Zirconium tetra-n-butylate modified with different organic acids: Hydrolysis and polymerization of the products

In this work, (a) complexation reaction of zirconium tetra-n-butylate, Zr(OBu ⁿ )₄, with MAc and different organic acids, (b) the hydrolysis reaction of modified Zr species, and (c) the polymerization reaction of complex products are studied. Zr(OBu ⁿ )₄ was reacted with different mole ratios of methacrylic acid (MAc) at room temperature and the maximum combination ratio was found to be 1:2 [Zr(OBu ⁿ )₄:MAc] by FT-IR. The modification of zirconium tetra-n-butylate with the acid mixtures [methacrylic acid-acetic acid (MeCOOH), methacrylic acid-propionic acid (EtCOOH), methacrylic acid-butyric acid (PrCOOH)] was made for a combination ratio of 1:1:1 [MAc:RCOOH:Zr(OBu ⁿ )₄; R: Me, Et, Pr] and the products were characterized by¹H-NMR, FT-IR, and UV spectroscopies. Following their synthesis, hydrolysis of the complexes with various amounts of water and polymerization with benzoyl peroxide were realized. The hydrolysis and polymerization products of the complexes were studied by Karl-Fischer coulometric titration and thermal analysis, respectively. Methyl ethyl ketone(MEK) and chloroform were chosen as solvents.     

Zirconium tetra-n-butylate modified with different organic acids: Hydrolysis and polymerization of the products

In this work, (a) complexation reaction of zirconium tetra-n-butylate, Zr(OBu ⁿ )₄, with MAc and different organic acids, (b) the hydrolysis reaction of modified Zr species, and (c) the polymerization reaction of complex products are studied. Zr(OBu ⁿ )₄ was reacted with different mole ratios of methacrylic acid (MAc) at room temperature and the maximum combination ratio was found to be 1:2 [Zr(OBu ⁿ )₄:MAc] by FT-IR. The modification of zirconium tetra-n-butylate with the acid mixtures [methacrylic acid-acetic acid (MeCOOH), methacrylic acid-propionic acid (EtCOOH), methacrylic acid-butyric acid (PrCOOH)] was made for a combination ratio of 1:1:1 [MAc:RCOOH:Zr(OBu ⁿ )₄; R: Me, Et, Pr] and the products were characterized by¹H-NMR, FT-IR, and UV spectroscopies. Following their synthesis, hydrolysis of the complexes with various amounts of water and polymerization with benzoyl peroxide were realized. The hydrolysis and polymerization products of the complexes were studied by Karl-Fischer coulometric titration and thermal analysis, respectively. Methyl ethyl ketone(MEK) and chloroform were chosen as solvents.     

Zirconium tetra-n-butylate modified with different organic acids: Hydrolysis and polymerization of the products

In this work; (a) complexation reaction of zirconium tetra-n-butylate, Zr(OBu ⁿ )₄, with MAc and different organic acids. (b) the hydrolysis reaction of modified Zr species, and (c) the polymerization reaction of complex products are studied. Zr(OBu ⁿ )₄ was reacted with different mole ratios of methacrylic acid (MAc) at room temperature and the maximum combination ratio was found to be 12 [Zr(OBu ⁿ )₄MAc] by FT IR. The modification of zirconium tetra-n-butylate with the acid mixtures [methacrylic acid-acetic acid (MeCOOH), methacrylic acid-propionic acid (EtCOOH), methacrylic acidbutyric acid (PrCOOH)] was made for a combination ratio of 111 [MAcRCOOHZr(OBu ⁿ )₄RMe. Et, Pr] and the products were characterized by¹H-NMR, FT-IR, and UV-spectroscopies. Following their synthesis, hydrolysis of the complexes with various amounts of water and polymerization with benzoyl peroxide were realized. The hydrolysis and polymerization products of the complexes were studied by Karl-Fischer Coulometric titration and thermal analysis respectively. Methyl-ethyl-ketone (MEK) and chloroform were chosen as solvents.     

