Synthesis of itaconimide/nadimide-functionalized benzoxazine monomers: Structural and thermal characterization

A novel series of itaconimide/nadimide-functionalized benzoxazine monomers (I-Bz/N-Bz) from imide-terminated amines, paraformaldehyde and phenol/m-cresol/cardanol/4-(hydroxyphenyl) benzoxazole were synthesized and characterized by FT-IR, ¹H and ¹³C NMR and HRMS analyses. The I-Bzs exhibited lower curing temperatures compared to the N-Bzs, which may be attributable to the presence of the 1,1-disubstituted double bond in itaconimide. The poly(I-Bz)s exhibited higher glass-transition temperatures (210–216 °C) compared to the poly(N-Bz)s (151–178 °C). The itaconimide- and nadimide-functionalized benzoxazines showed comparable thermal stability, but differences in their phenolic structures affected their thermal behavior (char yield and T_max). The poly(I-Bz)s (19–47%) showed higher char yields compared to the poly(N-Bz)s (18–41%), depending on the backbone structure. The highest lap-shear strength at 200 °C was observed in I-Bz/N-Bz derived from m-cresol.     

Effect of phenol substitution on the network structure and properties of linear aliphatic diamine-based benzoxazines

A series of aliphatic diamine-based benzoxazines with different phenolic substitutions have been synthesized and characterized. Molecular structure of the monomers is verified by ¹H and ¹³C NMR, FTIR, and elemental analysis. The site of polymerization is regiospecified and the type of linkage in the network structure is manipulated by selectively blocking the ortho, para, and meta positions in the aromatic rings of the monomer. The controlled network structures and their properties are compared to those formed by the polymerization of aliphatic diamine-based benzoxazines prepared from unsubstituted phenol in order to provide insight into their structures. Investigation on the melting point, polymerization kinetics, gelation, and T_g and sub-T_g thermal transition is all reported on these systematically controlled structure polybenzoxazines.     

Synthesis and polymerization behavior of novel liquid-crystalline benzoxazines

Novel liquid-crystalline (LC) benzoxazines were synthesized by using 4(4′-heptoxybenzoyloxy)benzylidene-4″-aminophenol, various alkylamines, and formalin in chloroform under reflux. Polarized optical microscopy (POM) and differential scanning calorimetry (DSC) were used to analyze the LC behavior of the synthesized benzoxazines. The novel benzoxazines showed nematic and smectic phases upon cooling cycle from the isotropic liquids. The LC benzoxazines also showed a nematic phase upon heating cycle, indicating that the novel benzoxazines are enantiotropic liquid crystals. The ring-opening polymerization behavior of the LC benzoxazines was investigated by DSC and IR analyses. POM observations showed that a polybenzoxazine film, prepared by thermally curing the LC benzoxazine up to 160 °C for 1 h, exhibited birefringence at room temperature.     

Bio-based benzoxazines based on sesamol: Synthesis and properties

Sesamol was used with furfurylamine, dehydroabietylamine, and stearylamine to prepare three fully-bio-based benzoxazines: S-fa, S-da, and S-sa, respectively. Their structures were confirmed by Fourier transform infrared spectroscopy (FTIR), ¹H-NMR, and ¹³C-NMR. FTIR and differential scanning calorimetry were performed to monitor the curing behaviors of S-fa, S-da, and S-sa. The thermal stability of the corresponding polybenzoxazines was supported by thermogravimetric analysis, and all polymers showed high thermal stability. The limiting oxygen indexes of all three polybenzoxazines were higher than 30, suggestive of good flame retardancy. The use of polybenzoxazine for the corrosion protection of Q235 low-carbon steel was also studied. The results of OCP curves and Tafel plots demonstrate that the polymer coatings provide good corrosion resistance and can be applied to this purpose. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48255.     

