RECYCLABLE AND BIO-BASED POLYESTERS AND POLYCARBONATES ENABLED BY BIOCOMPATIBLE METAL CATALYSTS

IN RECENT YEARS, THE GLOBAL SCIENTIFIC COMMUNITY HAS INTENSIVELY SOUGHT SOLUTIONS TO ADDRESS THE GROWING PROBLEM OF PLASTIC POLLUTION. THIS TRANSITION REQUIRES NOT ONLY THE ADOPTION OF BIO-BASED MATERIALS TO REPLACE PETROLEUM-BASED ONES, BUT ALSO THE IMPLEMENTATION OF EFFECTIVE END-OF-LIFE TREATMENTS, SUCH AS CHEMICAL RECYCLING. AMONG ECO-FRIENDLY ALTERNATIVES, ALIPHATIC POLYESTERS AND POLYCARBONATES STAND OUT FOR THEIR RENEWABLE ORIGIN, BIODEGRADABILITY, AND BIOCOMPATIBILITY. HOWEVER, CURRENT INDUSTRIAL PRODUCTION RELIES ON HIGHLY TOXIC TIN-BASED CATALYSTS. THEREFORE, THE PRIMARY OBJECTIVE OF THIS DOCTORAL THESIS WAS TO DEVELOP NEW CATALYTIC SYSTEMS CAPABLE OF SYNTHESIZING THE TARGETED POLYMERS USING NON-TOXIC AND ABUNDANT METALS, PARTICULARLY ZINC AND MAGNESIUM. THE STUDY INITIALLY FOCUSED ON A ZINC-NHC SYSTEM, APPLIED IN THE POLYMERIZATION OF TRIMETHYLCARBONATE (TMC) AND ITS ALKYL DERIVATIVES, MONOMERS SPECIFICALLY SYNTHESIZED VIA CO₂ FIXATION. THE SYSTEMS DEMONSTRATED A HIGH LEVEL OF CONTROL, WHICH WAS SUBSEQUENTLY EXPLOITED FOR THE SYNTHESIS OF PTMC BLOCK COPOLYMERS WITH POLYLACTIDE (PLA) AND POLYETHYLENE GLYCOL (PEG) THROUGH TWO DIFFERENT SYNTHETIC STRATEGIES. SUBSEQUENTLY, THE RESEARCH WAS EXTENDED TO A NEW LIBRARY OF ZINC AND MAGNESIUM COMPLEXES, USING NHC LIGANDS FUNCTIONALIZED WITH SYN- OR ANTI-PHENYL GROUPS COMBINED WITH N-TOLYL SUBSTITUENTS. ALL CATALYSTS PROVED ACTIVE IN BOTH THE POLYMERIZATION OF VARIOUS CYCLIC ESTERS AND THE METHANOLYSIS OF PLLA. INTERESTINGLY, THE ACTIVITY OF THE COMPLEXES IS STRONGLY INFLUENCED BY THE NATURE OF THE METAL AND THE MONOMER. IN A SECOND PHASE OF THE PROJECT, ATTENTION SHIFTED TO NOVEL HETEROLEPTIC ZINC AND MAGNESIUM COMPLEXES SUPPORTED BY TRIDENTATE NAPHTHOXY-IMINO-PYRIDINE LIGANDS. THESE NEW COMPLEXES WERE APPLIED IN THE HOMOPOLYMERIZATION OF VARIOUS BIODERIVED CYCLIC MONOMERS (BOTH ESTERS AND CARBONATES). FINALLY, CONFIRMING THE SYSTEM'S VERSATILITY, THE ZINC COMPLEX'S PERFORMANCE WAS EVALUATED IN THE COPOLYMERIZATION AND DEPOLYMERIZATION OF PTMC AND ITS COPOLYMERS, EXPLOITING MICROWAVES AS A MORE ENERGY-EFFICIENT ALTERNATIVE TO CONVENTIONAL HEATING METHODS. THE FINAL PART OF THE DOCTORAL PROJECT FOCUSED ON THE DEVELOPMENT OF DINUCLEAR CATALYTIC SYSTEMS USING MULTINUCLEATING LIGANDS, DESIGNED TO POSITION METAL CENTERS AT OPTIMAL INTERATOMIC DISTANCES. FIRST, SULFUR-FUNCTIONALIZED SALEN LIGANDS WERE SYNTHESIZED TO PREPARE MONO- AND BIMETALLIC ZINC COMPLEXES. ALTHOUGH THEIR EFFECTIVENESS IN POLYCARBONATE SYNTHESIS WAS ALREADY KNOWN, THIS WORK EVALUATED THEIR PERFORMANCE IN THE RING-OPENING POLYMERIZATION (ROP) OF ESTERS AND THE ALTERNATE RING-OPENING COPOLYMERIZATION (ROCOP) OF EPOXIDES AND ANHYDRIDES. SUBSEQUENTLY, WE INTRODUCED A NEW VARIANT OF HEXADENTATE SALEN LIGANDS, FUNCTIONALIZED WITH ORTHO-AMINE PENDANTS TO CREATE A COORDINATION POCKET FOR A SECOND METAL. THE SYNTHETIC STRATEGY AND PRELIMINARY STUDIES ON THE CORRESPONDING HOMO- AND HETERODINUCLEAR COMPLEXES IN ROCOP MODEL REACTIONS ARE DESCRIBED. TO FURTHER EXPLORE HETEROMETALLIC COOPERATIVITY, THE STUDY WAS EXTENDED TO INCLUDE HETEROTRIMETALLIC COMPLEXES BASED ON ZINC AND ALKALI METALS, SUPPORTED BY PENTADENTATE PROPHENOL LIGANDS. THIS THESIS PRESENTS A NOVEL APPLICATION OF THESE SYSTEMS TO THE POLYMERIZATION OF CYCLIC CARBONATES AND MACROLACTONES, REPRESENTING, TO OUR KNOWLEDGE, THE FIRST EVALUATION OF SUCH COMPLEXES WITH THESE SPECIFIC CLASSES OF MONOMERS.