Mechanically tough and highly stretchable poly(acrylic acid) hydrogel cross-linked by 2D graphene oxide

The mechanical performances of hydrogels are greatly influenced by the functionality of cross-linkers and their covalent and non-covalent interactions with the polymer chains. Conventional chemical cross-linkers fail to meet the demand of large toughness and high extensibility for their immediate applications as artificial tissues like ligaments, blood vessels, and cardiac muscles in human or animal bodies. Herein, we synthesized a new graphene oxide-based two-dimensional (2D) cross-linker (GOBC) and exploited the functionality of the cross-linker for the enhancement of toughness and stretchability of a poly(acrylic acid) (PAA) hydrogel. The 2D nanosheets of GO were modified in such a way that they could provide multifunctional sites for both physical and chemical bonding with the polymer chains. Carboxylic acid groups at the surfaces of the GO sheets were coupled with the acrylate functional groups for covalent cross-linking, while the other oxygen-containing functional groups are responsible for physical cross-linking with polymers. The GOBC had been successfully incorporated into the PAA hydrogel and the mechanical properties of the GOBC cross-linked PAA hydrogel (PAA-GOBC) were investigated at various compositions of cross-linker. Seven times enhancement in both toughness and elongation at break has been achieved without compromising on the modulus for the as-synthesized PAA-GOBC compared to the conventional N,N′-methylenebis(acrylamide) (MBA) cross-linked PAA hydrogel. This facile and efficient way of GO modification is expected to lead the development of a high-performance nanocomposite for cutting-edge applications in biomedical engineering.

Incorporation of a novel GO based cross-linker into the conventional poly(acrylic acid) hydrogel remarkably enhances the toughness and stretchability.     

Highly tough and rapid self-healing dual-physical crosslinking poly(DMAA-co-AM) hydrogel

Introducing double physical crosslinking reagents (i.e., a hydrophobic monomer micelle and the LAPONITE® XLG nano-clay) into the copolymerization reaction of hydrophilic monomers of N,N-dimethylacrylamide (DMAA) and acrylamide (AM) is reported here by a thermally induced free-radical polymerization method, resulting in a highly tough and rapid self-healing dual-physical crosslinking poly(DMAA-co-AM) hydrogel. The mechanical and self-healing properties can be finely tuned by varying the weight ratio of nanoclay to DMAA. The tensile strength and elongation at break of the resulting nanocomposite hydrogel can be modulated in the range of 7.5–60 kPa and 1630–3000%, respectively. Notably, such a tough hydrogel also exhibits fast self-healing properties, e.g., its self-healing rate reaches 48% and 80% within 2 and 24 h, respectively.

Introducing a micelle and LAPONITE® XLG nano-clay into N,N-dimethylacrylamide (DMAA)/acrylamide (AM) copolymerization reactions results in a highly tough and rapid self-healing dual-physical crosslinking poly(DMAA-co-AM) hydrogel.     

Inorganic/organic nanocomposite ion gels with well dispersed secondary silica nanoparticles

We have previously reported tough inorganic/organic nanocomposite (NC) ion gels composed of silica particles and poly(N,N-dimethylacrylamide) (PDMAAm) networks and a large amount of ionic liquid. In this study, the network structure and toughening mechanism of NC ion gels were investigated. The NC ion gels showed characteristic mechanical properties; i.e. the stress was significantly increased at a highly elongated state. In addition, the NC ion gels showed an almost elastic mechanical property, which was completely different from that of our other developed inorganic/organic tough ion gels named double-network (DN) ion gels. It was found from structural observation that secondary silica nanoparticles dispersed well in the NC ion gel. It was also found that some of the secondary silica nanoparticles had a ring-like structure which would incorporate PDMAAm chains. From the silica particle content dependency on stress–strain curves of inorganic/organic NC ion gels, it was inferred that the secondary silica particles could serve as a movable cross-linker of PDMAAm chains in the NC ion gel.

