Synthesis and characterization of functional poly(γ-benzyl-l-glutamate) (PBLG) as a hydrophobic precursor

Four kinds of functional poly(γ-benzyl-l-glutamate) (PBLG) copolymers containing chloro, azido, allyl or propargyl groups on the side chains were synthesized through ester exchange reactions of PBLG with functional alcohols without any protection and de-protection process. Hydrolysis of PBLG, which was found during the ester exchange reaction under low ratios of alcohol to the repeat units of PBLG, was thoroughly investigated, and could be successfully depressed by addition of certain amount of benzyl alcohol to the reaction system. Click chemistry reactions of the azidized or propargylated copolymers, thiol-ene reaction of the allyllated copolymer were taken successfully, indicating that the functional groups on the copolymers were still reactive. Microspheres were also formed, which showed the potential application of the functional polymers as micro-carriers. Characterizations including ¹H NMR, ¹³C NMR, FTIR, elemental analysis, DSC, TGA, ESEM, fluorescence microscope and SEC-MALS were taken.     

Synthesis and self-assembly of comb-like amphiphilic Doxifluridine-poly(?-caprolactone)-graft-poly(γ-glutamic acid) copolymer

Advances in amphiphilic copolymers can potentially be exploited in drug or gene delivery. This study develops novel comb-like amphiphilic copolymers that comprise poly(γ-glutamic acid) (γ-PGA) as a hydrophilic backbone and Doxifluridine-poly-(?-caprolactone) (5′-deoxy-5-fluorouridine-poly(?-caprolactone), 5′DFUR-PCL) as a hydrophobic side chain. A novel 5′DFUR-PCL polymer was synthesized with antitumor agent Doxifluridine (5′DFUR) as the initiator via the ring-opening polymerization of ?-caprolactone (?-CL) using tin(II) 2-ethylhexanoate (Sn(Oct)₂) as the catalyst. The 5′DFUR-PCL polymer was then grafted on γ-PGA to yield a 5′DFUR-PCL-γ-PGA comb-like copolymer with the help of 1-ethyl-3-(3-dimethyl-aminopropyl) carbodiimide (EDC). The characteristics of these copolymers were examined by ¹H NMR, FT-IR, GPC, contact angle measurement and thermal properties. Grafting 5′DFUR-PCL would significantly increase the contact angle and decrease the melting temperature (T_m) of the copolymers. The micelles self-assembled from these amphiphilic copolymers were formed in an aqueous phase and were examined via fluorescence approaches, dynamic light scattering (DLS) and transmission electron microscopy (TEM). The average sizes of the micelles were in the range from 130 to 230 nm and their zeta potentials were negative and less than −16.7 mV. The critical micelle concentration (CMC) was from 1.49 mg/L to 4.63 mg/L at 25 °C. TEM images demonstrated that the micelles were spherical and clearly had a core-shell structure.     

Helix-helix transition of poly(β-phenylpropyl l-aspartate) embedded in stable helical poly(γ-phenylethyl glutamate) matrix

We studied the helix-helix transition of poly(β-phenylpropyl l-aspartate) (3PLA) embedded in a right-handed α-helical (α_R) poly(γ-phenylethyl l-glutamate) (2PLG) or left-handed α-helical poly(γ-phenylethyl d-glutamate) (2PDG) matrix. Binary mixtures were prepared with 3PLA:2PLG (2PDG) mole fractions of 9:1 to 1:9. In all these mixtures, the 3PLA molecule exhibited helical sense inversion even if dispersed or isolated into the hard-rod matrix, and the inversion rate of the embedded 3PLA molecule was relatively higher than that of the pure system. Thus, it was concluded that the transition occurs in only a limited space and more easily for the isolated molecule. Further, the 3PLA molecule recognized the chiral environment produced by the surrounding polymers. For 3PLA surrounded by a 2PDG matrix, the helix-helix transition temperature was lower and the transition rate on cooling was slower than those for 3PLA surrounded by a 2PLG matrix. This is reasonable since the left-handed matrix helps right-handed to left-handed helical inversion.     

The heterogenization of l-phenylalanine–Ru(III) complex and its application as catalyst in esterification of ethyl alcohol with acetic acid

A simple route is demonstrated for the efficient immobilization of silica with l-(N-α-acetylphenylalanine)–ruthenium(III) complex. This catalyst was labelled as RHAPhe–Ru. The ²⁹Si MAS NMR showed the presence of T³, T², Q³ and Q⁴ silicon centers. The ¹³C MAS NMR showed the presence of three chemical shifts consistent with the three carbon atoms of the propyl group. The catalytic performance of RHAPhe–Ru was tested in the esterification of ethyl alcohol. A conversion of 82% was achieved, with 100% selectivity towards ethyl acetate. The catalyst could be regenerated by washing with ethanol and drying at 110 °C for 24 h without significant loss in reactivity.     

