Synergism and multiple mechanical relaxations observed in ternary systems based on benzoxazine,epoxy, and phenolic resins

The synergism in the glass‐transition temperature (T_g) of ternary systems based on benzoxazine (B), epoxy (E), and phenolic (P) resins is reported. The systems show the maximum T_g up to about 180 °C in BEP541 (B/E/P = 5/4/1). Adding a small fraction of phenolic resin enhances the crosslink density and, therefore, the T_g in the copolymers of benzoxazine and epoxy resins. To obtain the ultimate T_g in the ternary systems, 6–10 wt % phenolic resin is needed. The molecular rigidity from benzoxazine and the improved crosslink density from epoxy contribute to the synergistic behavior. The mechanical relaxation spectra of the fully cured ternary systems in a temperature range of −140 to 350 °C show four types of relaxation transitions: γ transition at −80 to −60 °C, β transition at 60–80 °C, α₁ transition at 135–190 °C, and α₂ transition at 290–300 °C. The partially cured specimens show an additional loss peak that is frequency‐independent as a result of the further curing process of the materials. The ternary systems have a potential use as electronic packaging molding compounds as well as other highly filled systems. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1687–1698, 2000     

Development of novel flame‐retardant thermosets based on benzoxazine–phenolic resins and a glycidyl phosphinate

Modified novolac resins with benzoxazine rings were prepared and copolymerized with a glycidyl phosphinate. Their curing behavior and the thermal properties of the curing resins were studied. Copolymerization was studied with model compounds considering the functionality of the benzoxazine‐based phenolic resins and the easy isomerization of the glycidyl phosphinate. Phenolic novolac resin acts as an initiator but p‐toluensulfonic acid had to be used to decrease the curing temperature and to prevent glycidyl phosphinate from isomerizing. The materials obtained exhibited high glass‐transition temperatures and retardation on thermal degradation rates. V‐0 materials were obtained when the materials were tested for ignition resistance with the UL‐94 test. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 279–289, 2004     

Synthesis of a novel benzoxazine monomer‐intercalated montmorillonite and the curing kinetics of polybenzoxazine/clay hybrid nanocomposites

Polybenzoxazine (PBZ), which has a structure similar to that of phenolic resin, is formed through the thermal self‐curing of benzoxazine, that is through a heterocyclic ring opening reaction that requires no catalyst and releases no condensation byproducts. We have used the solvent blending method to prepare PBZ/clay nanocomposites possessing various clay contents. We synthesized a monofunctional benzoxazine monomer (MBM) and then treated the clay with this intercalation agent. The results of X‐ray diffraction (XRD) analysis indicated that MBM intercalated into the galleries of the clay; the nanocomposite possessed an exfoliated structure at 3% clay content. To better understand the curing kinetics of the PBZ/clay nanocomposites, we performed dynamic and isothermal differential scanning calorimetry (DSC) measurements. We describe the thermodynamics of the curing process, using all three of the Kissinger, Ozawa, and Kamal models. The Kissinger and Ozawa methods gave fairly close results for the calculated activation energies, which decreased upon increasing the clay content. The Kamal method, based on an autocatalytic model, suggested a total reaction order of between 2.4 and 2.8. The glass transition temperature (T_g) decreased upon increasing the clay content. Thermogravimetric analysis (TGA) indicated that the nanocomposites have higher decomposition temperatures than does the pristine PBZ; this finding suggests an enhancement in their thermal stability. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 347–358, 2006     

High‐Tg and low‐dielectric epoxy thermosets based on a propargyl ether‐containing phosphinated benzoxazine

