Ring-opening Polymerization Of E-caprolactone Research Articles

(Z)-N-(pyridin-2-yl)benzimidate dimethylaluminum complexes: synthesis, structures and ring-opening polymerization of ε-caprolactone

The easy synthesis and characterization of three new N,O-coordination aluminum complexes (Al1-Al3) bearing (Z)-N-(pyridin-2-yl)benzimidate ligand are presented, as well as their ring-opening polymerization (ROP) of ε-caprolactone (ε-CL). The three aluminum complexes were simply synthesized by single-step reactions of unsubstituted and substituted N-(pyridin-2-yl)benzamides (RC5H4N)NHCOC6H5 (R = H, 1; R = 5-Me, 2; R = 6-Me, 3) with AlMe3; The reactions involved the tautomerization of the original N-(pyridin-2-yl)amide ligands to (Z)-configurational N-(pyridin-2-yl)imidates which acts as N,O-bidentate ligands. Molecular structures of the three obtained aluminum complexes were determined by NMR spectroscopy, single-crystal X-Ray diffraction and elemental analysis. The aluminum complexes (Al1-Al3) were found to catalyze the ring-opening polymerization of ε-caprolactone with moderate activities. The GPC test showed that the produced polycaprolactones with narrow molecular weight distributions (Mw/Mn < 1.14) when the polymerization time within 25 min. For the present system, the introduction of electron-donating methyl substituents at the pyridine ring of the ligand resulted in an apparent increase in catalytic activity. Particularly, among the three investigated aluminum complexes, Al3 showed the highest activity up to 99% conversion rate with [CL]0/[Al]0/[BnOH]0 = 100/1/1 at 80°C for 25 min.

Synthesis of PEGylated amphiphilic block copolymers with pendant linoleic moieties by combining ring-opening polymerization and click chemistry.

This study focused on synthesizing and characterizing PEGylated amphiphilic block copolymers with pendant linoleic acid (Lin) moieties as an alternative to enhance their potential in drug delivery applications. The synthesis involved a two-step process, starting with ring-opening polymerization of ε-caprolactone (CL) and propargylated cyclic carbonate (MCP) to obtain PEG-b-P(CL-co-MCP) copolymers, which were subsequently modified via click chemistry. Various reaction conditions were explored to improve the yield and efficiency of the click chemistry step. The use of anisole as a solvent, N-(3-azidopropyl)linoleamide as a substrate, and a reaction temperature of 60°C proved to be highly efficient, achieving nearly 100% conversion at a low catalyst concentration. The resulting copolymers exhibited controlled molecular weights and low polydispersity, confirming the successful synthesis. Furthermore, click chemistry allows for the attachment of Lin moieties to the copolymer, enhancing its hydrophobic character, as deduced from their significantly lower critical micelle concentration than that of traditional PEG-b-PCL systems, which is indicative of enhanced stability against dilution. The modified copolymers exhibited improved thermal stability, making them suitable for applications that require high processing temperatures. Dynamic light scattering and transmission electron microscopy confirmed the formation of micellar structures with sizes below 100 nm and minimal aggregate formation. Additionally, 1H NMR spectroscopy in deuterated water revealed the presence of core-shell micelles, which provided higher kinetic stability against dilution.

Aluminum Complexes Bearing Aminoquinoline Ligands with Different Pendant Donors: Remarkable Impact of Hemilability on the Ring-Opening Polymerization of ε-Caprolactone

Aluminum Complexes Bearing Aminoquinoline Ligands with Different Pendant Donors: Remarkable Impact of Hemilability on the Ring-Opening Polymerization of ε-Caprolactone

One-pot in situ bulk polymerization of triblock copolymer PCL-b-PA6-b-PCL based on PA6 by using tetraphenyl tin

The preparation of polyesteramides (PEAs) with regular block structure has long been a challenge, owing to the occurrence of the ester-amide exchange during the polymerization at high tempereture. In this work, we report a simple and green method to prepare polyamide 6 (PA6) based triblock PEA whose structure is poly(ε-caprolactone)-block-PA6-block-poly(ε-caprolactone) (PCL-b-PA6-b-PCL) using tetraphenyl tin as catalyst without solvent. The first segment PA6 was synthesized via cationic ring-opening polymerization (ROP) of ε-caprolactam (CPL), later, ROP of ε-caprolactone (CL) was involved to extend polycaprolactone (PCL) segments by using tetraphenyl tin as catalyst. By varying the proportion of CPL and CL, series PA6-based PEAs was prepared and characterized by gel permeation chromatography, 1H, DOSY, and 13C NMR. The results showed that PEA containing more proportion of CL presented a higher molecular weight with narrow polydisperse index. In particular, the lower water absorption and lower oligomers content infers that the PEA could have a prospective application in processing precision electronic devices.

