| In the modern era the production of chemicals from sustainable natural resources as an alternative to petrochemicals is an absolute necessity. Among the major commodity polymers, potential candidates for synthesis from renewable natural resources are polyesters and polycarbonates. A series of porphyrin metal (III) compounds of general formula LMX (L = tetraphenylporphyrin (TPP), octaethylporphyrin (OEP), tetrakispentafluorophenylporphyrin (TFPP), M = aluminum, chromium, cobalt, X = Cl, OEt (for Al); Cl, OAc, OH (for Cr); Cl, OAc (for Co)) has been synthesized and used as catalysts to produce polypropylene carbonate and propylene carbonate. These catalysts are further investigated for the copolymerization of propylene oxide with succinic anhydride (SA) or phthalic anhydride (PA) to produce polypropylene succinate and polypropylene phthalate. The metal catalyzed copolymerization process provides an alternative "greener" synthetic route to the preparation of these polymers using renewable feedstocks e.g. CO2 and succinic acid.;The electronic nature of the porphyrin ligand, the choice of metal center and the addition of Lewis basic cocatalysts e.g. DMAP or PPN+Cl- showed dramatic influence on the catalytic TOF, product selectivity and polymer quality. Detailed kinetic and mechanistic investigations were carried out to elucidate the nature of various reactive intermediates i.e. M-alkoxide, M-carbonate and M-carboxylates, involved in the polymerization processes. These comparative analyses show how the electronic environment around the metal center and the binding of added Lewis base cocatalysts influence the reactivity of the various metal-oxygenate intermediates, and thereby control the individual reaction steps and equilibria involved in the polymerization processes. |