A propargyl ether‐containing benzoxazine (4) was prepared from a potassium carbonate‐catalyzed nucleophilic substitution of propargyl bromide and a phenolic OH‐containing benzoxazine (3) , which was prepared from 1‐(4‐hydroxyphenyl)‐1‐(4‐aminophenyl)‐1‐(6‐oxido‐6H ‐dibenz <c,e><1,2> oxaphosphorin‐6‐yl)ethane (1) by a three‐step procedure. The curing reactions of (4) were monitored by IR and DSC. A reaction mechanism was proposed based on the observation. Benzoxazines (3) and (4) were applied as epoxy curing agents. The microstructure and the structure‐property relationship of the resulting thermosets are discussed. The double‐strand structure in (4) ‐cured epoxy thermosets afforded higher crosslinking density, and led to higher thermal properties. In addition, the (4) ‐cured epoxy thermosets possess half the amount of highly polar hydroxyl groups than those of the (3) ‐cured epoxy thermosets, resulting in a lower dielectric constant, dissipation factor, and water absorption. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1359–1367     

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     

Facile,one‐pot synthesis of aromatic diamine‐based benzoxazines and their advantages over diamines as epoxy hardeners

Three aromatic diamine‐based benzoxazines were successfully prepared by a facile, clean, one‐pot procedure from 1,4‐phenylenediamine ( 1 ), 4,4′‐diaminodiphenyl ether ( 2 ), and 4,4′‐diaminodiphenyl methane ( 3 ), respectively. Their structures were confirmed by NMR spectra and single crystal diffractogram. The effect of the reactivity of diamines on the purity of the resultant benzoxazines was discussed. The resultant benzoxazines were applied as hardeners for cresol novolac epoxy (CNE). The processing window, the latent curing characteristic, and the miscibility of benzoxazine/CNE systems were discussed. Compared with diamines ( 1 and 3 ), ( 1 and 3 )‐based benzoxazines show latent curing characteristic as epoxy hardeners, and wide processing windows can be obtained. Compared with diamine ( 2 ) which is immiscible with CNE in the molten state, ( 2 )‐based benzoxazine shows good miscibility with CNE. Dynamic mechanical analysis shows the T_gs of the benzoxazine/CNE thermosets are as high as 242–243 °C. Thermogravimetric analysis shows the outstanding thermal stability of the resultant thermosets. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2430–2437, 2010     

Bifunctional benzoxazines: Synthesis and polymerization of resorcinol based single isomers

Aside from their outstanding properties such as thermal and chemical stability and excellent mechanical performance, benzoxazines suffer from high polymerization temperatures. Isomeric mixtures of bifunctional benzoxazines based on resorcinol proved already to be highly reactive monomers enabling polymerizations at lower temperatures. This contribution describes the polymerization behavior of single benzoxazine isomers and furthermore the influence of different substituents at the aniline moiety on the curing temperature. Single isomers of bifunctional benzoxazines are now accessible in a straightforward one‐pot synthesis starting from resorcinol and the appropriate N‐phenyl functionalized aniline component. The asymmetric benzoxazine monomers bearing no (R‐a: T_peak = 179 °C) or electron‐donating substituents in meta position to N (R‐3,5dma: T_peak = 183 °C) succeed in lowering the polymerization temperature. Additionally, the impact of several initiating systems was studied resulting in a decrease of the polymerization temperature for all studied resorcinol derived benzoxazine isomers (down to 144 °C). © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1243–1251     

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 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     

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     

Dynamic mechanical and thermal characterization of high-performance polybenzoxazines

Two polybenzoxazines are cured in an autoclave from the polyfunctional benzoxazine monomers, 8,8′-bis(3,4-dihydro-3-phenyl-2H-1,3-benzoxazine) and 6,6′-bis(2,3-dihydro-3-phenyl-4H-1,3-benzoxazinyl) ketone. The density and tensile properties of these polybenzoxazines are measured at room temperature. Dynamic mechanical tests are performed to determine the T_g, crosslink density, and the activation enthalpy of the glass-transition process for these two polybenzoxazines. The effect of postcure temperature on the T_g of the polymers is investigated and discussed in terms of crosslink density. Fourier transform infrared (FTIR) spectroscopy is also applied for the molecular characterization of the curing systems. Thermal properties of these polybenzoxazines are studied in terms of isothermal aging and decomposition temperature via thermogravimetric analysis. These two polybenzoxazines show mechanical and thermal properties similar to or better than bismaleimides and some polyimides. They also show very high char yield after being carbonized in a nitrogen atmosphere. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3257–3268, 1999     

