of polymer molecules (due only to PS-TEMPO adduct) throughout the course of poymeriza-tion (Problem 6.42).

Table 1. Bulk Polymerizations of Styrene (8 M) (100 equiv to [PE-I]o) with PE-I, Conventional Radical Initiator (I), and Catalyst (100 "C).

Example 7.2 The data for the bulk polymerization of styrene at 60°C with benzoyl peroxide as initiator are... 

The bulk polymerization of styrene at 100°C with benzoyl peroxide as the initiator resulted in a polymer of molecular weight 4.16 x 10. End-use tests showed that this product would be adequate provided the variation in molecular weight did not exceed 20%. However, to ensure better temperature control of the reactor, it was decided that the polymerization should be carried out in a solvent at a dilution factor of 2. The following solvents are available ... 

Figure 10.1 Vertical column reactor for the continuous bulk polymerization of styrene. (From Winding, C.C. and Hiatt, G.D., Polymeric Materials, McGraw-Hill, New York, 1961. With permission.)...

Alternatively, Chang et a/. prepared MWCNT-PE-TEMPO by the reaction of HO-PE-TEMPO with MWCNT-COCl, and used it to initiate bulk polymerization of styrene at 130 °C for 4 h, yielding copolymer-grafted MWCNT. 

Bulk polymerization is employed when some special properties are required, such as high molecular weight or maximum clarity, or convenience in handling. Industrially, bulk polymerization in special equipment can have economic advantages, as with bulk polymerization of styrene. This is discussed in Chapter 5. 

Figure 20-4. Variation in the viscosity-average degree of polymerization with conversion in the bulk polymerization of styrene at 50 C. The same initiator concentrations as in Figure 20-4 were used. (According to data of G. Henrici-Olive and S. Olive.)...

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