ISSN:
0021-8995
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
,
Physics
Notes:
The effect of diffusion control on the polymerization of vinyl chloride has been studied by observing the rate as well as the molecular weight and the thermal stability of the polymer formed. The polymerizations were performed at 97% of saturation pressure in a water-suspended system at 55°C, using emulsion PVC latex as seed and a water-soluble initiator. The monomer was charged as vapor from a storage vessel kept at a lower temperature. Characterization included determination of molecular weight distribution by GPC and viscometry, and thermal dehydrochlorination. The gas-liquid contact was varied by changing the speed of agitation and the design of the stirrer. With a propeller the polymerization rate increased with the agitation up to ca. 1000 rpm, where after it became almost constant. Simultaneously, the molecular weight and the thermal stability increased. This indicates diffusion control, and thus decreased monomer concentration, at low agitation speeds, while the polymerization becomes reaction controlled at higher speeds. By a comparison with earlier data, obtained at different pressures and under reaction control, the actual monomer concentration could be calculated, which allowed an evaluation of the mass transfer constant. The possibilities to encounter problems with diffusion control in commercial polymerization of vinyl chloride is discussed. It is demonstrated that diffusion control is utilized in continuous polymerization of vinyl chloride, which explains the lower thermal stability of such materials.
Additional Material:
7 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/app.1988.070360111
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