Synthesis of Daidzein and Thiophene Containing Benzoxazine Resin and Its Thermoset and Carbon Material

In this work, a novel bio-based high-performance bisbenzoxazine resin was synthesized from daidzein, 2-thiophenemethylamine and paraformaldehyde. The chemical structure was confirmed using nuclear magnetic resonance spectroscopy (NMR) and Fourier-transform infrared spectroscopy (FT-IR). The polymerization process was systematically studied using differential scanning calorimetry (DSC) and in situ FT-IR spectra. It can be polymerized through multiple polymerization behaviors under the synergistic reaction of thiophene rings with benzopyrone rather than a single polymerization mechanism of traditional benzoxazines, as reported. In addition, thermogravimetric analysis (TGA) and a microscale combustion calorimeter (MCC) were used to study the thermal stability and flame retardancy of the resulting polybenzoxazine. The thermosetting material showed a high carbon residue rate of 62.8% and a low heat release capacity (HRC) value of 33 J/gK without adding any flame retardants. Based on its outstanding capability of carbon formation, this newly obtained benzoxazine resin was carbonized and activated to obtain a porous carbon material doped with both sulfur and nitrogen. The CO₂ absorption of the carbon material at 0 °C and 25 °C at 1 bar was 3.64 mmol/g and 3.26 mmol/g, respectively. The above excellent comprehensive properties prove its potential applications in many advanced fields.

Sesamol-based polybenzoxazines for ultra-low-k, high-k and hydrophobic coating applications

Sesamol-based polybenzoxazines, their dielectric behavior, and superhydrophobic properties for microelectronic insulation applications.

Synthesis and characterization of chalcone based benzoxazine-magnetite nanocomposites

Here, we proposed an approach to develop magnetic chalcone based benzoxazine using different contents of magnetite nanoparticles. A chalcone containing benzoxazine was prepared from 3-(4-hydroxyphenyl)-1-phenylprop-2-en-1-one), stearyl amine and paraformaldehyde through Mannich condensation reaction in a cosolvent of ethanol/toluene (1/1)(v/v). The chemical structure of the prepared benzoxazine monomer was confirmed by FTIR and 1H NMR. Both monomer and monomer mixed with different contents of magnetite were exposed to UV irradiation to induce dimerization via [2p + 2p] cycloaddition followed by thermal curing of oxazine moiety. The crystal structure of magnetite nanoparticles was studied by X-ray diffraction (XRD) analysis. Scanning electron microscope (SEM) was used to examine the surface morphology of the resulted materials. The average size of magnetite nanoparticles was determined by transmission electron microscope (TEM) to be 30–40 nm. The magnetization properties of these materials were measured by vibrating sample magnetometer (VSM). The thermal properties of thermosets were evaluated and compared with nanocomposites using TGA and DSC. The thermosets exhibited good thermal stability and improved with increasing the magnetite contents in the feed.

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.

Benzoxazine Formation Mechanism Evaluation by Direct Observation of Reaction Intermediates

Benzoxazine formation is a fundamental step in the preparation of polybenzoxazine resins, and a detailed description of the mechanism governing the formation of benzoxazine and side products is vital for improving the properties and performance of these resins. Determination of the nature and properties of reaction intermediates is not trivial. Therefore, a Mannich-type condensation of aniline, formaldehyde, and phenol was evaluated as a potential method to form benzoxazine. Coupling positive mode electrospray ionization mass spectrometry (ESI(+)-MS) with infrared multiple photon dissociation (IRMPD) spectroscopy allowed unambiguous determination of an iminium-based mechanism and the direct observation of iminium intermediates. The benzoxazine formation mechanism was indirectly confirmed by the observation of side products that are relevant to the polymerization step, and directly confirmed by the identification of four distinct reaction intermediates that were completely characterized by IRMPD spectroscopy. The benzoxazine monomer was also shown to undergo isomerization under standard ESI-MS analysis conditions, suggesting the presence of a mixture of three isomers during their usual ESI-MS analysis.

Well-defined benzoxazine/triphenylamine-based hyperbranched polymers with controlled degree of branching

Well-defined thermally polymerizable hyperbranched polymers (TPA–BZs) containing various numbers of triphenylamine (TPA) and benzoxazine (BZ) units have been prepared using a “click-like” reaction concept, through one-pot Mannich condensations of 4-(bis(4-aminophenyl)amino)phenol (TPA–2NH₂–OH, as the AB₂ branching groups), aniline (as the focal groups), CH₂O, and phenol in 1,4-dioxane, with a unique feeding approach. Two design strategies for the chemical construction were applied: (i) simple hyperbranched TPA–BZs, such as those containing one or three TPA units, developed from the focal or the terminal group direction to form the resultant monomers; (ii) three dendritic TPA–BZs containing four TPA units possessing different degrees of branching (DBs) for the conformation study. The exothermic temperature for the dendritic TPA–BZs decreased upon increasing the DB. The bathochromic shifts of the dendritic TPA–BZs increased upon increasing the number of TPA units, in UV-Vis absorption and PL emission spectra, presumably because of an increase in the effective conjugation length. In addition, the polymerized dendritic TPA–BZ DG1 possessed thermal properties superior to those of the hyperbranched TPA–BZ polybenzoxazines, possibly because the segmental mobility in the polymer network was restricted by the dendrimer core group and because of its symmetrical construction. The hyperbranched TPA–BZ possessed unique photophysical properties, suggesting potential applications in optoelectronic devices.

