Cobalt-mediated radical polymerization: an elegant tool of the synthesis of thermoresponsive N-vinylamide based copolymers

Organometallic-Mediated Radical Polymerization (OMRP) is an emerging class of controlled radical polymerization based on the reversible deactivation of the growing radical chains by a metal complex. OMRP based on Co(acac)2 (CMRP) is very efficient for non-conjugated and reactive monomers such as vinyl esters or vinyl amides. Kinetics and theoretical investigations revealed the preponderance of an intramolecular cobalt chelation in the CMRP mechanism. The latter reinforces the cobalt-polymer bond at the polymer chain-end. The effects of the carbonyl donor power in the formation of the chalated structure, of the ring strain for the cyclic amides (lactams) and of hydrogen bonding for secondary vs. tertiary amides have been rationalized with help of DFT calculations. Such represents a unique opportunity to imporve the control of the polymerizations, especially for the synthesis of well-derined poly(N-vinhyl amide)s which sustain numerous applications.

Because poly(N-)vinylcaprolactam)s (PNVCL) represent an important class of biocompatible and thermoresponsive material, a series of NVCL-based copolymers was synthezized via CMRP. Lower critical solution temperature (LCST) were tuned up and down by introduction of vinylacetamides or vinyl esters comonomers. CMRP also allowed the syntbhesis of new diblock copolymers having double thermoresponsive poroperties whereas the corresponding NVCL-based triblock copolymers were obtained by the cobalt-mediated raidical coupling (CMRC) method developed in our research center. The thermo-responsive properties and self-assembly behavior of these new di-and tri-block copolymers were studied by turbidimetry analysis and dynamic light scattering (DLS).