Synthesis, curing behavior and thermal properties of fluorene containing benzoxazines

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.

Ethynylene-linked multifunctional benzoxazines: effect of ethynylene group and packing on thermal behavior

Benzoxazine is a promising next-generation thermosetting resin featuring catalyst-free curing, high thermal stability, and low volume shrinkage upon curing. Mono-, di- and tri-functional benzoxazines, 3-(4-(phenylethynyl)phenyl)-3,4-dihydro-2H-[1,3]benzoxazine (1), 1,4-bis((4-(2H-3(4H)-[1,3]benzoxazinyl)phenyl)ethynyl)benzene (2) and 1,3,5-tris((4-(2H-3(4H)-[1,3]benzoxazinyl)phenyl)ethynyl)benzene...

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.

Propargylamine: an attractive amine source for designing high-performance benzoxazine resins with low polymerization temperatures

A series of benzoxazine resins using propargylamine as the amine source were synthesized to achieve highly thermally stable thermosets with low polymerization temperatures.

Synthesis of thioamide containing polybenzoxazines by the Willgerodt–Kindler reaction

Benzoxazines with thioamide linkages were successfully prepared by the Willgerodt–Kindler route.

Design of High-Performance Polybenzoxazines with Tunable Extended Networks Based on Resveratrol and Allyl Functional Benzoxazine

A novel resveratrol-based bio-benzoxazine monomer (RES-al) containing an allyl group has been synthesized using resveratrol, allylamine, and paraformaldehyde via Mannich condensation reaction, and its chemical structures have been characterized by FT-IR spectroscopy and NMR techniques. The polymerization behavior of this benzoxazine resin has been investigated using in situ FT-IR and differential scanning calorimeter (DSC) measurements, and the thermal-mechanical properties of its corresponding polybenzoxazines are evaluated by DMA and TGA. We show that by controlling the curing process of the oxazine ring, the C=C bond in resveratrol, and the allyl group in RES-al, the cross-linking network of the polybenzoxazine can be manipulated, giving rise to tunable performance of thermosets. As all curable functionalities in RES-al are polymerized, the resulted polybenzoxazine exhibits a good thermal stability with a Tg temperature of 313 °C, a T_d5 value of 352 °C, and char yield of 53% at 800 °C under N₂.

Synthesis and thermal properties of phenol- and amine-capped main-chain benzoxazine oligomers with multiple methyl substitutions

A series of main-chain benzoxazine oligomers with different methyl substitutions are successfully synthesized. Chemical structures are analyzed by Fourier transform infrared spectroscopy, proton nuclear magnetic resonance spectroscopy, and gel permeation chromatography. Effects of methyl substitutions on chemical shifts of protons in oxazine ring and thermal properties, including glass transition temperature, thermal stability, and char yield, are discussed. The influences of methyl substitutions on different positions are demonstrated: (i) substitution on phenols induces obvious increase in curing temperature while substitution on amine does not show apparent impact; (ii) substitution at different positions results in T g variation, following the sequence of none-substitution > substitution at end-capping > substitution on diamines in main-chain > substitution on bisphenols in main-chain; and (iii) substitution at end-capping would cause apparent deterioration in thermal stability while substitution on diamines in main-chain would benefit thermal stability and char yield. Experimental results and related explanations are provided in detail.

A naringenin-based benzoxazine with an intramolecular hydrogen bond as both a thermal latent polymerization additive and property modifier for epoxy resins

Epoxy resins are constantly attracting attention from industrial applications due to their excellent comprehensive properties. However, the traditional curing agents for liquid epoxy resins react with epoxides even at room temperature, which causes difficulties in processing since such mixtures cannot be directly used as single-component materials. In order to improve the shelf life of the mixtures, we have designed an intramolecular hydrogen bond-containing benzoxazine monomer as a smart thermal latent polymerization agent for epoxy resins. The newly obtained benzoxazine, NAR-a, has been synthesized from the Mannich condensation of naringenin, aniline and paraformaldehyde. In addition to playing the role of a curing agent, NAR-a has also performed as an excellent property modifier for epoxy thermosetting systems. The resulting thermoset based on the NAR-a/epoxy thermosetting system exhibits high thermal stability and good intrinsic flame retardance, with a T _g temperature of 201 °C, a T _d5 temperature of 349 °C, a low CET value (32.4 ppm per °C) and low heat release capacity (HRC of 159.1 J g^-1 K^-1). The combined long-term storage stability and versatility of the intramolecular hydrogen bond-containing benzoxazine/epoxy system provide a new strategy for the development of one-component epoxy-related thermosetting resins for application in high-performance areas.

