Polycondensation Catalyst Research Articles

Functionalized UiO‐66 as an efficient catalyst for the synthesis of bio‐based poly(1,3‐propylene sebacate)

AbstractOrganometallic catalysts such as titanium‐based ones are often used for the melt polycondensation to obtain polyesters. However, they are prone to hydrolysis and may discolor, which may have adverse effects on the molecular weight of the resulting polyesters and their applications. This work aims to use functionalized UiO‐66 catalysts for the melt polycondensation of polyesters composed of 1,3‐propanediol and 1,10‐decanedioic acid ether. The melt polycondensation proceeds in two steps: esterification and polycondensation. A catalytic mechanism is proposed. Compared with tetrabutyl titanate, a classical catalyst, the functionalized UiO‐66 ones are more water resistant, less toxic to, and do not discolor. It yields poly(1,3‐propylene sebacate) with higher molecular weights. Thus, they are efficient and greener catalysts.

Syntheses of Cyclic Poly(l‐lactide)s by Means of Zinc‐Based Ring‐Opening Polymerization with Simultaneous Polycondensation (ROPPOC) Catalysts

AbstractRing‐opening polymerizations of l‐lactide are studied in bulk at 140 or 160 °C with zinc n‐hexanoate, zinc 4‐chlorothiophenolate, and zinc pentafluoro thiophenolate (ZnSPF) as catalysts. The reactivity increases in the given order. With all three catalysts a high fraction of cycles is obtained only at polymerization (annealing) times around 7 d. With ZnSPF weight average molecular weights (Mw) up to 178 000, a Tm around 199 °C and a ΔHm around 99 J g−1 w ere achieved. The samples annealed for 4 or 7 d also display a saw tooth pattern of the mass peak distribution in the matrix‐assisted laser desorption/ionization time of flight spectra indicating transesterification reactions across the surface of extended ring crystals. This process optimizes the thermodynamical properties of the crystalline cyclic polylactides and is responsible for the high Tm and ΔHm values.

Preparation of Titania-Silica Composite Aerogel at Atmospheric Pressure and Its Catalytic Performance in the Synthesis of Poly (Butylene Succinate).

Titanates are widely used in the synthesis of polyesters, such as Poly (butylene succinate) (PBS), due to their excellent catalytic activity for polycondensation. However, the hydrolysis sensitivity of titanate and side reactions at high temperatures restrict the further improvement of the molecular weight of polyesters and lead to the high content of end carboxyl group content in the products. In this work, we prepared titania-silica composite aerogels with resistance to hydrolysis and large specific surface area, which were further explored as an efficient catalyst for polycondensation reactions. A series of titania-silica composite aerogel catalysts for PBS polycondensation were successfully prepared by the sol-gel method. The influence of a Ti/Si ratio on the surface morphology and structure of the aerogels was examined. Titania-silica composite aerogel exhibits the surface characteristics of high specific surface area and high Lewis acid content. The specific surface area of titania-silica composite aerogels can reach 524.59 m2/g, and the Lewis acid content on the surface can reach 370.29 μmol/g. Furthermore, the catalytic performance for the polycondensation reaction of PBS was investigated. The intrinsic viscosity of PBS synthesized by catalysis with the composite catalyst with a Ti/Si ratio of 9/1 reaches 1.74 dL/g, with the Mn of 7.72 × 104 g/mol. The hydrolysis resistance stability of the titania-silica composite aerogel is greatly improved compared with traditional tetrabutyl titanate (TBT), and the end carboxyl group content of PBS is effectively reduced to lower than 30 mol/ton.

