Polyperfluoroalkyl oxetanes: A new class of thermally stable polymers

Abstract

AbstractTwo perfluoroalkyl oxetanes, 2‐heptafluoropropyloxetane and 3‐ethyl‐3‐nonafluorobutyloxetane, were synthesized and polymerized. The 2‐heptafluoropropyloxetane was prepared by the ring closure of heptafluoro‐1,3‐hexanediol with sulfuric acid and sodium hydroxide. The 3‐ethyl‐3‐nonafluorobutyloxetane was prepared from diethyl ethylmalonate and perfluorobutyryl chloride. The sodium salt of the ester was acylated with the acid chloride. The resulting ketodiester was reacted with sulfur tetrafluoride to give diethyl α‐ethyl‐α‐perfluorobutylmalonate. This ester was then reduced with lithium aluminum hydride to give 2‐ethyl‐2‐perfluorobutyl‐1,3‐propanediol. This diol was then converted to the oxetane with sulfuric acid and sodium hydroxide. These oxetanes were polymerized in methylene chloride solution with boron trifluoride as the catalyst. Both polymers were viscous oils. The oxetane polymers were exposed as thin molten films to air at 300°F. Also tested under these conditions were polyethylene oxide, polypropylene oxide, polytrimethylene oxide, poly(3,3‐dimethyl)oxetane, and Teracol 30. The polymer from 2‐perfluoropropyloxetane was more stable than all the nonfluorinated polyethers tested. After an initial high weight loss, attributed to impurities, the polymer from 3‐ethyl‐3‐perfluorobutyloxetane was the most stable polyether tested.