Complexation of Zirconium Alkoxides with 3-Pentenoic Acid and Hydrolytic Stability of Their Products

Reactions of Zr(OPr ⁿ )₄ and Zr(OBu ⁿ )₄ with 3-pentenoic acid (PA) in 1:1 molar ratio were studied in propanol and butanol solution at room temperature by the sol–gel process. The complexations were investigated by ¹³C{¹H}, ¹H-NMR and FTIR spectroscopy. The ¹³C{¹H}, ¹H-NMR and FTIR spectra showed that PA completely reacted with Zr(OPr ⁿ )₄ and Zr(OBu ⁿ )₄. The new products were hydrolyzed by water in a ratio of 1:4 (Zr(OR ⁿ )₄/ H₂O, R = propyl, butyl). The stability of hydrolyzed products was investigated spectroscopically. After hydrolysis, it was observed that no PA was released from the complexes, [Zr(OPr ⁿ )₃(PA)] and [Zr(OBu ⁿ )₃(PA)], under the reaction conditions.     

Physico-chemical characterization of hybrid polymers obtained by 2-hydroxyethyl(methacrylate) and alkoxides of zirconium

Hybrid monolithic materials were prepared through polymerisation of 2-hydroxyethyl methacrylate (HEMA) mixed with zirconium alkoxides (Zr(OBuⁿ)₄, Zr(OPrⁿ)₄ and Zr(OEt)₄), modified by acetylacetonate groups. The molar ratio HEMA/Zr varied between 1 and 4. Thermo-Gravimetry coupled with Mass Spectroscopy (TG-MS) analyses, ¹³C MAS NMR and Dynamical Mechanical Thermal Analysys (DMTA) indicated the polymeric chains were interconnected by the inorganic component.The presence of zirconium alkoxides modified substantially the poly-HEMA properties. Glass transition temperature of hybrid materials derived from butoxy and propoxy was found in the range 50-80 °C, depending on the composition. The typical swelling of p-HEMA in the water, was suppressed by the presence of zirconium compounds. After immersion in distilled water, hybrid polymers showed an initial slight weight increase, followed by a small mass loss, which increases proportionally to the length of alkoxyl group (ethoxide(propoxide(butoxide) and reaches a constant value after about 40 days. The hybrids remained always rigid and transparent. Flexural modulus and strength of about 400-900 and 4-8 MPa were measured.     

Synthesis,Characterization, and Application of Hybrid Inorganic–Organic Composites (K/Na)ZrSi(R)O<Subscript>x</Subscript>

Hybrid inorganic–organic composites, (K/Na)ZrSi(R)O_x, were synthesized from the hydrolysis of the mixture of zirconium n-propoxide (Zr(OPrⁿ)₄) and 3-glycidyloxypropyltrimethoxy silane (GPTS) in 1:1 mol ratio. The hydrolysis reaction was carried out with 0.1 molar HCl in 150 ml of butanol. Then, the synthesized Zr(OPrⁿ)₄-GPTS-hydrolyzate reacted with KOBu^t and NaOSiMe₃ in 1:1 mol ratio at 40 and 50 °C for 24 h, respectively. After these stages, composites were washed and dried under vacuum. Composites and their oxide prepared at 1250 °C by calcinations were characterized by a combination of powder X-ray diffraction, scanning electron microscope, energy dispersive X-ray, Brunauer–Emmett–Teller analysis, Barrett–Joyner–Halenda analysis, and Fourier transform infrared spectroscopies. These hybrid inorganic–organic composites except oxides were used as catalysts in order to see their activities in the polymerization of ε-caprolactone (ε-CL). This study showed that new composite materials except their oxides were effective catalyst in ε-CL polymerization.     

Effect of the chemical modification of the precursor of ZrO2 films on the adhesion of organic coatings

ZrO₂ films were deposited on low carbon steel by a sol-gel process as a chemical pretreatment before the application of a polyester paint. The films were obtained by a dip-coating technique using solutions of Zr(OBuⁿ)4 containing complexing agents (acetylacetone or acetic acid). These additives modified the alkoxide at the molecular level, so a new precursor was formed in solution. This new compound shows slower rates of hydrolysis and condensation than Zr(OBuⁿ)4, which allows the stability of solutions and the morphology of the gel to be controlled. Moreover, the length and the temperature of the thermal treatment influence the structure of the gel by reducing the amount of organic residues. The behavior of the films in promoting the adhesion of organic coatings was evaluated by measuring the detachment of the paint from a cross-scratch of samples which had been exposed for different times in a salt fog chamber. Tests using electrochemical impedance spectroscopy were also carried out. According to the results, most of the samples pretreated with zirconia layers showed a good performance, even better than commercial chemical treatments, when acetic acid was used as a modifier of the alkoxide precursors.     

