Copolyesters of ε-caprolactone and l-lactide catalyzed by a tetrabutylammonium phthalimide-N-oxyl organocatalyst

Aliphatic polyesters are biocompatible materials that can be used in biomedical applications. We report here the use of tetrabutylammonium phthalimide-N-oxyl catalyst (TBAPINO), as a thermally stable organocatalyst for the ring-opening polymerization (ROP) of cyclic esters under mild conditions. In the solution ROP of ε-caprolactone (ε-CL), quantitative conversion and M_n of ∼20 000 g mol⁻¹ are achieved in a wide temperature range from −15 to 60 °C. Under bulk condition, the conversion of ε-CL reaches over 85% at 120 °C within 2 h. The living ROP character of l-lactide (l-LA) catalyzed over TBAPINO is proved by multiple additions of monomer in the bulk polymerization. The catalyst shows comparable selectivity towards the ring-opening polymerization of l-LA and ε-CL. Their copolymerization over TBAPINO is carried out in one-pot bulk condition in terms of the reaction time, monomer feed ratio, and sequence of addition. The colorless poly(ε-caprolactone-co-lactide) (PCLA) is obtained with considerable conversion of both monomers with the M_n over 22 000 g mol⁻¹.

By utilizing tetrabutylammonium phthalimide-N-oxyl organocatalyst, copolymer PCLA with M_n over 20 000 g mol⁻¹ was synthesized by sequential ring-opening polymerization of ε-caprolactone and l-lactide under bulk conditions.     

High Tm linear poly(l-lactide)s prepared via alcohol-initiated ROPs of l-lactide

Alcohol-initiated ROPs of l-lactide were performed in bulk at 160 °C for 72 h with variation of the catalyst or with variation of the initiator (aliphatic alcohols). Spontaneous crystallization was only observed when cyclic Sn(ii) compounds were used as a catalyst. Regardless of initiator, high melting crystallites with melting temperatures (T_m) of 189–193 °C were obtained in almost all experiments with Sn(ii) 2,2′-dioxybiphenyl (SnBiph) as catalyst, even when the time was shortened to 24 h. These HT_m poly(lactide)s represent the thermodynamically most stable form of poly(l-lactide). Regardless of the reaction conditions, such high melting crystallites were never obtained when Sn(ii) 2-ethylhexanoate (SnOct₂) was used as catalyst. SAXS measurements evidenced that formation of HT_m poly(l-lactide) involves growth of the crystallite thickness, but chemical modification of the crystallite surface (smoothing) seems to be of greater importance. A hypothesis, why the “surface smoothing” is more effective for crystallites of linear chains than for crystallites composed of cycles is discussed.

By variation of reaction conditions and catalysts a cyclic tin(ii) compound was found, which enables synthesis of high melting (>190 °C) poly(l-lactide) via ROP of l-lactide, whereas the technically used catalyst SnOct₂ does not show such a performance.     

pH-responsive polymeric vesicles from branched copolymers

A new type of branched copolymer, poly(l-lactide)₂-b-poly(l-glutamic acid) (PLLA₂–PLGA), based on polypeptide PLGA is synthesized by the ring-opening polymerization (ROP) of N-carboxyanhydride of γ-benzyl-l-glutamate (BLG–NCA) with amino-terminated PLLA₂–NH₂ and subsequent deprotection. The branched copolymer is characterized by ¹H NMR, FTIR and GPC measurements. The self-assembly of the copolymers in aqueous media has been systematically discussed. A pyrene probe has been used to demonstrate the aggregated formation of PLLA₂–PLGA in solution by measuring the critical micelle concentration (cmc). The morphology and size of the micelles have further been studied by transmission electron microscopy (TEM), dynamic light scattering (DLS) and field emission scanning electron microscopy (ESEM). We demonstrated that the Rh of the vesicle is depending on solution pH and salt concentration. The vesicles show good stability with remained shapes and sizes during the lyophilizing process. These vesicles have great potential in the application of drug delivery.

A new type of branched copolymer, poly(l-lactide)₂-b-poly(l-glutamic acid), based on polypeptide PLGA is synthesized by the ring-opening polymerization of N-carboxyanhydride of γ-benzyl-l-glutamate with amino-terminated PLLA₂–NH₂ and subsequent deprotection.     