Morphology and mechanical properties of nanostructured blends of epoxy resin with poly(?-caprolactone)-block-poly(butadiene-co-acrylonitrile)-block-poly(?-caprolactone) triblock copolymer

Poly(?-caprolactone)-block-poly(butadiene-co-acrylonitrile)-block-poly(?-caprolactone) triblock copolymer was synthesized via the ring-opening polymerization of ?-caprolactone with dihydroxyl-terminated butadiene-co-acrylonitrile random copolymer. The amphiphilic block copolymer was used to toughen epoxy thermosets via the formation of nanostructures. The morphology of the thermosets was investigated by means of atomic force microscopy, transmission electronic microscopy and small-angle X-ray scattering. It was judged that the formation of the nanostructures in the thermosets follows the mechanism of reaction-induced microphase separation. The thermal and mechanical properties of the nanostructured thermosets were compared to those of the ternary blends composed of epoxy, poly(butadiene-co-acrylonitrile) and poly(?-caprolactone) with the identical content of the modifiers. It is noted that at the same composition the nanostructured thermosets displayed higher glass transition temperatures (T_gs) than the ternary blends, which was evidenced by dynamic mechanical analysis. The fracture toughness of the thermosets was evaluated in terms of the measurement of critical stress field intensity factor (K_1C). It is noted that at the identical composition the nanostructured blends significantly displayed higher fracture toughness than the ternary blends. In addition, the K_1C of the nanostructured thermosets attained the maximum with the content of the modifier less than their counterpart of ternary blending.     

Synthesis and characterization of nanoflaky maghemite (γ-Fe2O3) as a versatile anode for Li-ion batteries

In this study, nanoflaky maghemite (γ-Fe₂O₃) was successfully prepared by heating of synthesized lepidocrocite (γ-FeO(OH)). Once maghemite obtained, the electrochemical performance of nanoflaky maghemite, as an anode for Li-ion batteries, was investigated. Synthesis of lepidocrocite was optimized by adjusting the heating time and ratio of ethylene glycol (EG) to water in solution. The results revealed that with equal ratio of EG to water, the obtained phase was crystalline lepidocrocite whereas in other ratios lepidocrocite was not the only emerged phase. Field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) results revealed that increasing heating time has no effect on morphology. This increment only led to the slight crystallite growth and agglomeration of precipitation. The optimized lepidocrocite were heated at 230?°C for 2?h to form maghemite, which was confirmed by using XRD. FESEM, high-resolution transmission electron microscopy, and nitrogen adsorption-desorption results disclosed that the particles have flaky morphology with thickness of less than 10?nm and surface area of 105?m² g^?1. Cyclic voltammetry results of anode body (prepared using nanoflaky maghemite) demonstrated reversible formation pathway of iron and lithium oxide through discharging and charging. Moreover, galvanostatic charge–discharge cycling showed a reversible capacity of about 480?mAh?g^?1 after 50 cycles at current density of 500?mA?g^?1. Good cyclability, and capacity retention of the anode is due to the nananometric size and flaky shape of the maghemite particles. These particles’ shape made it easier for them to expand and contract in thickness direction with minimized destructions imposed.     

Synthesis of novel poly(ethylene-ter-1-hexene-ter-dicyclopentadiene)s using bis(β-enaminoketonato)titanium catalysts and their applications in preparing polyolefin-graft-poly(?-polycaprolactone)

Novel terpolymers containing ethylene, 1-hexene and dicyclopentadiene (DCPD) were synthesized using bis(β-enaminoketonato)titanium catalysts [PhNC(R₂)CHC(R₁)O]₂TiCl₂ (1a: R₁ = Ph, R₂ = CF₃; 1b: R₁ = CF₃, R₂ = CH₃). In the presence of modified methylaluminoxane, these catalysts afforded terpolymers with a broad range of monomer compositions and unimodal molecular weight distributions. ¹³C NMR spectra reveal the exclusive insertion manner of DCPD maintained under various reaction conditions. DSC results show the melting temperature and the glass transition temperature are very sensitive to the terpolymer composition and the morphology can be easily tuned from semicrystalline state to amorphous state. With ethylene/1-hexene/DCPD molar ratio about 67/28/5, the terpolymer exhibits low glass transition temperature (T_g = −50 °C) and has a great potential to serve as polyolefin elastomer. Additionally, the terpolymer containing 4.3 mol% 1-hexene and 1.6 mol% DCPD was served as the “reactive intermediate polyolefin” for PCL graft reaction. The composition of graft copolymer was well controllable and high graft efficiency was observed. The microscopy studies in conjunction with the tensile tests revealed that PCL graft copolymer is the effective compatibilizer for polyethylene/polar polymer blends by improving the interfacial adhesion between separated phases.     