Inorganic–Organic Hybrid Materials of Zirconium and Aluminum and Their Usage in the Removal of Methylene Blue

Two novel inorganic–organic hybrid materials, Al-Pydca-3-APDEMS-H and Zr-Pydca-3-APDEMS-H, were prepared by the sol gel method in two steps. In the first step, Al(O^sBu)₂-Pydca and Zr(OPrⁿ)₃-Pydca complexes were prepared from the reactions of aluminum sec-butoxide Al(O^sBu)₃ and zirconium n-propoxide Zr(OPrⁿ)₄ with 2,6-pyridinedicarboxylic acid, respectively. After 3 h of stirring, 3-aminopropyldiethoxymethyl silane (3-APDEMS) and dilute hydrochloric acid were added to the Al(O^sBu)₂-Pydca and Zr(OPrⁿ)₃-Pydca mixtures to hydrolyze the reactions and to form condensation products. These hybrid products were characterized by a combination of Fourier-transform infrared (FT-IR) spectroscopy, powder X-ray diffraction (XRD), scanning electron microscope (SEM), energy-dispersive X-ray (EDX) spectroscopy, Brunauer–Emmett–Teller (BET) analysis, Barrett-Joyner-Halenda (BJH) and other analysis methods. These hybrid materials were used for the removal of methylene blue (MB), a cationic organic dye. The removal efficiency of hybrid materials was measured by UV–Vis spectroscopy.

     

Complexation of Titanium Alkoxides with Cis-2-butene-1,4-diol and Hydrolysis of Their Products

Reaction of Ti(OEt)₄ and Ti(OBu ⁿ )₄ with cis-2-butene-1,4-diol (B.diol-2H) in 1:1 molar ratio was studied at room temperature using the sol-gel process. ¹³C{¹H}- and ¹H-NMR data showed that all the B.diol-2H completely reacted with both titanium alkoxides. Each of the products was hydrolyzed by water. The new hydrolyzed products were characterized by ¹³C- and ¹H-NMR spectroscopy and Karl–Fischer Titration. Thermogravimetric and differential thermal analyses (TGA-DTA) of the hydrolyzed-products were also studied.     

Modification of Different Zirconium Propoxide Precursors by Diethanolamine. Is There a Shelf Stability Issue for Sol-Gel Applications?

Modification of different zirconium propoxide precursors with H₂dea was investigated by characterization of the isolated modified species. Upon modification of zirconium n-propoxide and [Zr(OⁿPr)(OⁱPr)₃(ⁱPrOH)]₂ with ½ a mol equivalent of H₂dea the complexes [Zr₂(OⁿPr)₆(OCH₂CH₂)₂NH]₂ (1) and [Zr₂(OⁿPr)₂(OⁱPr)₄(OCH₂CH₂)₂NH]₂ (2) were obtained. However, ¹H-NMR studies of these tetranuclear compounds showed that these are not time-stable either in solution or solid form. The effect of this time instability on material properties is demonstrated by light scattering and TEM experiments. Modification of zirconium isopropoxide with either ½ or 1 equivalent mol of H₂dea results in formation of the trinuclear complex, Zr{η³μ₂-NH(C₂H₄O)₂}₃[Zr(OⁱPr)₃]₂(iPrOH)₂ (3) countering a unique nona-coordinated central zirconium atom. This complex 3 is one of the first modified zirconium propoxide precursors shown to be stable in solution for long periods of time. The particle size and morphology of the products of sol-gel synthesis are strongly dependent on the time factor and eventual heat treatment of the precursor solution. Reproducible sol-gel synthesis requires the use of solution stable precursors.     

Zirconia aerogels: Effect of acid used in the sol-gel process on morphological properties

Zirconia aerogels have been prepared from butanolic zirconium(IV) tetra-n-butoxide diluted in ethanol via stoichiometric hydrolysis with water in ethanol. Nitric acid or acetic acid were used to modify the sol-gel process. After calcination in air at 573 K, the aerogel prepared with nitric acid possesses a specific surface area of 240 m² · g^–1 and a unimodal pore size distribution with a maximum at ca. 24 nm, whereas the use of acetic acid results in an aerogel with specific surface area of 228 m² · g^–1 and bimodal pore size distribution with maxima at 3 and 65 nm. The crystalline fractions of both aerogels are predominantly tetragonal with a small contribution of monoclinic ZrO₂.     

