Initiators For Ring-opening Polymerization Research Articles

Tetrylenes based on tri- and tetradentate ONO-, NNO-, NNN-, and ONNO-type ligands: synthesis, structure, and reactivity

The review discusses the results of the authors’ research aimed at the synthesis of stable tetrylenes (germylenes and stannylenes) and the determination of the structure of these compounds, including their oligomeric degree. Substituted dialkanolamines, dialkylenetriamines, aminobisphenols, pyridine and phenanthroline-containing dialcohols, and some other derivatives were used as the ligands for the synthesis. The reactivity of monomeric and dimeric tetrylenes in the reactions proceeding with both the change and the retention of the oxidation state of the metal atom (2+) is discussed in detail, as well as the influence of the oligomeric degree on the reactivity. The use of tetrylenes in synthetically useful reactions as ligands for catalytically active transition metal complexes, as well as initiators for ring-opening polymerization of cyclic esters, is analyzed.

Homo‐ and random copolymerizations of ω‐pentadecalactone with ε‐caprolactone using isothiourea‐based dual catalysis

ABSTRACTIn this study, the catalytic behavior of dual catalysis based on isothioureas (ITUs) for ring‐opening polymerization (ROP) of macrolactone ω‐pentadecalactone (PDL) and its copolymerization with ε‐caprolactone (CL) has been investigated in detail. In the presence of benzyl alcohol (BnOH) initiator, 2,3,6,7‐tetrahydro‐5H‐thiazolo[3,2‐a]pyrimidine (THTP) acted as a representative organic compound, which coupled with magnesium halides (MgX2) as cocatalysts and catalyzed the polymerization in toluene at 70 °C. Under suitable conditions, an array of polymers with controlled molecular weights and relatively narrow molecular weight distributions were synthesized. The formation of homopolymers and copolymers with different architectures was verified using GPC, DSC, NMR, and matrix‐assisted laser desorption/ionization time‐of‐flight (MALDI‐ToF) mass. The MALDI‐ToF mass spectrometry (MS) analysis of poly(ω‐pentade‐calactone) (PPDL) provided direct evidence for the successful initiation of ROP of PDL using BnOH to obtain linear PPDL with a very small amount of oligomer. The NMR analysis indicated that the arrangements of PDL and CL units in the copolymer chains were completely random. The thermal stability of copolymers was composition dependent and increased with the increase in the content of PDL unit. Furthermore, the proposed polymerization mechanism is a dual catalytic mechanism. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019

Nonmigratory Poly(vinyl chloride)-block-polycaprolactone Plasticizers and Compatibilizers Prepared by Sequential RAFT and Ring-Opening Polymerization (RAFT-T̵-ROP)

Well-defined nonmigrating polymeric plasticizers, poly(vinyl chloride)-block-polycaprolactone (PVC-b-PCL), were synthesized by sequential reversible addition–fragmentation chain transfer (RAFT) polymerization and ring-opening polymerization (ROP) with 2-hydroxyethyl 2-(ethoxycarbonothioylthio)propanoate (HECP) as RAFT agent and incipient initiator for ROP of e-caprolactone (CL, oxepan-2-one). Kinetic experiments demonstrated that HECP provided good control in RAFT polymerization of vinyl chloride (VC) with dispersity (Đ) ∼ 1.2 for 3400 < Mn < 11000. Chain extension experiments with VC and vinyl acetate proved the high end-group fidelity of the macroRAFT agent formed. The hydroxy end-group of the PVC macroRAFT agent allowed its use as a ROP initiator in forming a series of PVC-b-PCL with different PCL block lengths by RAFT-T-ROP. Characterization by wide-angle X-ray diffraction (WAXD), polarized light microscopy (PLM), and differential scanning calorimetry (DSC) indicates that there is enhanced chain enta...

Real-time monitoring of stereocomplex formation of poly(l-lactide) and poly(d-lactide) decorated with a pyrene derivative as a fluorescence probe