Zr(IV)?Fe(III), ?Ga(III), and ?Sn(IV) Binary Metal Complexes as Synergistic and Reusable Esterification Catalysts

Synergism in catalytic activity with the combined use of Hf(O‐i‐Pr)₄ or Zr(O‐i‐Pr)₄ and Fe(O‐i‐Pr)₃ for direct esterification and a very simple method for their extraction with ionic liquids for their recovery and reuse are described. This Zr(IV) Fe(III) complex is an environmentally benign catalyst due to its high turnover number, extremely mild Lewis acidity, low toxicity, reusability, and commercial availability at low cost.     

Synthesis and micellization of an amphiphilic biodegradable β-cyclodextrin/poly(γ-benzyl L-glutamate) copolymer

β-Cyclodextrin/poly(γ-benzyl L-glutamate) (β-CD-PBLG) copolymers were synthesized by ring-opening polymerization of N-carboxy-γ-benzyl L-glutamate anhydride (BLG-NCA) in N,N-dimethylformamide(DMF) initiated by mono-6-amino-β-cyclodextrin(H₂N-β-CD). The structures of the copolymers were determined by IR, ¹H NMR and GPC. The fluorescence technique was used to determine the critical micelle concentration (CMC) of copolymer micelle solution. The diameter and the distribution of micelles were characterized by dynamic light scattering(DLS) and its shape was observed by transmission electron microscopy(TEM). The results showed that BLG-NCA could be initiated by H₂N-β-CD to produce copolymer. These copolymers showed an amphiphilic nature and could self-assemble into nano-micelles in water. The CMC of copolymer solution and the size of micelle reduced with the increasing of the proportion of hydrophobic parts. TEM images demonstrated the micelles are all spherical. Such copolymers could be expected to find applications in drug delivery systems and other biomedical domains.     

Star-like poly (n-butyl acrylate)-b-poly (α-methylene-γ-butyrolactone) block copolymers for high temperature thermoplastic elastomers applications

Thermoplastic elastomers based on well-defined 10- and 20 arm star-like block copolymers containing middle soft poly(n-butyl acrylate) (PBA) block and outer hard poly(α-methylene-γ-butyrolactone) (PMBL) block were synthesized by atom transfer radical polymerization (ATRP). Phase separated cylindrical or lamellar morphologies, depending on the copolymers composition and the annealing temperature of the films, were observed by atomic force microcopy and small-angle X-ray scattering. The mechanical and thermal properties of the copolymers were thoroughly characterized. The prepared copolymers retained their phase separated morphology even at temperatures exceeding 300 °C. Both tensile strength and elongation values for the star-like copolymers were considerably higher than for linear copolymers with similar composition.     

Self-organized thermosets involving epoxy and poly(?-caprolactone)-block-poly(ethylene-co-ethylethylene)-block-poly(?-caprolactone) amphiphilic triblock copolymer

In this work, we investigated the self-assembly behavior of poly(?-caprolactone)-block-poly(ethylene-co-ethylethylene)-block-poly(?-caprolactone) (PCL-b-PEEE-b-PCL) triblock copolymer in epoxy thermosets. The PCL-b-PEEE-b-PCL triblock copolymer was synthesized via the ring-opening polymerization of ?-caprolactone with a hydroxyl-terminated poly(ethylene-co-ethylethylene) as the macromolecular initiator. The hydroxyl-terminated poly(ethylene-co-ethylethylene) was prepared with the hydrogenation reaction of a hydroxyl-terminated polybutadiene. The triblock copolymer was incorporated into the precursors of epoxy to obtain the nanostructured thermosets. It was found that the self-organized nanophases were formed in the mixture before curing reaction and the nanostructures can be further fixed via curing reaction. The self-assembly behavior of the triblock copolymer in epoxy thermosets was investigated by means of atomic force microscopy (AFM), small-angle X-ray scattering (SAXS) and dynamic mechanical thermal analysis (DMTA). Differential scanning calorimetry (DSC) shows that the formation of the self-organized nanophase in the thermosets caused that a part of poly(?-caprolactone) subchains were demixed from epoxy matrix with the occurrence of curing reaction; the fractions of demixed PCL blocks were estimated according to the T_g-composition relation of the model binary blends of epoxy and PCL.     

