Synthesis, curing behavior and thermal properties of fluorene containing benzoxazines

A series of difunctional fluorene-based benzoxazine monomers were synthesized from the reaction of 9,9-bis-(4-hydroxyphenyl)-fluorene with formaldehyde and primary amines including aniline, o-toluidine, n-butylamine, and n-octylamine. Their chemical structures were confirmed by FT-IR, ¹H and ¹³C NMR analyses. The curing behaviors of the precursors were monitored by differential scanning calorimetry (DSC) and FT-IR. The thermal properties of cured polymers were evaluated with DSC and thermogravimetric analysis (TGA). The fluorene-based polybenzoxazines show the typical curing characteristic of oxazine ring-opening for difunctional benzoxazines centred at 231-250 °C, and remarkably higher glass transition temperature and better thermal stability ascribed to the high rigidity, high aromatic content, and intermolecular and intramolecular hydrogen bonding. The thermal decomposition temperature and char yield of aromatic amine-fluorene-based polybenzoxazines are much higher than those of aliphatic amine-based polybenzoxazines.     

双官能度手性和消旋苯并噁嗪的合成及热性能研究

采用无溶剂法合成了新型双酚A和双酚AF(六氟双酚A)基手性和消旋苯并噁嗪单体,利用红外光谱(FTIR)、核磁共振氢谱(1H-NMR)、旋光仪和高效液相色谱(HPLC)对单体结构和性质进行了表征,通过差式扫描量热仪(DSC)和热重分析仪(TGA)对苯并噁嗪的固化行为及聚合物的热性能进行了研究.结果表明,无溶剂法合成苯并噁嗪单体具有反应速度快、产率高、对环境友好等特点;双官能度消旋苯并噁嗪单体由内消旋和外消旋异构体组成,且内消旋苯并噁嗪单体含量高于外消旋;手性和消旋苯并噁嗪单体具有相同的开环聚合行为;由于消旋苯并噁嗪分子的立体构型不同,使得聚苯并噁嗪的自由体积减小,分子链的堆积更加致密,因而消旋聚苯并噁嗪的玻璃化转变温度(Tg)和热稳定性均高于手性聚苯并噁嗪和传统的双酚A-苯胺型聚苯并噁嗪;此外,C—F键具有高的解离能,因而双酚AF基聚苯并噁嗪的热性能显著提高.     

Cyclohexane and phosphorus based benzoxazine-bismaleimide hybrid polymer matrices: thermal and morphological properties

Benzoxazine monomers namely 1,1-bis (3-methyl-4-hydroxyphenyl)cyclohexane benzoxazine (CB_DDM) and bis(4-maleimidophenyl) triphenylphosphine oxide benzoxazine (BMPB_BAPPPO) were synthesized and blended with bismaleimide (BMPM) to improve thermal properties of polybenzoxazine. The benzoxazine- bismaleimide (Bz-BMI) hybrid polymer matrices were prepared via in-situ polymerization and their thermal and morphological properties were studied. The chemical reaction of benzoxazines with the bismaleimide was carried out thermally and the resulting product was analyzed by FT-IR spectra. The glass transition temperature, curing behavior, thermal stability, char yield and flame resistance of the hybrid polymer matrices were analyzed using DSC and TGA. The homogeneous structure of the hybrid polymer matrices was determined by SEM and visual observations. Data obtained from thermal studies infer that these hybrid materials possess high thermal stability which can be used as adhesives, sealants, coating and matrices for high performance automobile and microelectronic applications.     

