Application In Ring-opening Polymerization Research Articles

Fast and living ring-opening polymerization of ε‑caprolactone by aluminum complexes bearing amino-quinoline ligands

Catalysts drive innovation in sustainable polymers because of their reactivity and selectivity. In this context, the synthesis and characterization of a series of Al complexes (Al1 − Al5) bearing N,N-bidentate amino-quinoline ligands are described, as well as their applications in ring-opening polymerization (ROP) of ε-caprolactone (ε-CL). The amido-coordination Al complexes were directly synthesized by reactions of imino-quinoline compounds with AlMe3 via methyl migration from Al to the carbon atom of imine, as indicated by both NMR spectroscopy and X-ray diffraction. In the presence of BnOH, complexes Al1 − Al5 showed significant reactivity for ROP of ε-CL with good control over molar mass (Mn) and dispersity (Đ < 1.2), and polycaprolactones (PCLs) with high molecular weights (Mn up to 129 kDa) were readily synthesized. Remarkably, immortal catalysis with excess of BnOH (up to 20 equiv. to Al) was achieved to prepare PCLs with predictable Mns, low dispersities, and end groups using an extremely low loading of Al complex (0.05 mol% to ε-CL monomer).

Towards a selective synthetic route for cobalt amino acid complexes and their application in ring opening polymerization of rac-lactide.

Catalysts based on cobalt amino acids and 2,2 bipyridine (bipy) present an attractive and cost-effective alternative as ring opening polymerization catalysts, yet this system remains underexplored despite the advantageous coordination properties of amino acids and bipy as ligands combined with the variety of accessible oxidation states and coordination geometries of cobalt. Here, metal complexes of type [Co(aa)2(bipy)] with amino acids (aa: glycine, leucine and threonine) as ligands are reported. The complexes were characterized spectroscopically (IR, UV-vis and 1H, 13C NMR for diamagnetic species), and by MS spectrometry and elemental analysis. The data reveal that the 2,2 bipyridine acts as a neutral bidentate donor coordinating to the metal ion through two nitrogen atoms and the amino acid acts as a bidentate ligand coordinating through the carboxylate and amino group forming a stable five membered ring and a pseudo-octahedral geometry around the Co center. The activity of the complexes for the ring opening polymerization (ROP) of rac-lactide is presented. The complexes are effective initiators for the ROP of rac-lactide (Kobs = 9.05 × 10−4 s−1) at 100 : 1 [rac-lactide] : [catalyst] 1 M overall concentration of lactide in toluene at 403 K.

Structure and activity relationship studies of N-heterocyclic olefin and thiourea/urea catalytic systems: application in ring-opening polymerization of lactones

Structure–activity relationship studies of N-heterocyclic olefin and thiourea/urea catalytic systems were performed and applied to ROP of lactones.

(Benz)Imidazolin-2-iminato Aluminum, Zinc, and Magnesium Complexes and Their Applications in Ring Opening Polymerization of ε-Caprolactone.

Synthesis and characterization of a new family of aluminum, magnesium, and zinc complexes supported by (benz)imidazolin-2-iminato ligands are reported herein. Under different reaction conditions, (benz)imidazolin-2-imine ligands reacted with metal alkyl precursors to afford the corresponding complexes, displaying mononuclear, binuclear, and trinuclear structures. Reaction in 1:1 stoichiometry at room temperature afforded the simple Lewis acid-base adducts, which exhibited distorted tetrahedral geometries around the metal centers, whereas high temperature reactions gave rise to dimeric complexes, with each metal bridging two (benz)imidazolin-2-imine ligands to form a four-membered metallacycle ring at the center of the complexes. The catalytic ring opening polymerization (ROP) of ε-caprolactone was studied using these complexes as precatalysts in the presence of isopropanol, and very high activities were observed, affording high/medium molecular weight poly(ε-caprolactone) products with low polydispersity indices. Detailed kinetic studies revealed that the polymerizations proceeded in a living manner and molecular weights of the polymers could be precisely controlled.