SiO2-PDMS as oil removal system

This work presents an oil removal system design based on the use of hydrophobic silica (SiO2/PDMS) obtained by the co-condensation of silica with polydimethylsiloxane (PDMS) using DBTL as a polycondensation catalyst. The amount of PDMS in the SiO2/PDMS structure varied from 10 to 40%w. The SiO2/PDMS was impregnated into a sponge system and the amount of hydrophobic silica trapped in the sponge was evaluated by gravimetry; in addition, infrared spectroscopy will allow the identification of the hydrophobic silica in the sponge and the main functional groups of the sponge. The hydrophobic character was determined by changing the water absorption capacity of the sponge and by measuring the contact angle. On the other hand, optical microscopy allowed the identification of changes in the sponge surface due to the presence of SiO2/PDMS. Finally, the effect of the amount of PDMS on the oil-in-water removal capacity was determined.

In-reactor engineering of bioactive aliphatic polyesters via magnesium-catalyzed polycondensation for guided tissue regeneration

Aliphatic polyesters have been widely used in biomedicine owning to their combination of biodegradability, biocompatibility and controllable mechanical properties. Polycondensation is certainly one of the most versatile and robust methods for the synthesis of aliphatic polyesters in a large scale. Nevertheless, traditional catalysts for polycondensation, such as Sb2O3, GeO2 and SnCl2, have potential biotoxicity and need to be completely removed before using in biomedicine. Furthermore, pure aliphatic polyesters do not possess the required functionality and additional work is required for increasing their bioactivity in many biomedical applications. Here, a series of magnesium compounds were used as catalysts for the polycondensation of dicarboxylic acids and diols. We confirmed that the in situ formed magnesium dicarboxylate not only serves as the real catalyst but also endows the resultant polyester with bioactivity because of its osteogenic activity and anti-inflammatory property. Finally, the bioactive polyester was applied to guided tissue regeneration, in which the degree of bone regeneration after 16 weeks is higher than commercial PLA film. This work provides a strategy for the in-reactor engineering of bioactive polyesters within one step on a large scale, and shows promising applications for use in the biomaterial field.

Preparation of TiO<sub>2</sub> Sols with High Solid Contents by Sol Gel Method

Titanium oxide has been extensively used as a photocatalytic material because of its excellent UV light-responsive effect, high refractive index, and high chemical stability. TiO₂ in anatase phase for applications in optical or electronic devices and photocatalysis has generally been used in the form of a thin film. The aim of this study was to prepare a stable TiO₂ sol with high solid content. Therefore one can use less coating time to have a mono layer of TiO₂ film on the substrate. In this study, TiCl₄ was slowly added to the distilled water in an ice bath. Aqueous solution of sodium hydroxide was added to adjust the pH of the solution to between 8 and 12 to form titanium hydroxide gel. After aging for a period of time, the Ti(OH)₄ gel was filtered and sufficiently washed. The filtered cake was repulped in water. Hydrochloric acid, as a catalyst for polycondensation, was slowly added to the solution with stirring. After poly-condensation reaction and crystallization, a transparent suspended TiO₂ sol was formed. XRD results show that the crystalline phase was anatase. The suspended TiO₂ particles were rhombus primary particles with the major axis ca. 20 nm and the minor axis ca. 5 nm. The sample prepared at pH 8 had the largest BET surface area of 141 cm³/g among all samples. The best preparation condition to have the smallest TiO₂ particles are Ti: H = 1: 1 (atomic ratio), 10% solid content of TiO₂, and hydroxypropyl cellulose with viscosity of 150-400 cps as a surfactant. The thin film was obtained by dip-coating the glass in TiO₂ sol. Since the sol had high solid content, the coating time became less. The dip-coating on glass was less than three times to have one monolayer TiO₂. The transparent TiO₂ thin film had super-hydrophilicity after illumination by UV light.