Tough inorganic/organic nanocomposite (NC) ion gels with silica nanoparticle aggregates having a characteristic structure.     

Decarboxylative aldol reaction of α,α-difluoro-β-ketocarboxylate salt: a facile method for generation of difluoroenolate

We developed a decarboxylative aldol reaction using α,α-difluoro-β-ketocarboxylate salt, carbonyl compounds, and ZnCl₂/N,N,N′,N′-tetramethylethylenediamine. The generation of difluoroenolate proceeded smoothly under mild heating to provide α,α-difluoro-β-hydroxy ketones in good to excellent yield (up to 99%). The α,α-difluoro-β-ketocarboxylate salt was bench stable and easy to handle under air, which realizes a convenient and environmentally friendly methodology for synthesis of difluoromethylene compounds.

A ZnCl₂/N,N,N′,N′-tetramethylethylenediamine complex promoted decarboxylative aldol reaction of α,α-difluoro-β-ketocarboxylate salt with carbonyl compounds has been developed.     

The synthesis of N,N′-disulfanediyl-bis(N′-((E)-benzylidene)acetohydrazide) from (E)-N′-benzylideneacetohydrazide and S8

Herein we report an oxidative coupling reaction for N–S/S–S bond formation from (E)-N′-benzylideneacetohydrazide and S₈ to furnish substituted N,N′-disulfanediyl-bis(N′-((E)-benzylidene) acetohydrazide). It provides a direct approach for the synthesis of disulfides with good yields.

Herein we report an oxidative coupling reaction for N–S/S–S bond formation substituted N,N′-disulfanediyl bis(N′-((E)-benzylidene)acetohydrazide). It provides a direct approach for the synthesis of disulfides with good yields.     

Facile construction of a hyperbranched poly(acrylamide) bearing tetraphenylethene units: a novel fluorescence probe with a highly selective and sensitive response to Zn2+

Thermo-responsive hyperbranched copoly(bis(N,N-ethyl acrylamide)/(N,N-methylene bisacrylamide)) (HPEAM-MBA) was synthesized by using reversible addition–fragmentation chain-transfer polymerization (RAFT). Interestingly, the zinc ion (Zn²⁺) was found to have a crucial influence on the lowest critical solution temperature (LCST) of the thermo-responsive polymer. The tetraphenylethylene (TPE) unit was then introduced onto the backbone of the as-prepared thermo-responsive polymer, which endows a Zn²⁺-responsive “turn-off” effect on the fluorescence properties. The TPE-bearing polymer shows a highly specific response over other metal ions and the “turn-off” response can even be tracked as the concentration of Zn²⁺ reduces to 2 × 10⁻⁵ M. The decrement of fluorescence intensity was linearly dependent on the concentration of Zn²⁺ in the range of 4–18 μmol L⁻¹. The flexible, versatile and feasible approach, as well as the excellent detection performance, may generate a new type of Zn²⁺ probe without the tedious synthesis of the moiety bearing Zn²⁺ recognition units.

A novel fluorescent HPEAM-TPEAH, possessing a highly selective and sensitive response to Zn²⁺, was synthesized using RAFT.     

Synthesis and evaluation of (S)-5′-C-aminopropyl and (S)-5′-C-aminopropyl-2′-arabinofluoro modified DNA oligomers for novel RNase H-dependent antisense oligonucleotides

