Preparation and surface properties of novel low surface free energy fluorinated silane-functional polybenzoxazine films

Development of an Atomic-Oxygen-Erosion-Resistant, Alumina-Fiber-Reinforced, Fluorinated Polybenzoxazine Composite for Low-Earth Orbital Applications

An atomic-oxygen-erosion-resistant fluorinated benzoxazine resin and composite were developed. The benzoxazine resin, abbreviated as “BAF-oda-fu,” consists of four benzoxazine rings, and was synthesized from bisphenol AF (BAF), 4,4′-oxydianiline (oda), furfurylamine (fu), and paraformaldehyde. The resin was characterized by infrared spectroscopy (FT-IR), proton nuclear magnetic resonance spectroscopy (1H NMR), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). An analysis of the solvent-washed product showed a technical grade purity (>95%) and a yield of approximately 85%. Subsequent polymerization of the resin was successfully performed by heating step-wise and opening the benzoxazine rings to form a crosslinked network. Thermal analyses showed a melting temperature of 115 °C and polymerization temperature of 238 °C, both being characteristic values of benzoxazine monomers. The benzoxazine resin was also blended with polyoctahedral sisesquoxane (POSS) and reinforced with alumina fibers. The Tg of the resin, as determined by DMA of the composite, could reach as high as 308 °C when post-curing and the POSS additive were utilized. The low-Earth orbit atomic-oxygen erosion rate was simulated by an RF plasma asher/etcher. The atomic-oxygen resistance of poly(BAF-oda-fu) fell along an established trend line based on its fluorine content.

A Methyl-Modified Silica Layer Supported on Porous Ceramic Membranes for the Enhanced Separation of Methyl Tert-Butyl Ether from Aqueous Solution

As a kind of volatile organic compound (VOC), methyl tert-butyl ether (MTBE) is hazardous to human health and destructive to the environment if not handled properly. MTBE should be removed before the release of wastewater. The present work supported the methyl-modified silica layer (MSL) on porous α-Al₂O₃ ceramic membranes with methyltrimethoxysilane (MTMS) as a precursor and pre-synthesized mesoporous silica microspheres as dopants by the sol-gel reaction and dip-coating method. MTMS is an environmentally friendly agent compared to fluorinated alkylsilane. The MSL-supported Al₂O₃ ceramic membranes were used for MTBE/water separation by pervaporation. The NMR spectra revealed that MTMS evolves gradually from an oligomer to a highly cross-linked methyl-modified silica species. Methyl-modified silica species and pre-synthesized mesoporous silica microspheres combine into hydrophobic mesoporous MSL. MSL makes the α-Al₂O₃ ceramic membranes transfer from amphiphilic to hydrophobic and oleophilic. The MSL-supported α-Al₂O₃ ceramic membranes (MSL-10) exhibit an MTBE/water separation factor of 27.1 and a total flux of 0.448 kg m⁻² h⁻¹, which are considerably higher than those of previously reported membranes that are modified by other alkylsilanes via the post-grafting method. The mesopores within the MSL provide a pathway for the transport of MTBE molecules across the membranes. The presence of methyl groups on the external and inner surface is responsible for the favorable separation performance and the outstanding long-term stability of the MSL-supported porous α-Al₂O₃ ceramic membranes.

Review on the Accelerated and Low-Temperature Polymerization of Benzoxazine Resins: Addition Polymerizable Sustainable Polymers

Due to their outstanding and versatile properties, polybenzoxazines have quickly occupied a great niche of applications. Developing the ability to polymerize benzoxazine resin at lower temperatures than the current capability is essential in taking advantage of these exceptional properties and remains to be most challenging subject in the field. The current review is classified into several parts to achieve this goal. In this review, fundamentals on the synthesis and evolution of structure, which led to classification of PBz in different generations, are discussed. Classifications of PBzs are defined depending on building block as well as how structure is evolved and property obtained. Progress on the utility of biobased feedstocks from various bio-/waste-mass is also discussed and compared, wherever possible. The second part of review discusses the probable polymerization mechanism proposed for the ring-opening reactions. This is complementary to the third section, where the effect of catalysts/initiators has on triggering polymerization at low temperature is discussed extensively. The role of additional functionalities in influencing the temperature of polymerization is also discussed. There has been a shift in paradigm beyond the lowering of ring-opening polymerization (ROP) temperature and other areas of interest, such as adaptation of molecular functionality with simultaneous improvement of properties.