Preparation and Performance of the Hyperbranched Polyamine as an Effective Shale Inhibitor for Water-Based Drilling Fluid

Seeking effective solutions to control and mitigate the interaction between drilling fluids and clay formations has been a challenge for many years, and various shale inhibitors have shown excellent results in problematic shale formations around the world. Herein, the hyperbranched polyamine (HBPA) inhibitor with a higher ratio of amine groups and obvious tendentiousness in protonation was successfully synthesized from ethylenediamine, acryloyl chloride and aziridine by five steps, in which the metal-organic framework (MOF) was employed as a catalyst for ring-open polycondensation (ROP). The structure and purity were confirmed by nuclear magnetic resonance hydrogen spectroscopy and high-performance liquid chromatography (HPLC) respectively. The HBPA displays more excellent performance than EDA and KCl widely applied in the oil field. After aging at 80°C and 180°C, the YP of a slurry system containing 25 wt.% bentonite and 2 wt.% HBPA are just 8.5 Pa and 5.5 Pa (wt.%: percentage of mass), respectively. The swelling lengths of 2 wt.% HBPA are estimated to be 1.78 mm, which falls by 70% compared with that of freshwater. Under a hot rolling aging temperature of 180°C, the HBPA system demonstrates a significant inhibition with more than 85% shale cuttings recovery rate and is superior to conventional EDA and KCl. Mechanism analysis further validates that the HBPA can help to increase the zeta potential.

Influence of introducing organic solvents of different nature on the gelation time of a binder based on methylphenyl organosilicon oligomer during curing

The influence of the type of organic solvent, the acidity index, and the content of MF-12 methylphenyl organosilicon oligomer on the gelation time during polycondensation for the manufacture of heat-resistant electrical insulating materials is considered. The choice of the type of solvent that provides the best viscosity characteristics during impregnation and the greatest stability of the properties of the binder intended for use in combination with selective latent polycondensation catalysts, which exclude the effects of undesirable processes in the production and storage of pre-impregnated materials, has been justified.

Ceramic densification effect on corrosion resistance and thermal conductivity

Thermal barrier Coatings (TBC) are a system of layers covering a surface with the aim to increase its insulation as well as protect the core of oxidation. In this paper the use of silica ceramics modified by polydimethylsiloxane (PDMS) as a new TBC for steel surface is proposed. The ceramics were obtained according to sol-gel methodology forming a stable sol mixing tetraethoxyetilsilicate (TEOS) at different percentage of PDMS (10, 20, 40 and 100%); the gelling was done using DBTL (dibutildilaurate tin) as a polycondensation catalyst. Therefore, the sol was applied on AISI-1018 steel surface by inmersion and a densification process is applied. The ceramic was characterized by infrared spectroscopy to observe its silica structure changes produced by the thermal treatment. Finally, the analysis the densification effect on properties on thermal conductivity and corrosion resistance was carried on.

Homoconjugated Acids as Low Cyclosiloxane-Producing Silanol Polycondensation Catalysts.

Polycondensation of α,ω-disilanols is a foundational technology for silicones producers. Commercially, this process is carried out with strong Brønsted acids and bases, which generates cyclosiloxane byproducts. Homoconjugated acids (a 2:1 complex of acid:base or a 1:1 complex of acid:salt), a seldom used class of silanol polycondensation catalysts, were evaluated for their ability to polymerize α,ω-disilanols while forming low levels of cyclosiloxane byproducts. Homoconjugated acid catalysts were highly active for silanol polycondensation, even when made from relatively mild acids such as acetic acid. Both the acid and base (or cation) component of the homoconjugated species was important for activity and avoiding cyclosiloxane byproduct formation. Stronger acids and bases were found to positively affect reactivity, and the pKa of the acid was found to correlate with cyclosiloxane byproduct formation. The individual components of the homoconjugated species (the acid and base) were ineffective as catalysts by themselves, and compositions with fewer than 2 mol of acid to 1 mol of base were much less reactive. Homoconjugated trifluoroacetic acid tetramethylguanidinium and tetrabutylphosphonium complexes were found to be privileged catalysts, able to give high-molecular-weight siloxanes (Mn > 60 kDa) while generating less than 100 ppm of octamethylcyclotetrasiloxane byproduct. Finally, a mechanism has been proposed where silanols are electrophilically and nucleophilically activated by the homoconjugated species, leading to silanol polycondensation.