Efficiency of liquid tin(ii) n-alkoxide initiators in the ring-opening polymerization of l-lactide: kinetic studies by non-isothermal differential scanning calorimetry

Novel soluble liquid tin(ii) n-butoxide (Sn(OnC₄H₉)₂), tin(ii) n-hexoxide (Sn(OnC₆H₁₃)₂), and tin(ii) n-octoxide (Sn(OnC₈H₁₇)₂) initiators were synthesized for use as coordination–insertion initiators in the bulk ring-opening polymerization (ROP) of l-lactide (LLA). In order to compare their efficiencies with the more commonly used tin(ii) 2-ethylhexanoate (stannous octoate, Sn(Oct)₂) and conventional tin(ii) octoate/n-alcohol (SnOct₂/nROH) initiating systems, kinetic parameters derived from monomer conversion data were obtained from non-isothermal differential scanning calorimetry (DSC). In this work, the three non-isothermal DSC kinetic approaches including dynamic (Kissinger, Flynn–Wall, and Ozawa); isoconversional (Friedman, Kissinger–Akahira–Sunose (KAS) and Ozawa–Flynn–Wall (OFW)); and Borchardt and Daniels (B/D) methods of data analysis were compared. The kinetic results showed that, under the same conditions, the rate of polymerization for the 7 initiators/initiating systems was in the order of liquid Sn(OnC₄H₉)₂ > Sn(Oct)₂/nC₄H₉OH > Sn(Oct)₂ ≅ liquid Sn(OnC₆H₁₃)₂ > Sn(Oct)₂/nC₆H₁₃OH ≅ liquid Sn(OnC₈H₁₇)₂ > Sn(Oct)₂/nC₈H₁₇OH. The lowest activation energies (E_a = 52, 59, and 56 kJ mol⁻¹ for the Kissinger, Flynn–Wall, and Ozawa dynamic methods; E_a = 53–60, 55–58, and 60–62 kJ mol⁻¹ for the Friedman, KAS, and OFW isoconversional methods; and E_a = 76–84 kJ mol⁻¹ for the B/D) were found in the polymerizations using the novel liquid Sn(OnC₄H₉)₂ as the initiator, thereby showing it to be the most efficient initiator in the ROP of l-lactide.

The efficiency of homogeneous liquid tin(ii) n-alkoxide initiators in the ROP of l-lactide was reported in this work by non-isothermal DSC kinetic approaches.     

Tailor-made block copolymers of l-, d- and rac-lactides and ε-caprolactone via one-pot sequential ring opening polymerization by pyridylamidozinc(ii) catalysts

Three-coordinated Zn(ii) complexes bearing sterically encumbered bidentate monoanionic [N,N⁻] pyridylamido ligands efficiently catalyze the ring opening polymerization of lactide (LA) and ε-caprolactone (CL). Owing to the polymerization controlled nature and high rate, precise stereodiblock poly(LLA-b-DLA) with different block lengths can be easily produced by one-pot sequential monomer addition at room temperature in short reaction times. NMR, SEC and DSC analyses confirm the production of highly isotactic diblock copolymers which crystallize in the high melting stereocomplex phase. Stereo-triblock and tetrablock copolymers of l-LA, d-LA and rac-LA have been synthesized similarly. Finally, a diblock poly(CL-b-LA) has been easily obtained by sequential addition of ε-caprolactone and lactide under mild conditions.

New 3-coordinated Zn ROP catalysts afford lactide stereo-block copolymers with variable block lengths and steric structures and diblock ε-caprolactone-lactide copolymers at room temperature and in short reaction times.     