Synthesis, curing kinetics and thermal properties of bisphenol-AP-based benzoxazine

A novel bisphenol-AP-aniline-based benzoxazine monomer (B-AP-a) was synthesized from the reaction of 4,4′-(1-phenylethylidene) bisphenol (bisphenol-AP) with formaldehyde and aniline. The chemical structures were identified by FT-IR, ¹H and ¹³C NMR analyses. The polymerization behavior of the monomer and the types of hydrogen bonding species were monitored by differential scanning calorimetry (DSC) and FT-IR. The curing kinetics was studied by isothermal DSC and the isothermal kinetic parameters were determined. The thermal properties of cured benzoxazine were measured by DSC and thermogravimetric analysis (TGA). The bisphenol-AP-aniline-based polybenzoxazine (poly(B-AP-a)) exhibited higher glass transition temperature (T_g) and better thermal stability than corresponding bisphenol A-aniline-based polybenzoxazines (poly(BA-a)). The T_g value of poly(B-AP-a) is 171 °C. The temperatures corresponding to 5% and 10% weight loss is 317 and 347 °C, respectively, and the char yield is 42.2% at 800 °C. The isothermal curing behavior of B-AP-a displayed autocatalysis and diffusion control characteristics. The modified autocatalytic model showed good agreement with experimental results.     

Benzoxazine modified diglycidyl ether of bisphenol-a/silicon/siliconized epoxy hybrid polymer matrices: Mechanical,thermal, electrical and morphological properties

Benzoxazines modified epoxy hybrid polymer matrices were developed using benzoxazines (CB_DDM and BMPB_DDM) and epoxy resins (DGEBA, SE and EP-HTPDMS) to make them suitable for high performance applications. The benzoxazine-epoxy hybrid polymer matrices were prepared via in-situ polymerization and were investigated for their thermal, thermo-mechanical, mechanical, electrical and morphological properties. Two types of skeletal modified benzoxazines namely 1,1-bis(3-methyl-4-hydroxyphenyl)cyclohexane benzoxazine (CB_DDM) and bis(4-maleimidophenyl) benzoxazine (BMPB_DDM) were synthesized by reacting paraformaldehyde and 4,4′-diaminodiphenylmethane with 1,1-bis (3-methyl-4-hydroxyphenyl)cyclohexane and N-(4-hydroxyphenyl)maleimide respectively. Epoxy resins viz., diglycidyl ether of bisphenol-A (DGEBA), silicon incorporated epoxy (SE) and siliconized epoxy resin (EP-HTPDMS) were modified with 5, 10 and 15 wt% of benzoxazines using 4,4′-diaminodiphenylmethane as a curing agent at appropriate conditions. The chemical reaction of benzoxazines with the epoxy resin was carried out thermally and the resulting product was analyzed by FT-IR spectra. The glass transition temperature, curing behavior, thermal stability, char yield and flame resistance of the hybrid polymers were analysed by means of DSC, TGA and DMA. Mechanical properties were studied as per ASTM standards. The benzoxazines modified epoxy resin systems exhibited lower values of dielectric constant and dielectric loss with an enhanced values of of arc resistance, glass transition temperatures, degradation temperatures, thermal stability, char yield, storage modulus, tensile strength, flexural strength and impact strength.     

Copolymerization of fluorene‐based main‐chain benzoxazine and their high performance thermosets

A series of fluorene‐based benzoxazine copolymers were synthesized from the mixture of 9,9‐bis(4‐hydroxyphenyl)fluorene and bisphenol A, and 4,4′‐diaminodiphenyloxide and paraformaldehyde. And the cured polybenzoxazine films derived from these copolymers were also obtained. Fourier transform infrared spectroscopy (FTIR) and hydrogen nuclear magnetic resonances confirmed the structure of these benzoxazines. Their molecular weight was estimated by gel permeation chromatography. The curing behavior of the precursors was monitored by FTIR and differential scanning calorimetry. Dynamic mechanical analysis and thermogravimetric analysis were performed to study the thermal properties of the cured polymers. The cured polybenzoxazines exhibit excellent heat resistance with glass transition temperatures (T_g) of 286–317°C, good thermal stability along with the values of 5% weight loss temperatures (T₅) over 340°C, and high char yield over 50% at 800°C. The mechanical properties of the cured polymers were also measured by bending tests. Copyright © 2015 John Wiley & Sons, Ltd.     