Copper(II) Acetate/Oxygen‐Mediated Nucleophilic Addition and Intramolecular C?H Activation/C?N or C?C Bond Formation: One‐Pot Synthesis of Benzimidazoles or Quinazolines

Diarylcarbodiimides or benzylphenylcarbodiimides are converted to 1,2‐disubstituted benzimidazoles or 1,2‐disustituted quinazolines via addition/intramolecular C H bond activation/C‐N or C C bond forming reaction using copper(II) acetate/oxygen [Cu(OAc)₂/O₂] as the oxidant at 100 °C in one‐pot cascade procedure.     

Synthesis of novel ABA triblock and (ABA)n multiblock copolymers comprised of polyisobutylene and poly(γ-benzyl-l-glutamate) segments

The synthesis of ABA triblock copolymers comprised of polyisobutylene (PIB) and poly(γ-benzyl-l-glutamate) (PBLG) segments has been demonstrated for the first time by the polymerization of γ-benzyl-l-glutamate N-carboxyanhydride (BLG-NCA) initiated with well-defined α,ω-primary amino-functional PIBs. The ammonium-mediated polymerization of BLG-NCA provided better control of molecular weights and lower polydispersity indices (PDIs) compared to the conventional polymerization. The compositional homogeneity of the block copolymers has been confirmed by GPC-MALLS and ¹H NMR spectroscopy. Since the resulting ABA triblock copolymer possessed primary amino groups at α,ω-ends, further extension reaction with 4,4′-methylene-bis(phenyldiisocyanate) was possible to afford a novel (ABA)_n multiblock copolymer.     

Synthesis of Isoquinolines via Rhodium(III)‐Catalyzed Dehydrative C?C and C?N Coupling between Oximines and Alkynes

Isoquinolines have been synthesized from the redox‐neutral dehydrative C N and C C cross‐coupling between oximines and alkynes using a catalytic amount of (pentamethylcyclopentadiene)rhodium dichloride dimer {[RhCp*Cl₂]₂} and cesium acetate (CsOAc), a process that involves ortho C H activation of oximines and subsequent functionalization with alkynes. This redox‐neutral catalytic isoquinoline synthesis operates under mild conditions, and is insensitive to moisture or air. A broad scope of coupling partners has been established, and a likely mechanism has been suggested.     

Aryl and Arylalkyl Substituted 3-Hydroxypyridin-2(1H)-ones: Synthesis and Evaluation as Inhibitors of Influenza A Endonuclease

Seasonal influenza infections are associated with an estimated 250–500 000 deaths annually. Resistance to the antiviral M2 ion-channel inhibitors has largely invalidated their clinical utility. Resistance to neuraminidase inhibitors has also been observed in several influenza A virus (IAV) strains. These data have prompted research on inhibitors that target the cap-snatching endonuclease activity of the polymerase acidic protein (PA). Baloxavir marboxil (Xofluza®), recently approved for clinical use, inhibits cap-snatching endonuclease. Resistance to Xofluza® has been reported in both in vitro systems and in the clinic. An X-ray crystallographic screening campaign of a fragment library targeting IAV endonuclease identified 5-chloro-3-hydroxypyridin-2(1H)-one as a bimetal chelating agent at the active site. We have reported the structure–activity relationships for 3-hydroxypyridin-2(1H)-ones and 3-hydroxyquinolin-2(1H)-ones as endonuclease inhibitors. These studies identified two distinct binding modes associated with inhibition of this enzyme that are influenced by the presence of substituents at the 5- and 6-positions of 3-hydroxypyridin-2(1H)-ones. Herein we report the structure–activity relationships associated with various para-substituted 5-phenyl derivatives of 6-(p-fluorophenyl)-3-hydroxypyridin-2(1H)-ones and the effect of using naphthyl, benzyl, and naphthylmethyl groups as alternatives to the p-fluorophenyl substituent on their activity as endonuclease inhibitors.     