Ring opening polymerization of d,l-lactide and ε-caprolactone catalysed by (pyrazol-1-yl)copper(ii) carboxylate complexes

1,2-Bis{(3,5-dimethylpyrazol-1-yl)methyl}benzene (L) reacts with [Cu(OAc)₂] and C₆H₅COOH, 4-OH-C₆H₄COOH, 2-Cl-C₆H₄COOH and (3,5-NO₂)₂-C₆H₃COOH to afford the copper complexes [Cu₂(C₆H₅COO)₄(L)₂] (1), [Cu₂(4-OH-C₆H₄COO)₄(L)₂] (2), [Cu₂(2-Cl-C₆H₄COO)₄(L)₂]_n (3) and [Cu{(3,5-NO₂)₂-C₆H₃COO}₂L]_n (4) which are characterised by IR, mass spectrometry, elemental analyses, and X-ray crystallography. The structural data revealed two geometries that are adopted by the complexes: (i) paddle wheel in 1, 2·7H₂O, 3 and (ii) regular chains in 3 and 4. Magnetic studies show strong antiferromagnetic couplings in the paddle wheel complexes and a weak antiferromagnetic coupling in the monometallic chain one. Catalysis studies performed with these complexes (1–4) showed that they initiate ring opening polymerization (ROP) of ε-caprolactone (ε-CL) under solvent-free conditions and d,l-lactide in toluene at elevated temperatures. Polycaprolactone (PCL) and poly(d,l-lactide) (PLA) obtained from the polymerization reactions are of low molecular weights (858 for PCL and 602 Da for PLA for initiator 1) and polydispersity indices (typically 2.16 for PCL and 1.64 for PLA with 1 as the initiator). End group analysis of the polymers, determined by MALDI-ToF MS, indicates that the polymers have benzoate, hydroxyl, methoxy and cyclic end groups.

We report the synthesis, structure and complete characterization of four new pyrazolyl carboxylate-based copper(ii) complexes that catalyze the ring opening polymerization of ε-caprolactone under solvent-free conditions and of d,l-lactide in toluene.     

Preparation of thermo-responsive drug-loaded nanofibrous films created by electrospinning

We prepared thermosensitive and biocompatible drug-loaded nanofibrous films by an electrospinning technique using a block copolymer, poly(N-isopropylacrylamide)-b-poly(l-lactide) (PNLA), and poly(l-lactide) (PLLA). The copolymer PNLA was synthesized by the radical polymerization of N-isopropylacrylamide (NIPAAm), followed by the ring-opening polymerization of l-lactide. The properties of PNIPAAm and PNLA were selectively discussed based on the results of NMR, FT-IR, GPC, and CA analyses. Because of the low molecular weight of PNIPAAm and PNLA and the hydrolysis of PNLA resulting from its hydrophilicity, these copolymers were inappropriate for electrospinning separately. Hence, a mixture of PNLA and PLLA was used to prepare electrospun nanofibrous films. SEM images of the PNLA/PLLA electrospun films showed that homogeneous fibres with smooth surfaces were obtained. In vitro release studies indicated that the drug-release rate of the PNLA/PLLA electrospun nanofibrous films can be adjusted by the content and molecular weight of PNLA and by the environmental temperature. The results demonstrate that electrospinning is a promising way to create stimuli-responsive fibrous films with potential applications in the design of controllable drug delivery systems.

Thermosensitive and biocompatible PNLA/PLLA drug-loaded nanofibrous films with different morphologies and controlled drug release behaviors by electrospinning technique.     

Influence of poly(lactide) stereocomplexes as nucleating agents on the crystallization behavior of poly(lactide)s

The influence of the addition of linear and four-arm poly(lactide) (PLA) stereocomplexes (scPLAs) on the non-isothermal and isothermal crystallization behavior of poly(l-lactide) (PLLA) and poly(d-lactide) (PDLA) from the molten state was investigated. The linear PLAs and four-arm PLA with a similar chain length for each arm were synthesized by ring-opening polymerization. The linear and four-arm scPLAs were then prepared by solution blending and characterized by ¹H-NMR, FTIR, and WAXD analysis. Various mass ratios of the scPLAs were subsequently added to PLLA and PDLA as nucleating agents and specimens were prepared by solution casting. The isothermal and non-isothermal crystallization behavior of the specimens was examined by differential scanning calorimetry and polarized optical microscopy. The SC crystallites effectively promoted the nucleation of the PLAs, thereby increasing the general crystallization rate of the matrix. A 10% content of stereocomplex nucleating agent increased the crystallization rate of PDLA and PLLA by more than 55% and 70%, respectively. Compared with the linear scPLA, the four-arm scPLA more strongly promoted crystallization at higher temperatures. This might be because the greater degree of branching and larger steric hindrance of the four-arm scPLA led to the formation of defective SC crystallites, which was more beneficial for adsorption of the matrix on the crystal surface and permitted the nucleation and growth at higher temperatures. These results demonstrate that scPLAs can potentially be used as nucleating agents to improve the performance and transparency of PLA films.

