Carboxylic acid-containing benzoxazines as efficient catalysts in the thermal polymerization of benzoxazines

Hydrothermal Stability of Hydrogen-Selective Carbon-Ceramic Membranes Derived from Polybenzoxazine-Modified Silica-Zirconia

This work investigated the long-term hydrothermal performance of composite carbon-SiO₂-ZrO₂ membranes. A carbon-SiO₂-ZrO₂ composite was formed from the inert pyrolysis of SiO₂-ZrO₂-polybenzoxazine resin. The carbon-SiO₂-ZrO₂ composites prepared at 550 and 750 °C had different surface and microstructural properties. A carbon-SiO₂-ZrO₂ membrane fabricated at 750 °C exhibited H₂ selectivity over CO₂, N₂, and CH₄ of 27, 139, and 1026, respectively, that were higher than those of a membrane fabricated at 550 °C (5, 12, and 11, respectively). In addition to maintaining high H₂ permeance and selectivity, the carbon-SiO₂-ZrO₂ membrane fabricated at 750 °C also showed better stability under hydrothermal conditions at steam partial pressures of 90 (30 mol%) and 150 kPa (50 mol%) compared with the membrane fabricated at 500 °C. This was attributed to the complete pyrolytic and ceramic transformation of the microstructure after pyrolysis at 750 °C. This work thus demonstrates the promise of carbon-SiO₂-ZrO₂ membranes for H₂ separation under severe hydrothermal conditions.

Synthesis, ring-opening polymerization, and properties of benzoxazines based on o- and p-hydroxybenzyl alcohols

Two series of bifunctional benzoxazines were synthesized from o- and p-hydroxybenzyl alcohols ( oHBA and pHBA), three aliphatic diamines containing ether linkage (Jeffamines D230 and D400 and 4,7,10-trioxa-1,13-tridecanediamine (TTDDA)), and paraformaldehyde. The chemical structures of the benzoxazines were confirmed by 1H and 13C nuclear magnetic resonance and Fourier transform infrared (FTIR) spectroscopy. The ring-opening polymerization of the benzoxazines was studied by differential scanning calorimetry and FTIR, respectively. oHBA-based benzoxazines respectively exhibit lower onset temperatures of ring-opening polymerization than pHBA-based counterparts due to the O–H∙∙∙O intramolecular hydrogen-bonding interaction between the hydrogen of ortho-methylol group and the oxygen in oxazine ring, and oHBA-based polybenzoxazines respectively show lower glass transition temperatures ( Tgs) than pHBA-based counterparts due to the difference in crosslinking density caused by the steric hindrance effect of the position of methylol group on the polymerization of benzoxazine monomers. In each of the two series of benzoxazines, the onset temperature of ring-opening polymerization of D230-based benzoxazine is close to that of TTDDA-based analogue and lower than that of D400-based counterpart owing to the steric effect of the chain length and chain volume of the bridging structure between the oxazine rings on the polymerization, and the Tg of D230-based polybenzoxazine is close to that of TTDDA-based analogue and much higher than that of D400-based counterpart owing to the difference in crosslinking density caused by the steric hindrance effect of the bridging structure on the polymerization of benzoxazine monomers. In addition, all the polybenzoxazines exhibit thermally induced shape memory effect. In each of the two series of polybenzoxazines, the shape recovery rate and ratio of D400-based polybenzoxazine are respectively close to those of D230-based counterpart and higher than those of TTDDA-based analogue due to the difference in network architecture.

Preparation and properties of silicon-containing benzoxazine with high thermal stability

A silicon-containing benzoxazine (PDpsp-a) was synthesized from bis( p-hydroxyphenyl)diphenylsilane, aniline, and paraformaldehyde. The structure of the monomer was supported by 1H-NMR and FTIR spectra. The curing behavior of benzoxazine was evaluated by differential scanning calorimetry and in-situ FTIR spectra. The thermal properties were studied by MDSC, TGA, and Py-GC/MS. The results indicated that the characteristic peak of oxazine ring began to disappear when the temperature was heated to 180°C and completely disappeared at 260°C. The polybenzoxazine (PDpsp-a) possessed a high glass transition temperatures (174°C) and had good thermal stability (T10 = 420°C). In the pyrolysates of polybenzoxazine (PDpsp-a), no silicon-containing compounds, no phenol species, and more benzene were detected, we speculated that the Ar-Si bond would fracture with the increase of temperature. The benzene was volatilized from the system as a pyrolysis product and the silicon could react with oxygen to form siloxanes remained in the carbon residue in the form of siloxane compounds. The formed silica layer could endow the silicon-containing polybenzoxazine high thermal degradation stability and high char yield.