In this study, the stereocomplexation of poly-l-lactide (PLLA) and poly-d-lactide (PDLA) was monitored in real time using fluorescence spectroscopy. To introduce fluorescence probes at the beginning (i.e., α position) of the PLLA and PDLA chains, a pyrene derivative was employed as an initiator for ring-opening polymerization of l,l-lactide (LLA) and d,d-lactide (DLA), respectively, and the post-polymerization functionalization of the hydroxyl end-groups of the PLLA were obtained by initiating LLA using the BuOH/Sn(Oct)2 system to form polylactide decorated with a pyrene moiety on the opposite polymer chain-end (i.e., ω position). Using these approaches, linear Py-PLLA-OH, Py-PDLA-OH, and Bu-PLLA-Py with molar masses equal to 3100, 3350 and 3300 g mol−1, respectively, were prepared. Next, equimolar compositions of Py-PLLA-OH/Py-PDLA-OH and Py-PDLA-OH/Bu-PLLA-Py in different solvents were prepared, and the stereocomplexation, which is related to excimer formation between the Py end-groups, was directly observed using fluorescence measurements of the excimer emission at 470 nm in both AcCN and THF solutions, respectively. The kinetic curves based on the IE/IM ratio as a function of time are complex in shape and indicate interaction of two enantiomeric chains occurred. In addition, at the beginning of the association, the PLA enantiomeric pairs form stereocomplex crystallites. The probability of parallel and antiparallel interactions of PLA enantiomers during stereocomplexation is similar and consistent with Cantow's calculations. In addition, the DSC analysis of the final PLA products confirmed that only stereocomplex crystallites were formed in these two solvents.

Ligand-free scandium alkyl and alkoxide complexes for immortal ring-opening polymerization of lactide

Ligand-free Ln (CH2SiMe3)3 (THF)2 (1: Ln = Sc; 2: Ln = Lu; 3: Ln = Er; 4: Ln = Y) and La(CH2C6H4-o-NMe2)3 (5) are employed as the initiators for ring-opening polymerization (ROP) of rac-lactide (rac-LA). Complex 4 solely is active but uncontrolled, while complex 1 is inert. In presence of excess benzhydrol, complexes 1–5 can promote the ROP of LA smoothly, in which the molecular weight distribution values of the resultant polymer are related to the radii of the rare-earth metals. Complex 1 displays high activity for the controlled ROP of LA, in which the benzhydrol act a dual role as chain-transfer agent and activator. The polymerizations proceed smoothly and efficiently in a wide range of benzhydrol feeding (3–150 equiv). The molecular weights of the obtained PLAs can be precisely controlled by the monomer loading with respect to that of benzhydrol, while the molecular weight distribution (MWD) maintains a very narrow level (PDI = 1.05–1.18). Every scandium centre by means of chain-transfer reaction with benzhydrol to generate the active species Sc(OCHPh2)3·THF (6), grows apparently up to 150 PLA polymer chains, showing a typical feature of an immortal polymerization.

Aluminum Complexes Based on Tridentate Amidoalkoxide NNO-Ligands: Synthesis, Structure, and Properties

A series of novel NNO-type ligands 12a-17a, LH2, R1N(CH2CH2NHTs)CHR2CR3R4OH (R1 = Bn, R3 = R4 = H; R2 = H (12a), R2= (S)-Ph (13a), R2= (S)-Bn (14a), R2= (S)-i-Bu (15a); R1 = R2= (R)-Me, R3 = H, R4= (S)-Ph (16a); R1 = Bn, R2= (S)-i-Bu, R3 = R4 = Ph (17a)) was obtained; the ligands LH2 feature various degree of substitution, steric bulkiness, and chirality. Treatment of 11a (R1 = Me, R2 = R3 = R4 = H), 12a-17a, and 18a (R1 = Me, R2 = H, R3 = R4 = Ph) with AlMe3 afforded the complexes 11b-18b, [LAlMe]n (n = 1, 2). It was demonstrated that the structure of the ligand determines the monomeric (16b-18b, R3, R4 = Ph) or dimeric (11b-15b, R3 = R4 = H) structure of the complexes. The discussion of the stereochemical consequences caused by dimerization and chirality of the ligands is performed. The molecular structures of dimeric 11b, 12b, 15b, and monomeric 17b were studied by single-crystal X-ray diffraction. Complexes 11b, 12b, 14b, and 17b are active initiators in ring-opening polymerization of l-lactide in the absence of alcohol. Furthermore, 11b-13b, 17b, and 18b demonstrate an outstanding catalytic activity and selectivity in alcoholysis of l-lactide to give (S,S)-methyl lactyllactate.