Easily Processable Thermosets with Outstanding Performance via Smart Twisted Small-Molecule Benzoxazines

High-performance aromatic polymers have excellent thermal, mechanical, and electrical properties and are lightweight, but it is highly challenging to deliver outstanding performances while still maintaining good processability of the precursors. Here, a new family of small-molecule benzoxazine resins with ortho-maleimide functionality is reported, which strikes an exceptional balance between the processability and performance. The excellent processability is attributed to the twisted molecular configurations of ortho-maleimide-substituted benzoxazines, which prevent intermolecular packing in the resin systems. The new benzoxazines can polymerize through multiple routes, which eliminate the twisted structures and create highly cross-linked polymer networks. The resulting new polymers are found to possess fascinating properties such as a high thermal stability (no T_g can be detected before 400 °C), excellent flame retardancy (a heat release capacity of 42.5 J g^-1 K^-1 ), and low dielectric constants (2.62-2.30 in the frequency range of 1 Hz to 10 MHz). The combined processability and versatility highlight the potential of smart benzoxazines in the preparation of high-performance thermosets, with important new applications that may span aerospace, transportation, and electronic packaging materials.

An apigenin-based bio-benzoxazine with three polymerizable functionalities: sustainable synthesis, thermal latent polymerization, and excellent thermal properties of its thermosets

An apigenin-based benzoxazine exhibiting a thermal latent polymerization behavior, high thermal stability and low flammability has been synthesized from sustainable resources.

Synthesis of novel allylamine-fluorene based benzoxazine and its copolymerization with typical benzoxazine: curing behavior and thermal properties

Poly(t-BF-sa-a) showed much better thermal properties and glass transition temperatures than traditional fluorene-based benzoxazine monomers.

Synthesis and characterization of siloxane-containing benzoxazines with high thermal stability

To understand the influence of phenyl substituents on silicon and to improve the glass transition temperature ( T g) and thermal stability, phenol/bis ( p-aminophenoxyl) dimethylsiloxane-based benzoxazine (P-adms), phenol/bis ( p-aminophenoxyl) methylphenylsiloxane-based benzoxazine (P-amps), and phenol/bis ( p-aminophenoxyl) diphenylsiloxane-based benzoxazine (P-adps) were designed and synthesized. The structure of the siloxane-containing benzoxazines were confirmed by proton and carbon nuclear magnetic resonance imaging and Fourier transform infrared spectra. The curing reaction of the obtained benzoxazines was studied by differential scanning calorimetry (DSC) and in situ infrared spectra. The influence of the aromatic content on the T g and thermal stability were investigated by modulated DSC and thermogravimetric analysis. Compared to aminopropylsiloxane-based benzoxazines, the bis ( p-aminophenoxyl) siloxane-based benzoxazines possessed relatively higher T g about 140°C due to the replacement of flexible propyl chain by phenoxyl chain. With increasing phenyl substituents on silicon, the polybenzoxazines possessed lower T g and higher thermal stability. It is notedthat the phenol/bis ( p-aminophenoxyl) diphenylsiloxane-based benzoxazine (P-adps) still has low viscosity despite high aromatic content due to the flexible ether linkage (Ar–O–Si).

Synthesis and thermal properties of silicon-containing benzoxazine

A novel benzoxazine, containing silicon (Si) in the main chain and bonded to two benzene ring, was synthesized from aniline, bis( p-hydroxyphenyl)dimethylsilane, and paraformaldehyde. The structure was characterized by proton nuclear magnetic resonance and Fourier transform infrared (FTIR) spectra. The curing behavior of the benzoxazine was evaluated by differential scanning calorimeter and in situ FTIR. The thermal stability of the resulting polybenzoxazine was studied by thermogravimetric analysis under nitrogen and air atmospheres. The results indicated that the Si-containing polybenzoxazine possessed significantly higher initial degradation temperature and char yield than conventional bisphenol A/aniline-based polybenzoxazine.

