Ultraproductive, Zinc-Mediated, Immortal Ring-Opening Polymerization of Trimethylene Carbonate Marion Helou, Olivier Miserque, Jean-Michel Brusson, Jean-François Carpentier, and Sophie M. Guillaume 2008

Immortal Polymerization Pioneered by Inoue for the ROP of epoxides by an Aluminum porphyrin/alcohol system Immortal polymerization is living polymerization where growing chains don’t "die" For anionic polmerizations, chains continue to grow even in the presence of protic solvents S. Inoue, J. Polym. Sci. Part A, 2000, 38,

Immortal Polymerization Rapid and reversible chain transfer between the growing polymer chain and an alcohol molecule :

Immortal Polymerization Allows good MW control, with low polydispersity Need very little initiator : n polymer =n initiator +n chain transfer agent High speed by using bulky Lewis acid inert to growing chains to activate the monomer Choice of chain transfer agent can give telechelic polymers or star polymers

Zinc-mediated ROP of TMC Trimethylene carbonate is easily obtainable from renewable 1,3-propanediol Poly(trimethylene carbonate) (PTMC) has biomedical applications Zinc is attractive for such applications, since it participates to the human metabolism The use of immortal polymerization reduces the amount of metal centers required Productivity of immortal catalytic systems was not as good as that of catalysts used for polymerization of olefins, and it had never been applied to the ROP of cyclic carbonates

Reaction Solvent-free reaction

Results Moderate activity Little control Benzyl alcohol is the actual initiator A fast, reversible exchange takes place between the growing chains and the free alcohol moieties Much higher activity and productivity than the maximum values reported for the TMC/Zn(acac) 2 system (TOF= h -1 at 110°C) Unprecedented for a carbonate or even a lactone polymerization initiated by a Zinc derivative

Results Evidence that the transfer between BnOH and the growing chain takes place [TMC] 0 /[BnOH] 0 =25,000:20 Controlled "living" character under a broad range of conditions Hints that the Zn species is able to withstand large amount of alcohol, a good stability most likely provided by the ancillary bdi ligand

Results End groups have been identified by 1 H NMR as a benzyloxy and a hydroxyl function, supporting a coordination- insertion mechanism No evidence of decarboxylation of the PTMC has been found, contrary to what often happens in ROP of carbonates

Conclusion A carbonate monomer has been polymerized using an immortal ROP for the first time The low amount of catalyst (as low as 20ppm to polymerize 50,000 equivalent of monomer), coupled with the low toxicity of Zinc makes this system relevant to biomedical applications The nature of the chain transfer alcohol provides a good versability and affords the possibility to eventually tune the end-functionality of the polymers and access telechelic and star polymers.