Synthesis and thermal cure of high molecular weight polybenzoxazine precursors and the properties of the thermosets

High molecular weight polybenzoxazine precursors have been synthesized from aromatic or aliphatic diamine and bisphenol-A with paraformaldehyde. The precursors were obtained as soluble white powder. Molecular weight was estimated from the size exclusion chromatography to be several thousands. The structure of the precursors was confirmed by IR, ¹H NMR and elemental analysis, indicating the presence of cyclic benzoxazine structure. The ratio of the ring-closed benzoxazine structure and the ring-opened structure in the high molecular weight precursor was estimated from ¹H NMR spectrum and also from the exotherm of DSC, showing that the ratio of the ring-closed benzoxazine structure was 77–98%. The precursor solution was cast on glass plate, giving transparent and self-standing precursor films, which was thermally cured up to 240 °C to give brown transparent polybenzoxazine films. The toughness of the crosslinked polybenzoxazine films from the high molecular weight precursors was greatly enhanced compared with the cured film from the typical low molecular weight monomer. Tensile measurement of the polybenzoxazine films revealed that polybenzoxazine from aromatic diamine exhibited the highest strength and modulus. While, polybenzoxazine from longer aliphatic diamine had higher elongation at break. The viscoelastic analyses showed that the glass transition temperature of the polybenzoxazines derived from the high molecular weight precursors were as high as 238–260 °C. Additionally, these novel polybenzoxazine thermosets showed excellent thermal stability.     

Design of thermosetting polymeric systems based on benzoxazines modified with maleic anhydride

A novel benzoxazine (BzPFA) with carboxylic acid groups in its structure was synthesized in a two‐step process. First, BzPOH monomer was obtained from bisphenol A, paraformaldehyde, and ethanolamine with an initial molar ratio 1:4:2. Then, BzPOH was reacted with maleic anhydride using a stoichiometric 1:1 ratio of oxazine ring:maleic anhydride to produce a mixture of oligomeric species named BzPFA. The products were characterized by nuclear magnetic resonance, size‐exclusion chromatography, and Fourier transform infrared spectroscopy. BzPFA presented a weight‐average molecular weight of 50,000 g mol^?1. Mixtures of the novel precursor and the conventional benzoxazine based on bisphenol A (BzBA) (60:40 and 40:60 weight ratios) were prepared and three different curing conditions were considered in order to study the effect of BzPFA on curing and final properties. Blends exhibited improved properties respect to BzBA even at relatively low curing temperatures. These results can be associated to the network crosslinked by ester bonds that promotes a high rigidity. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46183.     

丙烯酸酯无皂水溶胶涂料热固化性能的研究

用红外光谱法和差热分析法研究了热固性丙烯酸酯无皂水溶胶与六甲氧基甲基三聚氰胺(HMMM)的固化过程。实验表明水溶胶的固化是分两步进行的,羟基和羧基与固化剂HMMM上的甲氧基在不同的温度区间交联固化,并且羟基的交联固化反应温度低于羧基的。同时,考察了固化剂用量对固化温度和固化度的影响。     

Dynamic mechanical and shape memory properties of copolymers based on o‐allylphenol type benzoxazines and diglycidyl ether of bisphenol‐A

Three benzoxazines based on o‐allylphenol and 1,6‐hexamethylenediamine (HDA) or 4,4′‐diaminodiphenyl methane (DDM) or 4,4′‐diaminodiphenyl ether (DDE) were respectively blended with diglycidyl ether of bisphenol‐A (DGEBA) in various weight ratios followed by thermal polymerization to prepare three series of benzoxazine/DGEBA copolymers. With increasing DGEBA content, the peak temperature of the exothermic peaks in the DSC curves shows a systematic increase for the three series of benzoxazine/DGEBA blends. Each copolymer shows a single glass transition temperature (T_g). As the content of DGEBA is increased, T_g reaches a minimum for the copolymer system based on HDA but a maximum for the two systems based on DDM and DDE. For the same benzoxazine/DGEBA weight ratio, copolymers based on DDM and DDE show high T_g values over those based on HDA. The three series of benzoxazine/DGEBA copolymers exhibit a one‐way dual shape memory effect based on T_g, and the shape memory properties of the copolymers under tensile deformation mode vary with the variation of both diamine bridge structure and DGEBA content. © 2018 Society of Chemical Industry     