Synthesis and curing of amino‐containing benzoxazine as a novel hardener for diglycidyl ether of bisphenol‐A

Benzoxazines containing various additional functional groups have been extensively reported to improve the properties of polybenzoxazines. In this work, a novel amino‐containing benzoxazine (PDETDA‐NH₂) was conveniently synthesized from diethyltoluenediamine (DETDA), 2‐hydroxybenzaldehyde, and paraformaldehyde and was used as a hardener for diglycidyl ether of bisphenol‐A (DGEBA). The curing behaviors of PDETDA‐NH₂ and PDETDA‐NH₂/DGEBA systems were studied by DSC, FT‐IR, and ¹H NMR. When curing, PDETDA‐NH₂ was firstly polymerized to N,O‐acetal‐type polymer and then rearranged to Mannich‐type polymer at elevated temperature, while the addition reaction between amino and benzoxazine was discouraged because of the steric hindrance of alkyl substituents. During PDETDA‐NH₂/DGEBA curing, it was found that the reactions happened in the order of addition polymerization of amino and epoxide, ring‐opening polymerization of benzoxazine, etherification between phenolic hydroxyl of the polymerized benzoxazine, and epoxide. Compared with DETDA cured DGEBA, PDETDA‐NH₂ cured DGEBA showed higher modulus, higher char yield, and much lower water uptake.     

Thermally curable polyvinylchloride via click chemistry

Novel side‐chain benzoxazine functional polyvinylchloride (PVC‐Benzoxazine) was synthesized by using “Click Chemistry” strategy. First, approximately 10% of chloro groups of PVC were converted to azido groups by using NaN₃ in N,N‐dimethylformamide. Propargyl benzoxazine was prepared independently by a ring closure reaction between p‐propargyloxy aniline, paraformaldehyde, and phenol. Finally, azidofunctionalized PVC was coupled to propargyl benzoxazine with high efficiency by click chemistry. The spectral and thermal analysis confirmed the presence of benzoxazine functionality in the resulting polymer. It is shown that PVC containing benzoxazine undergoes thermally activated curing in the absence of any catalyst forming PVC thermoset with high thermal stability. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3512–3518, 2008     

Studies on thermal and flame retardant behaviour of mixtures of bis(m-aminophenyl)methylphosphine oxide based benzoxazine and glycidylether or benzoxazine of Bisphenol A

The curing of mixtures of bis(m-aminophenyl)methylphosphine oxide based benzoxazine and glycidylether or benzoxazine of Bisphenol A has been studied. In all samples the molar ratio of benzoxazine monomers or the benzoxazine-epoxy system was varied to achieve different phosphorus content. The phosphorus-containing polybenzoxazines have been characterized by dynamic mechanical and thermogravimetric analysis. Limiting oxygen index values indicate good flame retardant properties.     

Deprotection‐free preparation of propargyl ether‐containing phosphinated benzoxazine and the structure–property relationship of the resulting thermosets

Generally, protection and deprotection procedures of amino groups are required in preparing propargyl ether‐containing benzoxazines. In this study, we report a facile, deprotection‐free preparation of a propargyl ether‐containing phosphinated benzoxazine (2) from the nucleophilic substitution of a phenolic OH‐containing phosphinated benzoxazine (1) and propargyl bromide in the catalysis of potassium carbonate. The structure of (2) was characterized and confirmed by a high‐resolution mass spectrum, ¹H, ¹³C, ¹H‐¹H, ¹H‐¹³C nuclear magnetic resonance (NMR) spectra, and X‐ray single crystal diffractogram. infrared (IR) and differential scanning calorimetry were used to monitor the ring‐opening of benzoxazine and crosslinking of propargyl ether. The microstructure and the structure–property relationship of the resulting homopolymers and copolymers are discussed. The T_g of homopolymer of (2) is 208 °C by dynamic mechanical analysis, the coefficient of thermal expansion is 43 ppm/°C, and T_d 5% (N₂) is 393 °C, respectively, which are higher than those of the homopolymer of (1) . Similar trends were observed in the copolymerization system. The results demonstrate the beneficial effect of crosslinking afforded by the propargyl ether group is higher than that by the phenolic OH group. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Ethylene‐based copolymers with tunable content of polymerizable hindered phenols as nonreleasing macromolecular additives