Polymerization of N-Substituted Glycine N-Thiocarboxyanhydride through Regioselective Initiation of Cysteamine: A Direct Way toward Thiol-Capped Polypeptoids

Because of the high reactivity, N-carboxyanhydride (NCA) can be initiated by the thiol group. On the contrary, N-thiocarboxyanhydride (NTA) is more stable and is able to tolerate it. Herein, we apply cysteamine as a regioselective initiator for ring-opening polymerization (ROP) of N-substituted glycine N-thiocarboxyanhydride (NNTA) to synthesize well-defined thiol-capped polypeptoids. ROPs of sarcosine NTA (Sar-NTA) and N-ethylglycine NTA (NEG-NTA) are well controlled when [M]/[I] ≤ 100 with high yields (>87.5%) producing polypeptoids with designable molecular weights and low polydispersity indices (<1.2). All the polypeptoid chains contain a thiol end group, which is confirmed by NMR analyses, MALDI-ToF MS spectra, and Ellman’s assay. Through radical-mediated thiol–ene reaction with styrene, all the thiol chain ends are transferred to oligostyrene, revealing the convenience of further modification. Benefiting from the thiol–ene click chemistry, thiol-capped polysarcosine (PSar) and poly(N-ethylglycine) (PNEG) are promising candidates to replace PEG for their nontoxicity and biocompatibility.

Synthesis and structures of aluminum ion-pair complexes that act as L- and racemic-lactide ring opening polymerization initiators

Seven aluminum ion-pair complexes (1–7) were synthesized by reaction of NNO Schiff base ketoimines with differing substituents with tris(2,6-dimethylphenoxy) aluminum dimer in an inert atmosphere glovebox at room temperature. The complexes were characterized with 1H, 13C, and 19F nuclear magnetic resonance spectroscopy, absorbance spectroscopy, and elemental analysis. Furthermore, the dinuclear nature of the complexes was elucidated with single crystal X-ray crystallography and 27Al NMR. The ion-pair complexes consisted of a bis-ligating homoleptic ketoiminate with octahedral coordination as an aluminum cation complex and a tetrahedral aluminum anion complex of 2,6-dimethylphenoxide. Each ion-pair was used to initiate the ring opening polymerization (ROP) of L- and rac-lactide to poly-lactic acid (PLA) in toluene at 100 °C at a 100:1 [LA]:[ion-pair] ratio. Proton NMR spectra showed percentage conversions of monomer to polymer of 96–99% in 18 h. The isolated polymeric materials were determined to have moderate molecular weights with low to moderate polydispersity index values using gel permeation chromatography. The bis-ligated aluminum cation and tetraphenoxide aluminate anions of 1 were isolated into separate compounds (8 and 9) with unreactive counter ions, and each yielded low molecular weight PLA under the polymerization conditions. Thus, lactide polymerization appeared to require both ion-pair components to yield the moderately high molecular weight PLA, and this was investigated spectroscopically.

An Insight into the Anionic Ring-Opening Polymerization with Tetrabutylammonium Azide for the Generation of Pure Cyclic Poly(glycidyl phenyl ether)

We evaluate the use of tetrabutylammonium azide (N3NBu4) as an anionic ring-opening polymerization initiator for synthesizing azide-terminated linear poly(glycidyl phenyl ether) and then generating monocyclic structures with high purity. In particular, we perform a detailed study on the end-group fidelity of polymers obtained by initiation with N3NBu4 in the presence and absence of trisisobutylaluminum (iBu3Al) and evaluate the purity of the cyclic structures obtained via copper-catalyzed alkyne–azide cycloaddition “click” reaction. We demonstrate that in contrast to the polymerization initiated by N3NBu4 alone, the polymerization performed in the presence of iBu3Al allows the formation of polymers with high end-group fidelity (azide groups at the α-position) for Mn < 20 kDa. The cyclic purity is evaluated by SEC with triple detection and dielectric spectroscopy. The latter technique, although not conventional for such a purpose, is shown to be very convenient to ensure cyclic purity in polymers showing a...

API-ammonium ionic liquid – Polymer compounds as a potential tool for delivery systems

The objective of the present study was to synthesized a novel drug delivery system based on ammonium ionic liquid containing active pharmaceutical ingredients (API) grafted–Poly(L-lactide) (API-IL-PLA). Sparingly water soluble mefenamic acid (MEF) was used as a model drug for the studying of drug loading efficiency and drug release performance. The synthesis of two mefenamic acid (MEF)-ionic liquid compounds composed of MEF in an anionic form and ammonium cation (choline, MEF1), or {di(2-hydroxyethyl)dimethyl ammonium} (MEF2) were presented. The synthesized compounds of MEF1 and MEF2 were used as initiator for ring opening polymerization (ROP) of lactide (LA) with stannous octoate (SnOct2) as a catalyst. The effect of temperature, SnOct2:LA, and MEF:LA ratios on the polymerization process were examined. The PMEF1 and PMEF2 were used for formulation of nanoparticles (NPs) by emulsion-solvent evaporation technique. NPs have spherical shapes and controlled sizes of 330nm to 569nm with high encapsulation efficiency up to 94%. Solid NPs were evaluated for in vitro release in phosphate–buffered saline (pH=7.4) by using dialysis bags at temperature 37°C. Both NPs have shown controlled and sustained release up to 72h and 264h, respectively. The obtained data from drug release profile were characterized by different drug release models and they were fitted with pseudo second order kinetics model with high correlation coefficient (R2=0.999).