Effects of End-Caps on the Atropisomerization, Polymerization, and the Thermal Properties of ortho-Imide Functional Benzoxazines

A new type of atropisomerism has recently been discovered in 1,3-benzoxazines, where the intramolecular repulsion between negatively charged oxygen atoms on the imide and the oxazine ring hinders the rotation about the C⁻N bond. The imide group offers a high degree of flexibility for functionalization, allowing a variety of functional groups to be attached, and producing different types of end-caps. In this work, the effects of end-caps on the atropisomerism, thermally activated polymerization of ortho-imide functional benzoxazines, and the associated properties of polybenzoxazines have been systematically investigated. Several end-caps, with different electronic characteristics and rigidities, were designed. ¹H and 13C nuclear magnetic resonance (NMR) spectroscopy and density functional theory (DFT) calculations were employed to obtain structural information, and differential scanning calorimetry (DSC) and in situ Fourier transform infrared (FT-IR) spectroscopy were also performed to study the thermally activated polymerization process of benzoxazine monomers. We demonstrated that the atropisomerization can be switched on/off by the manipulation of the steric structure of the end-caps, and polymerization behaviors can be well-controlled by the electronic properties of the end-caps. Moreover, a trade-off effect were found between the thermal properties and the rigidity of the end-caps in polybenzoxazines.

Examining the effect of hydroxyl groups on the thermal properties of polybenzoxazines: using molecular design and Monte Carlo simulation

The influence of methylol and phenolic hydroxyl on the thermal properties of polybenzoxazines has been studied using two monofunctional benzoxazine monomers synthesized from para methylol-/ethyl- phenol, aniline and paraformaldehyde. The chemical structures of the synthesized monomers are confirmed by ¹H nuclear magnetic resonance (NMR), ¹³C NMR and Fourier transform infrared spectroscopy (FT-IR). Polymerizations are monitored by differential scanning calorimetry (DSC). The glass transition temperature (T _g) of each polybenzoxazine is measured by DSC as well as dynamic mechanical analysis (DMA), indicating the greatly increased T _g via incorporation of methylol functionality into benzoxazine moiety. Monte Carlo simulations are also applied to further investigate the underlying structure-property relationship between intermolecular hydrogen-bonding network originating from different types of hydroxyl groups and thermal properties of polybenzoxazines. The agreement between the experimental and simulation results provide us with a fundamental understanding of the designing roles in highly thermally stable polybenzoxazines.

Phosphorus-containing polymers from THPS. IV: Synthesis and properties of phosphorus-containing polybenzoxazines as a green route for recycling toxic phosphine (PH3) tail gas

A convenient route to convert the highly toxic phosphine (PH₃) tail gas into high-performance polybenzoxazines was first described in this paper. Two aliphatic polyamines, namely tris(aminomethyl)phosphine oxide and bis(aminomethyl)phenylphosphine oxide, were synthesized from tetrakis(hydroxymethyl)phosphonium sulfate (THPS), a green derivative of PH₃ tail gas. And then two novel phosphorus-containing benzoxazine monomers, tris(3,4-dihydro-2H-1,3-benzoxazin-3-yl-methyl)phosphine oxide (TBOz) and benzylbis(3,4-dihydro-2H-1,3-benzoxazin-3-yl-methyl) phosphine oxide (BBOz) were prepared by three-steps procedure. FT-IR and DSC technologies were adopted to study the thermal-initiated polymerization behaviors of two benzoxazine monomers. Thermal properties of these crosslinked polymers were studied by TGA and DMA. The results display that the polybenzoxazines (PTBOz and PBBOz) exhibite good thermal stabilities and high glass transition temperatures. The char yield of polybanzoxazine is high as 47% and indiactes that phosphorus-containing polybenzoxazines show high fire-retardancy. The surface free energies of the PTBOz and PBBOz are 37.1 and 40.4mJm^-2 by Owens two-liquid method. The dielectric properties of the PTBOz and PBBOz remaine near constant in the experimental frequency range.

Study on thermal degradation mechanism of a cured aldehyde-functional benzoxazine

Thermal degradation mechanism of a cured aldehyde-functional benzoxazine.

A novel high performance oxazine derivative: design of tetrafunctional monomer, step-wise ring-opening polymerization, improved thermal property and broadened processing window

A novel tetrafunctional oxazine monomer containing benzoxazine and fluorene-oxazine was prepared for the first time using a Mannich condensation reaction of 2,7-dihydroxy-9,9-bis-(4-hydroxyphenyl)fluorene with paraformaldehyde and n-butylamine.

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.