Epoxy resins. II. The preparation,characterization, and curing of epoxy resins and their copolymers

A polymer with high aromatic ring content in the chain backbone usually has high heat and flame resistance. Three diglycidyl ethers of epoxy resins were prepared from bisphenol A (DGEBA), phenolphthalein (DGEPP), and 9,9-bis(4-hydroxyphenyl)fluorene (DGEBF) in a study of the relation between the cured polymer structure and properties. The epoxy resin prepared from phenolphthalein was separated by liquid chromatography and three fractions were obtained. The fractions had a basic structure of 3,3-disubstituted phthalide and differed only in molecular weight. The DGEPP resin changed color from yellow to red after mixing with trimethoxyboroxine (TMB), the curing agent, and to orange after completing the curing cycle. To prepare a highly crosslinked material with good thermal stability, TMB with three active Lewis sites in a molecule was used as the curing agent. The reactivity of the three different resins toward TMB, measured by differential scanning calorimetry (DSC), was DGEBA > DGEBF > DGEPP. For the same curing conditions the order of crosslink density was DGEBA > DGEPP > DGEBF. To modify the flammability of DGEBA, the conventional epoxy resin, it was copolymerized with DGEPP and DGEBF, the higher-performance epoxy resins. The glass transition temperatures of poly(DGEBA-co-DGEPP) and poly(DGEBA-co-DGEBF) systems deviated from this relationship. The DGEBF copolymers showed an increased char residue (40 wt % at 700°C) at 20 mole % of DGEBF. This deviation may be due to the lower crosslinking density of this system.     

Synthesis of novel tri‐benzoxazine and effect of phenolic nucleophiles on its ring‐opening polymerization

A trifunctional benzoxazine, 1,3,5‐tris(3‐phenyl‐3,4‐dihydro‐2H‐benzo[1,3]oxazin‐6‐yl)benzene (T‐Bz) was synthesized and in an effort to reduce its curing temperature (curing maxima at 238 °C), it was mixed with various phenolic nucleophiles such as phenol (PH), p‐methoxy phenol (MPH), 2‐methyl resorcinol (MR), hydroquinone (HQ), pyrogallol (PG), 2‐naphthol (NPH), 2,7‐dihydroxy naphthalene (DHN), and 1,1'‐bi‐2‐naphthol (BINOL). The influence of these phenolic nucleophiles on ring‐opening polymerization temperature of T‐Bz was examined by DSC and FTIR analysis. T‐Bz undergoes a complete ring‐opening addition reaction in the presence of bi‐ and trifunctional phenolic nucleophiles (MR/HQ/PG/DHN) at 140 °C (heated for 3 h) and forms a networked polybenzoxazine (NPBz). The NPBzs showed a high thermal stability with T_d20 of 350–465 °C and char yield of 67–78% at 500 °C; however, a diminutive weight loss (6.9–9.8%) was observed at 150–250 °C (T_d5: 215–235 °C) due to degradation of phenolic end groups. This article also gives an insight on how the traces of phenolic impurities can alter the thermal properties of pure benzoxazine monomer as well as its corresponding polymer. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2811–2819     

Poly(urethane‐co‐benzoxazine)s via reaction of phenol terminated urethane prepolymers and benzoxazine monomer and investigation of their properties