Lewis Acids As Highly Active Silanol Polycondensation Catalysts Affording Low Levels of Cyclosiloxanes

Silanol polycondensation is an important industrial process that is used to produce high-molecular-weight silicones for a wide array of applications. This technology is practiced commercially using...

Facile Fabrication of High-Performance Si/C Anode Materials via AlCl3-Assisted Magnesiothermic Reduction of Phenyl-Rich Polyhedral Silsesquioxanes.

Si/C composites, combining the advantages of both carbon materials and Si materials, have been proposed as the promising material in lithium-ion storage. However, up to now, the most common fabrication methods of Si/C composites are too complicated for practical application. Here, we first use phenyl-substituted cagelike polyhedral silsesquioxane (Tn-Ph, n = 8, 12) as both carbon and silicon precursors to prepare the high-performance Si/C anode materials via a low-temperature and simple AlCl3-assisted magnesiothermic reduction. AlCl3 plays two roles in the reduction process, on the one hand, it acts as liquid medium to promote the reduction of siloxane core in such a mild condition (200 °C), and on the other hand, it act as catalyst for phenyl groups polycondensation into carbon materials, which makes the procedure of fabrication feasible and controllable. Impressively, T12-Si/C exhibits an excellent lithium anodic performance with a reversible capacity of 1449.2 mA h g-1 with a low volume expansion of 16.3% after 100 cycles. Such superior electrochemical performance makes the Si/C composites alternative anode materials for lithium-ion batteries.

Sol-gel based coatings for the protection of cultural heritage textiles

In this paper, the procedure for the development of sol-gel silica coatings for the protection of cultural heritage textiles, using a multistep approach, is described. With this aim, Tetraethoxysilane precursor was used at two different concentrations to realize coatings onto textile samples, using Dibutyltindiacetate as polycondensation catalyst for sol-gel reactions. The relationship between the presence of the catalyst, the number of coating layers deposited on cotton fabrics, and the influence of such architecture on several properties of treated textiles, were investigated. In particular, the chemical structure of thin films and their morphology were studied by infrared spectroscopy and scanning electron microscopy, respectively. The thermo-oxidative properties and the abrasion resistance of sol-gel treated cotton fabrics were studied, as well as the durability of the coatings after different washing cycles. Both silica coatings provided high adhesion onto cotton textiles, while the higher silica concentration resulted in higher thermal stability and washing fastness of treated fabrics. An enhancement in the washing fastness and abrasion resistance for the two different concentrations of precursor in the presence of the catalyst was also observed. All experimental findings demonstrated the efficiency of sol-gel based materials specifically tailored to the protection and preservation of cultural heritage textiles.

Effect of Polycondensation Catalyst on Fiber Structure Development in High-Speed Melt Spinning of Poly (Ethylene Terephthalate).

We conducted a preliminary study on fiber structural development in the high-speed melt spinning of environmentally friendly polyethylene terephthalate (Ti-PET) synthesized with 25 ppm of titanium-based catalyst, which was compared with conventional PET (Sb-PET) synthesized with 260 ppm of antimony-based catalyst. Gel permeation chromatography of Ti- and Sb-PET resins of intrinsic viscosity 0.63 confirmed that both resins have similar molecular weights and distributions. However, differential scanning calorimetry revealed that the Ti-PET resin exhibited a lower melt–crystallization peak and isothermal melt-crystallization rate than the Sb-PET resin. High-speed melt spinning of the Ti- and Sb-PET was possible up to a spinning velocity of 6 km/min. Two-dimensional wide-angle X-ray diffraction analyses showed that the molecular orientation of the obtained as-spun Ti- and Sb-PET fibers increased with spinning velocity, and a highly oriented, crystalline structure by orientation-induced crystallization started to appear from 5 km/min. Notably, Ti-PET fibers showed a lower degree of crystalline structural development and lower tensile strength compared with Sb-PET fibers under the high-speed spinning conditions. Our results suggest that the catalyst in PET resins can act as nucleating agents in thermal- and orientation-induced crystallization, and that differences in catalyst content can influence PET fiber structure development under extreme conditions in high-speed melt spinning.