The influence of the addition of linear and four-arm poly(lactide) stereocomplexes on the crystallization behavior of poly(l-lactide) and poly(d-lactide) from the molten state was investigated.     

Mechanistic study on substitution reaction of a citrato(p-cymene)Ru(ii) complex with sulfur-containing amino acids

The reactions of a dichloro(p-cymene)ruthenium(ii) dimer, [RuCl₂(p-cymene)]₂, with citric acid and sulfur-containing amino acids gave only [Ru(L)(p-cymene)]-type complexes (L = citrate (Cit), l-penicillaminate (l-Pen), S-methyl-l-cysteinate (S-Me-l-Cys) and l-methioninate (l-Met)) in aqueous solutions at various pHs and molar ratios of the reactants, where Cit and the amino acids act as a tridentate ligand. These sulfur-containing amino acid complexes with bound nitrogen, oxygen and sulfur atoms and η⁶-p-cymene take S absolute configuration around Ru(ii) selectively, having the α-proton oriented in the opposite direction from the Ru(ii) center. The concentration dependences of the observed pseudo-first-order rate constants were provided for the substitution reactions of the citrato complex, [Ru(Cit)(p-cymene)], with a large excess of the sulfur-containing amino acids at various temperatures at pH 7.3, where solvolysis path was observed for S-Me-l-Cys and l-Met as an intercept but not for l-Pen. The activation parameters for the substitution reactions by the direct attack of the amino acids were changed significantly, indicating that the reaction mechanism varies sensitively with the amino acids from an associative mechanism to an interchange one. The pH dependences of the rate constants of the substitution reactions suggest that the carboxylate group is an attacking group for S-Me-l-Cys and l-Met under neutral conditions and the thiol group of l-Pen acts as an entering group constantly at any pH showing a considerably smaller activation energy compared with S-Me-l-Cys and l-Met. Differences in stabilities of the amino acid complexes were obtained from the equilibrium constants for the substitution reactions between the amino acids. These results indicate that the activation energies for the substitution reactions of the citrato complex with the amino acids are moderately correlated with the stabilities of the formed amino acid complexes.

Thorough kinetic study revealed characteristics of the reaction mechanism for arene ruthenium(ii) complexes with bio-related ligands.     

Nanostructured poly(l-lactic acid)–poly(ethylene glycol)–poly(l-lactic acid) triblock copolymers and their CO2/O2 permselectivity

Biodegradable poly(l-lactic acid)–poly(ethylene glycol)–poly(l-lactic acid) (PLLA–PEG–PLLA) copolymers were synthesized by ring-opening polymerization of l-lactide using dihydroxy PEG as the initiator. The effects of different PEG segments in the copolymers on the mechanical and permeative properties were investigated. It was determined that certain additions of PEG result in composition-dependent microphase separation structures with both PLLA and PEG blocks in the amorphous state. Amorphous PEGs with high CO₂ affinity form gas passages that provide excellent CO₂/O₂ permselectivity in such a nanostructure morphology. The gas permeability and permselectivity depend on the molecular weight and content of the PEG and are influenced by the temperature. Copolymers that have a higher molecular weight and content of PEG present better CO₂ permeability at higher temperatures but provide better CO₂/O₂ permselectivity at lower temperatures. In addition, the hydrophilic PEG segments improve the water vapor permeability of PLLA. Such biodegradable copolymers have great potential for use as fresh product packaging.

Biodegradable PLLA copolymers, containing higher molecular weight and content of PEG present better CO₂ permeability and CO₂/O₂ permselectivity, have great potential for use as fresh product packaging.     

