Solution polymerization of methyl methacrylate

In the literature there is only one serious attempt to develop a detailed mechanistic model of free radical polymerization at high conversions (l. > ) This model after Cardenas and 0 Driscoll is discussed in some detail pointing out its important limitations. The present authors then describe the development of a semi-empirical model based on the free volume theory and show that this model adequately accounts for chain entanglements and glassy-state transition in bulk and solution polymerization of methyl methacrylate over wide ranges of temperature and solvent concentration. 

In this short initial communication we wish to describe a general purpose continuous-flow stirred-tank reactor (CSTR) system which incorporates a digital computer for supervisory control purposes and which has been constructed for use with radical and other polymerization processes. The performance of the system has been tested by attempting to control the MWD of the product from free-radically initiated solution polymerizations of methyl methacrylate (MMA) using oscillatory feed-forward control strategies for the reagent feeds. This reaction has been selected for study because of the ease of experimentation which it affords and because the theoretical aspects of the control of MWD in radical polymerizations has attracted much attention in the scientific literature. 

A critical survey of the literature on free radical polymerizations in the presence of phase transfer agents indicates that the majority of these reactions are initiated by transfer of an active species (monomer or initiator) from one phase to another, although the exact details of this phase transfer may be influenced by the nature of the phase transfer catalyst and reaction medium. Initial kinetic studies of the solution polymerization of methyl methacrylate utilizing solid potassium persulfate and Aliquat 336 yield the experimental rate law ... 

Table 3.3. The overall energy of activation for bulk and solution polymerization of methyl methacrylate, 54)... 

For the bulk polymerization of methyl methacrylate at 77°C with azo-bis-isobutyronitrile as the initiator, the initial rate of polymerization was 1.94 x 10 mol/l-s. The concentrations of the monomer and initiator were 9 mo 1/1 and 2.35x10 mol/1, respectively. To reduce the heat transfer problems, the polymerization was repeated in a solution of benzene by the addition of 4.5 1 of benzene with an initiator concentration of 2.11 X 10 1/mol. Assuming that the rate constants are the same for both the bulk and solution polymerizations, calculate the rate of solution polymerization of methyl methacrylate. If there is no transfer to the solvent and the initial rate of initiation is 4 x 10 mol/l-s, what is the ratio of the number-average degree of polymerization for bulk-to-solution polymerization Comment on your results. 

The situation is less clear-cut for RAFT systems. For a dithiocarbonate-mediated styrene polymerization studied by Goto and co-workers, the steady-state kinetic analysis applied both in the presence and absence of a BPO initiator (Figure 3.10). Similarly, for the solution polymerization of methyl methacrylate, mediated by dithioesters containing a-cyanobenzyl groups in the presence of AIBN initiator, pseudo-first-order plots were obtained although a significant induction period was detected. 

Figure 5.2 Rate of polymerization versus monomer conversion for the free radical solution polymerization of methyl methacrylate (from [14]).

Adebekun, A. K., Kwalik, K. W., and Schork, F. J. (1989) Steady state multiplicity during solution polymerization of methyl methacrylate in a CSTR, Chem. Eng. Sci. 44, 2269-81. 

Ghosh, R Gupta, S.K. Saraf, D.N. (1998) An experimental study on bulk and solution polymerization of methyl methacrylate with responses to step changes in temperature. Chemical Engineering Journal, 70, 25-35. 

Ghosh, P., Gupta, K.S., Saraf, D.N., 1998. An Experimental Study on Bulk and Solution Polymerization of Methyl Methacrylate with Responses to Step Changes in Temperature. Chemical Engineering Journal 70 25-35. 

Cherfi, A. and G Fevotte, On-Line Conversion Monitoring of the Solution Polymerization of Methyl Methacrylate Using Near-Infrared Spectroscopy. MocromoZ. Chem. Phys., 2002. 203 1188-1193. 

NIR has been used to monitor the polymerization of acrylic acid [4], for the solution polymerization of methyl methacrylate (MMA) in toluene [5], for following the emulsion polymerization of MMA and butyl acrylate [6], and for monitoring the copolymerization of MMA and N,N-dimethylacrylamide (Figure 20.2) [33]. The density of linear low-density polyethylene was monitored using NIR and a partial least-squares (PLS) calibration model [7]. 

Cherfi A, Fevotte G. On-line conversion monitoring of the solution polymerization of methyl methacrylate using near-infrared spectroscopy. Macromol Chem Phys 2002 203 1188-1193. 

Figure 17.3 shows the rate of polymerization plotted versus monomer conversion for the free radical solution polymerization of methyl methacrylate. Unlike a more common reaction in which the rate of reaction falls mono-tonically with conversion, the rate of reaction rises with conversion due to the onset of the gel effect. Thus, the system can be thought of as autocatalytic. At high conversion, the polymerization becomes monomer starved and the rate of polymerization falls to zero. At a fixed residence time, there must be a specific rate of polymerization to produce a given monomer conversion. The mass balance is represented by the dotted lines in Figure 17.3. The slope of the mass balance line will vary with operating conditions bnt it will always pass through the origin since at zero reaction rate the monomer conversion is zero. Inspection of Fignre 17.3 reveals that for mass balances (operating lines) with slopes between the two dotted lines, three steady states exist since an intersection of the reaction rate curve and the operating line defines a steady state.

FIGURE 17.3 Rate of polymerization versus monomer conversion for free radical solution polymerization of methyl methacrylate. With permission from Reference 19, Kwalik KM. Bifurcation characteristics in closed-loop polymerization reactors [PhD thesis]. Atlanta School of Chemical Engineering, Georgia Institute of Technology 1988. 

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