Bis(benzoxazine-maleimide)s as a novel class of high performance resin: Synthesis and properties

A new class of benzoxazine-containing monomers, namely bis(benzoxazine-maleimide)s, has been prepared from hydroxyphenylmaleimide, paraformaldehyde and various diamines. This series of difunctional maleimide benzoxazines has been difficult to synthesize using previously reported benzoxazine synthesis conditions. The structures of the monomers are confirmed by Fourier transform infrared spectroscopy (FTIR), ¹H and ¹³C nuclear magnetic resonance spectroscopy (NMR) and elemental analysis. Polymerization behavior of the monomers is studied by differential scanning calorimetry (DSC), showing two exotherms at different temperature ranges. The 1st exotherm is due to the combination of benzoxazine ring-opening polymerization and addition-polymerization of bismaleimide. FTIR is also used to investigate the polymerization process. The dynamic mechanical analyses (DMA) of the obtained polymers reveal the glass-transition temperatures as high as 289-307 °C. Thermogravimetric analyses (TGA) show the 5% weight loss temperatures ranging from 374 to 383 °C with char yield ranging from 55% to 62% at 800 °C in N₂ atmosphere.     

Benzoxazine-bismaleimide blends: Curing and thermal properties

A blend of bisphenol A based benzoxazine (Bz-A) and a bismaleimide (2,2-bis[4(4-maleimidophenoxy) phenyl] propane (BMI), was thermally polymerised in varying proportions and their cure and thermal characteristics were investigated. The differential scanning calorimetric analysis, supplemented by rheology confirmed a lowering of the cure temperature of BMI in the blend implying catalysis of the maleimide polymerisation by benzoxazine. FTIR studies provided evidences for the H-bonding between carbonyl group of BMI and -OH group of polybenzoxazine in the cured matrix. The cured matrix manifested a dual phase behaviour in SEM and DMTA with the minor phase constituted by polybenzoxazine dispersed in an interpenetrating polymer network (IPN) of polybenzoxazine and cured BMI. The IPN possessed improved thermal stability over the constituent polybenzoxazine. A benzoxazine monomer possessing allyl functional groups, 2,2′-bis(8-allyl-3-phenyl-3,4-dihydro-2H-1,3-benzoxazinyl) propane (Bz-allyl) was reactively blended with the same bismaleimide in varying stoichiometric ratios (Bz-allyl/BMI), where the curing involved mainly Alder-ene reaction between allyl- and maleimides groups and ring-opening polymerisation of benzoxazine. The rheological analysis showed the absence of catalytic polymerisation of BMI in this case. The overall processing temperature was lowered in the blend owing to the co-reaction of the two systems to form a single-phase matrix. The cured resins of both Bz-A/BMI and Bz-allyl/BMI blends exhibited better thermal stability than the respective polybenzoxazines. The T_g of the IPN was significantly improved over that of polybenzoxazine (Bz-A). However, the co-reaction resulted in a marginal decrease in the T_g of the system in comparison to the polybenzoxazine (Bz-allyl).     

Methylol‐functional benzoxazines as precursors for high‐performance thermoset polymers: Unique simultaneous addition and condensation polymerization behavior

A new class of high‐performance resins of combined molecular structure of both traditional phenolics and benzoxazines has been developed. The monomers termed as methylol‐functional benzoxazines were synthesized through Mannich condensation reaction of methylol‐functional phenols and aromatic amines, including methylenedianiline (4,4′‐diaminodiphenylmethane) and oxydianiline (4,4′‐diaminodiphenyl ether), in the presence of paraformaldehyde. For comparison, other series of benzoxazine monomers were prepared from phenol, corresponding aromatic amines, and paraformaldehyde. The as‐synthesized monomers are characterized by their high purity as judged from ¹H NMR and Fourier transform infrared spectra. Differential scanning calorimetric thermograms of the novel monomers show two exothermic peaks associated with condensation reaction of methylol groups and ring‐opening polymerization of benzoxazines. The position of methylol group relative to benzoxazine structure plays a significant role in accelerating polymerization. Viscoelastic and thermogravimetric analyses of the crosslinked polymers reveal high T_g (274–343 °C) and excellent thermal stability when compared with the traditional polybenzoxazines. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis and characterization of fluid 1,3‐benzoxazine monomers and their thermally activated curing

