Bulk density polymerization

Durham route, the metathesis polymerization of 7,8-bis(trifluoromethyl)tricyclo[4.2.2.0]deca-3,7,9-triene gives a high-molecular weight soluble precursor polymer that is thermally converted to polyacetylene (equation 19.6). The precursor polymer is soluble in common organic liquids and easily purified by reprecipitation. The end product can be aligned giving a more compact material with bulk densities on the order of 1.05 —1.1 g/cm. ... 

A wide range of polymeric materials can be prepared from HIPEs. Polymerisation of the continuous phase yields highly porous cellular polymers with a monolithic structure. These are known as PolyHIPE polymers, and possess a number of unique properties including, in most cases, an interconnected cellular structure and a very low dry-bulk density. Their very high porosity favours their use as supports for catalytic species, precursors for porous carbons and inert matrices for the immobilisation of enzymes and micro-organisms. 

A catalyst, prepared from isoprenylaluminum and titanium tetrachloride has been used to prepare polymers with a highly irregular shape (5). The polymerization is performed at 70-80°C with an ethylene partial pressure of 0.16-0.27 M Pa. A bulk density of 0.16-0.23 gem-3 is obtained. Such materials are intended to be used as filter elements. 

Another method, the emulsion process, was developed in Europe to meet the demand for a resin with small particle size, high bulk density, and low plasticizer absorption properties. These characteristics are especially desirable in making plastisols and organosols, where the resins are dispersed in liquid plasticizers. In this polymerization process, emulsifiers are added, and the solution is agitated to keep the monomer droplets dispersed. The initiators must be water soluble it is usually an inorganic persulfate or an organic hyperperoxide. 

The crospovidone grades are obtained with different specific surface areas, depending on the polymerization conditions, and their particle size. The micronization process has less influence on the specific surface than small modifications of the polymerization conditions. When a normal crospovidone was micronized the specific surface only increased from l m2/g to i.8 m2/g (N2-BET method). The micronized crospovidone of the lowest bulk density available in the market has the highest specific surface of 2.5 to 6 m2/g (Table 118). 

Polypivalolactone (PPL) is insoluble in most solvents at temperatures below 100°C. We therefore envisaged conducting the polymerization in an inert diluent from which the polymer precipitates, and in which the lactone monomer and initiator may or may not be soluble. The diluent should be capable of dissipating the heat of polymerization, and the morphology of the product (bulk density, powder flow, etc.) should be as good as possible. In addition, the reaction rates should be practical, and the polymer should fulfill product requirements such as thermal stability. 

After treatment to cause the polymerization of undesirable contaminants the high grade phthalic anhydride is vacuum distilled to yield the commercial product. This product is usually passed through a flake machine to produce phthalic anhydride flakes in which form about 80 per cent of the material is marketed. The flaked form lias considerable advantage over the needle crystal fonn since its bulk density is much higher and any discoloration is more readily detected. 

Polyoxymethylene is obtained as a finely divided solid. The bulk density of the product, which is very important for ease of handling in subsequent manufacturing steps, is influenced by many reaction variables, including solvent type, polymerization temperature, and agitation. 

PVC is insoluble in VCM. The precipitated polymer tends to coagulate in the conversion range of 1-8%. As the conversion continues, the precipitated polymer absorbs more and more monomer, and at a 15-20% conversion, the reactor contains solid polymer swollen with monomer in a monomer atmosphere. The horizontal autoclave prevents the formation of large polymer blocks by breaking them up. Advantages claimed for this process are the higher bulk density, improved particle size distribution, and more rapid plasticizer absorption. Talamini and coworkers (J ) have demonstrated that the bulk polymerization process is kinetically equivalent to suspension polymerization. 

Table 8.9. Shrinkage accompanying polymerization calculated from bulk densities of monomer and polymer 4>...

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