Solvent-free Ring-opening Polymerization Research Articles

N-Butyltin(IV) trichloride initiator for the solvent-free ring-opening polymerization of ε-caprolactone: evaluation of the structure-reactivity relationship of tin(IV) derivatives

n-Butyltin(IV) trichloride initiator for the solvent-free ring-opening polymerization of ε-caprolactone: evaluation of the structure-reactivity relationship of tin(IV) derivatives

Non-isothermal kinetics of the organocatalytic ring-opening polymerization of ε-caprolactone with metal-free α‑hydroxy acids: Eco-friendly and facile synthesis process

Metal-free and green α‑hydroxy acids (AHA) such as l-malic (MA), DL-mandelic acid (MDL), and citric acid (CA) were successfully and effectively utilized as an effective initiator for the solvent-free ring-opening polymerization (ROP) of ε-caprolactone (ε-CL). The performance of AHAs in the polymerization of ε-CL was completely and powerfully investigated via the non-isothermal differential scanning calorimetry (DSC). The proceed of ROP of ε-CL with AHAs could be real-time monitored by the obtained polymerization exotherms at different heating rates. The polymerization exotherms obtained from the ROP of ε-CL with CA occurred at a lower temperature range than MA, and MDA, respectively. From the kinetics study, the average activation energy (Ea) values for the ROP of ε-CL with CA (38.0 ± 1.8 kJ mol−1) were lower than MA (45.2 ± 3.6 kJ mol−1) and MDA (48.8 ± 6.2 kJ mol−1). Using the first-order model fitting, the values of pre-exponential factor (lnA0) for the ROP of ε-CL with CA, MA, and MDA were 7.0 ± 0.3, 8.5 ± 0.2, and 8.9 ± 0.3, respectively. The effectiveness of AHAs in the synthesis of PCL was clarified by conducting a larger-scale (4.0000 g) polymerization using conventional heating and microwave (MW) irradiation methods. From conventional heating, the green AHAs produced PCL with the number average molecular weight (Mn) and dispersity (Đ) values in the range of 5.18 × 103 - 1.43 × 104 g mol−1 and 1.14–2.02, respectively. The irradiation by MW could enhance the synthesis of PCL by reducing the synthesis time. By using the MW power of 450 W and irradiation time of 30 min, the PLC was obtained from the ROP of ε-CL with MA and MDA initiators, and the Mn of the obtained PCL from MW heating was 4.28 × 103 - 8.45 × 103 g mol−1. The mechanism for the ROP of ε-CL with all AHAs was proposed through the activated monomer mechanism.

Synthesis, characterization, luminescence, and catalytic properties of a zinc(II) complex with a N,O-donor ligand generated in situ from topiroxostat

Abstract By utilizing the well-known selective xanthine oxidase inhibitor topiroxostat, a new zinc(II) complex Zn(L)2(H2O)2 (1) [HL = 4-(3-(pyridine-4-yl)-1H-1,2,4-triazol-5-yl)picolinic acid] has been hydrothermally synthesized, involving in-situ ligand formation upon hydrolysis of topiroxostat. The complex has been structurally characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis, powder X-ray diffraction, and single-crystal X-ray diffraction. X-ray structural analysis revealed that complex 1 is a N,O-chelating mononuclear Zn(II) complex. Complex 1 shows good thermal stability and exhibits photoluminescence in the solid state at room temperature. Moreover, complex 1 has been shown to be effective in the solvent-free ring-opening polymerization of ε-caprolactone without any co-catalyst or initiator.

Microwave-assisted solvent-free ring-opening polymerization of ε-caprolactone initiated by n-butyltin(IV) chlorides

Microwave-assisted solvent-free ring-opening polymerization of ε-caprolactone initiated by n-butyltin(IV) chlorides

Solvent-free ring-opening polymerization of ε-caprolactone initiated by Mg(II), Sn(II), Zn(II), Al(III), and Sn(IV) derivatives: a comparative study

Solvent-free ring-opening polymerization of ε-caprolactone initiated by Mg(II), Sn(II), Zn(II), Al(III), and Sn(IV) derivatives: a comparative study