Preparation and Characterization of Porous SiO2-Al2O3-ZrO2 Prepared by the Sol-Gel Process

An experimental strategy was developed to obtain Si—Al—Zr transparent sols via the sol-gel process. The sol was prepared from Al(OBu^s)₃ (OBu^s: C₂H₅CH(CH₃)O), Zr(OPrⁿ)₄ (OPrⁿ: OCH₂CH₂CH₃) and Si(OEt)₄. The chelating agents acetylacetone (2, 4 pentanedione, acacH), and itaconic anhydride (2-methylenesuccinic anhydride, anhH) were employed separately to stabilize Al and Zr precursors in order to control their chemical reactivity, avoiding precipitation. In all cases a prehydrolyzed tetraethyl orthosilicate (TEOS) sol was the Si source. We use the Partial Charge Model as a theoretical indication of the stabilization of the Al and Zr species derived from the reaction with anhH and acacH. The sols were polymerized at room temperature (293 K) to obtain gels and these were dried and calcined at 673, 773 and 873 K in air. The characterization techniques were Small Angle X-ray Scattering (SAXS), Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), Thermal Gravimetric (TGA) and Differential Thermal Analyses (DTA). The porosity and surface area of solids calcined at 673, 773 and 873 K were determined by N₂ adsorption/desorption isotherms. The corresponding average pore diameter was evaluated using the methods BJH, HK and DA. These models were used because all together cover the full range of the pore size.     

Complexation of titanium alkoxides with pentenoic acid and allylacetoacetate and their hydrolysis and addition reactions with H‐silanes

Complexation reactions of titanium tetraethoxide [Ti(OEt)₄] and titanium tetra‐n‐butoxide [Ti(OBuⁿ)₄] with 3‐pentenoic acid (PA) and allylacetoacetate (AAA), in a 1 : 1M ratio, were studied in ethanol solution at room temperature. ¹³C‐NMR and FTIR spectra showed that all PA and AAA completely reacted with both titanium alkoxides. Hydridosilane compounds such as triethoxysilane and triethylsilane were added to titanium chelate complexes in a 1 : 1M ratio. The investigation of products by ¹³C‐ and ²⁹Si‐NMR and FTIR showed additions of ? SiH to the C?C double bond. The hydrolysis of titanium–PA and AAA complexes, by water in 1 : 4 ratios, resulted in released PA in an amount of 10% and AAA of 20%. The stability of hydrolyzed products was investigated by ¹³C‐NMR, ²⁹Si‐NMR, and FTIR. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 790–796, 2005     

Manipulation of Lewis acid–base complexation in the Zr-centered quaternary system for monodisperse spherical zircons

Zircon (ZrSiO₄) is a distinctive material widely investigated and applied for its superb physicochemical advantages. To date, great challenges remain in the synthesis of high-quality zircon powders for their stringent crystallization requirements at elevated temperature and inherent preferential growth along the [200] direction. Herein we, for the first time, present monodisperse spherical zircon (MSZ) powders synthesized via a facile one-step hydrothermolysis at 200 °C by rationally manipulating the Lewis acid–base complexation of zirconium with competitive ions (Lewis basic R ligands) in a Zr–OH–R–F quaternary system. Systematical investigations were revealed encircling the complexation of Zr⁴⁺ with the R ligands from various sources, which involve the adjusting acids (HR), Zr/Si reactants and halogen-containing mineralizers. Sufficient acidity from the adjusting acid and weak enough Zr–R affinity are confirmed as two paramount factors modulating the crystallization and growth of high-quality MSZ crystals, which undergo a unique metamorphic morphological transition from monolayered, to multilayered, to donut-shaped and ultimately to micrometer-sized spherical particles. The hydrothermal zircons are first confirmed as Zr-deficient (Zr/Si ratios <1.0) zirconium silicates as (ZrO₄)_1–xSi[(OH)_1–y·R_y]_4x, rather than the Si-deficient Zr(SiO₄)_1–x[(OH)·R]_4x as initially proposed and hitherto generally accepted. The MSZ powders exhibit fair thermal stability and terrific monodispersity even after calcination at 1100 °C, superior photoreflectance and much lower thermal conductivity (0.18–0.48 W m^?1 K^?1) over non-spherical zircons. The novel MSZ powders provide arresting prospects to extend the applications of zircon in many traditional and emerging fields.     