Flexible NHC-aryloxido aluminum complex and its zwitterionic imidazolium aluminate precursor in ring-opening polymerization of ε-caprolactone.

Anionic donor-functionalized NHC (N-heterocyclic carbene) complexes of Al are rare. We report one such case here, an NHC-aryloxido AlMe2 complex [Al(L)Me2] (2), following a stepwise synthesis from the proligand [HO-4,6-tBu2-C6H2-2-CH2{CH(NCHCHNAr)}]Br [LH2Br; Ar = 2,6-iPr2-C6H3 (Dipp)] and AlMe3via the zwitterionic intermediate [Al(LH)Me2Br] (1). The ligand's flexibility in 2 is evident from the conformational fluxionality revealed by VT-1H NMR spectroscopic analysis. The ∠O-Al-C (ca. 100.5°) bite angle is also wider than the ∠O-Ti-C (ca. 80.6°) as seen in our recently reported Ti complex [Ti(L)(NMe2)2Br]. DFT analysis showed that the CNHC-Al bond is significantly ionic, as is the CNHC-Ti bond. Both 1 and 2 are active in the ring-opening polymerization (ROP) of ε-caprolactone (CL). 2, similar to [Ti(L)(NMe2)2Br], exhibits bifunctional MLC-type monomer activation, but only at an elevated temperature. However, the 2/BnOH combination is catalytically active at room temperature, likely through a zwitterionic [Al(LH)Me2(OBn)]. The 1/BnOH combination follows a similar mechanism but surprisingly at a faster rate.

Mixed-magnesium/zinc calix[4]arene complexes: structure, and ring opening polymerisation studies.

Different combinations of organomagnesium reagents and zinc bromide react with either 1,3-dimethoxy-4-tert-butylcalix[4]areneH2 (L(OMe)2H2) or trialkoxycalix[4]arenes (L(OR)3H) (R = n-Pr, n-pentyl) to afford mixed-metal calix[4]arene systems. Intriguing molecular structures are formed and the systems are capable of the ring opening polymerisation of ε-caprolactone under N2, air, or as melts.

Eco-Conscious Approach to Thermoresponsive Star-Comb and Mikto-Arm Polymers via Enzymatically Assisted Atom Transfer Radical Polymerization Followed by Ring-Opening Polymerization.

This study explores the synthesis, characterization, and application of a heterofunctional initiator derived from 2-hydroxypropyl cyclodextrin (HP-β-CD), having eight bromoester groups and thirteen hydroxyl groups allowing the synthesis of mikto-arm star-shaped polymers. The bromoesterification of HP-β-CD was achieved using α-bromoisobutyryl bromide as the acylation reagent, modifying the cyclodextrin (CD) molecule as confirmed by electrospray ionization mass spectrometry (ESI-MS), nuclear magnetic resonance (NMR), attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy analysis, and differential scanning calorimetry (DSC) thermograms. The initiator's effectiveness was further demonstrated by obtaining star-comb and mikto-arm polymers via an enzymatically assisted atom transfer radical polymerization (ATRP) method and subsequent ring-opening polymerization (ROP). The ATR polymerization quality and control depended on the type of monomer and was optimized by the way of introducing the initiator into the reaction mixture. In the case of ATRP, high conversion rates for poly(ethylene oxide) methyl ether methacrylate (OEOMA), with molecular weights (Mn) of 500 g/mol and 300 g/mol, were achieved. The molecular weight distribution of the obtained polymers remained in the range of 1.23-1.75. The obtained star-comb polymers were characterized by different arm lengths. Unreacted hydroxyl groups in the core of exemplary star-comb polymers were utilized in the ROP of ε-caprolactone (CL) to obtain a hydrophilic mikto-arm polymer. Cloud point temperature (TCP) values of the synthesized polymers increased with arm length, indicating the polymers' reduced hydrophobicity and enhanced solvation by water. Atomic force microscopy (AFM) analysis revealed the ability of the star-comb polymers to create fractals. The study elucidates advancements in the synthesis and utilization of hydrophilic sugar-based initiators for enzymatically assisted ATRP in an aqueous solution for obtaining complex star-comb polymers in a controlled manner.