Metal-to-ligand ratio-controlled assembly of two Ca(II) complexes: Synthesis, structures, reactant-induced reversible transformation, and catalytic properties

Hydrothermal reactions of Ca(NO3)2·4H2O and topiroxostat with different metal-to-ligand ratios yielded two new complexes {[Ca2(L)2(H2O)6]·H2O}n (1) and Ca(HL)2(H2O)4 (2) [H2L = 4-(3-(pyridine-4-yl)-1H-1,2,4-triazol-5-yl)picolinic acid], involving ligand in situ formation by hydrolysis of topiroxostat. X-ray structural analysis revealed that complex 1 has a 1D coordination polymeric structure while complex 2 displays a 0D discrete molecule. Both complexes exhibit interesting reactant-induced reversible structural transformation properties. Thermogravimetric analysis and temperature-dependent PXRD patterns indicated that the network of 1 keep high thermal stability up to 400 °C. The catalytic performance of the complexes for the solvent-free ring-opening polymerization of ε-caprolactone has been investigated.

Heterogeneous Double Metal Cyanide Catalyzed Synthesis of Poly(ε-caprolactone) Polyols for the Preparation of Thermoplastic Elastomers

A series of polycaprolactones (PCLs) with molecular weights of 950–10,100 g mol−1 and Ð of 1.10–1.87 have been synthesized via one-pot, solvent-free ring-opening polymerization (ROP) of ε-caprolactone (CL) using a heterogeneous double metal cyanide (DMC) catalyst. Various initiators, such as polypropylene glycol, ethylene glycol, propylene glycol, glycerol, and sorbitol, are employed to tune the number of hydroxyl end groups and properties of the resultant PCLs. Kinetic studies indicate that the DMC-catalyzed ROP of CL proceeds via a similar mechanism with the coordination polymerization. Branched PCLs copolymers are also synthesized via the DMC-catalyzed copolymerization of CL with glycidol. The α,ω-hydroxyl functionalized PCLs were successfully used as telechelic polymers to produce thermoplastic poly(ester-ester) and poly(ester-urethane) elastomers with well-balanced stress and strain properties.

A 3D copper(II)-sodium(I)-containing Strandberg-type phosphomolybdate-based coordination framework with a flexible bis(triazole) ligand: Synthesis, crystal structure and catalytic properties

A new copper(II)-sodium(I)-containing phosphomolybdate-based coordination framework, namely, {[EMIm][Cu1.5Na(btmx)2.5(H2O)2(HP2Mo5O23)]·0.5H2O}n (denoted as CZU-6, EMIm = 1-methyl-3-ethyl imidazolium, btmx = 1,4-bis(1,2,4-triazole-1-ylmethyl)-2,3,5,6-tetramethyl benzene), was synthesized by using ionic liquid EMIm-Br as a template under hydrothermal conditions. The X-ray structural analysis revealed that CZU-6 features the first example of 3D anionic polyoxometalate-based coordination framework with trinodal (4,4,4)-connected sqc topological net. Moreover, CZU-6 could be directly adopted as an efficient heterogeneous catalyst for the solvent-free ring-opening polymerization of ε-caprolactone, and the catalyst could be easily recovered and reused several times without loss of its crystallinity and activity.

Synthesis and characterization of biocompatible poly (L-lactide) using zinc (II) salen complex

A biocompatible zinc (II) complex based on a tetradentate N,N,O,O-type salen ligand was synthesized, characterized and used for the solvent-free ring-opening polymerization (ROP) of L-lactide in bulk at 180 °C to prepare high molecular weight poly(L-lactide) (Mn : 82,600 Da; Mw : 140,000 Da; PDI: 1.70). Poly(L-lactide) (PLLA) was characterized using FTIR, 1H NMR, 13C NMR, GPC, TGA, DSC, WAXD, and MALDI-ToF. Kinetic measurement was carried out and first-order behavior to monomer was observed. The k app was found as 6 ± 0.001 × 10−4 s−1. The biocompatibility of the PLLA was confirmed by in vitro cytotoxicity against NIH/3T3 fibroblast cell line and can be used in biomedical applications.