Novel mono‐ and difunctional aliphatic oxyalcohol‐based benzoxazines have been synthesized and characterized in detail. Molecular structures of the monomers were investigated by spectral analysis. The obtained benzoxazine monomers exhibit fluidic behavior, which makes them particularly useful for many applications compared to other traditional benzoxazines. Differential scanning calorimetry was used to monitor the thermal crosslinking behavior of synthesized monomers. Mono‐ and bifunctional benzoxazine monomers exhibited low curing exhothermic peak with the onset around 173 and 180 °C, respectively. Relatively, low ring‐opening polymerization temperature was due to the hydroxyl groups present in the structure of the monomers. The hydrogen bonding of hydroxyl groups may cause alignment of the monomers in the liquid state. Thermal stabilty of the polybenzoxazines was studied by thermogravimetric analysis. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009     

A conjugated alkyne functional bicyclic polybenzoxazine with superior heat resistance

A difunctional benzoxazine (coPh‐apa) with a conjugated alkyne group is synthesized by the oxidative coupling reaction from a monocycle‐benzoxazine (Ph‐apa) containing an alkyne group. A model compound, 1,4‐diphenylbutadiyne (coPa), is used to study the curing reaction process of coPh‐apa by DSC, Fourier transform infrared spectroscopy, and ¹³C NMR, and the results suggest that the conjugated alkyne groups are involved in the crosslinking reaction via the trimerization reaction of the conjugated alkynyl groups and the Diels–Alder reaction. Furthermore, thermal properties of the polybenzoxazine are studied by dynamic thermomechanical analysis and thermogravimetric analysis. A glass‐transition temperature (T_gs) of as high as 412 °C and a char yield of 75.6% at 800 °C under nitrogen are obtained with the aid of the conjugated alkyne groups. Its excellent heat resistance dominates most thermosetting resins and will serve for heat shields. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1587–1592     

Synthesis of aromatic diamine-based benzoxazines and effect of their backbone structure on thermal and flammability properties of polymers

Three kinds of novel aromatic diamine-based benzoxazines containing naphthalene, propane-2,2-diyldibenzene and neopentyl groups in the backbone, respectively (designated as BAPNCP, BAPBACP and BAPNPGCP, respectively), were synthesized and characterized. In addition, the effects of backbone structures on curing behaviors of the monomers and thermal and flammability properties of the resulting polymers were systematically studied. The results indicated that BAPNPGCP displayed the highest enthalpy of the curing reaction associated with the ring-opening of benzoxazine, which was due to the effect of benzoxazine ring content per unit mass. Interestingly, the 5 wt% weight loss temperature and char residue after thermogravimetric test for poly(BAPNPGCP) were 8 °C and 7% higher than those of poly(BAPBACP). Meanwhile, the total heat release of poly(BAPNPGCP) was less than half of that for poly(BAPBACP), indicating the substantial effect of benzoxazine ring content on flammability and char formation. Furthermore, it was found that poly(BAPNCP) gave the best thermal stability and flame retardancy, which was due to the synergistic effect between naphthalene group and benzoxazine ring content. This study provides new insight into the curing behavior of benzoxazine and further understanding on the high performance of polybenzoxazine.     