N,O-Amino-phenolate Mg(II) and Zn(II) Schiff base complexes: Synthesis and application in ring-opening polymerization of ε-caprolactone and lactides

Solventless grinding of 2-aminophenol and the corresponding aldehyde furnished compounds 2-(pyridin-2-ylmethylene)aminophenol (L1), 2-(pyridin-4-ylmethylene)aminophenol (L2), 2-(thiophen-2-ylmethylene)aminophenol (L3) and 2-(furan-2-ylmethylene)aminophenol (L4), in excellent yields of 97–99%. Reaction of ligands L1–L4 with zinc or magnesium alkyl solutions produced complexes [Mg(L1)2] (1), [Mg(L2)2] (2), [Mg(L3)2] (3) and [Mg(L4)2] (4) or [Zn(L1)2] (5), [Zn(L2)2] (6), [Zn(L3)2] (7) and [Zn(L4)2] (8). The complexes were characterized by 1H NMR, 13C NMR and IR spectroscopies, elemental analysis and mass spectrometry. Complexes 1 was further analysed by single-crystal X-ray crystallography. The complexes were investigated as catalysts/initiators in the ring-opening polymerization (ROP) of ε-caprolactone (ε-CL), ʟ-lactide (ʟ-LA) and rac-lactide (rac-LA). Mg(II) complexes 1–4 (kapp = 0.12–0.58 h−1) were more efficient catalyst as compared to the Zn(II) complexes 5–8 (kapp = 0.04–0.24 h−1). The catalytic activity was enhanced by adding of alcohol co-initiators. Comprehensive kinetic and mechanistic investigations revealed that the polymerization reaction follows pseudo-first-order kinetics. Moderate molecular weights increased from 1234 to 4567 g mol−1 with an increase in catalyst concentration with polydispersity (PDIs) ranging from 1.4 to 2.0. The enthalpy ΔHp were found to be 23.5 and 63.9 kJ mol−1 while the entropy of activation (ΔSp) values were −157 and −33 JK−1 mol−1 for ε-CL and ʟ-LA monomers, respectively.

Zinc and Magnesium Complexes Bearing Oxazoline-Derived Ligands and Their Application for Ring Opening Polymerization of Cyclic Esters.

A family of different substituents aza(oxazoline) ligand-based zinc and magnesium complexes were synthesized. These complexes can catalyze ring opening polymerization of ε-caprolactone (ε-CL) and lactide (LA) to produce poly-ε-caprolactone and polylactide with good conversions. Polymerization studies showed that the zinc complexes 1a–4a had moderate activity toward LA and ε-CL polymerization. In situ IR spectroscopy research of zinc complexes showed that the N-donor group-substituted complexes had higher activity than that of the O-ether donor group. The substituted analogies and the flexibility of the amino backbone had a distinct influence on the activity of LA and ε-CL polymerization. The alternates of zinc with magnesium produced complexes 5a–8a, which achieved an obviously increased polymerization activity. Among these magnesium complexes, 7a showed the highest activity in the polymerization of LA. At [M]/[cat] = 1000, the reaction progress was stabilized in 5 min with up to 97% conversion of a monomer at ambient temperature.

Zinc bis-pyrrolide-imine complexes: Synthesis, structure and application in ring-opening polymerization of rac-lactide

A series of bis-ligated zinc complexes with pyrrole-imine ligands were successfully synthesized and characterized by 1H and 13C{1H} NMR, and by X-ray crystallography for Zn1 and Zn3. These zinc complexes were used as catalysts for the ring-opening polymerization of rac-lactide in a toluene solution, under bulk conditions, in the presence and absence of benzyl alcohol. The complexes proved to be active in the presence of benzyl alcohol as co-initiator and chain transfer agent. Polymers were formed with high conversions and with well-matched experimental and calculated molar mass values. Under solvent-free conditions, high conversions were obtained after 1 h with good molecular control and satisfactory polydispersity. The homo-decoupled 1H NMR spectra of the methine regions of the PLA samples were consistent with the formation of polymer chains with slightly tendency to heterotacticity.

Synthesis, Characterization of Zinc Complexes with Neutral α-Diimine Ligands and Application in Ring-opening Polymerization of ε-Caprolactone.

A series of neutral α-diimine ligands with diacetyl and acenaphthenequinone skeletons were prepared by the reaction between diacetyl and the corresponding aromatic amine. These ligands reacted with ZnCl2 to generate symmetric α-diimine zinc complexes C1-C10. Experimental results indicated that the α-diimine zinc complexes with a diacetyl skeleton (C1-C4) were active in ring-opening polymerization (ROP) of ε-caprolactone (ε-CL). The complexes with an acenaphthenequinone skeleton showed a small steric effect (C5, C8 and C9) but the complex substituted with an electron-withdrawing group (C10) showed high activity in the monomer conversion rate during ROP of ε-CL. The ROP catalysts of ε-CL demonstrated the mechanism of monomer activation in the presence of benzyl alcohol.

Synthesis of dinuclear aluminum complexes bearing bis-phenolate ligand and application in ring-opening polymerization of ε-caprolactone

Dinuclear zwitterionic aluminum complexes were prepared and applied as efficient catalysts toward ROP of ε-CL in a controlled manner.