In the present work, a new method was developed for the combination of polyurethanes (PUs) and polybenzoxazine (PBz) to obtain novel thermoset poly(urethane‐co‐benzoxazine)s with good thermal, mechanical, and electrical properties as well as low temperature curing profile. Knowing the catalytic effect of compounds possessing free phenolic groups on ring opening polymerization of benzoxazine monomers, preparation of phenol terminated urethane oligomers (PTPU) as the macroinitiator for a benzoxazine monomer (Ba) was considered. Firstly, NCO‐terminated urethane prepolymers were prepared from the reaction of poly(tetramethyleneether glycol), and 2,4‐tolylene diisocyanate, and then end functionalized with bisphenol‐A under proper condition. DSC, DMTA, and gel content measurements were applied to find optimum ring opening polymerization condition (170°C for 1 hr and 200°C for 15 min). Various kinds of thermoset polymers were prepared by the reaction of PTPU at different molecular weights with variable contents of Ba. All of monomeric and polymeric materials were characterized by conventional spectroscopic methods and their thermal, mechanical, viscoelastic, and electrical properties were measured and properties were correlated to their structure. Due to the interesting properties of these new materials, the possibility of using them as electrical insulators with higher service temperature in comparison to common PUs were examined and their potential applicability was confirmed. Copyright © 2010 John Wiley & Sons, Ltd.     

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.     

Synthesis and characterization of a vinyl‐terminated benzoxazine monomer and its blends with poly(ethylene oxide)

A vinyl‐terminated benzoxazine (VB‐a), which could be polymerized through ring‐opening polymerization, was synthesized through the Mannich condensation of bisphenol A, formaldehyde, and allylamine. This VB‐a monomer was then subjected to blending with poly(ethylene oxide) (PEO), followed by thermal curing, to form poly(VB‐a)/PEO blends. The specific interactions, miscibility, morphology, and thermal properties of these blends were investigated with Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry, dynamic mechanical analysis (DMA), and scanning electron microscopy (SEM). Before curing, we found that PEO was miscible with VB‐a, as evidenced by the existence of a single composition‐dependent glass transition temperature (T_g) for each composition. The FTIR spectra revealed the presence of hydrogen‐bonding interactions between the hydroxyl groups of poly(VB‐a) and the ether groups of PEO. Indeed, the ring‐opening reaction and subsequent polymerization of the benzoxazine were facilitated significantly by the presence of PEO. After curing, DMA results indicated that the 50/50 poly(VB‐a)/PEO blend exhibited two values of T_g: one broad peak appeared in the lower temperature region, whereas the other (at ca. 327 °C, in the higher temperature region) was higher than that of pristine poly(VB‐a) (301 °C). The presence of two glass transitions in the blend suggested that this blend system was only partially miscible. Moreover, SEM micrographs indicated that the poly(VB‐a)/PEO blends were heterogeneous. The volume fraction of PEO in the blends had a strong effect on the morphology. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 644–653, 2007     

Styrylpyridine-based epoxy resins: Synthesis and characterization

Polymers containing rigid aromatic structures in the chain backbone usually gave high thermal stability and good flammability resistance. Three glycidyl ethers of epoxy resins were prepared from 2,4-di(p-hydroxystyryl)pyridine (2,4-DGESP), 2,6-di-(p-hydroxystyryl)pyridine (2,6-DGESP), and 2,4,6-tri-(p-hydroxystyryl)pryidine (2,4,6-TGESP) to study the relationships of structure to polymer degradation. To prepare a highly crosslinked material, trimethoxyboroxine (TMB) was used as the curing agent. The relative char yields of the three different resins, as measured by TGA, were 2,4-DGESP ≈ 2,6-DGESP > 2,4,6-TGESP. The char yield of the cured 2,6-DGESP varied with different amounts of the TMB curing agent, and was higher than the uncured 2,6-DGESP. The oxygen index increased as a function of thermal curing time for the 2,6-DGESP epoxy resin. An intermolecular Diels–Alder reaction with 2,6-DGESP is proposed as a primary reaction during thermal curing.     