Synthesis and stereocomplex formation of enantiomeric alternating copolymers with two types of chiral centers,poly(lactic acid-alt-2-hydroxybutanoic acid)s

Stereocomplex (SC) formation was reported for the first time for enantiomeric alternating copolymers consisting of repeating units with two types of chiral centers, poly(lactic acid-alt-2-hydroxybutanoic acid)s [P(LA-alt-2HB)s]. l,l-Configured poly(l-lactic acid-alt-l-2-hydroxybutanoic acid) [P(LLA-alt-l-2HB)] and d,d-configured poly(d-lactic acid-alt-d-2-hydroxybutanoic acid) [P(DLA-alt-d-2HB)] were amorphous. Blends of P(LLA-alt-l-2HB) and P(DLA-alt-d-2HB) were crystallizable and showed typical SC-type wide-angle X-ray diffraction profiles similar to those reported for stereocomplexed blends of poly(l-lactic acid) and poly(d-lactic acid) homopolymers and of poly(l-2-hydroxybutanoic acid) and poly(d-2-hydroxybutanoic acid) homopolymers, and of l,l-configured poly(l-lactic acid-co-l-2-hydroxybutanoic acid) [P(LLA-co-l-2HB)] and d,d-configured poly(d-lactic acid-co-d-2-hydroxybutanoic acid) [P(DLA-co-d-2HB)] random copolymers. The melting temperature values and melting enthalpy values at 100% crystallinity for stereocomplexed solvent-evaporated and precipitated P(LLA-alt-l-2HB)/P(DLA-alt-d-2HB) blends were correspondingly 187.5 and 187.9 °C, and 98.1 and 91.8 J g⁻¹. Enantiomeric polymer blending of P(LLA-alt-l-2HB) and P(DLA-alt-d-2HB) can confer crystallizability by stereocomplexation and the biodegradable materials with a wide variety of physical properties and biodegradability are highly expected to be prepared by synthesis of alternating copolymers of various combinations of two types of chiral α-substituted 2-hydroxyalkanoic acid monomers and their SC crystallization.

Stereocomplex formation was reported for alternating copolymers of chiral α-substituted 2-hydroxyalkanoic acids which can be utilized for preparation of biodegradable materials with a variety of physical properties and biodegradability.     

Photopolymerized poly(l-lactide-b-N-vinyl-2-pyrrolidone) network resists cell adhesion in situ

A three-armed star-shaped poly(l-lactide) (PLLA) oligomer was synthesized using glycerol to ring-opening and polymerize l-lactide. The resultant oligomer introduced photoreactive groups at the terminal of PLLA chains by a coupling reaction with monoethyl fumarate (FAME). Photopolymerizable resin has been prepared by mixing PLLA 3-FAME, N-vinyl-2-pyrrolidone (NVP) as a reactive diluent and Irgacure 2959 as a photoinitiator. The PLLA 3-FAME/NVP cross-linked network could be formed by UV curing and was characterized through mechanical property tests, cytotoxicity experiments and cell adhesion experiments. In the dry state, Young''s modulus and tensile strength of the network were significantly higher than those of pure PLLA formed by fused deposition modeling (FDM) printing, due to the formation of the cross-linked net. In the wet state, however, Young''s modulus and tensile strength of the network were reduced by less than those of PLLA since the water-absorbed NVP content was easy to stretch. Moreover, the resultant network not only exhibited no obvious cytotoxicity but also resisted the adhesion of L929 fibroblasts. Combined with Digital Light Processing (DLP) technology, the poly(l-lactide-b-N-vinyl-2-pyrrolidone) network may be widely used in the field of anti-adhesion barrier materials and/or biological anti-fouling materials with customization requirements.

The poly(l-lactide-b-N-vinyl-2-pyrrolidone) network could be formed by UV curing, and resist the adhesion of L929 fibroblasts. It could be used in the field of biological anti-fouling material with customization requirements.     

Simultaneous removal of Sb(iii) and Cd(ii) in water by adsorption onto a MnFe2O4–biochar nanocomposite

In this study, a jacobsite–biochar nanocomposite (MnFe₂O₄–BC) was fabricated and used to simultaneously remove Sb(iii) and Cd(ii) from water via adsorption. The MnFe₂O₄–BC nanocomposite was prepared via a co-precipitation method and analyzed using various techniques. The results confirm the successful decoration of the biochar surface with MnFe₂O₄ nanoparticles. The maximum Sb(iii) removal efficiency was found to be higher from bi-solute solutions containing Cd(ii) than from single-solute systems, suggesting that the presence of Cd(ii) enhances the removal of Sb(iii). The Langmuir isotherm model describes well Sb(iii) and Cd(ii) removal via adsorption onto the MnFe₂O₄–BC nanocomposite. The maximum adsorption capacities are 237.53 and 181.49 mg g⁻¹ for Sb(iii) and Cd(ii), respectively, in a bi-solute system. Thus, the prepared MnFe₂O₄–BC nanocomposite is demonstrated to be a potential adsorbent for simultaneously removing Sb(iii) and Cd(ii) ions from aqueous solutions.