Titanium alkoxides immobilized on magnetic mesoporous silica nanoparticles and their characterization by solid state voltammetry techniques: Application in ring opening polymerization

In this paper, we present the synthesis of mesoporous silica coated Fe3O4 core–shell nanoparticles or magnetic mesoporous silica nanoparticles (MMSNs) via a surfactant templated sol–gel method using magnetite nanoparticles (MNPs) stabilized with tartrate as nucleation seeds. The synthetic parameters have been carefully controlled in order to scale up the synthetic procedure to obtain more than 1 g of stable, high quality core–shell and biocompatible MMSNs per synthesis. MMSNs have been used as support to prepare heterogeneous titanium catalysts for ring opening polymerization (ROP) of ε-caprolactone. The prepared materials have been fully characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF) N2 adsorption-desorption, transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TG-DTG), UV–vis and DRUV-vis techniques. In addition, extensive solid state electrochemical studies have been carried out in aqueous and organic medium demonstrating the coating of MNPs with a layer of mesoporous silica and the immobilization of titanium as electroactive species.

Zinc bis-Schiff base complexes: Synthesis, structure, and application in ring-opening polymerization of rac-lactide

A series of bis-ligated zinc complexes supported by Schiff base ligands were successfully synthesized and characterized by 1H, 13C NMR, elemental analysis, and X-ray crystallography. These zinc complexes can be used as catalysts for the polymerization of rac-lactide in solution as well as in molten lactide. The results show that all catalysts exhibited high catalytic activity and obtained moderate heterotactic PLAs with the expected molecular weight. Complex 1 can catalyze the polymerization of rac-lactide under controllable conditions with living and immortal character in toluene solution. In addition, the steric hindrance and electronic effects has a great influence on the catalytic activity and selectivity of catalysts.

ChemInform Abstract: Aluminum Alkyl Complexes: Synthesis, Structure, and Application in ROP of Cyclic Esters

AbstractReview: 112 refs.

Designing ancillary ligands for heteroleptic/homoleptic zinc complex formation: synthesis, structures and application in ROP of lactides.

Synthesis and characterization of a series of new amino-phenol/naphthol ligands (L(1,2)-H) have been developed and their respective zinc complexes ( 1 and 2-Zn ) have been synthesized. The molecular structures of L(1)-H and 1, 2-Zn were explored in detail by NMR, single-crystal X-ray studies and DFT calculations, which confirmed the existence of complexes as stabile dimers both in a solution and in the solid state. All complexes mediate the ring-opening polymerization (ROP) of lactide highly efficiently, at room temperature, in a controlled fashion. The influence of the architecture of the ligand on the desired homo/heteroleptic complex formation, as well as the relationship between the initiator design and the catalytic activity have been investigated.

Zinc complexes supported by methyl salicylato ligands: synthesis, structure, and application in ring-opening polymerization of l-lactide

Two novel zinc alkoxides supported by chelating methyl salicylato (MesalO; MesalOH = methyl salicylate) ligands were successfully synthesized and characterized. Reaction of MesalOH with ZnEt2 (2:1) gives a tetranuclear cluster [Zn(MesalO)2]4 (1), which by addition of pyridine is transformed to the mononuclear compound [Zn(MesalO)2(py)2] (2). Compounds 1 and 2 were characterized by elemental analysis, NMR, IR, and single crystal X-ray diffraction. The catalytic activity of both compounds was tested for the ring-opening polymerization (ROP) of L-lactide (L-LA). It was found that compounds 1 and 2 are efficient initiators of the ROP of L-LA, yielding cyclic PLLA with weight average molecular weights up to 100 kDa for 2. The treatment of 2 with 1 equiv. of BnOH in toluene afforded a dimeric compound [Zn(OBn)(MesalO)(py)]2 (3). The addition of L-LA to a combination of 1 and 4 equiv. of BnOH in THF or 2 and 1 equiv. of BnOH in toluene led to the rapid and efficient generation of PLLA with end-capped BnO groups.