Aluminum and titanium complexes bearing 2,6-Bis(2-hydroxyphenyl)pyridines for ring-opening polymerization of lactide, ε-caprolactone and their copolymerization: Effect of a ligand on coordination chemistry and reactivity

In ring-opening polymerization (ROP) of cyclic esters, the rational design of the catalyst is generally applied to solve the task of providing polyester biocompatibility (non-toxicity) and the problem of copolymer homogeneity when using comonomers of different nature (e. g. lactones and lactides). In the present work, we report the synthesis of aluminum and titanium complexes, based on substituted 2,6-bis(2-hydroxyphenyl)pyridine pro-ligands 1 and 2. It was found that the structure of the pro-ligand drastically affect the structure of the reaction product. Pro-ligand 2 with a bulky tert‑butyl group leads to the monomeric complexes 6 (LAlMe) and 7 (LTi(OiPr)2), while the ligands with less bulky groups lead to the oligomeric Al-containing compounds 3 and 4, and in the case of Ti bis-ligand complex 5 is formed. Complexes 6 (in presence of BnOH) and 7 turned out to be active in the ROP of ε-caprolactone and l-lactide and gave PCL and PLA with high molecular masses. Compound 6 was an effective initiator of copolymerization of ε-caprolactone and l-lactide which led to statistical copolymer poly(LA-stat-CL) with comonomer subunits ratio of 1:1.

Ring-opening polymerization of ε-caprolactone by Zr(IV) tris(β-diketonates): Electronic character of complexes in initiation and propagation steps

A series of zirconium β-diketonates, i.e., tris(acetylacetonato)zirconium(IV) chloride (1), tris(benzoylacetonato)zirconium(IV) chloride (2), tris(dibenzoylmethanato)zirconium(IV) chloride (3), and tris(benzoyltrifluoroacetonato)zirconium(IV) chloride (4) work as efficient catalysts in the ring-opening polymerization (ROP) of ε-caprolactone (ε-CL) to generate poly(ε-CL) with repeating unit up to 68. The activity of the complexes was in the order of 2 > 4 > 1 > 3, with more Lewis acidic complexes 2 and 4 gave higher catalytic activity. DFT calculations showed that a trifluoromethyl moiety in the ligand decreases the oxygen nucleophilicity at intermediate complexes, and thus inhibiting the propagation process. Three possible states of the complex before ε-CL coordination in the ROP were proposed as follows: (i) dissociation of one ligand; (ii) dissociation of one coordinated-oxygen of the ligand from zirconium and (iii) direct insertion of sp2-oxygen of ε-CL into Zr (no change of the complex geometry). The thermodynamic analysis via the Gibbs energy calculations at DFT level revealed that a direct insertion of sp2-oxygen of ε-CL into zirconium is the most plausible pathway for the ROP.

Co/Mn-based 2D coordination polymers: synthesis, structure and ring opening polymerization

The two-dimensional coordination polymers [Co(DMF)2L2]∙0.65H2O and [Mn(DMF)2L2]∙0.4H2O (L = N,N′-bis(glycinyl)pyromellitic diimide) have been prepared and structurally characterized by a variety of techniques including FTIR spectroscopy, powder and single crystal X-ray diffraction. Results for their use as catalysts in the ring opening polymerization of ε-caprolactone (ε-CL) and δ-valerolactone (δ-VL) are reported. High conversions were achievable at 130 °C, resulting in the formation of mostly cyclic polycaprolactone (PCL) and polyvalerolactone (PVL), respectively, with only a small number of linear polymers formed. Kinetic studies revealed the presence of two distinct rate steps, the second of which is assigned to the formation of an active decomposition product.