We designed and synthesized two novel thymidine analogs: (S)-5′-C-aminopropyl-thymidine and (S)-5′-C-aminopropyl-2′-β-fluoro-thymidine. Then, DNA oligomers containing these analogs were synthesized, and their functional properties were evaluated. Compared with the naturally occurring thymidine, it was revealed that (S)-5′-C-aminopropyl-2′-arabinofluoro-thymidine was sufficiently thermally stable, while (S)-5′-C-aminopropyl-thymidine featured thermal destabilization. The difference in thermal stability resulted from a moderate change in the secondary structure of the DNA/RNA duplexes and a molecular fluctuation in monomers derived from the (S)-5′-C-aminopropyl side chain, as well as from a variation in sugar puckering derived from the 2′-arabinofluoro modification. Meanwhile, the incorporation of these analogs significantly enhanced the nuclease resistance of the DNA oligomers. Moreover, the (S)-5′-C-aminopropyl-2′-arabinofluoro-modified DNA/RNA duplexes showed a superior ability to activate RNase H-mediated cleavage of the RNA strand compared to the (S)-5′-C-aminopropyl-modified DNA/RNA duplexes.

We designed and synthesized two novel thymidine analogs: (S)-5′-C-aminopropyl-thymidine and (S)-5′-C-aminopropyl-2′-β-fluoro-thymidine.     

P-stereocontrolled synthesis of oligo(nucleoside N3′→O5′ phosphoramidothioate)s – opportunities and limitations

3′-N-(2-Thio-1,3,2-oxathiaphospholane) derivatives of 5′-O-DMT-3′-amino-2′,3′-dideoxy-ribonucleosides (_NOTP-N), that bear a 4,4-unsubstituted, 4,4-dimethyl, or 4,4-pentamethylene substituted oxathiaphospholane ring, were synthesized. Within these three series, _NOTP-N differed by canonical nucleobases (i.e., Ade^Bz, Cyt^Bz, Gua^iBu, or Thy). The monomers were chromatographically separated into P-diastereomers, which were further used to prepare N_NPSN′ dinucleotides (3), as well as short P-stereodefined oligo(deoxyribonucleoside N3′→O5′ phosphoramidothioate)s (NPS-) and chimeric NPS/PO- and NPS/PS-oligomers. The condensation reaction for _NOTP-N monomers was found to be 5–6 times slower than the analogous OTP derivatives. When the 5′-end nucleoside of a growing oligomer adopts a C3′-endo conformation, a conformational ‘clash’ with the incoming _NOTP-N monomer takes place, which is a main factor decreasing the repetitive yield of chain elongation. Although both isomers of N_NPSN′ were digested by the HINT1 phosphoramidase enzyme, the isomers hydrolyzed at a faster rate were tentatively assigned the R_P absolute configuration. This assignment is supported by X-ray analysis of the protected dinucleotide ^DMTdG^iBu_NPSMeT_OAc, which is P-stereoequivalent to the hydrolyzed faster P-diastereomer of dG_NPST.

Separated P-diastereomers of 3′-N-(2-thio-1,3,2-oxathiaphospholane) derivatives of 5′-O-DMT-3′-amino-2′,3′-dideoxy-ribonucleosides were used to prepare P-stereodefined N_NPSN′ dinucleotides and short NPS-, NPS/PO- and NPS/PS-oligomers.     

Relationship between dynamic fatigue crack propagation properties and viscoelasticity of natural rubber/silicone rubber composites

In this paper, dynamic fatigue crack propagation properties of natural rubber/silicone rubber (NR/VMQ) composites are studied under constant tearing energy (G) input. Through dynamic fatigue crack growth testing, it is found that with the increase of VMQ fraction, NR/VMQ exhibits a lower crack growth rate (dc/dN). The viscoelastic parameters have been recorded in real-time during crack propagation, including the storage modulus E′, loss factor tan δ, and loss compliance modulus J′′, and their relationships with crack propagation behaviour have been established. The improved crack propagation resistance is attributed to the reduced J′′, resulting from the synergistic effect of increased E′ and decreased tan δ, and thus more energy dissipation occurred in the linear viscoelastic region in front of the crack tip, which consumed part of the energy for crack growth. Finally, good correlation between dc/dN and J′′ could be successfully established.

The successfully established relationship between dynamic fatigue crack propagation behaviour and viscoelasticity of NR/VMQ composites.     