Toughening of poly(l-lactide) with poly(ε-caprolactone): Combined effects of matrix crystallization and impact modifier particle size

Enhancing matrix crystallization has been demonstrated to be an effective method to simultaneously improve the impact toughness and heat resistance of poly(l-lactide) (PLLA) modified with flexible polymers, such as poly(ε-caprolactone) (PCL). Unfortunately, increasing PLLA matrix crystallinity alone cannot guarantee the enhancement of impact toughness in most cases, so other structural parameters should be considered. In this work, taking PLLA/PCL (80/20) blend as an example, the combined roles of matrix crystallization and impact modifier particle size in the toughening have been investigated. PLLA matrix crystallinity was controlled by adding a highly effective nucleating agent and PCL particle size was tailored by varying processing conditions while maintaining constant interfacial adhesion. It is interesting to find that toughening is efficient only if matrix crystallinity and particle size are well matched. With the significant increase of matrix crystallinity, an evident decrease of optimum particle size for toughening PLLA has been identified for the first time. Therefore, suitable particle size is the precondition for highly crystalline matrix to work effectively in the toughening because only small particles (0.3–0.5 μm) are effective in trigger shear yielding mechanism of the matrix needed for good toughness, whereas relatively large particles (0.7–1.1 μm) are only capable of toughening amorphous matrix effectively by initiating multiple crazing of the matrix. Importantly, our findings can be used to well explain the reason for the different roles of matrix crystallization in the toughening of different PLLA blends reported in the literature. Furthermore, the heat resistance of the blend with a highly crystalline matrix is much better than that of the blend with an amorphous one as expected. This work could not only provide a new insight into the synergistic roles of matrix crystallization and modifier particle size in the toughening of PLLA but also set up a universal framework for designing high-performance PLLA products with both good impact toughness and high heat resistance.     

Synthesis of α-SiC/α-SiAlON composites by spark plasma sintering: Phase formation and microstructures development

α-SiC/α-SiAlON composites with 80 wt% α-SiC (6H phase) were fabricated by spark plasma sintering at 1800-2000 °C in a 0.6 atm nitrogen atmosphere. The effects of the temperatures on the phase development, microstructures and mechanical properties were investigated. The results showed the Si₃N₄, AlN, Al₂O₃, and Y₂O₃ particles were isolated by the 6H-SiC to prevent α-SiAlON formation at 1800 °C. The Si₃N₄ decomposed at 1900 °C and above, thus added Si in the phase compositions. The α-SiC grains grew anisotropic in the sintering liquids at 1800 °C and 1900 °C, forming the self-reinforcing microstructures, and accordingly increased the flexural strength and fracture toughness. In cooling down immediately after the temperature reached 2000 °C, a transitory hold at 1700 °C transformed the 6H-SiC into the 3C polytype in 30 s. The electric current was suspected of activating this polytype transformation.     

Synthesis and characterization of a functionalized biodegradable copolymer: poly(l-lactide-co-RS-β-malic acid)

The ring-opening copolymerization of l-lactide (l-LA) and RS-β-benzyl malate (MA) was performed in the presence of stannous octoate. Copolymers were successfully synthesized using different feeding doses. ¹H NMR analysis revealed that the compositions of the copolymers with high MA contents were similar to the feeding doses. GPC measurements showed that the molecular weight of the copolymers decreased as the MA content increased. The hydrophilicity of these copolymers was remarkably improved after they were hydrogenolyzed over palladium on charcoal, which removed the pendant benzyl groups. These de-protected copolymers had higher glass transition temperatures (T_g) than both the corresponding protected copolymers and the PLLA homopolymer due to the formation of intermolecular hydrogen bonds between the pendant carboxyl groups. The morphology of the copolymers changed from crystalline to amorphous with increasing RS-β-malic acid content.     

pH/temperature-responsive poly(dimethylaminoethyl methacrylate) grafted κ-carrageenan copolymer: Synthesis and physicochemical properties

κ-Carrageenan-graft-poly(dimethylaminoethyl methacrylate) (CRG-g-PDMA) was synthesized via free-radical copolymerization under microwave irradiation. ¹³C-Nuclear magnetic resonance spectroscopy (¹³C-NMR), fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and X-ray diffraction (XRD) methods were used for characterization of the CRG-g-PDMA structure. The effect of reaction variables including the concentrations of the initiator and dimethylaminoethyl methacrylate (DMA) as well as the microwave irradiation time and power on graft ratio and conversion was investigated, and their highest values were obtained to be 179 and 76%, respectively. The lower critical solution temperatures (LCSTs) of the CRG-g-PDMA copolymers were determined at various pH conditions, and their value in distilled water was found as 47°C. Besides, the swelling capacity of the copolymers under different pH levels was investigated and it was seen that the swelling capacity of the copolymer increased with the decrease in the pH value of the medium. The CRG-g-PDMA copolymer exhibited excellent swelling performance in acidic pH conditions and possessed responsiveness to pH and temperature stimuli.