Corrosion Resistance of Mild Steel Coated with Phthalimide-Functionalized Polybenzoxazines

Herein, we synthesized two new phthalimide-functionalized benzoxazine monomers, pPP-BZ and oPP-BZ, through Mannich reactions of 2-(4-hydroxyphenyl)isoindoline-1,3-dione (pPP) and 2-(2-hydroxyphenyl)isoindoline-1,3-dione (oPP), respectively, with p-toluidine and paraformaldehyde. The structures of these two monomers were confirmed using Fourier transform infrared (FTIR) and nuclear magnetic resonance spectroscopy. We used differential scanning calorimetry, FTIR spectroscopy, and thermogravimetric analysis to study the polymerization behavior and thermal stability of the monomers and their corresponding polybenzoxazines. Poly(pPP-BZ) and poly(oPP-BZ) were formed on mild steel (MS) through spin-coating and subsequent thermal curing polymerization. We used various corrosion testing methods to examine the effect of the curing temperature on the corrosion resistance of the coated MS samples in 3.5 wt.% aqueous solution of NaCl. Among our tested systems, the corrosion rate reached a low of 2.78 µm·Y−1 for the MS coated with poly(pPP-BZ)180 (i.e., the coating that had been cured at 180 °C); this value is much lower than that (4.8 µm·Y−1) reported for a maleimide-based benzoxazine compound (MI-Bz)/33 wt.% ACAT (amine-capped aniline trimer) blend. Thus, the incorporation of the imide functional group into the PBZ coatings is an effective strategy for affording high-performance corrosion resistance.

Mesoporous Silica Membranes Silylated by Fluorinated and Non-Fluorinated Alkylsilanes for the Separation of Methyl Tert-Butyl Ether from Water

It is of great significance to separate hazardous methyl tert-butyl ether (MTBE) from water in terms of environmental protection and human health. In the present work, α-Al₂O₃-suppotred silica membranes were prepared by the sol-gel and dip-coating technique. Two fluorinated alkylsilanes (1H,1H,2H,2H-perfluorooctyltriethoxysilane (PFOTES) and trifluoropropyltriethoxysilane (TFPTES)) and two non-fluorinated alkylsilanes (octyltriethoxysilane (OTES) and propyltriethoxysilane (PTES)) were adopted to silylate the silica membrane by the post-grafting method which is used for the separation of MTBE from water by pervaporation. The results show that silylation enhances the hydrophobicity of silica membranes. The silylated silica membranes are selective towards MTBE, and the MTBE/water separation factor varies with grafting agents in the order: PFOTES > TFPTES > OTES > PTES. Membranes silylated with fluorinated carbon chains seem to be more selective towards MTBE than those with non-fluorinated carbon chains. The total flux is proportional to the pore volume of silica membranes, which depends on grafting agents in the order: PTES > PFOTES > OTES > TFPTES. Considering both total flux and selectivity, the PFOTES-SiO₂ membrane is most effective in separation, with a MTBE/water separation factor of 24.6 and a total flux of 0.35 kg m^-2 h^-1 under a MTBE concentration of 3.0% and a feed temperature of 30 °C.

Developing Further Versatility in Benzoxazine Synthesis via Hydrolytic Ring-Opening

In this study, 2-(aminomethyl)phenol and its derivatives, the reactants for 2-substituted 1,3-benzoxazines, are synthesized by HCl hydrolysis from the typical benzoxazines. The phenol/aniline-based mono-oxazine benzoxazine, PH-a, and the bisphenol A/aniline-based bis-oxazine benzoxazine, BA-a, are used as examples to demonstrate the feasibility of this new approach. Their chemical structures are characterized by nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR) and Raman spectroscopies, and are further verified by elementary analysis. Their thermal properties are studied by differential scanning calorimetry (DSC). These two 2-(aminomethyl) phenolic derivatives are reacted with paraformaldehyde to close the oxazine rings. A benzoxazine with a phenyl substituent at the 2-position of the oxazine ring is obtained from the 2-((phenylamino)methyl)phenol (hPH-a) and benzaldehyde. All these results highlight the success of the HCl hydrolysis and the formation of stable intermediates, namely 2-(aminomethyl) phenolic derivatives, from readily available benzoxazine monomers. This further demonstrates the feasibility of using these intermediates as reactants for a novel benzoxazine synthesis.