Sustainable xanthophylls-containing poly(ε-caprolactone)s: synthesis,characterization, and use in green lubricants

Three xanthophylls [(3R,3′R,6′R)-lutein (1), (3R,3′S)-zeaxanthin (2), and (3R,3′S)-astaxanthin (3)] were used for the first time as initiators in the ring-opening polymerization (ROP) of ε-caprolactone (CL) catalyzed by tin(ii) 2-ethylhexanoate [Sn(Oct)₂] for the synthesis of novel sustainable xanthophyll-containing poly(ε-caprolactone)s (xanthophylls-PCL). The obtained polyesters were characterized by ¹H and ¹³C NMR, FT-IR, DSC, SEC, and MALDI-TOF MS, and their use as additives in green lubricants was evaluated using a sliding friction test under boundary conditions. Xanthophylls-PCL were obtained with good conversions and with molecular weights determined by SEC to be between 2500 and 10 500 Da. The thermal properties of xanthophyll-polyesters showed a crystalline domain, detected by DSC. Lastly, the green lubricant activity of these polymers was evaluated and the results showed that xanthophylls-PCL could be employed as additives for biodegradable lubricant applications since they have better tribological behavior than current additives, which demonstrates their potential as future commercial materials with interesting eco-friendly properties for diverse applications.

Sustainable polyesters initiators from renewable resources and additives in green lubricants.     

P-Stereodefined phosphorothioate analogs of glycol nucleic acids—synthesis and structural properties

Enantiomerically pure, protected acyclic nucleosides of the GNA type (glycol nucleic acids) (^GN′), obtained from (R)-(+)- and (S)-(−)-glycidols and the four canonical DNA nucleobases (Ade, Cyt, Gua and Thy), were transformed into 3′-O-DMT-protected 2-thio-4,4-pentamethylene-1,3,2-oxathiaphospholane derivatives (OTP-^GN′) containing a second stereogenic center at the phosphorus atom. These monomers were chromatographically separated into P-diastereoisomers, which were further used for the synthesis of P-stereodefined “dinucleoside” phosphorothioates ^GN_PST (^GN = ^GA, ^GC, ^GG, ^GT). The absolute configuration at the phosphorus atom for all eight ^GN_PST was established enzymatically and verified chemically, and correlated with chromatographic mobility of the OTP-^GN′ monomers on silica gel. The ^GN_PS units (derived from (R)-(+)-glycidol) were introduced into self-complementary PS-(DNA/GNA) octamers of preselected, uniform absolute configuration at P-atoms. Thermal dissociation experiments showed that the thermodynamic stability of the duplexes depends on the stereochemistry of the phosphorus centers and relative arrangement of the ^GN units in the oligonucleotide strands. These results correlate with the changes of conformation assessed from circular dichroism spectra.

The stability of P-stereodefined PS-(DNA/GNA) duplexes depends on the stereochemistry of the phosphorus centers and arrangement of –^GN_PS– units in the strands.     

Incorporation of N-phenyl in poly(benzimidazole imide)s and improvement in H2O-absorbtion and transparency

5-Amine-2-(4-amino-benzene)-1-phenyl-benzimidazole (N-PhPABZ) was successfully synthesized and polymerized with 3,3′,4,4′-biphenyl tetracarboxylic dianhydride (BPDA) to obtain a novel N-phenyl-poly(benzimidazole imide) (N-Ph-PBII). The successful incorporation of N-phenyl addressed the issue of high H₂O-absorption of traditional PBIIs while retained the superheat resistance property. The resulting N-Ph-PBII possessed a high glass-transition temperature (T_g) up to 425 °C and a low affinity for water of 1.4%. Furthermore, the loose molecular packing and noncoplanar structures led to an increase in optical transparency for the modified PBII.

A novel modified PBII was achieved. The incorporation of N-phenyl group not only improved the properties but also healed the problem of high H₂O-absorption for traditional PBIIs.     

