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.

Synthesis, characterization, and properties of a novel aromatic ester-based polybenzoxazine

Polybenzoxazines with molecular design flexibility have excellent properties by using suitable raw materials. A new benzoxazine monomer terephthalic acid bis-[2-(6-methyl-4H-benzo[e][1,3]oxazin-3-yl)]ethyl ester (TMBE) with bis-ester groups has been synthesized from the simple esterification reaction of terephthaloyl chloride and 2-(6-methyl-4H-benzo[e][1,3]oxazin-3-yl)-ethanol (MB-OH). The chemical structure of TMBE was characterized by Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance spectroscopy (¹H-NMR, ¹³C-NMR). Polymerization behavior of TMBE was studied by differential scanning calorimetry (DSC) and FT-IR after each cure stage. The cross-linked polybenzoxazine (PTMBE) gave a transparent film through the thermal casting method. The dynamic mechanical analysis of PTMBE showed that the T_g was 110 °C. Thermogravimetric analysis reveals better thermal stability as evidenced by the 5% and 10% weight-loss temperatures (T_d5 and T_d10) of PTMBE, which were 263 and 289 °C, respectively, with a char yield of 27% at 800 °C. The tensile test of the film revealed that the elongation at break was up to 14.2%.

A novel benzoxazine monomer contain ester group was obtained by an indirect molecular design method. Its polymer showed excellent flexibility.

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).

Outstanding dielectric and thermal properties of main chain-type poly(benzoxazine-co-imide-co-siloxane)-based cross-linked networks

A high performance cross-linked polymer with a very low dielectric constant was achieved via a newly designed main-chain type poly(benzoxazine-co-imide-co-siloxane).

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.

Combining polybenzoxazines and polybutadienes via simultaneous inverse and direct vulcanization for flexible and recyclable thermosets by polysulfide dynamic bonding

Simultaneous inverse and direct vulcanization of a benzoxazine and a polybutadiene gave recyclable films through dynamic S–S bonding.

Synthesis and Crosslinking of Polyether-Based Main Chain Benzoxazine Polymers and Their Gas Separation Performance

The poly(ethylene glycol)-based benzoxazine polymers were synthesized via a polycondensation reaction between Bisphenol-A, paraformaldehyde, and poly(ether diamine)/(Jeffamine^®). The structures of the polymers were confirmed by proton nuclear magnetic resonance spectroscopy (¹H-NMR), indicating the presence of a cyclic benzoxazine ring. The polymer solutions were casted on the glass plate and cross-linked via thermal treatment to produce tough and flexible films without using any external additives. Thermal properties and the crosslinking behaviour of these polymers were studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Single gas (H₂, O₂, N₂, CO₂, and CH₄) transport properties of the crosslinked polymeric membranes were measured by the time-lag method. The crosslinked PEG-based polybenzoxazine membranes show improved selectivities for CO₂/N₂ and CO₂/CH₄ gas pairs. The good separation selectivities of these PEG-based polybenzoxazine materials suggest their utility as efficient thin film composite membranes for gas and liquid membrane separation technology.

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

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

Recycling and Self-Healing of Polybenzoxazines with Dynamic Sulfide Linkages

In this work, a recycling and self-healing strategy for polybenzoxazines through both S-S bond cleavage-reformation reaction and supramolecular attractions is described. Both recyclable and self-healable polybenzoxazines can be prepared from low cost chemicals with a simple procedure in only 30 minutes. For this purpose, inverse vulcanization of poly(propylene oxide)benzoxazine (PPOB) and diallybenzoxazine (B-al) with elemental sulfur was performed at 185 °C. The obtained cross-linked polymer films exhibited thermally driven recycling ability up to 5 cycles. Moreover, the self-healing ability of a test specimen was shown. Spectral characterizations, thermal stability and fracture toughness of the films were investigated after each recycling.

Synthesis of self-curable polysulfone containing pendant benzoxazine units via CuAAC click chemistry

Synthesis, characterization, and properties of new thermally curable polysulfone containing benzoxazine moieties in the side chain were investigated. First, chloromethylation and subsequent azidation processes were performed to form polysulfone containing pendant clickable azide groups. Independently, antagonist 3,4-dihydro-3-(prop-2-ynyl)-2H-benzoxazine was prepared by using paraformaldehyde, phenol and propargylamine. The following copper(I) catalyzed azide-alkyne cycloaddition click reaction was applied to obtain self-curable polysulfone with pendant benzoxazine units. The polymer and intermediates at various stages were characterized by ¹H-NMR, ¹³C-NMR and FT-IR spectroscopies. The thermal properties and curing behavior of final polymer were investigated by differential scanning calorimetry and thermal gravimetric analysis. Compared to the neat polysulfone, the obtained polymers exhibited thermally more stable polymers.

Polybenzoxazine/Polyhedral Oligomeric Silsesquioxane (POSS) Nanocomposites

The organic/inorganic hybrid materials from polyhedral oligomeric silsesquioxane (POSS, inorganic nanoparticles) and polybenzoxazine (PBZ) have received much interesting recently due to their excellent thermal and mechanical properties, flame retardance, low dielectric constant, well-defined inorganic framework at nanosized scale level, and higher performance relative to those of non-hybrid PBZs. This review describes the synthesis, dielectric constants, and thermal, rheological, and mechanical properties of covalently bonded mono- and multifunctionalized benzoxazine POSS hybrids, other functionalized benzoxazine POSS derivatives, and non-covalently (hydrogen) bonded benzoxazine POSS composites.

Effect of phenol on the synthesis of benzoxazine

The kinetic parameters of benzoxazine synthesis approximately equaled those of phenol consumption revealing that phenol was the key starting material.

A curing system of benzoxazine with amine: reactivity, reaction mechanism and material properties

In addition to providing an acceleration effect on curing, suitable amines react with benzoxazine to form desired structures and improve the materials properties of the cured resins.

Synthesis and properties of main-chain oligomeric benzoxazine precursor containing cyclotriphosphazene units

A linear oligobenzoxazine precursor with cyclotriphosphazene ring was prepared through the Schiff base route. The resulting polymers showed higher molecular weight and better thermal stability than those from the traditional Mannich polycondensation method. The oligomeric benzoxazine precursor can form a high-quality transparent yellow film; however, it was fragile after being cured. In order to identify the effect of end groups on the cured polymer, an aniline-capped polymer was prepared by the same Schiff base method and then was changed into a benzoxazine end group. The results indicated that the uncapped polymer exhibited higher stability than the capped polymer. This can be ascribed to different chemical structures resulting from different end groups.

A simple method to introduce phosphoester groups into a polybenzoxazine backbone as multifunctional modifiers

Phosphoester groups were conveniently introduced into benzoxazine monomers by chemical bonding through nucleophilic reaction of a benzoxazine ring with diethyl phosphite (DEP).

Synthesis of novel furan-containing tetrafunctional fluorene-based benzoxazine monomer and its high performance thermoset

Synthesis of novel furan-containing tetrafunctional fluorene-based benzoxazine monomer and its high performance thermoset.

Dendritic organic–inorganic hybrid polyphenol and branched benzoxazine monomers with low curing temperature

A novel dendritic organic–inorganic hybrid polyphenol (T2) based on cyclotriphosphazene was synthesized by the condensation reaction of T1 and phenol catalysed by phosphotungstic acid.