Low-temperature and purification-free stereocontrolled ring-opening polymerisation of lactide in supercritical carbon dioxide

A stereoselective, solvent-free ring-opening polymerisation (ROP) of lactide (LA) in supercritical carbon dioxide (scCO2) is reported for the first time.

Pyridyl-urea catalysts for the solvent-free ring-opening polymerization of lactones and trimethylene carbonate

The ring-opening polymerization (ROP) of lactones is an effective method for the preparation of biocompatible and biodegradable aliphatic polyesters, for which the development of efficient organocatalysts with high activity and good controllability is highly desirable. A series of novel pyridyl-urea catalysts has been synthesized and applied in the solvent-free ROP of lactones and trimethylene carbonate. Combined with 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD), the pyridyl-urea/MTBD systems showed a fast and living/controlled behavior in the ROP, generating polymers with narrow molecular weight distributions. The influences of catalyst structure, type of base, pyridyl-urea/base ratio, feed ratio of monomer/initiator and reaction temperature on the catalytic properties were investigated. A possible mechanism was proposed on the basis of NMR titration and dilution experiments.

New Dual Functional PHB-Grafted Lignin Copolymer: Synthesis, Mechanical Properties, and Biocompatibility Studies.

Poly(3-hydroxybutyrate) (PHB) is a sustainable and biodegradable biopolymer from bacteria, but its brittle nature greatly limits its applications. In this study, we developed a lignin-PHB copolymer to enhance the mechanical properties of PHB. β-Butyrolactone was grafted onto the lignin core by using solvent-free ring-opening polymerization (ROP). Then different amounts of lignin-PHB copolymers were blended into PHB and then engineered into nanofibers via electrospinning. The composite nanofibers with lignin-PHB copolymer exhibit much stronger mechanical properties than pure PHB fibers. Composite nanofibers with 2% lignin copolymer demonstrate the best mechanical performance with tensile strength increasing from 1.45 ± 0.36 MPa to 5.61 ± 0.63 MPa, Young's modulus increasing from 54.7 ± 1.2 MPa to 84.6 ± 10.0 MPa, and elongation increasing from 9.6 ± 2.2% to 93.5 ± 7.6%. Moreover, PHB/lignin nanofibers demonstrate tunable antioxidant activity, allowing the neutralization of excess free radicals in our body. Animal studies also demonstrate that the PHB/lignin nanofibers are nonirritating and biocompatible. Hence, these new PHB/lignin nanofibers hold great potential for biomedical applications.

Engineering PCL/lignin nanofibers as an antioxidant scaffold for the growth of neuron and Schwann cell.

Antioxidant is critical for the successful of nerve tissue regeneration, and biomaterials with antioxidant activity might be favorable for peripheral nerve repair. Lignin, a biopolymer from wood with excellent antioxidant properties, is still "unexplored" as biomaterials. To design an antioxidative bioscaffold for nerve regeneration, here we synthesized lignin-polycaprolactone (PCL) copolymers via solvent free ring-opening polymerization (ROP). Then such lignin-PCL copolymers were incorporated with PCL and engineered into nanofibrous scaffolds for supporting the growth of neuron and Schwann cell. Our results showed that the addition of lignin-PCL enhanced the mechanical properties of PCL nanofibers and endowed them with good antioxidant properties (up to 98.3 ± 1.9% free radical inhibition within 4 h). Cell proliferation assay showed that PCL/lignin-PCL nanofibers increased cell viability compared to PCL fibers, especially after an oxidative challenge. Moreover, Schwann cells and dorsal root ganglion (DRG) neurons cultured on the nanofibers to assess their potential for nerve regeneration. These results suggested that nanofibers with lignin copolymers promoted cell proliferation of both BMSCs and Schwann cells, enhanced myelin basic protein expressions of Schwann cells and stimulated neurite outgrowth of DRG neurons. In all, these sustainable, intrinsically antioxidant nanofibers may be a potential candidate for nerve TE applications.