In this study, a jacobsite–biochar nanocomposite (MnFe₂O₄–BC) was fabricated and used to simultaneously remove Sb(iii) and Cd(ii) from water via adsorption.     

Novel Schiff base cobalt(ii) phthalocyanine with appliance of MWCNTs on GCE: enhanced electrocatalytic activity behaviour of α-amino acids

A novel tetra-4-{(E)-[(8-aminonaphthalen-1-yl)imino]methyl}-2-methoxyphenol Co(ii) phthalocyanine (CoTANImMMPPc) was synthesized using a precursor protocol and characterized via electroanalytical and spectroscopic techniques. The FT-IR spectra of the synthesized compounds showed significant peaks corresponding to the functional groups of the precursors and phthalocyanine (Pc) compound. The mass and NMR spectra confirmed the formation of the target precursor compounds. A film of CoTANImMMPPc was deposited on the surface of an electrode and applied for the detection and monitoring of l-alanine and l-arginine. The cyclic voltammetric studies of l-alanine and l-arginine using the (CoTANImMMPPc/MWCNTs/GC) electrode showed a linear response in the range of 50–500 nM and the limit of detection was found to be 1.5 and 1.2 nM, respectively. Differential pulse voltammetry and chronoamperometry showed that the catalytic response for l-alanine and l-arginine is in the range of 50–500 nM with an LoD of 1.8 and 2.3 nM, respectively. The oxidation-active CoTANImMMPPc film significantly enhanced the current response in the chronoamperometric method and displayed a selective and sensitive response towards l-alanine and l-arginine in the presence of various other bio-molecules. The developed electrode showed good working stability and was applied for the analysis of real samples, which yielded satisfactory results. Therefore, CoTANImMMPPc-MWCNTs/GCE shows good analytical performance, is economical and produced via a simple synthetic method and can be applied as a sensor for the detection of l-alanine and l-arginine.

A novel CoTANImMMPPc complex was synthesized using a precursor protocol and characterized via electroanalytical and spectroscopic techniques with enhanced electrocatalytic behaviour of α-amino acids.     

One-pot route to graft long-chain polymer onto silica nanoparticles and its application for high-performance poly(l-lactide) nanocomposites

A facile “one-pot” synthetic route to modify SiO₂ nanoparticles with long-chain polymer was developed. The structure and morphology of SiO₂ grafted with poly(l-lactide) (SiO₂-g-PLA) were characterized by FTIR, TGA, GPC, and TEM. Furthermore, a series of PLA/SiO₂-g-PLA nanocomposites were prepared with different nanofiller loadings, and their related performances were investigated. As an effective nucleating agent, the SiO₂-g-PLA had a positive effect to improve the crystallization rate and increase the crystallinity. Meanwhile, the PLA nanocomposites presented outstanding mechanical properties including excellent toughness and high stiffness. In addition, the PLA materials kept good transparency with less than 3 wt% nanofillers. Overall, this work provides a useful method for preparing high-performance polymer nanocomposites.

A facile “one-pot” synthetic route is used to modify SiO₂ nanoparticles with a long-chain polymer, and to prepare high-performance poly(l-lactide) nanocomposites.     