Use of samarium(III)–amino acid complexes as initiators of ring-opening polymerization of cyclic esters

Poly(e-caprolactone) (PCL) and poly(l-lactide) (PLA) were prepared by ring-opening polymerization (ROP) using samarium(III) acetate (SmAc3) and amino acid complexes of samarium(III) as initiators. The catalytic behavior of samarium(III) acetate and their respective amino acid complexes, Sm(2,2′-bipyridine)(Ln)3 (L1 = l-aspartic acid; L2 = l-glutamic acid and L3 = glycine), was studied. It could be observed that the amino acid structure and chemical bond type have great influence on the catalytic activity. Polymerization reaction temperature was 125 °C and the effect of time reaction on the conversion of monomers to polymers and the molecular weight were studied. The results indicate that the initiators induce the polymerization of e-caprolactone (e-CL) and l-lactide (l-LA). Polymers were characterized by size exclusion chromatography (SEC) and nuclear magnetic resonance (1H-NMR) and size exclusion chromatography (SEC). Polyesters with average-number molar mass of 1.50 × 103 − 104 Da were obtained. Based on the 1H-NMR end group analysis of low molecular weight of polymers, a coordination–insertion mechanism is proposed for the polymerization of lactones. Kinetics study indicated a polymerization rate of first order with respect to monomer concentration. Differences in the rates of polymerization in the four initiators appeared to be governed by the different degrees of steric hindrance in the initiator structure and monomer.

Hydroxyl Group Tolerated Polymerization of N-Substituted Glycine N-Thiocarboxyanhydride Mediated by Aminoalcohols: A Simple Way to α-Hydroxyl-ω-aminotelechelic Polypeptoids

N-Carboxyanhydride (NCA) polymerization cannot tolerate nucleophilic groups that have the ability of initiation, e.g., hydroxyl group. In contrast, N-thiocarboxyanhydride (NTA) is a much more stable monomer to tolerate them. In this contribution, we investigate aminoalcohols including 2-amino-1-ethanol (AE), 3-amino-1-propanol (AP), 4-aminomethylbenzyl alcohol (AMB), 6-amino-1-hexanol (AH), and 12-amino-1-dodecanol (AD) as initiators for ring-opening polymerization of N-substituted glycine N-thiocarboxyanhydride (NNTA) to prepare α-hydroxyl-ω-aminotelechelic water-soluble polypeptoids. Hydroxyl groups of AE, AP, and AMB are activated by hydrogen bonding with amino groups, which results in a mixture of α,ω-diaminotelechelic and α-hydroxyl-ω-aminotelechelic polypeptoids confirmed by 1H NMR, MALDI-ToF, and SEC measurements. Pure α-hydroxyl-ω-aminotelechelic polypeptoids are synthesized for the first time initiated by AH and AD with controlled molecular weights (1.3–12.4 kg/mol) and low polydispersity indices...

Synthesis and characterization of divinyl-fumarate poly-ε-caprolactone for scaffolds with controlled architectures

A vinyl-terminated polycaprolactone has been developed for tissue engineering applications using a one-step synthesis and functionalization method based on ring opening polymerization (ROP) of ε-Caprolactone, with hydroxyl ethyl vinyl ether (HEVE) acting both as the initiator of ROP and as photo-curable functional group. The proposed method employs a catalyst based on aluminium, instead of the most popular Tin(II) 2-ethylhexanoate, to reduce the cytotoxicity. Following the synthesis of the vinyl-terminated polycaprolactone, its reaction with fumaryl chloride (FuCl) results in a divinyl-fumarate polycaprolactone (VPCLF). The polymers obtained were thoroughly characterized using Fourier transform infrared spectroscopy (FTIR) and gel permeation chromatography (GPC) techniques. The polymer has been successfully employed, in combination with N-vinyl pyrrolidone (NVP), to fabricate films and computer-designed porous scaffolds by micro-stereolithography (μ-SL) with gyroid and diamond architectures. Characterization of the networks indicated the influence of NVP content on the network properties. Human mesenchymal stem cells adhered and spread onto VPCLF/NVP networks showing good biological properties and no cytotoxic effect. Copyright © 2016 John Wiley & Sons, Ltd.