Aryloxy and benzyloxy compounds of hafnium: Synthesis, structural characterization and studies on solvent-free ring-opening polymerization of ε-caprolactone and δ-valerolactone

A large variety of aryloxy compounds and benzyloxy derivatives of Hf(IV) were synthesized from Hf(O-tBu)₄ using the alcoholysis route. These compounds were completely characterized using various spectroscopic and analytical methods along with single crystal X-ray diffraction studies. Multinuclear NMR studies prove high degree of fluxional behavior of these compounds in solution. They adopt a dimeric structure in the solid-state as seen from X-ray diffraction studies on a few of them. These compounds are powerful catalysts for the ring-opening polymerization of ε-caprolactone (CL) and δ-valerolactone (VL) resulting in high number average molecular weight (M_n) polymers and controlled molecular weight distributions (MWDs). Significant control in the polymerization was achieved with these compounds as initiators in comparison to their titanium and zirconium analogues. Kinetic studies reveal that the rates of such polymerizations are in general slower than the corresponding titanium and zirconium derivatives. ¹H NMR and MALDI-TOF studies of low molecular weight oligomers suggest that these polymerizations proceed by the activated monomer mechanism.     

Investigation of the tetracarbonatozirconate ion by electrospray mass spectrometry in aqueous media

Reported here is the study of zirconium (IV) aqueous solutions in carbonate media by electrospray ionisation mass spectrometry (ESI–MS). Spectra analysis lead to consider the existence in the spray of the initial pseudomolecular labile species [Zr(CO₃)₄(HCO₃)]⁵⁻, xH⁺, (6−x) K⁺ (or Na⁺). The existence of this species confirms the associative exchange mechanism of carbonate ions with [Zr(CO₃)₄]⁴⁻ ion.     

Investigation of Dynamic Intra‐ and Intermolecular Processes within a Tether‐Length Dependent Series of Group 4 Bimetallic Initiators for Stereomodulated Degenerative Transfer Living Ziegler–Natta Propene Polymerization

The series of bimetallic complexes, [(η⁵‐C₅Me₅)Zr(Me)₂]₂ [N(t‐Bu)C(Me)N (CH₂)_n NC(Me)N(t‐Bu)] 3 (n=8), 4 (n=6), and 5 (n=4) were prepared in high yield through a simple, one‐pot synthesis involving 2 equiv. of in situ generated (η⁵‐C₅Me₅)Zr(Me)₃ and the corresponding bis‐carbodiimide, (t‐Bu)NCN (CH₂)_n NCN(t‐Bu). Compounds 3 – 5 were found to be highly isoselective for the living Ziegler–Natta polymerization of propene upon 100% activation using 2 equiv. of the borate co‐initiator, [PhNHMe₂] [B(C₆F₅)₄] ( 2 ), with the degree of stereoselectivity decreasing slightly as the two metal centers are brought closer together [cf., 3 (σ=0.92)> 4 (σ=0.91)> 5 (σ=0.89)]. Under conditions of sub‐stoichiometric activation by 2 , all three bimetallic initiators, 3 – 5 , were found to engage in degenerative transfer living Ziegler–Natta polymerization involving rapid and reversible methyl group transfer between active, (cationic) and dormant, (neutral) methyl, polymeryl zirconium centers. Under these conditions, the frequency of mr triad stereoerror incorporation into the polypropene (PP) microstructure decreases as the two metal centers are brought closer together as a result of increasing barriers for metal‐centered epimerization within the neutral metal site due to correspondingly greater non‐bonded steric interactions vis‐à‐vis mononuclear 1 .     