Rheological and thermal properties of blends of a long-chain branched polypropylene and different linear polypropylenes

Blends of a long-chain branched polypropylene (LCB-PP) and four linear polypropylenes (L-PP) having different molecular weights were prepared using a twin screw extruder. The linear viscoelastic properties suggested the immiscibility of the high molecular weight L-PP based blends, and the miscibility of the low molecular weight L-PP based blends. In addition, the Palierne emulsion model showed good predictions of the linear viscoelastic properties for both miscible and immiscible PP blends. However, as expected, the low-frequency results showed a clear effect of the interfacial tension on the elastic modulus of the blends for the high molecular weight L-PP based blends. A successful application of time-temperature superposition (TTS) was found for the blends and neat components. Uniaxial elongational properties were obtained using a SER unit mounted on an ARES rheometer. A significant strain hardening was observed for the neat LCB-PP as well as for all the blends. The influence of adding LCB-PP on the crystallinity, crystallization temperature, melting point, and rate of crystallization were studied using differential scanning calorimetry (DSC). It was found that the melting point and degree of crystallinity of the blends first increased by adding up to 20 wt% of the branched component but decreased by further addition. Adding a small amount of LCB-PP caused significant increase of the crystallization temperature while no dramatic changes were observed for blends containing 10 wt% LCB-PP and more. Furthermore, the crystalline morphology during and after crystallization of the various samples was monitored using polarized optical microscopy (POM). Compared to the neat linear polymers, finer and numerous spherulites were observed for the blends and LCB-PP. Dynamic mechanical (DMA) data of the blends and pure components were also analyzed and positive deviations from the Fox equation for the glass transition temperature, T_g, were observed for the blends.     

Synthesis and characterization of bio-based benzoxazines derived from thymol

In the present study, bio-based benzoxazine resins were synthesized from bio-based phenolic compound; thymol, and three different amines; ethylamine, aniline and 1,6-diaminohexane, and paraformaldehyde by solvent-free condensation reaction. The chemical structures of bio-based benzoxazines; T-ea (thymol, ethylamine), T-a (thymol, aniline), and T-dh (thymol, 1,6-diaminohexane) were characterized by proton nuclear magnetic resonance spectroscopy, Fourier transform infrared (FTIR) spectroscopy, elemental analysis, and high-resolution mass spectrometry. The curing studies of T-ea, T-a, and T-dh bio-based benzoxazines were performed by stepwise thermal treatment at 150, 175, 200, 225, and 250 °C. The polymerization (ring-opening and crosslinking reactions) of T-ea, T-a, and T-dh bio-based benzoxazines was investigated by FTIR spectroscopy. Cure analysis was conducted using differential scanning calorimetry and the changes in thermal properties of the T-ea, T-a, and T-dh bio-based benzoxazine resins and their corresponding thermally crosslinked polybenzoxazines PT-ea, PT-a, and PT-dh were studied by thermogravimetric analyzer. The results indicated that all the thymol-based polybenzoxazines have shown enhanced thermal stability. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47371.     

不同固化条件对聚苯并噁嗪固化行为的影响研究

为了制得耐热性能较好、可以固化"零"收缩的聚苯并噁嗪,采用差示扫描量热(DSC)法和热失重(TGA)法对不同固化条件下制取的一系列聚苯并噁嗪的固化行为和耐热性能进行了分析,同时对固化温度和固化时间与聚苯并噁嗪体积的变化关系进行了研究。结果表明:聚苯并噁嗪的耐热性随固化温度的升高而上升,延长固化时间试样的耐热性略有提高;在200℃/2h固化条件下制取的聚苯并噁嗪,其分解温度为410℃,500℃时的残炭率为51.8%,700℃时的残炭率为40.8%;固化所得聚苯并噁嗪的体积随固化温度的升高而减小,随固化时间的延长而增大;通过控制固化条件,聚苯并噁嗪可以实现固化"零"收缩。     

Effects of aluminium nitride silane-treatment on the mechanical and thermal properties of polybenzoxazine matrix