Investigations on the cure chemistry and polymer properties of benzoxazine-cyanate ester blends

Thermosetting polymer blends composed of bisphenol A based benzoxazine (BA-a) and cyanate ester (BACY) were prepared via co-curing of benzoxazine with cyanate ester. DSC results manifested a multiple curing pattern with associated heat of reaction implying a co-reaction between oxazine moiety and cyanate group. The catalysis during the co-curing of blend was ascribed to the cycloaddition reaction between the two groups followed by the ring-opening of benzoxazine and cyclotrimerisation of cyanate ester. The spectral and analytical data supported the possibilities of further polymerization through the insertion of the phenolic OH of polybenzoxazine to cyanate group to form the intermediate iminocarbonate, which further induce curing of cyanate ester to form polycyanurate. A co-reacted network composed of triazine ring as a part of polybenzoxazine matrix is postulated. The co-reaction temperature diminished with increase in cyanate ester content in the blend. A single T_g was observed in DMTA of the cured matrix that implied a linked homogeneous matrix containing both triazine and polybenzoxazine. This was substantiated by the TGA, DTA and SEM behavior of the cured polymer. The modulus of the cured blend was higher than those of the component resins of the blend. The co-reaction with cyanate ester enhanced the high temperature stability of polybenzoxazine.     

Low dielectric materials from fluorinated polybenzoxazines

Fluorinated monomers containing a benzoxazine moiety have been synthesized successfully by preparing the benzoxazines from fluorinated amines (4‐fluoroaniline, 2,4‐difluoroaniline, and 2,3,4‐trifluoroaniline). These monomers were polymerized by step curing process following a cure cycle of 100, 150, 200 and 250°C for 1 h at each temperature. The molecular structure of the monomers and their polymers was characterized by Fourier transform infrared and nuclear magnetic resonance techniques. The synthesized fluorinated polybenzoxazines were able to reduce the dielectric constant to 2.0 for polybenzoxazine from 2,3,4 trifluoroaniline (PTF)‐Bzo at a frequency of 1 MHz. Moreover, they possess high thermal stability and low moisture absorption, which makes it suitable for high‐temperature process of interlayer dielectrics. Copyright © 2014 John Wiley & Sons, Ltd.     

Resorcinol‐based benzoxazine with low polymerization temperature

The industrial applications of benzoxazines are limited due to their high curing temperatures. This drawback can be overcome by more reactive precursor compared to conventional benzoxazines or by application of efficient initiators. We report the synthesis of a new resorcinol‐based benzoxazine and its cationic polymerization with thermolatent super acids, namely organic sulfonium hexafluoroantimonates. This combination of a reactive precursor and an efficient initiator results in a curing temperature below 100 °C (differential scanning calorimetry onset) which is up to now one of the lowest polymerization temperatures for benzoxazine systems. Furthermore, the thermal stability of the formed polybenzoxazine has not been influenced by the applied initiators. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1693–1699     

Fluorinated benzoxazines and the structure‐property relationship of resulting polybenzoxazines

Three fluorinated benzoxazines ( 14–16 ), which cannot be synthesized by the traditional one‐step approaches, were synthesized by a three‐step procedure using fluorinated aromatic diamines ( 2–4 ) as starting materials. The structures of the monomers were confirmed by ¹H NMR, IR, and high‐resolution mass spectra. The low dielectric thermosets, P( 14–16 ), were prepared by ring‐opening of ( 14–16 ). IR analysis was utilized to monitor the ring‐opening reaction of ( 14–16 ) and to propose the structures of P( 14–16 ). The thermal and dielectric properties of P( 14–16 ) were studied and compared with a nonfluorinated polybenzoxazine P( 13 ), which is derived form the ring‐opening of 2,2‐bis(4‐aminophenoxy)phenyl)propane ( 1 ). Besides, the structure–property relationship of the P( 13–16 ) is discussed. According to T_g measurement, the ortho‐positioned CF₃ substituents impart greater steric hindrance for ring‐opening of benzoxazines than CF₃ substituents of hexafluoropropane. Incorporating a biphenol F‐based benzoxazine, ( F‐a ), into fluorinated benzoxazines ( 15–16 ) can dilute the effect of ortho‐positioned CF₃ substituents on steric hindrance, leading to a higher crosslinking density and consequently a higher Tg. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4970–4983, 2008     

Synthesis and characterization of sulfone containing main chain oligobenzoxazine precursors