Synthesis and Properties of Organosilicon-Grafted Cardanol Novolac Epoxy Resin as a Novel Biobased Reactive Diluent and Toughening Agent

The aim of this work is to develop a biobased functional reactive diluent for thermosetting epoxy resins suitable for high-performance applications. An advanced organosilicon-grafted cardanol novolac epoxy resin (SCNER) was synthesized from cardanol novolac epoxy resin and heptamethyltrisiloxane. After the chemical structure of SCNER was identified by Fourier transform infrared, ¹H NMR, and ¹³C NMR, it was used to modify the diglycidyl ether of the bisphenol A (DGEBA)/methylhexahydrophthalic anhydride system. The SCNER showed unique advantages, reducing the viscosity of DGEBA and improving the properties of the cured resin. With 10 wt % SCNER, the cured resin exhibited a higher tensile strength (78.84 MPa) and impact strength (32.36 kJ·m^-2). The single glass transition temperature (T _g) step proved the homogeneous phase structure of the cured resin. Inevitably, the T _g of the cured resin decreased for the addition of SCNER. The dynamic mechanical analysis results indicated that the storage modulus of the cured resin decreased with the increasing content of SCNER. The morphology showing the ductile fracture of the cured resin was testified by scanning electron microscopy. The dilution and toughening properties of SCNER paves the way to a wide range of possible "eco-friendly" applications, especially in the fields of coatings, paintings, and adhesives.

Direct synthesis of poly(benzoxazine imide) from an ortho-benzoxazine: its thermal conversion to highly cross-linked polybenzoxazole and blending with poly(4-vinylphenol)

A facile one-pot synthesis of a poly(benzoxazine imide), NDOPoda Bz, was prepared without the need for either the preparation of an amino-functionalized benzoxazine or subsequent thermal treatment.

Intramolecular Hydrogen Bonding in Benzoxazines: When Structural Design Becomes Functional

The future evolution of benzoxazines and polybenzoxazines as advanced molecular, structural, functional, engineering, and newly commercial materials depends to a great extent on a deeper and more fundamental understanding at the molecular level. In this contribution, the field of benzoxazines is briefly introduced along with a more detailed review of ortho-amide-functional benzoxazines, which are the main subjects of this article. Provided in this article are the detailed and solid scientific evidences of intramolecular five-membered-ring hydrogen bonding, which is supposed to be responsible for the unique and characteristic features exhibited by this ever-growing family of ortho-functionalized benzoxazines. One-dimensional (1D) (1)H NMR spectroscopy was used to study various concentrations of benzoxazines in various solvents with different hydrogen-bonding capability and at various temperatures to investigate in detail the nature of hydrogen bonding in both ortho-amide-functionalized benzoxazine and its para counterpart. These materials were further investigated by two-dimensional (2D) (1)H-(1)H nuclear Overhauser effect spectroscopy (NOESY) to verify and support the conclusions derived during the 1D (1)H NMR experiments. Only highly purified single-crystal benzoxazine samples have been used for this study to avoid additional interactions caused by any impurities.

Corrosion protection of hydrophobic bisphenol A-based polybenzoxazine coatings on mild steel

Hydrophobic bisphenol A-based polybenzoxazine coatings with excellent corrosion resistance were prepared through a simple dip coating and thermal curing method.

Semi fluorinated polymers as surface energy controlled layers for liquid crystal alignment

The effects of compounded hydrogenated–fluorinated surfaces formed by perfluorocyclobutane (PFCB)-containing polymers on the alignment of a liquid crystal, 4,4′-octylcycanobiphenyl (8CB), were investigated.

Multivalent photo-crosslinkable coumarin-containing polybenzoxazines exhibiting enhanced thermal and hydrophobic surface properties

Mono-, bi-, and trivalent coumarin-containing benzoxazine monomers were synthesized by facile Mannich reactions of 4-methyl-7-hydroxycoumarin and paraformaldehyde with aniline, bisphenol A–NH₂, and 1,3,5-tri(4-aminobenzene).

Bifunctional polybenzoxazine nanocomposites containing photo-crosslinkable coumarin units and pyrene units capable of dispersing single-walled carbon nanotubes

A new bifunctional benzoxazine monomer possessing both coumarin and pyrene groups for photo-crosslinking and dispersing single-walled carbon nanotubes.

An anomalous trade-off effect on the properties of smart ortho-functional benzoxazines

A series of ortho-difunctional benzoxazine monomers containing amide, imide and amide–imide groups have been synthesized in order to obtain basic design rules toward preparing higher performance polybenzoxazoles based on smart benzoxazine chemistry.

Supramolecular functionalized polybenzoxazines from azobenzene carboxylic acid/azobenzene pyridine complexes: synthesis, surface properties, and specific interactions

Supramolecular complex of azobenzene carboxylic acid/pyridine functionalized benzoxazine system featured significantly lower curing temperatures and maintain high water contact angles.

