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Cobalt promoters presently used in the polyester processing industry suffer from many shortcomings ranging from shelf instability to strong discoloration of the resins and relatively poor activity. This paper describes the various performance improvements obtainable with coordination complexes of cobalt which can be used as polymerization accelerators in presence of organic peroxide initiators. These complexes appear to present significant advantages over the conventional cobalt carboxylates. Catalytic activity up to ten times that of cobalt soap was recorded with some complexes in various resin systems, without deleterious effects on physical properties. As gel-cure modifiers, the compounds evaluated seem to increase the long term shelf stability of pre-promoted resins while reducing the discoloration and air inhibition during the curing process of polyester thin films.

The thermal stability of PVC resins, alone or in powder blends, and of their various processing products can be determined continuously with precision and reproductibility. This new method is based on the evaluation of the progressive changes resulting from the decomposition of long test samples subjected to incremental thermal exposure in a thermo‐isolated oven kept at a constant temperature. The test samples are then examined by scanning reflectometry under white—as well as UV—light in order to detect and measure the structural changes occurring in the polymer during its thermal degradation. The method may also be applied to the quality control in the extrusion or calendering plant, where a scanning fluoro‐reflectometer detects the decomposition threshold during processing.

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