Presence of δ-(l-α-Aminoadipyl)-l-Cysteinyl-d-Valine in Fermentations of Penicillium chrysogenum

Cultures of Penicillium chrysogenum, growth with [³⁵S]sulfate or labeled amino acids, were examined by ion-exchange chromatography for possible peptidic precursors of penicillin. A sulfur-containing compound, present in both the mycelial extracts and the culture filtrates, was eluted at the location of the synthetic lld-tripeptide δ-(l-α-aminoadipyl)-l-cysteinyl-d-valine. Since this compound was also labeled when the cultures were incubated with dl-[6-¹⁴C]α-aminoadipic acid, l-[3,3′-³H]cystine, or dl-[1-¹⁴C]valine, its identity with the synthetic lld-tripeptide can be accepted. No δ-(l-α-aminoadipyl)-l-cysteine or lll-tripeptide were detected. The implications of these findings for tripeptide and penicillin biosynthesis are discussed.     

Synthesis,structures, and catalytic efficiency in ring opening polymerization of rac-lactide with tridentate vs. bidentate cobalt(ii), zinc(ii), and cadmium(ii) complexes containing N-substituted N,N-bis((3,5-dimethyl-1H-pyrazol-1-yl)methyl)amine ligands

A series of Co(ii), Zn(ii), and Cd(ii) complexes supported by 1-(3,5-dimethyl-1H-pyrazol-1-yl)-N-((3,5-dimethyl-1H-pyrazol-1-yl)methyl)-N-(furan-2-ylmethyl)methanamine (L_A) and N,N-bis((3,5-dimethyl-1H-pyrazol-1-yl)methyl)-4-isopropylaniline (L_B) were synthesized. The direct chelation of CoCl₂·6H₂O, ZnCl₂, and CdBr₂·4H₂O by the ligands produced [L_nMX₂] (L_n = L_A or L_B; M = Zn or Co, with X = Cl; M = Cd, with X = Br) complexes in high yields. Structural studies revealed that [L_BCoCl₂] and [L_BZnCl₂] adopted distorted tetrahedral geometries, as L_B coordinated the metal centers in a bidentate fashion, while L_A coordinated the metal centers in a tridentate fashion through the nitrogen atoms of the pyrazole and amine moieties, so that [L_ACoCl₂] and [L_AZnCl₂] exhibited trigonal bipyramidal geometries and [L_ACdBr₂] a square pyramidal geometry. [L_BCdBr₂] has two Cd-containing structures per unit cell, whereby one Cd center adopted a distorted tetrahedral geometry and the other exhibited square bipyramidal geometry. The in situ-generated alkyl derivatives of the synthesized complexes were assessed in the ring-opening polymerization of rac-lactide. Heterotactic polylactides (PLAs) were furnished with all complexes. The [L_BZnCl₂]/MeLi system produced PLA with a superior heterotactic bias (P_r up to 0.94) at −25 °C. PLAs with wide-ranging polydispersity indices (1.16–2.23) and low molecular weights were produced in all cases, irrespective of the specific M(II) center and ancillary ligand utilized.

Co(ii), Zn(ii), and Cd(ii) complexes supported by bis-pyrazolyl ligands were applied to the ring-opening polymerization of rac-lactide to produce heterotactic polylactides (PLAs) with superior heterotactic bias i.e. P_r up to 0.94 at −25 °C.     

Application of temperature-controlled chiral hybrid structures constructed from copper(ii)-monosubstituted Keggin polyoxoanions and copper(ii)-organoamine complexes in enantioselective sensing of tartaric acid

Temperature usually occupies a crucial position in the construction of chiral compounds. By controlling the temperature of the reaction system, chiral and non-chiral compounds can be designed and synthesized. Given the above, three new chiral and non-chiral compounds based on copper(ii) monosubstituted polyoxoanions and Cu(en) complexes (en = ethylenediamine), d/l-[Cu(H₂O)(en)₂]₂{[Cu(H₂O)₂(en)][SiCuW₁₁O₃₉]}·5H₂O (1, d-1 and l-1) and [Cu(H₂O)(en)₂]{[Cu(en)₂]₂[SiCuW₁₁O₃₉]}·2.5H₂O (2), were successfully synthesized under hydrothermal conditions. The main synthesis conditions of compound 1 (d-1 and l-1) and compound 2 are the same, however, the only difference is that the reaction temperatures are 80 °C and 140 °C, respectively. What''s more, compounds 1 and 2 can form a 1D chiral chain by Cu–O and W/Cu–O–W/Cu bonds, respectively, and further obtain a 3D-supramolecular framework through hydrogen bonding interaction. Meanwhile, due to the asymmetry of chiral compound 1, optical second-harmonic generation (SHG) was used to investigate the second-order nonlinear optical effect and it was found that the observed SHG efficiency of compound 1 is 0.3 times that of urea. To further investigate the chiral properties, d-1 and l-1 were used in the electrochemical enantioselective sensing of d-/l-tartaric acid (d-/l-tart) molecules, respectively, which demonstrates that d-1 and l-1 have a good application prospect in sensing chiral substances.