Anticorrosive properties of PDMS-Silica coatings: effect of methyl, phenyl and amino groups

Hybrid silica coating obtained from TEOS and PDMS using Methyl, Phenyl and Amino as functional groups of siloxane chain were obtained using Dibutyl-dilaurate tin (DBTL) as a neutral poly-condensation catalyst under free solvent conditions. The hybrid silica coating was characterized using different characterization techniques. FT-IR shows the presence of main functional groups for silica network and PDMS. On the other hand, TGA confirmed the formation of coatings with 76%w of ceramic yield. The C1s XPS peak analysis shows that only 30% of organic material corresponds to alkoxy groups without hydrolyzer from TEOS. Furthermore, Si2p peak XPS analysis shows that around 30% of ceramic network corresponds to Si-D and similar concentration to Q2 silicon species, which are found binding to siloxane chain from PDMS. Similarly, the Sn concentration on hybrid silica network was negligible according to Sn3d peak XPS. Furthermore, the corrosion resistance analysis for the different ceramic shows that the amino and phenyl groups improve the corrosion resistance for aluminum according to NACE international criteria.

Bio-based polyester itaconates as binder resins for UV-curing offset printing inks

UV-curing inks have several economic and environmental advantages compared with standard printing inks, such as high printing velocities, low VOC emissions and good adhesion to nonabsorbing substrates. However, there are also some drawbacks, such as residual monomers, pungent odor and allergic potential of monomers and prepolymers derived from acrylic acid. In addition, only few examples of UV-curing inks derived from renewable resources are known. Herein, acrylate-free UV-curing polyester itaconates with a renewable content up to 100% and their application as binder resins in UV-curing offset ink formulations are presented. In order to obtain a high renewable content in the polyester resins, Zn(OAc)2 had to be used as polycondensation catalyst, as standard Bronsted acid catalyst led to undesired side reactions. The resins obtained with this synthetic protocol were tested on their reactivity, which was slightly lower than a commercial polyester acrylate. Printing inks formulated from these polyester itaconates showed interesting properties despite the fact that no acrylic acid was incorporated in the resins.

Core–Shell Fe@SiO2 Nanoparticles Synthesized via Modified Stober Method for High Activity in Cr(VI) Reduction

In this paper, Fe@SiO2 nanoparticles (α-Fe nanoparticles coated with SiO2 shell) were synthesized at room temperature using the modified Stöber method combined with potassium borohydride (KBH4) reduction process. The present study depicts the facile synthesis of Fe@SiO2 without the presence of surfactants and stabilizers. In this experiment, KBH4 acted both as a reducing agent for iron salt and a catalyst for hydrolysis and polycondensation of tetraethylorthosilicate (TEOS). The Fe@SiO2 nanoparticles were characterized using X-ray diffraction method, specific surface area (BET) technique, transmission electron microscope (TEM), and vibrating sample magnetometer (VSM). The optimal mass ratio of Fe in the form of anhydrous ferric chloride (FeCl3) and SiO2) in the form of TEOS was 4:1. α-Fe-Fe nanoparticles (size of about 45 nm) were coated with approximately 10 nm thick SiO2 shells. Moreover, Fe/SiO2 (Fe0 nanoparticles supported by silica nanoparticles) was synthesized to compare the results. Due to the silica shells, Fe cores cannot be oxidized when dipped in the concentrated sulfuric acid, and hence, the removal of Cr(VI) was not weakened in the acidic environment.

