Solution and Bulk Polymerization

For copolymerization of AN and styrene, the composition of polymers is determined by the composition of monomers participating in 

r and r2 are the monomer reactivity ratios, m is the molar ratio of the monomer feed, and p is the molar ratio of monomers instantly incorporated into the polymer. 

It has been found that the monomer reactivities vary by the method of polymerization, even for radical polymerization in different environments, i.e., in bulk, solution and microemulsion (5). The reactivity ratios for different methods of polymerization are given in Table 10.2 

The small reactivity ratio for AN indicates that a growing AN radical is reluctant to react with an AN monomer, but rather will react with a styrene monomer. On the other hand, even when a growing styrene radical reacts rather with an AN monomer, the tendency is not as marked. In the limiting case, if both monomer reactivity rations are going to zero, this effects the formation of strictly alternating polymers. The composition of the polymer can be controlled by the ratio of monomers in the monomer feed. In particular, since one of the monomers will be consumed faster that the other in a discontinuous process, the monomer feed can be adjusted accordingly in the course of polymerization. Also in a continuous process, in a cascade of reaction vessels, monomer can be fed into certain stages. 

For this reason, the monomer mixture initially fed into the reactor varies in composition throughout the reaction in the preparation of the copolymer, and correspondingly, the composition of polymers also changes with conversion. Thus, the SAN copolymer formed 

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In general, for solutions and bulk polymeric materials, viscosity follows the general relationship shown in Figure 7.7 where viscosity is constant over much of the fluid range but sharply increases near Tg. 

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. 

Equations, which are also applicable to suspension, solution, and bulk polymerization, form an extension of the Smith-Ewart rate theory. They contain an auxiliary parameter which is determined by the rate of initiation, rate constant of termination, and volume of the porticles. The influence of each variable on the kinetics of emulsion polymerization is illustrated. Two other variables are the number of particles formed and monomer concentration in the particles. Modifications of the treatment of emulsion polymerization are required by oil solubility of the initiator, water solubility of the monomer, and insolubility of the polymer in the monomer. 

These relations for rate and degree of polymerization, although based on a relatively simple chemical picture, agree well with experimental data obtained in solution and bulk polymerizations. In emulsion polymerization, however, a complication arises from the fact that the volume of the reaction mixture is subdivided into a very large number of very small volume elements, the particles, which are suspended in water. These particles are so small that they can accommodate only a limited number of polymer radicals at any one time. The peculiarities of emulsion polymerization stem from this limitation. Polymer radicals, being insoluble in water, are confined to the particle in which they are generated. Thus, a radical in one particle cannot be terminated by a radical in another particle. Therefore, the rate of termination in emulsion is much lower than that given by Equation 1. 

Generally, efficiency of CCT catalysis drops in emulsion polymerization. The following values of CCT chain-transfer constants may be compared with solution and bulk polymerization CcMMA =1100 M 1 s-1, CcEMA = 640 M-1 s 1, Ccn BMA = 520 M s-1, Cc2 EHMA = 400 M 1 s 1 (75 °C, water, 9a).342 In miniemulsion polymerization, the choice of catalyst depends on the choice of initiator (see Table 10).345... 

The molecular weight of CTPnBA is controlled by the polymerization temperature, initiator, and the chain transfer agent in both dilute solution and bulk polymerization. 

Commercial grade PVC is produced primarily by free-radical-initiated suspension and emulsion polymerization of vinyl chloride. Suspension polymerization accoimts for over 80% of PVC produced. Solution and bulk polymerization are also employed to some extent. However, there are difficulties with bulk polymerization because PVC is insoluble in its monomer and therefore precipitates. In suspension polymerization, vinyl chloride droplets are suspended in water by means of protective colloids such as poly(viEyl alcohol), gelatin, or methyl cellulose in pressure vessels equipped with agitators and heat... 

In this section some of the methods used to analyse for the chemical composition (CQ and chemical composition distribution (CCD) of binary and ternary copolymers (henceforth termed copolymers and terpolymers respectively) are discussed. Some practical examples from the literature are given to illustrate the methods. Further, the determination of the chemical composition of copolymers as function of their molar mass as well as the three-dimensicxial combination of the MMD and CCD, namely MMCCD, are treated. Examples of both emulsion polymers and polymers produced by solution and bulk polymerization are given, because with respect to the determination of molar mass and chemical composition emulsion (co)polymers do not require an essentially different approach. 

The only other study of this nature known to us describes the synthesis of two other A-B monomers [64] as well as their solution and bulk polymerization, but the proposed mechanism for their chain growth is unclear. The aim of this investigation was to prepare thermally stable materials and tha-efore the DA adducts in the polymers were aromatized by dehydration with acetic anhydride. 

TABLE 4. Solution and bulk polymerization of DCPD (98%). Curing conditions as in TABLE 3. 

In the case of bulk polymerization it should be mentioned that BHB and e-CL form a homogenous solution above 76 °C. Both techniques, solution and bulk polymerization lead to similar results with resist to polymer properties. In terms of sustainable chemistry bulk techniques are more ecologically efficient and therefore favorizable. 

One consequence of the compartmentalization of radicals in the particles is that the overall concentration of radicals in the system is much greater than in solution and bulk polymerization, and hence the polymerization rate is higher. 

It is an accepted fact that the termination reactions become diffusion-controlled at relatively low polymer concentrations and for solution and bulk polymerizations an increase in radical concentration and an acceleration in the rate of polymerization are experienced. The situation in emulsion polymerization is somewhat different, however [1,2,3]. From its birth a polymer particle is swollen with monomer and contains a relatively high concentration of polymer. In Stages I and II the termination constant is significantly lower than that observed for solution and bulk polymerization at the same conversion. The termination reactions in the polymer particles are diffusion-controlled from zero conversion. However, to experience an autoacceleration in rate of polymerization, polymer particles must contain two or more radicals and this usually is not the case in Stages I and II where instantaneous termination is often operative. As the polymer... 

The main process control challenges in solution and bulk polymerizations are the control of molecular weight averages [103], molecular weight distribution (MWD) [104], monomer conversion [105], and copolymer composition and copolymer composition distribution (CCD) [106, 107]. The development of mathematical models for solution and bulk processes is relatively easy, as it is not necessary to take into account mass transfer between different phases. The main challenge in this field is the proper description of the glass and gel effects, which is usually performed with the help of anpirical models [108]. Therefore, reliable process models are usually available for solution and bulk processes. 

Solution and bulk polymerization temperature 35°C, polymerization time 2 h... 

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