Synthesis,structure and catalytic properties of a novel zirconium guanidinato complex [Zr{ArNC(NMe2)N(SiMe3)}(μ2-Cl)Cl2]2[Ar = 2,6-iPr2-C6H3]

A novel non-symmetric zirconium guanidinato complex, [{Zr{ArNC(NMe₂)N(SiMe₃)}(μ₂-Cl)Cl₂}₂] (Ar = 2,6-ⁱPr₂-C₆H₃), was synthesized and structurally characterized. Catalytic studies showed that the zirconium complex was active for ethylene polymerization with the activity of 4.98 × 10⁵ g PE/mol Zr h. The influences of cocatalysts, Al/Zr molar ratios and ethylene pressures on the activities were investigated.     

Spirocycles as stable alternative of networks—polycondensations of oligoether diols with metal tetraalkoxides

Germanium, tin, titanium and zirconium tetraalkoxides were polycondensed with poly(ethylene glycol)s (PEGs) and poly(tetrahydrofuran) (PTHF) diols at temperatures between 100 and 200 °C. The lengths of the diols were varied from PEG-300 over PEG-400, PEG-600 and PEG-1000 to PEG-2000. In the case of PTHF diols number average molecular weights (M_ns) of 650, 1000 and 2000 were used. When Ge(OEt)₄ was polycondensed, all reaction products were soluble. In the case of Sn(OtBu)₄, all products obtained from diols with were soluble, whereas a stiff gel was obtained from PEG-400. From Ti(OnBu)₄ and Zr(OEt)₄ soluble spirocycles were only obtained for diols with M_ns≥1000, whereas the shorter diols yielded stiff networks. In the case of Ti(OnBu)₄ and PEG-1000, it was observed that at temperatures ≤120 °C initially a stiff gel was formed obviously by a kinetically controlled polycondensation. Upon heating to 140 °C this gel underwent an irreversible transformation into syrupy, soluble spirocycles due to equilibration of Ti-O-R bonds. The thermodynamic stability of the spirocycles is explained by strain-free rings and a gain in entropy. Preliminary experiments with the spirocycles of zirconium proved their usefulness as initiators for the ring-expansion polymerization of ε-caprolactone.     

Silica‐Supported Zirconium Complexes and their Polyoligosilsesquioxane Analogues in the Transesterification of Acrylates: Part 2. Activity,Recycling and Regeneration

The catalytic activity of both supported and soluble molecular zirconium complexes was studied in the transesterification reaction of ethyl acrylate by butanol. Two series of catalysts were employed: three well defined silica‐supported acetylacetonate and n‐butoxy zirconium(IV) complexes linked to the surface by one or three siloxane bonds, (SiO)Zr(acac)₃ ( 1 ) (SiO)₃Zr(acac) ( 2 ) and (SiO)₃Zr(O‐n‐Bu) ( 3 ), and their soluble polyoligosilsesquioxy analogues (c‐C₅H₉)₇Si₈O₁₂(CH₃)₂Zr(acac)₃ ( 1′ ), (c‐C₅H₉)₇Si₇O₁₂Zr(acac) ( 2′ ), and (c‐C₅H₉)₇Si₇O₁₂Zr(O‐n‐Bu) (3′ ). The reactivity of these complexes were compared to relevant molecular catalysts [zirconium tetraacetylacetonate, Zr(acac)₄ and zirconium tetra‐n‐butoxide, Zr(O‐n‐Bu)₄]. Strong activity relationships between the silica‐supported complexes and their polyoligosilsesquioxane analogues were established. Acetylacetonate complexes were found to be far superior to alkoxide complexes. The monopodal complexes 1 and 1′ were found to be the most active in their respective series. Studies on the recycling of the heterogeneous catalysts showed significant degradation of activity for the acetylacetonate complexes ( 1 and 2 ) but not for the less active tripodal alkoxide catalyst, 3 . Two factors are thought to contribute to the deactivation of catalyst: the lixivation of zirconium by cleavage of surface siloxide bonds and exchange reactions between acetylacetonate ligands and alcohols in the substrate/product solution. It was shown that the addition of acetylacetone to the low activity catalyst Zr(O‐n‐Bu)₄ produced a system that was as active as Zr(acac)₄. The applicability of ligand addition to heterogeneous systems was then studied. The addition of acetylacetone to the low activity solid catalyst 3 produced a highly active catalyst and the addition of a stoichiometric quantity of acetylacetone at each successive batch catalytic run greatly reduced catalyst deactivation for the highly active catalyst 1 .