Different well-defined benzoxazine/triphenylamine based hyperbranched polymers with controlled degree of branching were prepared and discussed.

Synthesis of a Bisbenzylideneacetone-Containing Benzoxazine and Its Photo- and Thermally Cured Thermoset

A bis(4-hydroxybenzylidene)acetone/aniline-based benzoxazine (BHBA-a) was prepared from a bisbenzylidene-containing bisphenol, bis(4-hydroxybenzylidene)acetone (BHBA), aniline, and paraformaldehyde through Mannich condensation in a cosolvent of toluene/ethanol (2:1, v/v). The structure of BHBA-a was successfully confirmed by Fourier transform infrared and ¹H and ¹³C NMR spectra. According to the differential scanning calorimetry (DSC) thermogram of BHBA, an immediate exothermic peak after the melting peak was observed, suggesting that BHBA is thermally active. NMR data of thermally treated BHBA confirm that the immediate exothermic peak after melting of BHBA in the DSC thermogram is resulted from the curing of a double bond. UV and ¹H NMR spectra of BHBA-a show that the bisbenzylideneacetone moiety underwent dimerization through the [2π + 2π] cycloaddition. Therefore, two procedures were applied to cure BHBA-a. The first one was thermal curing of the double bond of bisbenzylideneacetone and oxazine moieties. The second one was photocuring of the bisbenzylideneacetone moiety, followed by thermal curing of the oxazine moiety. The thermal properties of thermosets were evaluated based on these two procedures. Thermosets of BHBA-a exhibit T _g as high as 318 °C for curing procedure 1 and 342 °C for curing procedure 2. These values are much higher than that of a traditional bisphenol/aniline-based benzoxazine thermoset. We conclude that the thermal curing of the double bond of bisbenzylideneacetone and photodimerization of bisbenzylideneacetone contributes to the good thermal properties.

Benzoxazine/Triphenylamine-Based Dendrimers Prepared through Facile One-Pot Mannich Condensations

A series of thermally polymerizable dendrimers of various generations, equipped with triphenylamine (TPA) and benzoxazine (BZ) groups, is synthesized through facile one-pot Mannich condensations of N¹ ,N¹ -bis(4-aminophenyl)benzene-1,4-diamine (TPA-3NH₂ , as the core group), 4-(bis(4-aminophenyl)amino)phenol (TPA-2NH₂ -OH, as the AB₂ branching group), and CH₂ O in 1,4-dioxane. The ratios of the integrated areas in the ¹ H nuclear magnetic resonance spectra of these dendrimers are consistent with the theoretical numbers of protons, suggesting their successful syntheses. Bathochromic shifts of signals are evident in the UV-vis and photoluminescence spectra upon increasing the generation of the TPA-BZ dendrimers, consistent with an increase in the effective conjugation length. The TPA-BZ dendrimers are able to undergo thermal polymerization and display unique optical physical properties, resulting in thermoset TPA networks after thermal ring-opening polymerization.

Coumarin- and Carboxyl-Functionalized Supramolecular Polybenzoxazines Form Miscible Blends with Polyvinylpyrrolidone

In this study, we synthesized a novel multifunctional benzoxazine monomer (Coumarin-COOH BZ), possessing both coumarin and COOH groups, through the reaction of 4-methyl-7-hydroxycoumarin, 4-aminobenzoic acid, and paraformaldehyde in 1,4-dioxane, with the structure confirmed using ¹H and 13C nuclear magnetic resonance and Fourier transform infrared (FTIR) spectroscopy. Differential scanning calorimetry (DSC), FTIR spectroscopy, and thermogravimetric analysis were then employed to monitor the thermal curing behavior of Coumarin-COOH BZ and its blends with poly(N-vinyl-2-pyrrolidone) (PVP), both before and after photodimerization of the coumarin moieties. DSC revealed a single glass transition temperature for each Coumarin-COOH BZ/PVP blend composition; a large positive deviation based on the Kwei equation suggested that strong hydrogen bonding existed between the Coumarin-COOH BZ and PVP segments, confirmed through FTIR spectroscopic analyses. The thermal properties improved (i.e., increased glass transition and thermal degradation temperatures) as a result of the increased crosslinking density after photodimerization under UV exposure.

Light-switchable nanoparticles based on amphiphilic diblock, triblock and heterograft polyoxazoline

Photo-active nanoparticles (NP_D, NP_T, NP_H) were elaborated in water from amphiphilic diblock (D), triblock (T) and heterograft (H) copolymers based on a chromatic unit, coumarin, linked to an alkyl chain and a hydrophilic polyoxazoline chain.

Photo-sensitive benzoxazine II: chalcone-containing benzoxazine and its photo and thermal-cured thermoset

Chalcone-containing benzoxazine (BHP-a) was synthesized. Two procedures were applied to cure BHP-a, thermal curing of chalcone and oxazine moieties. Another one was photo curing the chalcone moiety, followed by thermal curing of the oxazine moiety.

Directly synthesized nitrogen-doped microporous carbons from polybenzoxazine resins for carbon dioxide capture

Highly ordered nitrogen-doped microporous carbons as CO₂ capturers from the cyano-functional benzoxazine monomer through thermal curing, carbonization, and KOH activation.

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.