Synthesis and Characterization of Multi-Alkali-Metal Tetraphenolates and Application in Ring-Opening Polymerization of Lactide

A series of alkali metal complexes supported by two bulky tetraphenols were synthesized and characterized. The reactions of α,α,α',α'-tetra(3,5-di-tert-butyl-2-hydroxyphenyl)-p-xylene(para-tetraphenol) with (n)BuLi, sodium, and KSi(NMe(2))(3) gave bimetallic complexes 1, 2, and 3, respectively. Treatments of the α,α,α',α'-tetra(3,5-di-tert-butyl-2-hydroxyphenyl)-m-xylene(meta-tetraphenol) with 2 or 4 equiv of (n)BuLi afforded complexes 4 or 5, while the reactions of meta-tetraphenol with sodium and KSi(NMe(2))(3) gave only trimetallic complexes 6 and 7 for the additional p-π interaction. Complexes 1-7 were all characterized by single-crystal X-ray diffraction techniques. In the presence of benzyl alcohol, all complexes are active catalysts for the ring-opening polymerization of L-lactide. Comparatively, bimetallic complexes 1, 2, and 3 are more efficient catalysts because of their symmetric structures, in which complex 3 presents as a rare highly active potassium catalyst for the ring-opening polymerization of lactide, leading to polymers with good molecular weight control and narrow molecular weight distributions.

Zinc Complexes Supported by Maltolato Ligands: Synthesis, Structure, Solution Behavior, and Application in Ring-Opening Polymerization of Lactides

A series of novel zinc alkoxides supported by chelating maltolato (MalO; MalOH = maltol) ligands were successfully synthesized and characterized. Reaction of MalOH with ZnEt2 (3:4) gives a trinuclear cluster [Zn3(Et)2(MalO)4] (1), which spontaneously disproportionates in solution to mononuclear species [Zn(MalO)2] (1a) and [Zn(Et)(MalO)] (1b); (1a) and (1b) form [Zn(MalO)2(py)] (2), [Zn(Et)(MalO)(py)] (3), [Zn(MalO)2]2 ((1a)2), [Zn(MalO)(OBn)]2 ((1c)2), and [Zn4(Et)2(OEt)2(MalO)4] (4) on addition of pyridine, benzyl alcohol (BnOH), or dry O2, respectively. Compounds 1, 2, (1a)2, and 4 were characterized by elemental analysis, NMR, ESI-MS, and single-crystal X-ray structural analysis. Variable-temperature NMR experiments showed that (1a)2 and (1c)2 are in equilibrium with the monomeric form in solution. The addition of l-lactide (l-LA) to a combination of 1 and 2 equiv of BnOH in dichloromethane at room temperature in different molar ratios leads to rapid and efficient generation of poly(l-LA) with end-cap...

Synthesis of Poly(lactide)s with Modified Thermal and Mechanical Properties

The use of poly(lactide)-based materials is, in part, limited by their physical and mechanical properties. This article reviews the methods that have been employed to enable enhancement of the materials properties through synthetic manipulation of the polymer structure including block copolymer synthesis and modification of the lactide monomer structure, focusing on the application of ring-opening polymerization. In turn the effect of these structural modifications on the properties of the resultant materials are reported.

Synthesis, characterization of sodium and potassium complexes and the application in ring-opening polymerization of L-lactide

Abstract A novel sterically bulky phenol (2,4-di-tert-butyl-6-(1-(3,5-di-tert-butyl-2-(2-(2-methoxyethoxy)ethoxy)phenyl)ethyl)phenol)(HL) and corresponding dimeric sodium and potassium complexes [ML]2 (1: M = Na, 2: M = K) have been prepared and structurally characterized. Experimental results showed that complexes 1 and 2 can efficiently initiate the ring-opening polymerization of lactide in a controlled fashion, yielding polymers with expected molecular weight and low polydispersity indexes.

Synthesis, characterization of potassium bulky phenolate and application in ring-opening polymerization of L-lactide

Abstract The reaction of 2,2′-ethylidenebis(4,6-di-tert-butylphenol) (EDBP-H2) with potassium gives [EDBPH·K·(THF)2] (1) in 92% yield. Experimental results show that potassium complex 1 is an efficient catalyst for the ring-opening polymerization of lactide in controlled fashion, yielding polymers with expectative molecular weight and low polydispersity indexes. Furthermore, the complex 1 has isotactic selectivity for the ring-opening polymerization of rac-lactide.

Synthesis, characterization of aluminum complexes and the application in ring-opening polymerization of l-lactide

Aluminum complexes supported by a sulfonamide/Shiff base ligand are described. Reaction of AlMe 3 with 1 equiv of ligand 1, gives methyl aluminum complex 2, and aluminum complex 3 is prepared by the reaction of complex 2 with 1 equiv of benzyl alcohol. Experimental results show that complex 3 is an efficient initiator for the ring-opening polymerization of lactide in controlled fashion, yielding polymers with expectative molecular weight and low polydispersity indexes. Furthermore, the complex 3 has isotactic selectivity for the ring-opening polymerization of rac-lactide.