The Fluorocarbene Exploit: Enforcing Alternation in Ring-Opening Metathesis Polymerization

Fluoroalkenes are known to be notoriously reluctant substrates
for olefin metathesis due to the generation of thermodynamically stable
Fischer-type fluorocarbene intermediates, which invariably fail to
undergo further reaction. In the present disclosure, we find that
fluorine substitution on the sp2 carbon also strictly suppresses
homopolymerization of norbornene derivatives (NBEs), and this can
be harnessed to achieve alternating ring-opening metathesis polymerization
(ROMP) with an appropriately electron-rich comonomer. Dihydrofuran
(DHF) is thereby shown to undergo alternating ROMP with fluorinated
norbornenes, the perfectly alternating structure of the resulting
copolymer having been unambiguously elucidated by 1H, 19F, and 13C NMR analyses. Furthermore, we find
that the degradability of the resultant copolymers in acidic media
via hydrolysis of enol ether moieties in the backbone can be predictably
modulated by the number of fluorine atoms present in the NBE comonomer,
affording an opportunity to engage with the desirable physical properties
of fluorinated polymers while limiting their attendant environmental
degradability issues.