Strong and biocompatible lignin /poly (3-hydroxybutyrate) composite nanofibers

Poly(3-hydroxybutyrate) (PHB) is an attractive biopolymer potential for various applications, but its brittle nature is a big handicap. In this study, we proposed lignin copolymers as mechanical reinforcement agents for PHB. A series of lignin copolymers (random and block) were synthesized via the solvent free ring-opening polymerization (ROP) of β-butyrolactone and/or ε-caprolactone onto lignin core. The lignin copolymers were characterized by nuclear magnetic resonance (NMR), gel permeation chromatography (GPC) and differential scanning calorimetry (DSC). Next, these lignin copolymers were incorporated into PHB nanofibers as reinforcement fillers, in order to improve their mechanical properties. It is found that the lignin block copolymer with poly(ε-caprolactone) (PCL) segment followed by PHB segment (LPC + H) displayed the best mechanical improvement. Tensile strength of PHB nanofibers enhanced from 1.81 MPa to 3.13 MPa, and elongation at break increased from 15% of 55%. In the reinforced system, lignin plays as a rigid core, PCL acts a rubbery layer and PHB segment forms strong bonding with fiber matrix. Moreover, PHB/lignin nanofibers were demonstrated with superior biodegradability and biocompatibility, indicating that the new nanofibrous system holds great potential for biomedical applications.

Lithium Complexes Derived of Benzylphosphines: Synthesis, Characterization and Evaluation in the ROP of rac-Lactide and ε-Caprolactone.

A series of lithium complexes ([Ph2P(o-C6H4-CH2Li·TMEDA)] (1-Li), [PhP(o-C6H4-CH3)(o-C6H4-CH2Li·TMEDA)] (2-Li), [PhP(o-C6H4-CH2Li·TMEDA)2] (2-Li2) and [P(o-C6H4-CH2Li·TMEDA)3] (3-Li3)) was prepared from mono-, di- and tri-benzylphosphines and varying amounts of nBuLi and was characterized extensively by IR and 1H, 7Li, 13C and 31P NMR spectroscopy. The molecular structures of complexes 1-Li and 2-Li were determined by single-crystal X-ray diffraction studies. The two complexes have monomeric structures in the solid state comprising seesaw lithium atoms. In each case, the ligand exhibits an asymmetric C-C η2-coordination mode and an intramolecular P-Li bond interaction. Theoretical calculations at Density functional theory (DFT) level M06/6111+G(2d,p) show that indeed a P-Li bond is established which can be explained as the P lone pair (sp1.26) being partially delocalized on an available sp2 orbital on Li (sp2.04) and additional bonding contribution of the phosphorous atom to Li stems from further delocalization of a σ P-C orbital into the sp2 orbital on Li. The observed short contact distances between an aromatic ipso carbon and Li in the crystal structures of 1-Li and 2-Li are explained as due to the interaction of a σ C-Li orbital into the π* orbital of a C-C aromatic bond. Preliminary tests show compounds 1-Li, 2-Li, 2-Li2 and 3-Li3 are active catalysts in the solvent free ring-opening polymerization (ROP) of ε-caprolactone (ε-CL) and rac-lactide (rac-LA). High conversions to polycaprolactones were obtained in short periods of time: 1–6 min at 25 °C. Additionally, all four lithium complexes behave as moderately good initiators for the ROP of rac-LA showing high conversions to polylactides at 140 °C in one hour.

Reactivity of Zinc Halide Complexes Containing Camphor-Derived Guanidine Ligands with Technical rac-Lactide

Three new zinc complexes with monoamine–guanidine hybridligands have been prepared, characterized by X-ray crystallography and NMR spectroscopy, and tested in the solvent-free ring-opening polymerization of rac-lactide. Initially the ligands were synthesized from camphoric acid to obtain TMGca and DMEGca and then reacted with zinc(II) halides to form zinc complexes. All complexes have a distorted tetrahedral coordination. They were utilized as catalysts in the solvent-free polymerization of technical rac-lactide at 150 °C. Colorless polylactide (PLA) can be produced and after 2 h conversion up to 60% was reached. Furthermore, one zinc chlorido complex was tested with different qualities of lactide (technical and recrystallized) and with/without the addition of benzyl alcohol as a co-initiator. The kinetics were monitored by in situ FT-IR or 1H NMR spectroscopy. All kinetic measurements show first-order behavior with respect to lactide. The influence of the chiral complexes on the stereocontrol of PLA was examined. Moreover, with MALDI-ToF measurements the end-group of the obtained polymer was determined. DFT and NBO calculations give further insight into the coordination properties. All in all, these systems are robust against impurities and water in the lactide monomer and show great catalytic activity in the ROP of lactide.