Ring-Opening Polymerization of rac-β-Butyrolactone Promoted by New Tetradentate Thioether-Amide Ligand-Type Zinc Complexes.

In this work, thioether-amide ligands featuring a combination of hard amide groups with soft donor groups have been employed to develop new zinc catalysts for the ring-opening polymerization of cyclic esters. All complexes were prepared in high yields through alkane elimination reactions with diethyl zinc and characterized using nuclear magnetic resonance (NMR) spectroscopy. Density functional theory (DFT) characterization provided insight into the parameters that influence catalytic activity, such as steric hindrance at the metal center, Lewis acidity and electronic density of thioether-amide ligands. In the presence of one equivalent of isopropanol, all complexes were active in the ring-opening polymerization of rac-β-butyrolactone. Quantitative conversion of 100 monomer equivalents was achieved within 1 h at 80 °C in a toluene solution. Number-average molecular weights increased linearly with monomer conversion; the values were in optimal agreement with those expected, and polydispersity index values were narrow and relatively constant throughout the course of polymerization. The most active complex was also effective in the ring-opening polymerization of ε-caprolactone and L-lactide. To propose a reliable reaction path, DFT calculations were undertaken. In the first step of the reaction, the acidic proton of the alcohol is transferred to the basic nitrogen atom of the amide ligand coordinated to the zinc ion. This leads to the alcoholysis of the Zn-N bond and the formation of an alcoholate derivative that starts the polymerization. In subsequent steps, the reaction follows the classical coordination-insertion mechanism.

Determination of HOMO and LUMO of bis(β-diketonate)zirconium(IV) compound used as a catalyst in the ring opening polymerization of ε-Caprolactone and δ-Valerolactone

Poly(ε-caprolactone) (PCL) and poly(δ-valerolactone) (PVL) are aliphatic polyesters that can generally be used for basic medical materials such as bone and dental implant materials, drug delivery systems, and scaffolds in tissue engineering. PCL and PVL belong to the polylactone group which have superior properties such as good biocompatibility, nontoxicity, flexibility, thermoplastic and can be biodegraded in a controlled manner. These superior properties make it the main choice in producing medical materials. This study aims to determine the degree of polymerization of PCL and PVL catalyzed using a bis(β-diketonate)zirconium(IV) complex. In addition, analysis of the Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) was also carried out on the catalyst complex. The ring-opening polymerization reaction (ROP) of ε-caprolactone (ε-CL) and δ-valerolactone (δ-VL) lasted for 4 h at 100 °C. The resulting PCL and PVL were then characterized for their chemical and thermal properties using FTIR, 1HNMR, XRD, DTA and TGA. Both PCL and PVL are semicrystalline. On the other hand, the resulting PCL has a melting point of 65.5 °C, with a degree of polymerization (DP) of 17. Meanwhile, the resulting PVL has a melting point of 63.4 °C with a DP of 8.

Chain-end functionalization of polyolefins prepared by α-diimine nickel catalysts using transfer to organometallic compounds

A method for chain-end functionalization is described for branched polyolefins obtained by living olefin polymerization initiated by α-diimine nickel catalysts. The method relies on transmetalation of living polymer chains from nickel growing centres to excess organozinc, organomagnesium or organoaluminium transfer agents followed by oxidation. Hydroxy-terminated polyolefins were obtained with efficiencies going from 25 to 99%. The resulting end-functionalized polyolefins were characterized by MALDI-TOF MS and employed as macroinitiators for ring opening polymerization of ε-caprolactone to provide amphiphilic block copolymers.

Vanadium Complexes Derived from O,N,O-tridentate 6-bis(o-hydroxyalkyl/aryl)pyridines: Structural Studies and Use in the Ring-Opening Polymerization of ε-Caprolactone and Ethylene Polymerization

