Synthesis of Heterometallic Rare Earth‐Zinc Aryloxido Complexes and Their Application in Macrocyclic Lactones Polymerization

ABSTRACT A series of heterometallic trinuclear aryloxides, [REZn 2 (sal‐Me) 4 Cl 3 (H 2 O)] (Hsal‐Me = methyl salicylate; RE III = Y III ( 3 ), Ho III ( 4 ), Er III ( 5 )), or hexanuclear aryloxides, [RE 2 Zn 4 (μ 3 ‐OH) 2 (μ‐OMe) 2 (sal‐Me) 6 Cl 4 ] (RE III = Y III ( 6 ), Ho III ( 7 ), Er III ( 8 )) were synthesized via the reaction of zinc precursors [Zn 4 (sal‐Me) 8 ] ( 1 ) or [Zn 4 (μ 3 ‐OMe) 2 (sal‐Me) 6 ] ( 2 ) with 2 equiv of rare earth chlorides (RECl 3 ). The catalytic activity of complexes 1 – 8 was evaluated in the ring‐opening polymerization (ROP) of pentadecanolide (PDL) and hexadecanolide (HDL) to assess the effect of the initiator structure on the polymerization process and the physicochemical properties of the resulting polyesters. The obtained low molecular weight polypentadecanolides (PPDLs) and polyhexadecanolides (PHDLs) were investigated as modifying agents for commercial polylactide (PLLA) resin and used to prepare PLLA/PPDL or PLLA/PHDL blends. Blending PLLA with PPDL or PHDL broadens its cold crystallization exotherm, shifts the T cc to higher temperatures, and hinders the growth of PLLA crystals, ultimately leading to reduced thermostability and faster degradation.