H-Bonding Organocatalysts for the Living, Solvent-Free Ring-Opening Polymerization of Lactones: Toward an All-Lactones, All-Conditions Approach

The developing urea class of H-bond donors facilitates the solvent-free ROP of lactones at ambient and elevated temperatures, displaying enhanced rates and control versus other known organocatalysts for ROP under solvent-free conditions. The ROPs retain the characteristics of living polymerizations despite solidifying prior to full conversion, and copolymers can be accessed in a variety of architectures. One-pot block copolymerizations of lactide and valerolactone, which had previously been inaccessible in solution phase organocatalytic ROP, can be achieved under these reaction conditions, and one-pot triblock copolymers are also synthesized. For the ROP of lactide, however, thioureas remain the more effective H-bond donating class. For all (thio)urea catalysts under solvent-free conditions and in solution, the more active catalysts are generally more controlled. A rationale for these observations is proposed. The triclocarban (TCC) plus base systems are particularly attractive in the context of solvent-f...

Highly Active N,O Zinc Guanidine Catalysts for the Ring-Opening Polymerization of Lactide.

New zinc guanidine complexes with N,O donor functionalities were prepared, characterized by X-Ray crystallography, and examined for their catalytic activity in the solvent-free ring-opening polymerization (ROP) of technical-grade rac-lactide at 150 °C. All complexes showed a high activity. The fastest complex [ZnCl2 (DMEGasme)] (C1) produced colorless poly(lactide) (PLA) after 90 min with a conversion of 52 % and high molar masses (Mw =69 100, polydispersity=1.4). The complexes were tested with different monomer-to-initiator ratios to determine the rate constant kp . Furthermore, a polymerization with the most active complex C1 was monitored by in situ Raman spectroscopy. Overall, conversion of up to 90 % can be obtained. End-group analysis was performed to clarify the mechanism. All four complexes combine robustness against impurities in the lactide with high polymerization rates, and they represent the fastest robust lactide ROP catalysts to date, opening new avenues to a sustainable ROP catalyst family for industrial use.

Sustainable and Antioxidant Lignin–Polyester Copolymers and Nanofibers for Potential Healthcare Applications

Lignin polymerization has been considered as an effective approach for lignin valorization. Herein we report the synthesis of a series of new lignin-based copolymers (lignin–poly(e-caprolactone-co-lactide), lignin–PCLLA) via solvent-free ring-opening polymerization. Lignin–PCLLA copolymers with tunable molecular weights (10 to 16 kDa) and glass transition temperatures (−40 to 40 °C) were obtained. Such copolymers were engineered into ultrafine nanofibers by blending with polyesters (polycaprolactone, PCL and poly(l-lactic acid), PLLA) via electrospinning. Both PCL/lignin–PCLLA and PLLA/lignin–PCLLA nanofibers displayed uniform and beadless nanofibrous morphology. The size (diameters ranging from 300 to 500 nm) and tensile tests of the obtained nanofibers indicated that the lignin copolymers are miscible with the polyester matrices and can significantly improve the mechanical properties of the nanofibers. Moreover, good antioxidant activity and biocompatibility of the lignin nanofibers were demonstrated in...

Coumarin salen-based zinc complex for solvent-free ring opening polymerization of ε-caprolactone

A new zinc complex based on a tetradentate N,N,O,O-type coumarin salen ligand (H2L) was prepared and characterized by elemental analysis, thermogravimetric analysis (TGA), and FT-IR, UV–vis and 1H NMR spectroscopy. The complex [Zn(L)(H2O)]·H2O was active in the ring opening polymerization (ROP) of ε-caprolactone under solvent-free conditions, producing polycaprolactone (PCL) with a molecular weight up to 17,700gmol−1 and a narrow molecular weight distribution. 1H NMR analysis showed that the PCL obtained was mainly linear, having hydroxymethylene groups in the chain ends. Differential scanning calorimetry (DSC) showed that the polymer had high crystallinity (61%) and that TGA had a decomposition temperature above 300°C.