Polymerization melt-bulk

A schematic of a continuous bulk SAN polymerization process is shown in Figure 4 (90). The monomers are continuously fed into a screw reactor where copolymerization is carried out at 150°C to 73% conversion in 55 min. Heat of polymerization is removed through cooling of both the screw and the barrel walls. The polymeric melt is removed and fed to the devolatilizer to remove unreacted monomers under reduced pressure (4 kPa or 30 mm Hg) and high temperature (220°C). The final product is claimed to contain less than 0.7% volatiles. Two devolatilizers in series are found to yield a better quaUty product as well as better operational control (91,92). 

The kind of single crystals discussed above are all made starting from solution. In industrial practice, bulk polymeric products are generally made from the melt, and... 

The a>-amino acids are available at high purity but are generally more expensive titan their lactams and only suitable for the small-scale preparation of polymers. As they are bulk polymerizations, the polymerization temperature is preferably above die melting temperature of the polymer. 

Chain-growth polymerizations are diffusion controlled in bulk polymerizations. This is expected to occur rapidly, even prior to network development in step-growth mechanisms. Traditionally, rate constants are expressed in terms of viscosity. In dilute solutions, viscosity is proportional to molecular weight to a power that lies between 0.6 and 0.8 (22). Melt viscosity is more complex (23) Below a critical value for the number of atoms per chain, viscosity correlates to the 1.75 power. Above this critical value, the power is nearly 3 4 for a number of thermoplastics at low shear rates. In thermosets, as the extent of conversion reaches gellation, the viscosity asymptotically increases. However, if network formation is restricted to tightly crosslinked, localized regions, viscosity may not be appreciably affected. In the current study, an exponential function of degree of polymerization was selected as a first estimate of the rate dependency on viscosity. 

In a 100 ml three-necked flask with stirrer and thermometer 1 mol% of p-toluenesul-fonic acid methyl ester (methyl tosylate) are added to 3 g (0.03 mol) of anhydrous 2-methyl-2-oxazoline.The reaction mixture is stirred under nitrogen at 100-120 °C.The bulk polymerization sets in immediately. After 30 min. the viscous polymer melt is poured in a dish where it solidifies within minutes. After cooling to room temperature about 2 grams are dissolved in 20 ml ethanol and precipitated in 500 ml THF.The collected precipitate is dried under vacuum. 

The simplest procedure for grafting copolymerization, in terms of number of components in the reaction medium, is a bulk polymerization of the monomer in mixture with the molten polyamide. This has been claimed in an earlier patent (2), related to improvements in dyeability and hydrophylic properties of the resulting yam, obtained by melt spinning of the product of reaction with monomers such as 2,5-dichloro styrene, lauryl methacrylate, N-vinyl pyrrolidone, and N-vinyl carbazole. 

Fig. 1 Fracture surface of granular (bulk-polymerized) poly(tetrafluorethylene (PTFE). The sample was held in the melt at 380 °C for an unspecified time followed by slow cooling and fracture after immersion in liquid N2. (Reprinted from Ref. [1] with permission from Wiley-Interscience)...

Table 7. Comparison of the productivity, molecular weight, melting point and isotaeticity obtained in polymerization experiments with various metallocene/MAO catalysts (bulk polymerization in 11 liquid propene at 70 °C, Al/Zr ratio 15000) showing the broad range of product properties) [96]...

Ludovice and Suter can be found in the Encyclopedia of Polymer Science and Engineering. References up to 1988 are included, and techniques such as Monte Carlo, molecular dynamics, and energy minimization are described. In that review, the authors refer to earlier work on glasses and liquids of compounds of low molecular weight in addition to polymeric melts. Most of the material, though, applies to bulk amorphous polymers. 

Another example of bulk (or melt) polymerization is the synthesis of polyamides through the direct interaction between a dicarboxylic acid and a diamine. Nylon 66, for example, can be produced from the reaction between hexamethylenediamine and adipic acid. In practice, it is preferable to ensure the existence of a 1 1 ratio of the two reactants by prior isolation of a 1 1 salt of the two. The overall procedure is summarized by the reaction scheme ... 

Considering the process constraints in Table I, the design of a melt-bulk polymerization process (8) must take four factors into account ... 

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