Active and Versatile ROP Aluminum Catalysts for the Controlled Limonene Oxide Polymerization and Copolymerization With Anhydrides

The aryloxide [AlXMe(OAr)] (OAr = 2,6‐bis(diphenylmethyl)‐4‐ tert ‐butylphenoxide, X = Cl ( 1 ), Me ( 2 )) and the hemisalen [AlX(L) 2 ] (L = N‐(2,6‐diisopropylphenyl)‐phenoxyimine, X = Cl ( 3 ), Me ( 4 )) aluminum complexes were tested as catalysts for the limonene oxide (LO) ringopening polymerization (ROP) and copolymerization (ROCOP) with phthalic anhydride (PA). Although compounds 1 ‐ 2 are active for the LO homopolymerization, 3–4 only gave LO rearrangement products. Interestingly the presence of a nucleophilic cocatalyst renders all the catalysts inactive. In contrast, all compounds were very active for the ROCOP of LO and PA when a cocatalyst such as 4‐dimethylaminopyridine (DMAP) is present. Full conversions were attained within 3 h at 140°C to give perfectly alternate polyesters with good M n and narrow dispersities. An increase in DMAP ratio resulted in an enhancement of the polymerization rate, while maintaining the M n and dispersity values. The role of DMAP as initiator was confirmed by MALDI‐TOF MS. Besides, the isolation of key intermediates and experimental evidence shows that the copolymerization initiates with the PA opening due to the combined action of the catalyst and DMAP. Furthermore, initial studies of the process scaling up using reactive extrusion (REX) conditions have been successfully performed.