Interaction of [VO(OiPr)3] with 6-bis(o-hydroxyaryl)pyridine, 2,6-{HOC(Ph)2CH2}2(NC5H3), LH2, afforded [VO(OiPr)L] (1) in good yield. The reaction of LNa2, generated in-situ from LH2 and NaH, with [VCl3(THF)3] led to the isolation of [VL2] (2) in which the pyridyl nitrogen atoms are cis; a regioisomer 3∙2THF, in which the pyridyl nitrogen atoms are trans, was isolated when using [VCl2(TMEDA)2]. The reaction of the 2,6-bis(o-hydroxyalkyl)pyridine {HOC(iPr)2CH2}2(NC5H3), L1H2, with [VO(OR)3] (R = nPr, iPr) led, following work-up, to [VO(OR)L1] (R = nPr (4), iPr (5)). Use of the bis(methylpyridine)-substituted alcohol (tBu)C(OH)[CH2(C5H3Me-5)]2, L2H, with [VO(OR)3] (R = Et, iPr) led to the isolation of [VO(μ-O)(L2)]2 (6). Complexes 1 to 6 have been screened for their ability to act as pre-catalysts for the ring opening polymerization (ROP) of ε-caprolactone (ε-CL), δ-valerolactone (δ-VL), and rac-lactide (r-LA) and compared against the known catalyst [Ti(OiPr)2L] (I). Complexes 1, 4–6 were also screened as catalysts for the polymerization of ethylene (in the presence of dimethylaluminium chloride/ethyltrichloroacetate). For the ROP of ε-CL, in toluene solution, conversions were low to moderate, affording low molecular weight products, whilst as melts, the systems were more active and afforded higher molecular weight polymers. For δ-VL, the systems run as melts afforded good conversions, but in the case of r-LA, all systems as melts exhibited low conversions (&lt;10%) except for 6 (&lt;54%) and I (&lt;39%). In the case of ethylene polymerization, the highest activity (8600 Kg·mol·V−1bar−1h−1) was exhibited by 1 in dichloromethane, affording high molecular weight, linear polyethylene at 70 °C. In the case of 4 and 5, which contain the propyl-bearing chelates, the activities were somewhat lower (≤1500 Kg·mol·V−1bar−1h−1), whilst 6 was found to be inactive.

Synthesis, structure, and catalytic activity of the neodymium tris(amidinate) complex [ButC(N-2,6-Me2C6H3)2]3Nd in ring-opening polymerization of ε-caprolactone

Synthesis, structure, and catalytic activity of the neodymium tris(amidinate) complex [ButC(N-2,6-Me2C6H3)2]3Nd in ring-opening polymerization of ε-caprolactone

Ring-opening polymerization of ε-caprolactone and L-lactide using ethyl salicylate-bearing zinc complexes as catalysts

A series of zinc complexes bearing ethyl salicylates were synthesized, and their catalytic activity in the polymerization of ε-caprolactone (CL) and l-lactide (LA) was investigated. In CL polymerization, the catalytic activity of Zn complexes was promoted by ligands with the substituents at the ortho position of phenolates, such as the 2-methyl group of L6MeZnEt (40 min, 94% conversion at 25 °C, [CL] = 2.0 M) and the 2,4-di‑tert‑butyl groups of LBuZnEt (55 min, 93% conversion at 25 °C, [CL] = 2.0 M). In LA polymerization, the catalytic activity was promoted by ligands with electron-donating substituents, such as the 4-methyl group of L4MeZnEt (55 min, 90% conversion at 50 °C, [LA] = 0.5 M) and the 2,4-di‑tert‑butyl group of LBuZnEt (60 min, 90% conversion at 50 °C, [LA] = 0.5 M). Density functional theory calculations revealed that the polymerization requires the detachment of a bridging alkoxide group from one Zn center to form an intermediate II-CL; bulky ligands may facilitate this unfavored dissociation process (from I-CL to II-CL). In LA polymerization, ligands with electron-withdrawing groups increase the Lewis acidity of Zn centers; the detachment of coordination atoms from the Zn atom is difficult; hence, the carbonyl group of ring-opening LA back binds to the Zn center to form a low-energy intermediate trip and then hinders another LA coordination.

Aluminum Salen Complexes Modified with Unsaturated Alcohol: Synthesis, Characterization, and Their Activity towards Ring-Opening Polymerization of ε-Caprolactone and D,L-Lactide.

