Solution-polymerized reactivation

In mass polymerization bulk monomer is converted to polymers. In solution polymerization the reaction is completed in the presence of a solvent. In suspension, dispersed mass, pearl or granular polymerization the monomer, containing dissolved initiator, is polymerized while dispersed in the form of fine droplets in a second non-reactive liquid (usually water). In emulsion polymerization an aqueous emulsion of the monomer in the presence of a water-soluble initiator Is converted to a polymer latex (colloidal dispersion of polymer in water). 

Solution Polymerization. Solution polymerization of vinyl acetate is carried out mainly as an intermediate step to the manufacture of poly(vinyl alcohol). A small amount of solution-polymerized vinyl acetate is prepared for the merchant market. When solution polymerization is carried out, the solvent acts as a chain-transfer agent, and depending on its transfer constant, has an effect on the molecular weight of the product. The rate of polymerization is also affected by the solvent but not in the same way as the degree of polymerization. The reactivity of the solvent-derived radical plays an important part. Chain-transfer constants for solvents in vinyl acetate polymerizations have been tabulated (13). Continuous solution polymers of poly(vinyl acetate) in tubular reactors have been prepared at high yield and throughput (73,74). 

AGE-Gontaining Elastomers. The manufacturing process for ECH—AGE, ECH—EO—AGE, ECH—PO—AGE, and PO—AGE is similar to that described for the ECH and ECH—EO elastomers. Solution polymerization is carried out in aromatic solvents. Slurry systems have been reported for PO—AGE (39,40). When monomer reactivity ratios are compared, AGE (and PO) are approximately 1.5 times more reactive than ECH. Since ECH is slightly less reactive than PO and AGE and considerably less reactive than EO, background monomer concentration must be controlled in ECH—AGE, ECH—EO—AGE, and ECH—PO—AGE synthesis in order to obtain a uniform product of the desired monomer composition. This is not necessary for the PO—AGE elastomer, as a copolymer of the same composition as the monomer charge is produced. AGE content of all these polymers is fairly low, less than 10%. Methods of molecular weight control, antioxidant addition, and product work-up are similar to those used for the ECH polymers described. 

Chemical Reactivity - Reactivity with Water No reaction Reactivity with Common Materials Corrosive, particularly when diluted. Attacks most common metals, including most stainless steels. Excellent solvent for many synthetic resins or rubber Stability During Transport Stable Neutralizing Agents for Acids and Caustics Dilute with water, rinse with sodium bicarbonate solution Polymerization Not pertinent Inhibitor of Polymerization Not pertinent. 

Chemical Reactivity - Reactivity with Water Reacts violently forming flammable hydrogen gas and a strong caustic solution Reactivity with Common Materials May ignite combustible materials if they are damp or moist Stability During Transport Stable if protected from air and moisture Neutralizing Agents for Acids and Caustics Caustic that is formed by the reaction with water should be flushed with water and then can be rinsed with dilute acetic acid solution Polymerization Not pertinent Inhibitor of Pofymerization Not pertinent. 

Chemical Reactivity - Reactivity with Water A slow, non-hazardous reaction occurs, forming propanolamine Reactivity with Common Materials No reactions Stability During Transport The product is stable if it is kept in contact with solid caustic soda (sodium hydroxide) Neutralizing Agents for Acids and Caustics Dilute with water and rinse with vinegar solution Polymerization This material will polymerize explosively when in contact with any acid Inhibitor of Potymerization Solid sodium hydroxide (caustic soda). 

Similar anomalies have been encountered by several workers in the bulk and solution polymerization of this monomer induced by classical free-radical initiators84-86) also, particularly low rates of conversion were observed. The most thorough kinetic study was carried out by Aso and Tanaka86) who again found normal results and a value of k jkt much lower than that for styrene. Copolymerization studies of 2-vinylfuran (Mj) have given the following values of the reactivity ratios ... 

The solvent in a bulk copolymerization comprises the monomers. The nature of the solvent will necessarily change with conversion from monomers to a mixture of monomers and polymers, and, in most cases, the ratio of monomers in the feed will also vary with conversion. For S-AN copolymerization, since the reactivity ratios are different in toluene and in acetonitrile, we should anticipate that the reactivity ratios are different in bulk copolymerizations when the monomer mix is either mostly AN or mostly S. This calls into question the usual method of measuring reactivity ratios by examining the copolymer composition for various monomer feed compositions at very low monomer conversion. We can note that reactivity ratios can be estimated for a single monomer feed composition by analyzing the monomer sequence distribution. Analysis of the dependence of reactivity ratios determined in this manner of monomer feed ratio should therefore provide evidence for solvent effects. These considerations should not be ignored in solution polymerization either. 

For very high melting polymers (Tm > 300°C), a solution polymerization is normally employed. If this is started from the reactive acid chloride, the reaction temperature can be low. Polymers from acid chlorides can also be prepared by the interfacial method. Semicrystalline PA can be postcondensed in the solid state to higher molecular weights. To do this, the polymer powder/particles are heated for many hours below their melting temperature in an inert atmosphere. 

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