Preparation of Poly(phosphoric acid piperazine) and Its Application as an Effective Flame Retardant for Epoxy Resin

A phosphorus-nitrogen containing flame retardant additive of poly(phosphoric acid piperazine),defined as PPAP,was synthesized by the salt-forming reaction between anhydrous piperazine and phosphoric acid,and the dehydration polymerization under heating in nitrogen atmosphere.Its chemical structure was well characterized by Fourier transform infrared (FTIR) spectroscopy,13C and 31p solid-state nuclear magnetic resonance measurements.The synthesized PPAP and curing agent m-phenylenediamine were blended into epoxy resin (EP) to prepare flame retardant EP thermosets.The effects of PPAP on the fire retardancy and thermal degradation behavior of cured EP/PPAP composites were investigated by limiting oxygen index (LOI),vertical burning (UL-94),thermogravimetric analysis/infrared spectrometry (TG-IR) and cone calorimeter tests.The morphologies and chemical compositions of char residues for cured epoxy resin were investigated by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS),respectively.The results demonstrated that the flame retardant EP thermosets successfully passed UL-94 V-0 flammability rating and the LOI value was as high as 30.8％ when incorporating 5wt％ PPAP into the EP thermosets.The TGA results indicated that the synthesized PPAP flame retardant additive possessed high thermal stability and excellent charring capability.Meanwhile,the incorporation of PPAP stimulated the epoxy resin matrix to decompose and charring ahead of time due to its catalytic decomposition effect,which led to a higher char yield at high temperature.The morphological structures and the analysis results of XPS for char residues of EP thermosets revealed that the introduction of PPAP benefited the formation of a sufficient,more compact and homogeneous char layer containing phosphorus-nitrogen flame retardant elements on the material surface during combustion.The formed char layer with high quality effectively prevented the heat transmission and diffusion,limited the production of combustible gases,and inhibited the emission of smoke,leading to the reduction of heat and smoke release.     

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.     

新型生物基苯并嗪的合成及性能

以生物基糠胺、 酚酞和多聚甲醛为原料, 制备了一种新型生物基苯并噁嗪树脂——酚酞糠胺型苯并噁嗪树脂(PPTL-F-BOZ), 采用FTIR, ¹H NMR和 ¹³C NMR等手段对其单体PTL-F-BOZ的结构进行了表征, 并对其固化反应、 耐热和阻燃性能进行分析. 结果表明, 与传统的化石基双酚型苯并噁嗪——双酚A苯胺型苯并噁嗪(BPA-A-BOZ)相比, PTL-F-BOZ显示出较低的固化反应温度, 且糠胺中呋喃环的存在会增加聚合物的交联密度, 并减缓苯氧结构向苯酚结构的重排反应, 致使其在DSC曲线中出现了2个固化峰. PPTL-F-BOZ树脂具有较高的T_5%(质量损失5%的温度)和800 ℃的残炭率, 其极限氧指数(LOI)高达36.2%, 在垂直燃烧中达到V-0等级, 表现出优异的热稳定性和阻燃性能.     

Synthesis and characterization of nanomagnetite thermosets based on benzoxazines

Nanomagnetite thermosets were obtained by thermally activated ring opening copolymerization of benzoxazine groups coated on the surface of the nanomagnetite with bare benzoxazine. For this purpose, carboxylic acid containing 1,3‐benzoxazine was synthesized and covalently bonded on magnetite nanoparticles by postcoating method. The average size of benzoxazine coated nanoparticles was 40–100 nm as determined by Dynamic Light Scattering (DLS), Atomic Force Microscopy (AFM) and Transmission Electron Microscopy (TEM) measurements. The crystal structure of benzoxazine coated nanoparticles was shown to be magnetite by X‐ray diffraction (XRD) analysis. Thermally activated curing behavior of nanomagnetite‐benzoxazines has also been studied by differential scanning calorimetry (DSC). Magnetic and thermal properties of the cured samples were investigated. It was shown that the precursor nanomagnetite benzoxazine and cured samples exhibited typical ferromagnetic character with low coercivities between 1.5 and 2.5 Oe. The cured samples showed high thermal stability. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6780–6788, 2008     