A highly efficient one-step approach to the macromonomer synthesis using modified aluminum complexes as catalysts of ring-opening polymerization (ROP) of ε-caprolactone and D,L-lactide was developed. The syntheses, structures, and catalytic activities of a wide range of aluminum salen complexes, 3a-c, functionalized with unsaturated alcohol (HO(CH2)4OCH=CH2) are reported. X-Ray diffraction studies revealed a tetragonal pyramidal structure for 3c. Among the complexes 3a-c, the highest activity in bulk ROP of ε-caprolactone and D,L-lactide was displayed by 3b, affording polyesters with controlled molecular weights at low monomer to initiator ratios (Mn up to 15,000 g mol-1), relatively high polydispersities (Ð~1.8) and high number-average functionalities (Fn up to 85%).

N-(2-(Diphenylphosphino)ethyl)-2-alkyl-5,6,7,8-tetrahydro-quinolin-8-amines iron(ii) complexes: structural diversity and the ring opening polymerization of ε-caprolactone.

A series of N-(2-(diphenylphosphino)ethyl)-2-alkyl-5,6,7,8-tetrahydroquinolin-8-amines was prepared and used in individually reacting with iron chloride under nitrogen atmosphere to form their iron(ii) complexes Fe1-Fe6. All compounds were characterized using FT-IR spectroscopy and elemental analyses, the organic compounds were confirmed with NMR measurements, and the iron complexes were submitted to single-crystal X-ray diffraction, revealing Fe1, Fe2, Fe4, Fe5, and Fe6 as either mono- or di-nuclear forms. Forming a binary system in situ with two equivalents of LiCH2SiMe3, all iron complexes Fe1-Fe6 efficiently initiated the ring opening polymerization of ε-caprolactone, achieving the TOF up to 8.8 × 103 h-1. More importantly, the resultant polycaprolactone (PCL) possessed high molecular weights with the Mn range of 9.21-24.3 × 104 g mol-1, being a rare case of the iron(ii) catalyst in producing PCL with such high molecular weight. The 1H NMR and MALDI-TOF investigations demonstrated that the PCLs were linear features capped with a methoxy group or CH2SiMe3 or cyclic structure that varied with the molar ratio of [ε-CL]/Fe.

Gallium (III) Complexes Based on Aminobisphenolate Ligands: Extremely High Active ROP-Initiators from Well-Known and Easily Accessible Compounds.

We report herein the synthesis and full characterizations of the first examples of gallium complexes based on "privileged" aminobisphenolate ligands which are easily available. These complexes turned out to be extremely active in the ring-opening polymerization of ε-caprolactone even at room temperature and highly active in the ROP of L-lactide. The combination of factors such as the easy availability of these compounds and the supposedly low toxicity, together with the extremely high activity in ROP, allows us to consider these compounds as suitable for use on an industrial scale for the synthesis of biodegradable polymers for biomedical applications.

Effect of the Lignin Structure on the Physicochemical Properties of Lignin-Grafted-Poly(ε-caprolactone) and Its Application for Water/Oil Separation

Lignin-grafted poly(ε-caprolactone) copolymers (lignin-g-PCLs) have shown wide application potentials in coatings, biocomposites, and biomedical fields. However, the structural heterogeneity of lignin affecting the structures and properties of lignin-g-PCL has been scarcely investigated. Herein, kraft lignin is fractionated into four precursors, namely, Fins, F1, F2, and F3, with declining molecular weights and increased hydroxyl contents. Lignin-g-PCLs are synthesized via ring-opening polymerization of ε-caprolactone with lignin and characterized by GPC, FTIR, 1H and 31P NMR, DSC, TGA, and iGC. The mechanical properties, UV barrier, and enzymatic biodegradability of the lignin-g-PCLs are evaluated. Results show that lignin with a higher molecular weight and aliphatic OH favors the copolymerization, leading to lignin-g-PCLs with longer PCL arms. Moreover, lignin incorporation improves the thermal stability, hydrophobicity, and UV-blocking ability but reduces the lipase hydrolyzability of the copolymers. We also demonstrated that the lignin-g-PCL-coated filter paper could successfully separate chloroform–, petroleum ether–, and hexane–water mixtures with an efficiency up to 99.2%. The separation efficiency remains above 90% even after 15 cycles. The structural differences of copolymers derived from the fractionation showed minimal influence on the separation efficiency. This work provides new insights into lignin-based copolymerization and the versatility of lignin valorization.