Controlled random copolymerization of rac‐lactide and ɛ‐caprolactone by well‐designed phenoxyimine Al complexes

Abstract

The random copolymers poly(LA-ran-CL) have improved properties of degradability, mechanical strength, elasticity, and permeability over the PLA and PCL homopolymers. However, the synthesis of such copolymers is still a great challenge in polymer chemistry. In this contribution, we develop a simple but well-designed phenoxyimine Al complex (4) with bulky Ph 2 CH groups, which achieves controlled random copolymerization of rac-LA and E-CL in a living manner (Ð 5 1.06-1.09). The reactivity ratios of rac-LA and E-CL (r LA and r CL ) are 1.09 and 1.05 and the average sequence lengths of the lactidyl unit (L LA ) and the caproyl unit (L CL ) are in the range of 1.9-2.0 at different stages of conversion. In marked contrast, Al complexes (1-3) having less bulky substituents on the ligands only produce gradient copolymers. Furthermore, this strategy of catalyst design would be readily extended to other catalytic systems including b-ketiminato Al complex (5). V C 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 611-617

Random copolymerization of l‐lactide and ε‐caprolactone by aluminum alkoxide complexes supported by N2O2 bis(phenolate)‐amine ligands

“…Moreover, Ma and Kan exhibited that the rigid backbone in the salen ligand could create a crowded environment around the metal center which reduces the rate of LA and affords the random CL/LA copolymerization . Recently, Li and coworkers have shown that, in a phenoxy‐imine aluminum catalyst system, the increase of steric hindrance around the aluminum center could lead to a strict random copolymer …”

“…[7][8][9][10] Therefore, the development of the efficient catalysts is a significantly challenging goal to meet the requirements of various applications. Several metal catalyst systems have been reported for the copolymerization of ε-CL and LA ranging from the traditional stannous octoate, 6 to main group catalysts, [11][12][13] transition metal catalysts, [14][15][16][17][18][19] and rare-earth catalysts [20][21][22] leading to varying degree of monomer distribution. In most reports, the truly random copolymer poly(LAran-CL), in which the average sequence lengths of caproyl unit (L CL ) and lactidyl unit (L LA ) equal to 2, 12,23,24 have been very challenging.…”

“…34 Recently, Li and coworkers have shown that, in a phenoxy-imine aluminum catalyst system, the increase of steric hindrance around the aluminum center could lead to a strict random copolymer. 12 From our previous work, we have been fascinated by the N 2 O 2 ligand framework where the N 2 O 2 bis(phenolate)-amine ligand can create a bowl-shaped structure around the metal center. In the aluminum complexes supported by N 2 O 2 bis(phenolate)-amine ligands having pyridine, dimethylamine and diethylamine as a side arm, the rates of the homopolymerization of LA were faster for the N 2 O 2 complex containing pyridine while the rates of homopolymerization of ε-CL were faster when the side arm was diethylamine.…”

Bulk Organocatalytic Synthetic Access to Statistical Copolyesters from l-Lactide and ε-Caprolactone Using Benzoic Acid

“…LA is typically incorporated first, although CL gives faster rates than LA in homopolymerization reactions. [21][22][23][24][25][27][28][29][31][32][33][34][35][36][37] Aluminum-based catalysts are most efficient for the statistical and controlled ROcP of LA and CL, 35,[38][39][40] thought less toxic catalysts based on zinc 41 and molybdenum 42 have also been successfully employed for this purpose.Organic catalysis for polymerization is a fast developing field in polymer chemistry, offering a number of advantages over metal-catalysis, such as more sustainable processes, reduced toxicity and cost, and easier catalyst synthesis, purification, handling andstorage. 43,44 In this regard, the organocatalyzed ring-opening polymerization (OROP) of LA and CL has been particularly…”

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

“…Over the past few years, aluminum complexes coordinated with different types of ligands were designed and prepared, to obtain highly efficient precatalyst for ROP of cyclic esters and produce (co)polyesters with structural diversity. [48][49][50][51][52][53][54] Among the various Al complexes, aluminum-salen complexes bearing salicylaldiminato moiety were found to be a versatile type of catalysts for ROP of both small ring-sized lactones and macrolactone. 9,[55][56][57][58][59] Meanwhile, this type of catalyst showed a certain of stereocontrol ability in the ROP of racemic LA (rac-LA), producing semicrystalline PLA from a mixture of L-LA and D-LA.…”