Synthesis of a biodegradable interpenetrating polymer network of Av-cl-poly(AA-ipn-AAm) for malachite green dye removal: kinetics and thermodynamic studies

This paper deals with the synthesis of a biodegradable interpenetrating polymer network (IPN) from the natural polysaccharide aloe vera (Av), acrylamide (AAm) and acrylic acid (AA), and its evaluation as a dye removal device. In the synthesis of Av-cl-poly(AA-ipn-AAm), ammonium persulfate (APS) was used as an initiator, N,N′-methylene bisacrylamide (MBA) as a cross-linker, AA and AAm as primary and secondary monomers, respectively. Soil burial and composting methods were used to study the biodegradability of the synthesized IPN and the results showed 94% degradation within 70 days using the composting method and 86% degradation within 77 days using the soil burial method. Biodegradation was confirmed by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) techniques. The synthesized IPN was used as a device for the removal of malachite green (MG) dye from aqueous solution. The maximum MG removal capacity of the synthesized IPN was found to be 97.3% under the optimal conditions (i.e. time = 180 min., pH = 4.5, adsorbent dose = 5 g L⁻¹). The adsorption kinetics of malachite green molecules onto synthesized IPN was studied and compared using pseudo-first-order and pseudo-second-order models and we found that the adsorption process is better represented by the pseudo-second-order model. The different adsorption isotherm models like Langmuir, Freundlich, Dubinin–Radushkevich, Temkin, Redlich–Peterson and Sips isotherms were studied. The best-fitting isotherm model for the present experiment is the Langmuir model.

This paper deals with the synthesis of a biodegradable interpenetrating polymer network (IPN) from the natural polysaccharide aloe vera (Av), acrylamide (AAm) and acrylic acid (AA), and its evaluation as a dye removal device.     

Influence of reduced graphene oxide on flow behaviour,glass transition temperature and secondary crystallinity of plasticized poly(vinyl chloride)

Understanding the rheological behaviour of thermoplastic nanocomposites is important to obtain a concrete knowledge of their processability. The viscoelastic properties of nanocomposites are a reflection of their morphology. The study of flow and deformation of nanocomposites provides essential information related to prevalent interactions in the system as well as contribution from the dispersion of incorporated nanofillers. In the present study, plasticized polyvinyl chloride/reduced graphene oxide nanocomposites (PPVC/RGO) were fabricated using melt mixing technique with different filler concentration. Flow behaviour of the nanocomposites was analyzed using small amplitude oscillatory shear (SAOS) measurements and it indicated an enhancement in the storage modulus (G′), loss modulus (G′′) and complex viscosity (η*) with RGO content. This can be attributed to very good dispersion and reinforcing effect of RGO in PPVC matrix as supported by TEM and FTIR results. Weak gel model is used to fit the rheological parameters and is found to be in excellent agreement with the SAOS experiments. Thermal history of the prepared nanocomposites was learned using differential scanning calorimetry. A shift in glass transition temperature (T_g) to higher temperature region could be seen, that manifest the effect of RGO in the amorphous portion of PPVC. An interesting property called secondary crystallinity was also found in these materials.

Understanding the rheological behaviour of thermoplastic nanocomposites is important to obtain a concrete knowledge of their processability.     

Controlled degradation of low-fouling poly(oligo(ethylene glycol)methyl ether methacrylate) hydrogels