Four comonomers bearing a highly efficient phenolic antioxidant unit and different methylene spacers between the aromatic ring and the double bond have been prepared and tested in copolymerization with ethylene using metallocene‐based catalysts. The possibility of obtaining a “masterbatch” suitable for melt blending with commercial polyolefins has been evaluated by modifying: (i) the structure of the functionalized comonomer, (ii) the kind of catalyst, and (iii) the polymerization conditions. Characterization of monomers and copolymers was accomplished by using ¹H and ¹³C NMR, size exclusion chromatography (SEC), differential scanning calorimetry (DSC), and thermal gravimetric analysis (TGA). Using the comonomer with the longest methylene spacer between the aromatic ring and the double bond, and rac‐(EBTHI)ZrCl₂ as catalyst, adjustable amounts of the antioxidant moiety can be incorporated into the polyethylene chains. TGA analysis carried out on some of the copolymers containing the antioxidant group showed no oxygen uptake before decomposition. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6393–6406, 2008     

Functional 1,3‐benzoxazine bearing 4‐pyridyl group: Synthesis and thermally induced polymerization behavior

1,3‐benzoxazine 1 , bearing 4‐pyridyl moiety on the nitrogen atom, was synthesized from p‐cresol, 4‐aminopyridine, and paraformaldehyde. The efficient synthesis was achieved by adding acetic acid to suppress the strong basicity caused by the presence of 4‐aminopyridine derivatives. Upon heating 1 at 180 °C, it underwent the thermally induced ring‐opening polymerization. The resulting polymer was composed of two types of repeating unit, i.e., (1) Mannich‐type one (‐phenol‐CH₂‐NR‐CH₂‐) that can be expected from the general ring‐opening polymerization of conventional benzoxazines and (2) a typical phenolic resin‐type one (‐phenol‐CH₂‐phenol‐) induced by release of 4‐aminopyridine and paraformaldehyde (unit B). Another structural feature of the polymer was that it possessed a benzoxazine moiety at the chain end. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 410–416     

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     

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     

Synthesis and curing kinetics of cardanol‐based curing agents for epoxy resin by in situ depolymerization of paraformaldehyde

Three novel cardanol‐based phenalkamines with good stability have been successfully prepared by Mannich reaction using phenolic compounds with paraformaldehyde and hexamethylenediamine (or its mixture with other amines). The structure of the prepared phenalkamines has been analyzed using liquid chromatography‐mass spectrometry, nuclear magnetic resonance, and Fourier transform infrared spectroscopy. The curing kinetics of the prepared epoxy resin/phenalkamine systems has been investigated using differential scanning calorimetry (DSC), and determined by Kissinger, Flynn–Wall–Ozawa, and Crane methods. Furthermore, the thermal properties of the cured materials have been evaluated using DSC and thermogravimetric analysis, and the mechanical properties of the cured materials have been analyzed systematically. The results demonstrate that the phenalkamine 1 (PAA1) had a lower reactivity and better toughness than phenalkamine 2 (PAA2) and phenalkamine 3 (PAA3). In addition, PAA1 is a solid curing agent, while PAA2 and PAA3 are liquid curing agents, which were more convenient for practical usage. Results indicate that the properties of the prepared phenalkamines strongly depend on the structures. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 472–480