Solubility parameter, specific molar cohesion, and the solubility of ethylene oxide in polymers

The polarity of polymers is commonly characterized by their solubility parameter to describe their interaction with small molecules or by their specific molar cohesion to describe interchain attraction. A linear relation between these two parameters is demonstrated. Ethylene oxide (EO) is used to sterilize containers and devices containing plastics or elastomers. The solubility parameter concept is applicable to the sorption of EO by such polymers provided crystallinity and rubbery/glassy state are taken into account. The delta value of EO, calculated from the temperature dependence of its vapour pressure, is 10.8 (cal/cm3)1/2. The highest EO solubility is in polyvinyl chloride and polycarbonate, whose solubility parameters match that of EO closely. The solubility in other polymers decreases as their solubility parameters diverge increasingly from 10.8. At comparable delta values, polymers in the rubbery state dissolve 6000 to 8000 ppm EO more than polymers in the glassy state. EO solubility in the amorphous fraction of polymers above their glass transition temperatures ranges from 20 800 ppm for plasticized polyvinyl chloride (delta = 9.2) to 800 ppm for polytetrafluorethylene (delta = 6.2).