Degradable low-fouling hydrogels are ideal vehicles for drug and cell delivery. For each application, hydrogel degradation rate must be re-optimized for maximum therapeutic benefit. We developed a method to rapidly and predictably tune degradation rates of low-fouling poly(oligo(ethylene glycol)methyl ether methacrylate) (P(EG)_xMA) hydrogels by modifying two interdependent variables: (1) base-catalysed crosslink degradation kinetics, dependent on crosslinker electronics (electron withdrawing groups (EWGs)); and, (2) polymer hydration, dependent on the molecular weight (M_W) of poly(ethylene glycol) (PEG) pendant groups. By controlling PEG M_W and EWG strength, P(EG)_xMA hydrogels were tuned to degrade over 6 to 52 d. A 6-member P(EG)_xMA copolymer library yielded slow and fast degrading low-fouling hydrogels suitable for short- and long-term delivery applications. The degradation mechanism was also applied to RGD-functionalized poly(carboxybetaine methacrylamide) (PCBMAA) hydrogels to achieve slow (∼50 d) and fast (∼13 d) degrading low-fouling, bioactive hydrogels.

To tune degradation rates of low-fouling hydrogels, a 6-member P(EG)_xMA copolymer library with different electronics and hydration levels was developed.     

The preparation,characterization and catalytic activity of Ni NPs supported on porous alginate-g-poly(p-styrene sulfonamide-co-acrylamide)

Herein, we report the synthesis of nickel nanoparticles under mild conditions using porous alginate-g-poly(p-styrene sulfonamide-co-acrylamide) as a protecting/stabilizing agent and sodium borohydride as a reducing agent. The porous cross-linked polymeric support was prepared via combining the use of sol–gel, nanocasting, and crosslinking techniques, in which the p-styrene sulfonamide monomer (PSSA) and N,N′-methylene-bis (acrylamide) (MBA) cross-linker underwent copolymerization on the surface of sodium alginate in the presence of a SiO₂ nanoparticle (NP) template (Alg–PSSA-co-ACA). The prepared catalyst (Alg–PSSA-co-ACA@Ni) showed high catalytic activity for the one-step synthesis of 1,3,4-oxadiazoles from the reaction of hydrazides and aryl iodides through isocyanide insertion/cyclization.

Ni NPs supported on novel porous alginate-g-poly(p-styrene sulfonamide-co-acrylamide) was investigated for the synthesis of 1,3,4-oxadiazoles.     

Efficient access to 3′-O-phosphoramidite derivatives of tRNA related N6-threonylcarbamoyladenosine (t6A) and 2-methylthio-N6-threonylcarbamoyladenosine (ms2t6A)

An efficient method of ureido linkage formation during epimerization-free one-pot synthesis of protected hypermodified N⁶-threonylcarbamoyladenosine (t⁶A) and its 2-SMe analog (ms²t⁶A) was developed. The method is based on a Tf₂O-mediated direct conversion of the N-Boc-protecting group of N-Boc-threonine into the isocyanate derivative, followed by reaction with the N⁶exo-amine function of the sugar protected nucleoside (yield 86–94%). Starting from 2′,3′,5′-tri-O-acetyl protected adenosine or 2-methylthioadenosine, the corresponding 3′-O-phosphoramidite monomers were obtained in 48% and 42% overall yield (5 step synthesis). In an analogous synthesis, using the 2′-O-(tert-butyldimethylsilyl)-3′,5′-O-(di-tert-butylsilylene) protection system at the adenosine ribose moiety, the t⁶A-phosphoramidite monomer was obtained in a less laborious manner and in a remarkably better yield of 74%.

A new convenient method of ureido linkage formation in t⁶A/ms²t⁶A nucleosides greatly enhances the availability of phosphoramidite monomers for the chemical synthesis of modified tRNA fragments.     

Novel 1′-homo-N-2′-deoxy-α-nucleosides: synthesis,characterization and biological activity

For the first time, a series of novel 1′-homo-N-2′-deoxy-α-nucleosides containing natural nucleobases as well as 5-fluoro and 5-iodopyrimidine analogs have been synthesized in an efficient manner. Additionally, a high yield protocol for the assembly of a dimeric scaffold containing two sugar moieties linked to the N-1 and N-3 positions of a single pyrimidine base has been accomplished. The structures of the novel homonucleosides were established by a single crystal X-ray structure of 1′-homo-N-2′-deoxy-α-adenosine and NMR studies. The biological activity of these 1′-homo-N-2′-deoxy-α-nucleosides as antiviral (HIV-1 and HBV) and cytotoxic studies was measured in multiple cell systems. The unique structure and easy accessibility of these compounds may allow their use in the design of new nucleoside analogs with potential biological activity and as a scaffold for combinatorial chemistry.