Synthesis and Application Studies of DOPO-Based Organophosphorous Derivatives to Modify the Thermal Behavior of Polybenzoxazine

The DOPO-based flame-retardant additives DOPO-HQ, DOPO-AP and DOPO-Van were synthesized in varying numbers of phenolic hydroxyl groups and amine groups. Moreover, their influence on the polymerization of a bisphenol F-based benzoxazine, as well as the thermal properties of the resulting materials, were studied. All DOPO-based derivatives influenced the polymerization temperature onset with a reduction of up to 20 °C, while thermo-mechanical properties remained high. Surprisingly, phosphorous content below 0.4 wt% significantly improved the reaction against small flames yielding an increase in the limited oxygen index by 2% and a V-0 rating in the UL-94 test. DOPO-HQ proved to be the most effective additive regarding the reaction against small flames at an astonishingly low phosphorous concentration of below 0.1 wt%, whereas DOPO-AP and DOPO-Van simultaneously lowered the polymerization temperature.

Solvent-free synthesis of a formaldehyde-free benzoxazine monomer: study of its curing acceleration effect for commercial benzoxazine

A new 2-substituted benzoxazine bearing a phenol was blended with commercial benzoxazine for improving curing and thermomechanical properties.

Thermal properties of polybenzoxazine exhibiting improved toughness: Blending with cyclodextrin and its derivatives

Polybenzoxazines are emerging as a class of high-performance thermoset polymers that can find their applications in various fields. However, its practical application is limited by its low toughness. The cyclic β-cyclodextrin and a newly synthesized derivative (β-cyclodextrin-MAH) were separately blended with benzoxazine to improve the toughness of polybenzoxazine. The results revealed that the maximum impact strength of the blend was 12.24 kJ·m−2 and 14.29 kJ·m−2 when 1 wt.% of β-Cyclodextrin and β-Cyclodextrin-MAH, respectively, were used. The strengths were 53% and 86% higher than that of pure polybenzoxazine. The curing reaction, possible chemical structures, and fractured surface were examined using differential scanning calorimetry, Fourier transform infrared spectroscopy, and scanning electron microscopy techniques to understand the mechanism of generation of toughness. The results revealed that the sea-island structure and the presence of hydrogen bonds between polybenzoxazine and β-cyclodextrin and β-cyclodextrin-MAH resulted in the generation of toughness. Furthermore, the curves generated during thermogravimetric analysis did not significantly change, revealing the good thermal properties of the system. The phase-separated structure and the hydrogen bonds present in the system can be exploited to prepare synergistically tough polybenzoxazine exhibiting excellent thermal properties. This can be a potential way of modifying the thermoset resins.

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.

Synthesis and Application of Arylaminophosphazene as a Flame Retardant and Catalyst for the Polymerization of Benzoxazines

A novel type of phosphazene containing an additive that acts both as a catalyst and as a flame retardant for benzoxazine binders is presented in this study. The synthesis of a derivative of hexachlorocyclotriphosphazene (HCP) and meta-toluidine was carried out in the medium of the latter, which made it possible to achieve the complete substitution of chlorine atoms in the initial HCP. Thermal and flammability characteristics of modified compositions were investigated. The modifier catalyzes the process of curing and shifts the beginning of reaction from 222.0 °C for pure benzoxazine to 205.9 °C for composition with 10 phr of modifier. The additive decreases the glass transition temperature of compositions. Achievement of the highest category of flame resistance (V-0 in accordance with UL-94) is ensured both by increasing the content of phenyl residues in the composition and by the synergistic effect of phosphorus and nitrogen. A brief study of the curing kinetics disclosed the complex nature of the reaction. An accurate two-step model is obtained using the extended Prout–Tompkins equation for both steps.

Effect of acetylacetone metal salts on curing mechanism and thermal stability of polybenzoxazine

To overcome high water absorption of inorganic metal salts and their poor compatibility with resin, acetylacetone metal salts (M(acac) n) were selected as the catalysts of benzoxazine resin. Their effects on the catalytic activity, structure, and thermal stability of polybenzoxazine had been estimated by dynamic differential scanning calorimetry, in situ Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and thermal gravimetric analyzer. The results revealed that M(acac) n of iron (Fe3+), cobalt (Co3+ and Co2+), and copper (Cu2+) exhibited high catalytic activity and reduced evidently activation energy, especially acetylacetone iron salt. The addition of M(acac) n was beneficial to the formation of Ph–N–Ph structure, which was easy to form a denser carbon layer during thermal degradation, prevented heat transfer and further decomposition of the resin, and finally led to the increase of carbon residue at high temperature.

