Bulk free radical polymerization

Experimental conversion-time data, obtained from the literature, on the bulk free radical polymerization of MMA initiated by AIBN at several temperatures and initiator concentrations, were described by the model. However, the expressions for the rate of conversion and gel effect index were first simplified and rearranged. ... 

Figure 5, Variation of the model parameters Cj (O) and Cb (X) u)ith temperature for the bulk free radical polymerization of MM A initiated by AIBN...

In this experiment you will perform a bulk free radical polymerization using readily available starting materials. You will observe the change in physical properties as the reaction proceeds. The polymer object that you make can be either a clear plastic piece or a casting containing some small object. 

If surfactant is added to a suspension polymerization system, a number of phenomena may occur. If the surfactant is added in small amounts (below the critical micelle concentration or CMC), the reduction in interfacial tension between the organic and aqueous phases will result in smaller monomer droplets, but it has hardly any other effect. If surfactant is added above the CMC, and an oil-soluble initiator is used, the process is commonly termed a microsuspension polymerization. Due to the reduced interfacial tension, the droplet diameter (and hence bead diameter) is reduced to approximately 10-40 pm. Little polymerization takes place in the aqueous phase or in particles generated from surfactant micelles because of the hydrophobic nature of the initiator. However, some smaller particles initiated from surfactant micelles may be found. The kinetics are still essentially those of a bulk free radical polymerization. Microsuspension polymerization is used to produce pressure-sensitive adhesives for repositionable notes. 

Styrene acrylonitrile copolymers were synthesized by bulk free radical polymerization at 60°C and 40°C over a wide range of initial monomer compositions (10). Copolymer compositions were determined by gas chromatography and verified by H1 NMR spectroscopy. The narrow MWD polystyrene standards (Pressure Chemicals) and the SAN copolymers were purified prior to the analysis by dissolution in THF and precipitation from absolute methanol. 

Due to the kinetics of the polymerization in small partides, emulsion polymerization allows for high polymerization rates and also high polymer molecular weights at the same time. This differs from bulk free-radical polymerization, where an increase in rate occurs at the expense of molecular weight and vice versa. However, this is obviously a feature of classical free-radical polymerization and must therefore not be considered further in the context of most transition metal-catalyzed polymerizations. 

Bhat, S. A. (2007). On-line optimizing control of bulk free radical polymerization of methyl methacrylate in a batch reactor using virtual instrumentation, Ph.D. Thesis, Indian Institute of Technology, Kanpur, 146 pages. 

The hkelihood of each of these events depends on the particular conditions of the system (e.g., number of polymer particles, emulsifier concentration, initiator concentration, monomer type and concentration,. ..). Within the polymer particles, polymerization fohows the same mechanisms as in bulk free-radical polymerization. These mechanisms involve chain transfer to smah molecules (e.g., monomers and CTAs), that yield small radicals. These small radicals may exit the polymer particles diffusing into the aqueous phase. Figure 6.2 illustrates the case in which monomer radicals are the exiting species. 

Three events are involved with chain-growth polymerization catalytic initiation, propagation, and termination [3], Monomers with double bonds (—C=C—R1R2—) or sometimes triple bonds, and Rj and R2 additive groups, initiate propagation. The sites can be anionic or cationic active, free-radical. Free-radical catalysts allow the chain to grow when the double (or triple) bonds break. Types of free-radical polymerization are solution free-radical polymerization, emulsion free-radical polymerization, bulk free-radical polymerization, and free-radical copolymerization. Free-radical polymerization consists of initiation, termination, and chain transfer. Polymerization is initiated by the attack of free radicals that are formed by thermal or photochemical decomposition by initiators. When an organic peroxide or azo compound free-radical initiator is used, such as i-butyl peroxide, benzoyl peroxide, azo(bis)isobutylonitrile, or diazo- compounds, the monomer s double bonds break and form reactive free-radical sites with free electrons. Free radicals are also created by UV exposure, irradiation, or redox initiation in aqueous solution, which break the double bonds [3]. 

The most common way to use ANN modeling is direct modeling, when output variables are correlated with inputs of the network. For instance, in the batch bulk free radical polymerization of methyl methacrylate, using (a,a -azobis(isobutyronitrile) as initiator, monomer conversion, polymerization degrees, and reaction viscosity are related to the working conditions (temperature, initial concentrations of reactants, and initiator and time) (Figiue 12.3a). 

Table 1.1. Primary Characteristics of Bulk Free Radical Polymerization and Emulsion Polymerization...

Figure 6 Change of propagation and termination rate constants during bulk free-radical polymerization. ...

The methacryloxyethyl derivatives of the various isomeric hydroxybenzaldehydes also are relatively low melting crystalline monomers that can be formulated to give both ternary and binary liquid mixtures (21). The synthesis of these monomers is shown in Fig. 4. These monomers may have application, if not as the main component of a dental resin binder, at least as a unique type of diluent. Clear, tough pol nners that are only partially soluble resulted from their bulk, free radical polymerization. Apparently, the aldehyde functionality enables these monomers to act as chain transfer agents which can delay the onset of gelation, and, perhaps, reduce residual vinyl unsaturation of dental monomer systems which utilize them as diluent comonomers. 

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