Alekha Kumar Sutar

Ring-opening polymerization by lithium catalysts: an overview

This critical review summarizes recent developments in the preparation and application of lithium catalysts/initiators such as, alkyl lithium, alkoxy lithium and bimetallic lithium compounds for ring-opening polymerization (ROP). The ROP of cyclic esters, cyclic carbonates, cyclo-silazanes, cyclo-silanes, cyclo-siloxanes, cyclo-carboxylate, cyclic phosphirene and quinodimethanes are covered in this review. The present paper emphasizes the polymerization kinetics and the control exhibited by the different types of lithium initiators/catalysts. For the cases where useful properties, such as high molecular weight, narrow PDI, or stereocontrol, have been observed, a more detailed examination of the mechanistic studies of the catalysts/initiators are provided. Furthermore, this review also focuses on the synthesis of block copolymers and graft copolymers by ROP principle. The topics covered in this review regarding lithium compounds toward ROP will be of interest to inorganic, organic and organometallic chemists, material, polymer and catalytic scientists due to its unique mode of activation as compared to transition and inner transition-metals. In addition, use of these compounds in catalysis is steadily growing, because of the complementary reactivity toward ROP as compared to other metals. Finally, some aspects and opportunities which may be of interest in the future are suggested (143 references).

Synthesis and structural studies of heterobimetallic alkoxide complexes supported by bis(phenolate) ligands: efficient catalysts for ring-opening polymerization of L-lactide.

A series of heterobimetallic titanium(IV) complexes [LTi(O(i)Pr)(mu-O(i)Pr)(2)Li(THF)(2)], [LTi(O(i)Pr)(mu-O(i)Pr)(2)Na(THF)(2)], [LTi(mu-O(i)Pr)(2)Zn(O(i)Pr)(2)], and [LTi(mu-O(i)Pr)(2)Mg(O(i)Pr)(2)] (where L = bidentate bisphenol ligands) have been synthesized and characterized including a structural determination of [L(1)Ti(mu(2)-O(i)Pr)(2)(O(i)Pr)Li(THF)(2)] (1a). These complexes were investigated for their utility in the ring-opening polymerization (ROP) of l-lactide (LA). Polymerization activities have been shown to correlate with the electronic properties of the substituent within the bisphenol ligand. In contrast to monometallic titanium initiator 1e, all the heterobimetallic titanium initiators (Ti-Li, Ti-Na, Ti-Zn, and Ti-Mg) show enhanced catalytic activity toward ring-opening polymerization (ROP) of l-LA. In addition, the use of electron-donating methoxy or methylphenylsulfonyl functional ligands reveals the highest activity. The bisphenol bimetallic complexes give rise to controlled ring-opening polymerization, as shown by the linear relationship between the percentage conversion and the number-average molecular weight. The polymerization kinetics using 2c as an initiator were also studied, and the experimental results indicate that the reaction rate is first-order with respect to both monomer and catalyst concentration with a polymerization rate constant, k = 81.64 M(-1) min(-1).

Synthesis and Immortal ROP of L-Lactide Using Copper Complex

In the present work, the -ONNO- tetradentate Schiff base ligand N, N′-bis (2-hydroxy-3-methoxybenzaldehyde) propylenediamine, [HMBPD] was synthesized. Further, complexation of this ligand with copper [HMBPD-Cu] was carried out and their reactivity for the ring-opening polymerization (ROP) of lactide (LA) has been studied. This monomeric copper complex is prepared by the reactions of copper solution with one molar equivalent of HMBPD Schiff-base ligand in ethanol under nitrogen atmosphere. This copper complex has been characterized by different spectroscopic methods, which showed square planner geometry. The copper complex is highly active towards ROP of LA. The rate of polymerization is heavily dependent on the initiator used. The copper complex allows controlled ring-opening polymerization as shown by the linear relationship between the percentage conversion and the number-average molecular weight. On the basis of literature reports, a mechanism for ROP of lactide has been proposed.