Cerium Salts: An Efficient Curing Catalyst for Benzoxazine Based Coatings

The effect of three different cerium salts (Ce(NO3)3.6H2O, CeCl3.7H2O and Ce(OOCCH3)3.5H2O) on the ring-opening polymerization (ROP) of a model diamine-based benzoxazine (4EP-pPDA) was investigated. With the incorporation of the cerium salts, the curing temperature of 4EP-pPDA is reduced substantially, and the glass transition temperatures of the resulting networks are increased significantly. The three cerium salts exhibit different catalytic activities, which were analyzed by FT-IR, NMR, and energy-dispersive X-ray (EDX). Ce(NO3)3.6H2O was found to exhibit the best catalytic effect, which seems to be related to its better dispersibility within 4EP-pPDA benzoxazine precursors.

In(NO3)3 catalyzed curing reaction of benzoxazine

Benzoxazine is a new kind of thermoset resin with excellent properties, but it suffers from high curing temperature and low char yield in the presence of catalyst without halogen. In(NO3)3 was herein used for the first time to efficiently catalyze the curing reaction of benzoxazine and to elevate the char yield at 800°C. The reaction of benzoxazine was catalyzed by In(NO3)3 after stirring at 35°C for 300 min, and the initial curing temperature decreased to 151°C. Polybenzoxazine/In(NO3)3 showed higher thermal stability and char yield at 800°C (increased by 7.5%) compared with those of polybenzoxazine. The possible pathway of coordination bonding between In3+ and benzoxazine was proposed. In the cross-linking process, two different structures, that is, the N, O-acetal bridge structure and arylamine Mannich bridge structure formed at 35°C, both existed, which ultimately affected the thermal stability of the cured product.

Cyanuric chloride as a potent catalyst for the reduction of curing temperature of benzoxazines

Cyanuric chloride (2,4,6-trichloro-1,3,5-triazine, TCT) was used as a catalyst to lower the ring opening polymerization (ROP) temperature of 1,3-benzoxazines.

One-Pot Synthesis of Amide-Functional Main-Chain Polybenzoxazine Precursors

Main-chain polybenzoxazines containing amide linkages were successfully prepared in one pot. Three different polymers were synthesized by reacting 3,4-dihydrocoumarine (DHC) and paraformaldehyde with 1,3-diaminopropane or 1,6-diaminohexane or Jeffamine ED-900. The one-pot reaction proceeded through the combination of the ring-opening of DHC with amines, and subsequent Mannich and ring-closure reactions occurring in a cascading manner. The obtained polymer from Jeffamine exhibited good film-forming properties, and free-standing flexible films were easily solvent- casted on Teflon plates. All polymeric precursors were characterized by spectroscopic analysis, and their curing behavior and thermal stability were investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA).

Coumarines as masked phenols for amide functional benzoxazines

Benzoxazines with amide linkages were successfully prepared from 3,4-dihydrocoumarine using either one-pot or stepwise pathways.

Development of Hydrogen-Rich Benzoxazine Resins with Low Polymerization Temperature for Space Radiation Shielding

A systematic study has been carried out to develop a material with significant protection properties from galactic cosmic radiation and solar energetic particles. The research focused on the development of hydrogen-rich benzoxazines, which are particularly effective for shielding against such radiation. Newly developed benzoxazine resin can be polymerized at 120 °C, which meets the low-temperature processing requirements for use with ultrahigh molecular weight polyethylene (UHMWPE) fiber, a hydrogen-rich composite reinforcement. This highly reactive benzoxazine resin also exhibits low viscosity and good shelf-life. The structure of the benzoxazine monomer is confirmed by proton nuclear magnetic resonance and Fourier transform infrared spectroscopy. Polymerization behavior and thermal properties are evaluated by differential scanning calorimetry and thermogravimetric analysis. Dynamic mechanical analysis is used to study chemorheological properties of the benzoxazine monomer, rheological properties of the cross-linked polybenzoxazine, and rheological properties of UHMWPE-reinforced polybenzoxazine composites. The theoretical radiation shielding capability of the composite is also evaluated using computer-based simulations.

Ring-Opening Polymerization of 1,3-Benzoxazines via Borane Catalyst

Tris(pentafluorophenyl)borane was used as Lewis acid catalyst to lower the ring opening polymerization temperature (ROP) of 1,3-benzoxazines. Dynamic scanning calorimeter studies revealed that on-set ROP temperatures were decreased as much as 98 °C for model benzoxazine compounds. Catalytic polymerization was traced by both FTIR and ¹H NMR, and revealed that tris(pentafluorophenyl)borane acted rapidly and fast curing achieved. Moreover, thermal properties of resulting polybenzoxazines were investigated by thermogravimetric analysis (TGA) and found out that the catalyst has high impact on char yield and even 3 mol % catalyst augmented char yields up to 13%.

Combining benzoxazine and ketene chemistries for self-healing of high performance thermoset surfaces

The use of oxoketene chemistry for self-healable polybenzoxazines is described.