Chain dynamics in [ring-fluoro]polycarbonate (an A-B alternating copolymer that has a single fluorine substituent on every fourth main chain ring) have been characterized by centerband only detection of exchange (CODEX) and rotating-frame C-13 spin-lattice relaxation. The slow motions detected by CODEX are facilitated by a mechanically active lattice reorganization that permits a flip of the fluorinated ring about its C-2 axis. Nonfluorinated rings undergo small-amplitude reorientations and C-2 flips, both of which are fast and not CODEX active. (c) 2008 Wiley Periodicals, Inc.