Novel 1′-homo-N-2′-deoxy-α-nucleosides and dimers.     

Three-dimensional graphene oxide cross-linked by benzidine as an efficient metal-free photocatalyst for hydrogen evolution

The use of low-cost photocatalysts to split water into H₂ fuel via solar energy is highly desirable for the production of clean energy and a sustainable society. Here three-dimensional graphene oxide (3DG) porous materials were prepared by cross-linking graphene oxide (GO) sheets using aromatic diamines (benzidine, 2,2′-dimethyl-4,4′-biphenyldiamine, 4,4′-diaminodiphenylmethane) that reacted with the carboxyl groups of the GO sheets at room temperature. The prepared 3DG porous materials were used as efficient metal-free photocatalysts for the production of H₂via water splitting under full-spectrum light, where the photocatalytic activity was highly dependent on the cross-linker and the 3DG reduction level. It was also found that the 3DG prepared with benzidine as the linker demonstrated a significantly higher H₂ evolution rate than the 3DGs prepared using 2,2′-dimethyl-4,4′-biphenyldiamine and 4,4′-diaminodiphenylmethane as the cross-linkers. The photoactivity was further tuned by varying the mass ratio of GO to benzidine. Among the prepared 3DG materials, 3DG-3, with an intermediate C/O ratio of 1.84, exhibited the highest H₂ production rate (690 μmol g⁻¹ h⁻¹), which was significantly higher than the two-dimensional GO (45 μmol g⁻¹ h⁻¹) and the noncovalent 3DG synthesized by a hydrothermal method (128 μmol g⁻¹ h⁻¹). Moreover, this study revealed that the 3DG photocatalytic performance was favored by effective charge separation, while it could be further tuned by changing the reduction level. In addition, these results could prompt the preparation of other 3D materials and the application of new types of photocatalysts for H₂ evolution.

Three-dimensional graphene oxide covalently linked by benzidine works as an efficient metal-free photocatalyst for H₂ evolution.     

Fluorinated β-diketonate complexes M(tfac)2(TMEDA) (M = Fe,Ni, Cu,Zn) as precursors for the MOCVD growth of metal and metal oxide thin films

Partially fluorinated β-diketonate complexes M(tfac)₂(TMEDA) (M = Fe 1, Ni 2, Cu 3, Zn 4; tfac = 1,1,1-trifluoro-2,4-pentanedionate; TMEDA = N,N,N′,N′-tetramethylethylenediamine) were synthesized and structurally (sc-XRD) and thermochemically (TGA) characterised. A new polymorph of Fe(tfac)₂(TMEDA) was found. The structural and physicochemical properties of 1–4 were compared with related M(acac)₂(TMEDA) and M(hfac)₂(TMEDA) (acac = 2,4-pentanedionate, hfac = 1,1,1,5,5,5-hexafluoro-2,4-pentanedionate) β-diketonate complexes to evaluate the effect of the degree of fluorination. A positive effect on the thermal behaviour of the metal acetylacetonates was observed, but no discernible trends. Application of complexes 1–4 as precursors in a MOCVD process yielded either metal (Ni, Cu) or metal oxide thin films (Fe₃O₄, ZnO), which were further oxidized to NiO, CuO and α-Fe₂O₃ films by calcination in air at 500 °C.

Novel trifluoroacetylacetonate complexes M(tfac)₂·TMEDA (M = Fe, Ni, Cu, Zn) were used as precursors for the MOCVD growth of metal and metal oxide thin films.