Highly efficient magnesium initiators for lactide polymerization

Abstract

Two monomeric, six-coordinated magnesium complexes with bulky aminophenolate ligands [(Htbpoa)2Mg] (1) and [(Htbpca)2Mg(THF)2] (2), where Htbpoa =N-[methyl(2-hydroxy-3,5-di-tert-butylphenyl)]-N-methyl-N-methyl-1,3-dioxolaneamine and Htbpca =N-[methyl(2-hydroxy-3,5-di-tert-butylphenyl)]-N-methyl-N-cyclohexylamine have been prepared, characterized and employed as initiators for lactide polymerization. The crystal structure of the homoleptic compound 1 has been determined and shows that the six-coordinate magnesium atom in 1 is surrounded by two tridendate tbpoa ligands. In the solution, however, complex 1 exists in equilibrium with a five-coordinate species 1a having one oxolane fragment dangling. The tbpoa and tbpca ligands in 1 and 2 play a dual role, as the ancillary ligand stabilizing the monomeric magnesium species and as the initiating polymerization group.

Improving the ring-opening polymerization of ε-caprolactone and l-lactide using stannous octanoate

“…The preparation of PCL and PLA, of which ring-opening polymerization (ROP) is the preferred method, has been studied intensively in recent years. Currently, metal catalysts [9][10][11][12][13][14][15][16] are used to initiate the ROP of related cyclic esters [17,18]. However, most are air sensitive and difficult to control without the glove box and vacuum lines.…”

Gold(I) N-heterocyclic carbene based initiators for bulk ring-opening polymerization of l-lactide

“…Furthermore, the polylactide polymers have found wide utility in medical and pharmaceutical applications because of their good mechanical strength and biodegradability [28,29]. Our specific interest in the bulk polymerization [30] of the L-lactide under solvent-free melt conditions, as opposed to the solution polymerization [31] is due to the preference for bulk polymerization for the large-scale production of PLAs. Though a much greater control is achieved in solution polymerization compared to the bulk polymerization, the solution polymerization suffers from certain limitations as owing to their higher reactivities they are often susceptible to the impurity levels and to the various unwanted reactions like, racemization and transesterification [32].…”

Well-controlled, zinc-catalyzed synthesis of low molecular weight oligolactides by ring opening reaction

“…Sn(Oct) 2 and ZnEt 2 (1 M solution in hexanes) were purchased from Sigma-Aldrich and used as received. The ligand precursor N-[methyl(2-hydroxy-3,5-di-tert-butylphenyl)]-N-methyl-N-cyclohexylamine (l-H) and zinc complex ZnL 2 were prepared according to published procedure [31,32]. Tetrahydrofurane (THF) was distilled from CuCl, predried over NaOH, and then distilled from Na/benzophenone; toluene, benzene-d 6 (C 6 D 6 ), and hexanes were dried under Na; CH 2 Cl 2 was dried over P 2 O 5 ; methanol was distilled from Mg; propargyl alcohol (PrgOH) was dried over sieves and distilled prior to use.…”

“…field of ROP catalysts, but some of them might have the tendency to indicate selectivity towards polymerization or alcoholysis of lactides depending on reaction conditions. This dual display of ROP reaction has been observed for homoleptic metal complexes with N,O-donor ancillary ligands [29][30][31]. Such complexes, based on biologically benign metals as for instance magnesium and zinc could constitute a versatile class of catalytic systems well suited for the synthesis of polymers from high to ultra-low-molecular-weight and new macromonomers for classical ROP and SAP processes.…”