Design of hydrophobic polydimethylsiloxane and polybenzoxazine hybrids for interlayer low k dielectrics

Graphical representation of layer-by-layer arrangement of polydimethylsiloxane based polybenzoxazine hybrids.

Fluorine-free superhydrophobic/hydrophobic polybenzoxazine/TiO2 films with excellent thermal stability and reversible wettability

A thermally stable superhydrophobic film with strong adhesion to glass substrates and reversibly switchable behavior was prepared from polybenzoxazine and TiO₂.

Calcination-free micropatterning of rare-earth-ion-doped nanoparticle films on wettability-patterned surfaces of plastic sheets

We demonstrate a patterning technique of rare-earth-ion-doped (RE) nanoparticle films directly on wettability-patterned surfaces fabricated on plastic sheets in one step. Self-assembled monolayers consisting of silane-coupling agent with hydrophobic groups were fabricated on plastic sheets. UV-ozone treatments were performed through a metal mask to selectively remove the self-assembled monolayers in a patterned manner, resulting in the formation of wettability-patterned surfaces on plastic sheets. Using a water dispersion of Er(3+) and Yb(3+)-codoped Y2O3 nanoparticles at a diameter of 100 nm, RE-nanoparticle films were fabricated on the wettability-patterned surfaces by a dip-coating technique. By adjusting the concentration of RE-nanoparticle dispersion, withdrawal speed, and withdrawal angle, amount of RE-nanoparticles, we were able to control the structures of the RE-nanoparticle films. Fluorescence microscope observations demonstrate that visible upconversion luminescence and near-infrared fluorescence were emitted from the RE-nanoparticle films on the wettability-patterned surfaces. This technique allows for the fabrication of flexible emitting devices with long-operating life time with minimized material consumption and few fabrication steps, and for the application to sensors, emitting devices, and displays in electronics, photonics, and bionics in the future.

Emission and surface properties of main-chain type polybenzoxazine with pyridinyl moieties

A main-chain type polybenzoxazine, PBz (1), with pyridinyl moieties was prepared. When the THF dilute solution of PBz (1) was protonated with HCl, a new absorption signal at 458 nm was observed in the UV-vis spectrum. After being excited at 458 nm, a strong emission at 570 nm was observed in the fluorescence spectrum. This result suggests that the pyridinyl-containing PBz (1) can be used as a proton sensor.

Azopyridine-functionalized benzoxazine with Zn(ClO4)2form high-performance polybenzoxazine stabilized through metal–ligand coordination

Azopyridine-functionalized benzoxazine (PBZ) was prepared and then blended with zinc ion through metal–ligand coordination to form a high performance polybenzoxazine after thermal curing.

Synthesis and surface properties of low surface free energy silane-functional polybenzoxazine films

A series of low surface free energy silane-functional polybenzoxazine films were prepared from alkylphenol, paraformaldehyde, and 3-aminopropyltrimethoxysilane (3-APTMOS) using a facile one-step thermal curing method. The chemical structures of these benzoxazine monomers were confirmed by FTIR and (1)H NMR. The surface properties of the series of polybenzoxazine films were proved through contact angle measurement, and the lowest surface energy of these films was 14.91 mJ/m(2). Moreover, the hydrogen bond network of the polybenzoxazine systems was studied using the FTIR spectra. The result showed that the intramolecular hydrogen bonding transformed into intermolecular hydrogen bonding with increasing curing time. Based on these findings, the transformation mechanism between the intermolecular and intramolecular hydrogen bonding during the progress of curing was proposed. The thermogravimetric analysis (TGA) results indicated that the silane-functional polybenzoxazine, with a high char yield of 57.01%, possessed excellent thermal stability.

Low dielectric and low surface free energy flexible linear aliphatic alkoxy core bridged bisphenol cyanate ester based POSS nanocomposites

The aim of the present work is to develop a new type of flexible linear aliphatic alkoxy core bridged bisphenol cyanate ester (AECE) based POSS nanocomposites for low k applications. The POSS-AECE nanocomposites were developed by incorporating varying weight percentages (0, 5, and 10 wt %) of octakis (dimethylsiloxypropylglycidylether) silsesquioxane (OG-POSS) into cyanate esters. Data from thermal and dielectric studies imply that the POSS reinforced nanocomposite exhibits higher thermal stability and low dielectric value of k = 2.4 (10 wt% POSS-AECE4) compared than those of neat AECE. From the contact angle measurement, it is inferred that, the increase in the percentage incorporation of POSS in to AECE, the values of water contact angle was enhanced. Further, the value of surface free energy was lower when compared to that of neat AECE. The molecular level dispersion of POSS into AECE was ascertained from SEM and TEM analyses.