Zirconium amine tris(phenolate): A more effective initiator for biomedical lactide

Here a zirconium amine tris(phenolate) is used as the initiator for the production of polylactide for biomedical applications, as a replacement for a tin initiator (usually tin octanoate). The ring opening polymerization (ROP) was carried out in the melt at 130°C. The zirconium-catalyzed PLA (PLA-Zr) required 30min, resulting in a polydispersity index (PDI) of 1.17, compared to 1h and PDI=1.77 for tin-catalyzed PLA (PLA-Sn). PLA-Zr and PLA-Sn supported osteosarcoma cell (MG63) culture to the same extent (cell number, morphology, extracellular matrix production and osteogenic function) until day 14 when the PLA-Zr showed increased cell number, overall extracellular matrix production and osteogenic function. To conclude, the reduction in reaction time, controllable microstructure and biologically benign nature of the zirconium amine tris(phenolate) initiator shows that it is a more effective initiator for ROP of polylactide for biomedical applications.

Investigation of the biocompatibility and cytotoxicity associated with ROP initiator and its role in bulk polymerization of l-lactide

Poly (l-lactide) (PLLA) is one of the most attractive polymers for use in biomedical applications. In such applications it is necessary to reduce the use of toxic chemicals and catalysts used in PLLA synthesis, to minimize any adverse effects. In view of this, we have performed ring opening polymerization (ROP) of l-lactide (LA) using biocompatible initiator, namely, Zinc l-Proline (ZnP) in bulk. High molecular weight PLLA (Mw up to 1.45 × 105 Da) was obtained using the ZnP complex. The ZnP complex is safe, easy to prepare, store and handle. 1H and 13C NMR spectra of PLLA were used to determine the extent of monomer conversion and stereo sequence respectively. Differential Scanning Calorimetry (DSC) and Size Exclusion Chromatography (SEC) were used to determine thermal properties, Mn, Mw and polydispersity index respectively. The mechanism of ROP of LA in the presence of ZnP was studied using Density Functional Theory (DFT) which was in good agreement with results from 1H NMR and Matrix-Assisted Laser Desorption/Ionization Spectrometry (MALDI-TOF). Biocompatibility/non toxicity of PLLA prepared using ZnP was studied in-vitro using MTT assay by examining the proliferation rate of mouse myoblast C2C12 cell line. Escherichia coli and Staphylococcus aureus were used for the study of antibacterial activity of PLLA.

Synthesis and Application of Bimetallic Zinc(II) Phenoxy-Imine Complexes as Initiators for Production of Lactide Polymers

This article reports the synthesis of two bimetallic zinc(II) complexes containing phenoxy-imine ligands and their application as initiators of ring opening polymerization (ROP) of L-lactide (LA). The phenoxy-imine ligands were obtained from salicylaldehyde derivatives and 2,3,5,6-tetramethylphenylenediamine, yielding two bidentate regions per ligand. The reactions of both phenoxy-imine ligands with ZnEt2 in the presence of n-BuOH afforded [Zn2(L1)(OBu)2] and [Zn2(L2)(OBu)2], which were characterized by elemental analysis, Fourier transform infrared (FTIR) and 1H nuclear magnetic resonance (NMR) spectroscopy. In addition, the geometries of both complexes were investigated by DFT (B3LYP/LACVP**) calculations. [Zn2(L1)(OBu)2] and [Zn2(L2)(OBu)2] were tested as initiators of ROP of LA at 180 °C using different LA/Zn molar ratios, namely 500, 1000 and 2500. Both complexes showed good activity, resulting in conversions up to 96% in 2 h. The poly-LLA exhibited average molecular weight (Mw) ranging from 45,000-92,000, relatively low polydispersity (Mw/Mn = 1.6-2.0) and high stereoregularity with melting temperature Tm = 164 °C.

Diaryliodonium salts as hydrosilylation initiators for the surface functionalization of silicon nanomaterials and their collaborative effect as ring opening polymerization initiators.