Synthesis and properties of flame‐retardant benzoxazines by three approaches

We propose three approaches to obtain flame‐retardant benzoxazines. In the first approach, we synthesize a novel benzoxazine (dopot‐m) from a phosphorus‐containing triphenol (dopotriol), formaldehyde, and methyl amine. Dopot‐m is copolymerized with a commercial benzoxazine [6′,6‐bis(3‐phenyl‐3,4‐dihydro‐2H‐1,3‐benzoxazineyl)methane (F‐a)] or diglycidyl ether of bisphenol A (DGEBA). The thermal properties and flame retardancy of the F‐a/dopot‐m copolymers increase with the content of dopot‐m. As for the dopot‐m/DGEBA curing system, the glass‐transition temperature of the dopot‐m/DGEBA copolymer is 252 °C, which is higher than that of poly(dopot‐m). The 5% decomposition temperature of the dopot‐m/DGEBA copolymer increases from 323 to 351 °C because of the higher crosslinking density caused by the reaction of phenolic OH and epoxy. In the second approach, we incorporate the element phosphorus into benzoxazine via the curing reaction of dopotriol and F‐a. After the curing, the thermal properties of the F‐a/dopotriol copolymers are almost the same as those of neat poly(F‐a), and this implies that we can incorporate the flame‐retardant element phosphorus into the polybenzoxazine without sacrificing any thermal properties. In the third approach, we react dopo with electron‐deficient benzoxazine to incorporate the element phosphorus. After the curing, the glass‐transition temperatures of polybenzoxazines decrease slightly with the content of dopo, mainly because of the smaller crosslinking density of the resultant polybenzoxazines. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3454–3468, 2006     

Improved thermal stability of polybenzoxazines by transition metals

The incorporation of various transition metal salts increases the char formation of polybenzoxazines. It is shown that the effect of the transition metal salt is not simply additive and is independent of the amine and phenol structures. While the metal salts have an insignificant effect on the polymerization, their presence in benzoxazine favors the formation of carbonyl functional groups. It is proposed that reduced flammability of polybenzoxazines is achieved through the evolution of CO₂ during thermal degradation.     

Self‐healing of poly(propylene oxide)‐polybenzoxazine thermosets by photoinduced coumarine dimerization

In this work, a self‐healing strategy for poly(propylene oxide)s bearing coumarine‐benzoxazine units (PPO‐CouBenz)s based on light induced coumarine dimerization reactions is described. Four different types of poly(propylene oxide) amines with molecular weights ranging from 440 to 5000 Da were reacted with formaldehyde and 4‐methyl‐7‐hydroxycoumarin to yield desired (PPO‐CouBenz)s. The crosslinked polymer films were prepared by solvent casting of various compositions of PPO‐CouBenzs in chloroform followed by thermal ring opening reaction of benzoxazine groups at 210–240 °C. Thermal curing and thermal stability of the initial PPOs and final products were investigated. Using allyl benzoxazine in the formulation, it was demonstrated that the toughness of the films was improved. Photoinduced healing of coumarin‐based cured PPO‐CouBenz polymer films was investigated. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2911–2918     

Synthesis and characterization of poly(urethane‐benzoxazine) films as novel type of polyurethane/phenolic resin composites

Poly(urethane‐benzoxazine) films as novel polyurethane ( PU )/phenolic resin composites were prepared by blending a benzoxazine monomer ( Ba ) and PU prepolymer that was synthesized from 2,4‐tolylene diisocyanate (TDI) and polyethylene adipate polyol (MW ca. 1000) in 2 : 1 molar ratio. DSC of PU/Ba blend showed an exotherm with maximum at ca. 246 °C due to the ring‐opening polymerization of Ba, giving phenolic OH functionalities that react with isocyanate groups in the PU prepolymer. The poly(urethane‐benzoxazine) films obtained by thermal cure were transparent, with color ranging from yellow to pale wine with increase of Ba content. All the films have only one glass transition temperature (T_g ) from viscoelastic measurements, indicating no phase separation in poly(urethane‐benzoxazine) due to in situ polymerization. The T_g increased with the increase of Ba content. The films containing 10 and 15% of Ba have characteristics of an elastomer, with elongation at break at 244 and 182%, respectively. These elastic films exhibit good resilience with excellent reinstating behavior. The films containing more than 20% of Ba have characteristics of plastics. The poly(urethane‐benzoxazine) films showed excellent resistance to the solvents such as tetrahydrofuran, N,N‐dimethyl formamide, and N‐methyl‐2‐pyrrolidinone that easily dissolve PU s. Thermal stability of PU was greatly enhanced even with the incorporation of a small amount of Ba . © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4165–4176, 2000     