The preparation of soluble and processable polybenzoxazine precursors capable of forming high performance networks is an important field of research with a broad spectrum of application. This study demonstrates an approach that utilizes aromatic sulfonediamine, bisphenol‐A, and formaldehyde in Mannich‐type polycondesation to prepare polybenzoxazine precursor. The structure of the oligomeric precursor (M_n = 2600) was confirmed by FTIR and ¹H NMR spectral analysis. The precursor contained both sulfone and benzoxazine ring structures in the backbone. It was shown that small amount of ring‐opened phenolic groups were also present. Thermally activated self‐curing behavior of precursor in the absence of catalyst was studied by differential scanning calorimetry. Thermal properties of the cured polymers were also investigated by thermo gravimetric analysis. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

A new strategy for polybenzoxazine–montmorillonite nanocomposites synthesis

New polyether substituted benzoxazine monomers were synthesized starting from bisphenol A and p-Cresole as phenolic component and various polyetheramines. The chemical structures were proved by FTIR, ¹H-NMR, ¹³C-NMR, ¹⁵N-NMR and gel permeation chromatography (GPC). The new benzoxazines were mixed with classical benzoxazine based on bisphenol A and benzylamine (BA-BZA) and reinforced with modified montmorillonite to give nanocomposites which were characterized by transmission electron microscopy (TEM). The structure of the nanocomposite is exfoliated only when a high compatibility is ensured between the benzoxazine comonomers and the modified montmorillonite, this being the case for the benzoxazine substituted with the same chain as that of modifier agent for montmorillonite.     

Synthesis and properties of new polybenzoxazines containing (substituted) cyclohexyl moieties

A series of new polybenzoxazines were synthesized based on diphenols containing (substituted) cyclohexyl moiety and were characterized by FT‐IR, ¹H‐NMR, and ¹³C‐NMR spectroscopy. These new benzoxazine monomers exhibited better processability with lower peak cure temperature and a wide cure controllable window (CCW) as manifested in differential scanning calorimetric analysis. The cure analysis was performed by FT‐IR spectroscopy. Glass transition temperature of new polybenzoxazines varied from 170 to 205°C. The cyclohexyl bridge groups facilitated ring opening, resulting in polymer with improved thermal stability in comparison to bisphenol A‐based benzoxazine as assessed by the various thermal analyses. The water contact angles of polybenzoxazines containing (substituted) cyclohexyl moieties were higher than that of bisphenol A‐based polybenzoxazine, implying their higher hydrophobicity. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis and characterization of novel bisphthalonitrile resins linked by different molecular weight main-chain polybenzoxazines

A series of novel type bisphthalonitriles with different molecular weight main-chain polybenzoxazines as linkages have been successfully synthesized using 4, 4′-diaminodiphenyl methane, paraformaldehyde, bisphenol A and 4-nitrophthalonitrile as initial materials. The structures were characterized by Fourier transform infrared (FT-IR) and proton nuclear magnetic resonance (¹H-NMR). The formation of benzoxazine and the existence of nitrile groups were confirmed by the absorbance at 950cm^?1 of benzene attached with oxazine ring and 2231 cm^?1 of nitrile groups. The characteristic resonance peaks observed at about 4.52 (C-CH₂-N) and 5.28 ppm (N-CH₂-O) also determined the structure of benzoxazine ring. The curing behaviors were monitored by differential scanning calorimetry (DSC) and FT-IR. Two-stage polymerization mechanisms were observed according to the ring-opening of benzoxazine and the polymerization of nitrile groups catalyzed by phenolic hydroxyl groups, which generated during the curing reaction of benzoxazine. The polymerization of these bisphthalonitriles exhibited self-promoted curing behaviors. The completion of polymerization was proved by the disappearance of the band located at 950 cm^?1 in FT-IR. Thermogravimetric analysis (TGA) was used to investigate the thermal stability, and the results showed that the cured polymers achieved extremely high char yield from 61.1% up to 74.2% at 800°C under nitrogen and exhibited increasing decomposition temperature as the contents of phthalonitrile groups increased, which indicated that the polymerization of phthalonitriles could improve the thermal stability.