Diaryliodonium salts were found to initiate hydrosilylation reactions on the surface of silicon nanosheets as well as silicon nanocrystals of different sizes. A variety of different functional substrates can be used to stabilize the surface of the photoluminescent materials. Additionally, the combination of hydride terminated silicon nanomaterials with diaryliodonium salts was found to initiate cationic ring opening polymerization, demonstrating the potential of silicon based nanomaterials as coinitiators and enabling a mild, straightforward reaction method.

Obtaining aliphatic branched polycarbonates via simple copolymerization of trimethylene carbonate with cyclic carbonate containing pendant ester groups

ABSTRACTDifferent possibilities for obtaining branched, functional carbonate copolymers are presented in this study. Copolymers were synthesized according to the ring‐opening polymerization (ROP) of the cyclic carbonate monomers, containing pendant ester groups. As an example, we chose copolymerization of ethyl 5‐methyl‐2‐oxo‐1,3‐dioxane‐5‐carboxylate (MTC‐Et) with trimethylene carbonate (TMC), using zinc (II) and lanthanum (III) acetylacetonates as ROP initiators. The transesterification processes of ester groups in pendant, short chains, appearing during conducted copolymerization, led to the establishment of two different fractions: first‐branched and high molecular weight fraction and second‐linear and low molecular weight. The content of this high‐molecular‐weight fraction increased with both: the amount of MTC‐Et in started reaction mixture and the time of conducted copolymerization. Reactivity constants in studied reaction were determined. It was possible to obtain the copolymer fraction (ca. 30%) with molecular weight of up to a million g/mol, with a highly branched chain microstructure using lanthanum (III) acetylacetonate as initiator. Conclusions were based on detailed NMR analysis, determining microstructure of the copolymer chains and additionally on GPC and DSC measurement. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 808–819

Controlled Ring-Opening Polymerization of O-Carboxyanhydrides Using a β-Diiminate Zinc Catalyst.

Recently O-carboxyanhydrides (OCAs) have emerged as a class of viable monomers which can undergo ring-opening polymerization (ROP) to prepare poly(α-hydroxyalkanoic acid) with functional groups that are typically difficult to achieve by ROP of lactones. Organocatalysts for the ROP of OCAs, such as dimethylaminopyridine (DMAP), may induce undesired epimerization of the α-carbon atom in polyesters resulting in the loss of isotacticity. Herein, we report the use of (BDI-IE)Zn(OCH(CH3 )COOCH3 ) ((BDI)Zn-1, (BDI-IE)=2-((2,6-diethylphenyl)amino)-4-((2,6-diisopropylphenyl)imino)-2-pentene), for the controlled ROP of various OCAs without epimerization. Both homopolymers and block copolymers with controlled molecular weights, narrow molecular weight distributions, and isotactic backbones can be readily synthesized. (BDI)Zn-1 also enables controlled copolymerization of OCAs and lactide, facilitating the synthesis of block copolymers potentially useful for various biomedical applications. Preliminary mechanistic studies suggest that the monomer/dimer equilibrium of the zinc catalyst influences the ROP of OCAs, with the monomeric (BDI)Zn-1 possessing superior catalytic activity for the initiation of ROP in comparison to the dimeric (BDI)Zn complex.

Controlled Ring‐Opening Polymerization of O‐Carboxyanhydrides Using a β‐Diiminate Zinc Catalyst

AbstractRecently O‐carboxyanhydrides (OCAs) have emerged as a class of viable monomers which can undergo ring‐opening polymerization (ROP) to prepare poly(α‐hydroxyalkanoic acid) with functional groups that are typically difficult to achieve by ROP of lactones. Organocatalysts for the ROP of OCAs, such as dimethylaminopyridine (DMAP), may induce undesired epimerization of the α‐carbon atom in polyesters resulting in the loss of isotacticity. Herein, we report the use of (BDI‐IE)Zn(OCH(CH3)COOCH3) ((BDI)Zn‐1, (BDI‐IE)=2‐((2,6‐diethylphenyl)amino)‐4‐((2,6‐diisopropylphenyl)imino)‐2‐pentene), for the controlled ROP of various OCAs without epimerization. Both homopolymers and block copolymers with controlled molecular weights, narrow molecular weight distributions, and isotactic backbones can be readily synthesized. (BDI)Zn‐1 also enables controlled copolymerization of OCAs and lactide, facilitating the synthesis of block copolymers potentially useful for various biomedical applications. Preliminary mechanistic studies suggest that the monomer/dimer equilibrium of the zinc catalyst influences the ROP of OCAs, with the monomeric (BDI)Zn‐1 possessing superior catalytic activity for the initiation of ROP in comparison to the dimeric (BDI)Zn complex.