Ring‐opening polymerization of (Macro)lactones by highly active mononuclear salen–aluminum complexes bearing cyclic β‐ketoiminato ligand

Abstract

In this contribution, we explored the catalytic ring-opening polymerization (ROP) of (macro)lactones using salen-aluminum complexes bearing cyclic β-ketoiminato ligand. The effects of bridge moiety and ring size in the benzocyclane skeleton on the catalytic activity of these complexes were thoroughly investigated. Complex 5 with 2,2-dimethylpropylene bridge and fivemembered cyclane ring can efficiently catalyze the ROP of ω-pentadecalactone (ω-PDL), showing higher catalytic activity (turnover frequency [TOF] up to 309.2 h −1 ) than the typical Alsalen analogs bearing salicylaldiminato ligand (TOF = 227.2 h −1 ). Thus, polyethylene-like polyester with high-molecular weight (up to 164.5 kg/mol) could be easily prepared under optimal conditions. In addition, complex 5 can also catalyze the ROP of lactide (LA) and ε-caprolactone (ε-CL) with extremely high activity (TOF is high up to 147.6 h −1 and 4752 h −1 , respectively). Here, we demonstrated a rare mono-nuclear salen-Al complex that can prompt the ROP of (macro)lactones with unprecedentedly high efficiency.

Synthesis of Semi‐Aromatic Di‐Block Polyesters by Terpolymerization of Macrolactones, Epoxides, and Anhydrides

“…The reason for these diverse behaviors can be ascribed to the different steric encumbrance of the two bimetallic complexes. [26] A first glance on the molecular weights of the samples obtained with catalyst 1 respect those obtained using 2 suggests that on the bimetallic catalyst two polymeric chains (one for metal center) are growing; although conversion factors for the molecular weights of the polymacrolactones determined by GPC on polystyrene standards are not available in the literature, a comparison of the data obtained in similar conditions with the monometallic catalyst roughly gives this indication (for instance, compare run 1, vs run 7, Table 1). This hypothesis is in agreement with data previously achieved in the polymerization of ɛ-caprolactone.…”

Thermo-Rheological and Shape Memory Properties of Block and Random Copolymers of Lactide and ε-Caprolactone

“…Synthetic strategies have therefore been used to control the design of the polymeric chains. Several research efforts have focused on the synthesis of well-defined LA/CL copolymeric chain, either block [ 17 , 18 , 20 , 24 ], or random [ 19 , 25 , 26 , 27 , 28 ].…”

Tuning the thermal properties of poly(ethylene)‐like poly(esters) by copolymerization of ε‐caprolactone with macrolactones, in the presence of a pyridylamidozinc(II) complex

“…Notably, tin octanoate, the industrial catalyst in the ROP of small and medium‐sized lactones and lactides, is almost not active toward the ROP of macrolactones. To date, several metal‐based catalysts active in the ROP of macrolides have been reported, based on early transition metals (Y) and main group metals (Zn, Al, Ca, Mg) . In this regard, we have expanded the use of dimethyl(salicylaldiminato) aluminum compounds not only to the homo‐ and copolymerization of conventional small and medium‐sized cyclic esters but also to the ROP of an unsaturated macrolactone, the ω‐6‐hexadecenlactone (6HDL) .…”