Kinetics study of the fully bio-based poly(propylene succinate) synthesis. Functional group approach

Currently, the increasing importance of the bio-based chemical compounds development is visible in the polymer chemistry, chemical engineering and materials science. It is well-known that the various purity level and different contaminants characterize petrochemical-based compounds compared to their bio-based counterparts. Therefore, it is necessary to find out the contaminants impact on the bio-based monomers synthesis. One of the most important information about the reaction pathway gave the kinetics study. In this work, the fully bio-based poly (propylene succinate)s were synthesized under various temperature conditions via two-step polycondensation reaction. The kinetics studies were investigated with the use of a functional group approach. The first step of the polycondensation reaction was autocatalytic esterification reaction. During the second step, the polycondensation catalyst was used. For macromolecular structure characteristics and the progress of the chemical reaction monitoring, Fourier Transform Infrared Spectroscopy, Proton Nuclear Magnetic Resonance, and Gel Permeation Chromatography were conducted. The activation energy value of 38.5 kJ/mol was determined for the first step of the bio-based polyols synthesis. The results of the investigations verified that the activation energy for the bio-based poly (propylene succinate) synthesis revealed lower value than the same polyester synthesis based on the petrochemical monomers. Thermal analysis by TGA measurements allowed confirmed the high thermal stability of the prepared bio-based polyols equaled ca. 418 °C.

Organic modified silica obtained from DBTL polycondensation catalyst for anticorrosive coating

DBTL as neutral polycondensation catalyst was employed to obtain organic modified silanes (ORMOSILs), which were studied as anticorrosive films for aluminum at saline corrosion. The ORMOSILs were synthesized using TEOS as silica precursor, different alkylalkoxysilanes (trimethoxy(methyl)silane, triethoxy(octyl)silane, 3-aminopropyl(triethoxy)silane and DBTL-catalyst were employed under the free solvent sol–gel process. Results of chemical characterization of ORMOSILs coatings show that under SEM technique coatings have homogenous films, and there are a crosslinking between silica and organic modified under the Infrared spectroscopy and 29Si CPMAS-NMR techniques. On the other hand, Brinell hardness and Pull-Off adhesion tests show that all ORMOSILs increase the aluminum surface hardness between 1 and 10%, and the ORMOSILs critical forces for adhesion are in the range of 106–132 N; therefore, the ORMOSILs coatings have an excellent adhesion to aluminum surface, furthermore, the saline corrosion test shows that organic modified silica avoid the pitting aluminum corrosion; corrosion rate decreases about 60–85%; the anticorrosive behavior according to modified-silica was determined as: SiO2–NH2 > SiO2–Me ∼ SiO2–Octyl.

One-pot spontaneous formation of submicron hexane-dispersible silica particles with the aid of amphiphilic reaction solvent

Hydrophobic submicron hybrid silica particles were spontaneously formed in the mixture of tetraethylorthosilicate (TEOS) and hexyltrimethoxysilane (HTMS) dissolved in diethylamine, which works as a catalytic Lewis basic amphiphilic reaction solvent. The obtained hybrid silica particles were stably dispersed in non-polar solvent such as hexane in the form of the primary-particle dispersion. The solvent diethylamine functioned not only as the catalyst for the silanol polycondensation but also as a superior dispersant for the primary-particle dispersion of the hydrophobic hybrid silica particles throughout the formation process. After the addition of TEOS, HTMS and water in diethylamine, the particle nucleation was promoted the ultrasonication for 30 s. Then, the uniform-sized submicron hydrophobic hybrid silica particles were spontaneously formed after the dispersion of the nuclear was kept still for 24 h. The surface of the hybrid silica particles became increasingly hydrophobic. This is because of the higher density of the non-polar pendant groups (hexyl groups) in the vicinity of the surface, which results from the lower reactivity of trifunctional HTMS than that of tetrafunctional TEOS. The merits of using diethylamine are summarized as follows; 1) Since diethylamine strongly catalyzes silanol condensation, the particle surface was thoroughly hydrophobized. 2) Since the hydrophobized particle had good affinity with diethylamine, the hybrid silica particles remained stably dispersed in it. Furthermore, even after the hybrid silica particles are air-dried, they are redispersed in hexane in the form of the primary-particle dispersed.