Synthesis,characterization, and polymerization of brominated benzoxazine monomers and thermal stability/flame retardance of the polymers generated

Novel monofunctional brominated benzoxazine 3‐(2,4,6‐tribromophenyl)‐3,4‐dihydro‐2H‐1,3‐benzoxazine (P‐bra) and bifunctional brominated benzoxazine 6,6′‐bis(3‐(2,4,6‐tribromophenyl)‐3,4‐dihydro‐2H‐1,3‐benzoxazinyl) isopropane (B‐bra) were prepared and highly thermally stable polybenzoxazines were obtained by the thermal cure of the corresponding benzoxazines monomers. The chemical structures of these novel monomers were confirmed by FITR, ¹H‐NMR and elemental analysis. FTIR spectra and differential scanning calorimetry (DSC) suggested that the polymerization was thermally initiated and occurred via ring‐opening of the monomer in each case. Thermogravimetric analysis (TGA) indicated that brominatation could have a profound effect on increasing char yield and on thermal degradation temperatures. The results of UL‐94 burn test showed that the polybenzoxazines prepared from P‐bra and B‐bra had good flame retardance. Copyright © 2009 John Wiley & Sons, Ltd.     

Kinetics and thermal properties of epoxy resins based on bisphenol fluorene structure

The fluorene-containing epoxy, diglycidyl ether of 9,9-bis(4-hydroxyphenyl) fluorene (DGEBF) was synthesized by a two-step reaction procedure. In order to investigate the relationship between fluorene structure and material properties, DGEBF and a commonly used diglycidyl ether of bisphenol A (DGEBA) were cured with 4,4-diaminodiphenyl methane (DDM) and 4,4-(9-fluorenylidene)-dianiline (FDA). The curing kinetics, thermal properties and decomposition kinetics of these four systems (DGEBA/DDM, DGEBF/DDM, DGEBA/FDA, and DGEBF/FDA) were studied in detail. The curing reactivity of fluorene epoxy resins was lower, but the thermal stability was higher than bisphenol A resins. The onset decomposition temperature of cured epoxy resins was not significantly affected by fluorene structure, but the char yield and T_g value were increased with that of fluorene content. Our results indicated that the addition of fluorene structure to epoxy resin is an effective method to improve the thermal properties of resins, but excess fluorene ring in the chain backbone can depress the curing efficiency of the resin.     

Synthesis and flammability of copolyisophthalamides. I. With phosphorus groups in the main chain

The influence of certain phosphorus substituted (OH, OMe, Me) 3,3'-diphenylphosphine oxides on flammability and thermal stability of 1,3-phenylene isophthalamide copolymers was investigated. Introduction of the above phosphorus groups along the backbone of poly(1,3-phenylene isophthalamide) was performed in a random manner to a degree of ca. 5-15 mol %. From the limiting oxygen index (LOI) measurements on copolymers, it was found that the diphenylphosphinic acid group has the highest flame retardance efficiency with an increase of LOI 44-56%. From thermogravimetric analysis (TGA), it was found that the action of phosphorus groups is limited in the solid phase, increasing the char yield to 27-42%. This was attributed to crosslinking reactions at the stage of amide bond decomposition. © 1992 John Wiley & Sons, Inc.     

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.