Polymer supported nickel complex: Synthesis, structure and catalytic application

AbstractIn the present investigation, a new synthetic route for a novel recyclable free [3-MOBdMBn-Ni] and polystyrene-anchored [P-3-MOBdMBn-Ni] nickel complexes is presented. The free and polymer-anchored metal complexes were synthesized by the reaction of nickel (II) with one molar equivalent of unsupported N N′-bis (2-Hydroxy-3-methoxybenzaldehyde) 4-Methylbenzene-1,2-diamine (3-MOBdMBn) or polymer-supported (P-3-MOBdMBn) Schiff-base ligand in methanol under nitrogen atmosphere. The advantages of these polymer-supported catalysts are the low cost of catalyst and recyclability up to six times, due to easy availability of materials and simple synthetic route. The higher efficiency of complexation of nickel on the polymer-anchored 3-MOBdMBn Schiff base than the unsupported analogue is another advantage of this catalyst system. The structural study reveals that nickel(II) complex of 3-MOBdMBn is square planar in geometry. The catalytic activity of nickel complex towards the oxidation of phenol was investigated in the presence of hydrogen peroxide. Experimental results indicate that the reactivity of P-3-MOBdMBn-Ni was dramatically affected by the polymer support compared to free 3-MOBdMBn-Ni. The rates of oxidation (Rp) for unsupported and supported catalysts are 1.37 × 10−6 mole dm−3 s−1 and 2.33 × 10−6 mole dm−3 s−1 respectively. Graphical AbstractThe catalytic activity of free [3-MOBdMBn-Ni] and polystyrene-anchored [P-3-MOBdMBn-Ni] nickel complexes were tested towards oxidation of phenol and the effect of the H2O2 concentration/phenol concentration/catalyst concentration is presented.

Retracted Article: Ring-Opening Polymerization of Lactide by Aluminium Catalyst

This review summarizes recent developments in the preparation and use of aluminium catalysts/initiators such as, monometallic aluminium and bimetallic aluminium compounds for the ring opening polymerization of lactide (L-lactide and rac-lactide). The organoaluminium catalysts/initiators have been synthesized and characterized by different spectroscopic techniques, including X-ray crystal structural studies and NMR data. Lactide polymerization has been analyzed by NMR and GPC methods. The present paper emphasizes on the polymerization kinetics and the control exhibited by the different types of aluminium initiators/catalysts. For the cases, where useful properties, such as high molecular weight, narrow PDI, or stereocontrol, have been observed, a more detailed examination of the catalysts/initiators are provided. Keywords Ring-opening polymerization, aluminium catalyst, poly(lactic acid), stereoselective, polydispersity index, living polymerization

Salicylaldimine Copper(II) complex catalyst: Pioneer for ring opening Polymerization of Lactide

AbstractSalicylaldimine copper complex has been synthesized and its reactivity for the ring-opening polymerization (ROP) of lactide has been studied. This monomeric copper complex was prepared by the reaction of copper(II) solution with one molar equivalent of salicylaldimine Schiff-base ligand in methanol under nitrogen atmosphere. This copper complex has been characterized by different spectroscopic methods, which showed square planar geometry. The molecular structure of the salicylaldimine Schiff-base has been determined by X-ray diffraction studies. The complex was tested as the initiator for the ring-opening polymerization of lactide, with variation in diamine group in ligand. The rate of polymerization is dependent on the diamine group in the following order: ethylene > propylene > phenyl. The salicylaldimine copper complex allows controlled ring-opening polymerization as indicated by the linear relationship between the percentage conversion and the number-average molecular weight. On the basis of literature reports, a mechanism for ROP of lactide has been proposed. Graphical AbstractThis article describes the synthesis and characterization of salicylaldimine copper(II) complexes, and their catalytic activity towards ring-opening polymerization of L-lactide.

Retraction: Ring-opening polymerization of lactide by aluminium catalyst

Retraction of ‘Ring-Opening Polymerization of Lactide by Aluminium Catalyst’ by Anita Routaray et al., Catal. Sci. Technol., 2015, DOI: 10.1039/c5cy00454c.