Plasticizer compatibility with the polymer, which implies that plasticizer and polymer will remain closely associated as the finished polymer product is used, is critically important in determining whether a flexible poly(vinyl chloride) (PVC) product will have an acceptably long service life. However, with traditional test methods, it is often difficult to distinguish degrees of compatibility among relatively compatible ingredients (ingredients that do not dissociate themselves from the polymer in a very short time or under very mild storage conditions). Dynamic mechanical analysis is a commonly used technique for measuring glass transition temperatures, which can be a useful property in comparing additives' compatibilities. Unlike many polymers, flexible PVC shows two glass transition temperatures, one for the polymer segments that show syndiotactic (but noncrystalline) stereochemistry, and one for the polymer segments that show atactic stereochemistry. The glass transition temperature for the atactic segments of flexible PVC provides some information about the plasticizer's compatibility. When the dynamic mechanical analysis temperature sweep for a plasticized PVC compound detects a particularly low glass transition for the atactic polymer segments, this can be an indication that the plasticizer is relatively incompatible with the PVC. (C) 2014 Society of Plastics Engineers