A pair of temperature-controlled chiral compounds, d- and l-[Cu(en)₂(H₂O)]₂{[Cu(en)(H₂O)₂][SiCuW₁₁O₃₉]}·5H₂O (en = ethanediamine) are isolated by hydrothermal method, having a good application prospect in sensing d-/l-tartaric acid.     

High voltage,solvent-free solid polymer electrolyte based on a star-comb PDLLA–PEG copolymer for lithium ion batteries

In this work, a novel star-comb copolymer based on poly(d,l-lactide) (PDLLA) macromonomer and poly(ethylene glycol)methyl ether methacrylate (PEGMA) was prepared, and the electrochemical properties were studied, with the aim of using it as a solid polymer electrolyte in lithium ion batteries. The six-arm vinyl functionalized PDLLA macromonomer was synthesized by a ring-opening polymerization (ROP) of d,l-lactide and subsequently an acylation of the hydroxy end-groups. A series of free-standing solid polymer electrolyte membranes from different ratios of PDLLA, PEGMA and LiTFSI were prepared through solvent-free free radical polymerization under UV radiation. The chemical structure of the obtained polymers was confirmed by ¹H NMR and FTIR. The as-prepared six-arm star-comb solid polymer electrolytes (PDLLA-SPEs) exhibit good thermal stability with T_d^5%s of ∼270 °C and low T_gs of −48 to −34 °C. The electrochemical characterization shows that the PDLLA-SPEs possess a wide electrochemical window up to 5.1 V with an optimal ionic conductivity of 9.7 × 10⁻⁵ S cm⁻¹ at 60 °C at an EO/Li⁺ ratio of 16 : 1. Furthermore, the all-solid-state LiFePO₄/Li cells display extraordinary cycling and rate performances at 60 °C by curing the PDLLA-SPEs directly on the cathode. These superior properties of the six-arm star-comb PDLLA-SPE make it a promising candidate solid electrolyte for lithium batteries.

In this work, a novel star-comb copolymer based on PDLLA macromonomer and PEGMA was prepared, and the electrochemical properties were studied, with the aim of using it as a solid polymer electrolyte in lithium ion batteries.     

Remarkable diastereomeric effect on thermoresponsive behavior of polyurethane based on lysine and tartrate ester derivatives

This study describes the long-distance diastereomeric effect on thermoresponsive properties in water-soluble diastereomeric polyurethanes (PUs) composed of an l-lysine ethyl ester diisocyanate and a trimethylene glycol l-/d-tartrate ester, which have differences in spatial arrangements of the ethyl esters in the mirror image. The PUs based on l-lysine and l-/d-tartrate ester, named l-PU and d-PU, were synthesized with various number average molecular weights from 4700 to 13 100. In turbidimetry, l-PU showed a steep phase transition from 100%T to 0%T within about 10 °C at 4 g L⁻¹, whereas d-PU did not change completely to 0%T transmittance even at 80 °C at 4 g L⁻¹. In addition, the thermoresponsive properties of l-PU were less affected by concentration than those of d-PU. This long-distance diastereomeric effect on thermoresponsive behavior between l-PU and d-PU appeared in common among 6 samples with 4700 to 13 100 number average molecular weight. In the dynamic light scattering experiments at each transmittance, the hydrodynamic diameter (D_h) of l-PU increased up to 1000 nm, while the D_h of d-PU remained almost at 200–300 nm. The C O stretching vibration of FT-IR spectra showed that d-PU has more hydrogen-bonded ester groups than L-PU. Thus, we speculated that the difference in the retention of polymer chains in the micelle to promote intermicellar bridging generates the long-distance diastereomeric effect.

The long-distance diastereomeric effect on thermoresponsive properties in a polyurethane system consisting of chiral monomers was reported.