A new kind of polymer composite, produced from the typical polybenzoxazine and 0–30 wt-% native and silane-treated aluminium nitride (T-AlN), was investigated. The mechanical tests revealed a significant increase in the microhardness and flexural properties upon adding the T-AlN particles compared to that obtained from the untreated ones. By adding 0–30 wt-% T-AlN, the tensile moduli were accurately reproduced by the Halpin-Tsai and Nielsen models. At 30 wt-% T-AlN, dynamic mechanical analysis showed a significant increase in the storage moduli and the glass transition temperature (T_g), reaching 3.2?GPa and 217°C, respectively. The thermal stability of these materials was significantly improved upon the addition of the T-AlN fillers. These improvements are attributed to the high thermal and mechanical properties of the fillers and their good dispersion and adhesion in and to the matrix as revealed by a morphological analysis.     

Synthesis and properties of a new crosslinkable polymer containing benzoxazine moiety in the main chain

Using difunctional phenolic and amine compounds, a new polymer with benzoxazine groups in the main chain has been synthesized through the Mannich reaction of a phenol, formaldehyde, and an amine. ¹H and ¹³C nuclear magnetic resonance spectroscopies, Fourier transform infrared spectroscopy, size exclusion chromatography, and elemental analysis are used to characterize the resulting polymer. Polymer with molecular weight of approximately 10,000 Da is obtained. The resultant polymer has a moderately broad polydispersity index. The thermal properties of the polymer have also been studied by differential scanning calorimetry and thermogravimetric analysis.     

Synthesis and characterization of novel main-chain benzoxazines containing cycloaliphatic and aliphatic structures and their thermal and dielectric properties

With the rapid development of ultra-large-scale integrated circuits and aerospace, the demand for materials with excellent overall performances is on the rise. In this study, we have successfully synthesized novel main-chain benzoxazine precursors ((BPA-AD/dd1)_main) containing both cycloaliphatic and aliphatic structures by employing adamantanediamine and Priamine 1074 for the first time, and their chemical structures and polymerization behaviors were characterized using Fourier transform infrared spectroscopy (FT-IR), NMR spectroscopy (¹H-NMR) and differential scanning calorimetry (DSC). The results showed that the exothermic onset of the (BPA-AD/dd1)_main shifted to lower temperatures with an increasing molar ratio of Priamine 1074. Furthermore, the thermal properties, dielectric properties, surface hydrophobicity, and tensile properties of P(BPA-AD/dd1)_main films were explored via dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), contact angle measuring instrument, an impedance analyzer and universal testing machine. The molar ratio of Priamine 1074 and 1,3-Bis(4-anilino)-adamantane (AD) significantly influenced the thermal properties, dielectric properties, and surface hydrophobicity of P(BPA-AD/dd1)_main. P(BPA-AD 0.75)_main exhibited a high T_g of 296.8°C, excellent dielectric properties (Dk = 2.58 and Df = 0.0055 @ 10 MHz), and large water contact angle as high as 105.8°, qualifying it as a potential candidate for interlayer materials in ultra-large-scale integrated circuits and resin matrix in high-performance composites.     

胶粘剂固化行为对性能的影响

研究了一种中温固化耐高温胶粘剂固化行为对胶粘剂力学性能和耐久性能的影响,表明胶粘剂只有达到一定的固化程度,才能获得一定的交联密度,耐热性能、粘接强度和耐久性能。同时胶粘剂的固化时间和温度存在等效性关系。     

Jatropha curcas oil based alkyd/epoxy/graphene oxide (GO) bionanocomposites: Effect of GO on curing,mechanical and thermal properties

Jatropha curcas oil based alkyd/epoxy/GO bionanocomposites were prepared by direct solution blending of alkyd/epoxy blend matrix with GO nano filler. Structures and properties of the bionanocomposites were characterized with Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy, differential scanning calorimetry, thermogravimetric analysis, and tensile testing. X-ray diffraction and transmission electron microscopy study demonstrates the formation of highly exfoliated GO layers and its homogeneous dispersion throughout the polymer matrix with 1 and 3 wt% GO. However, the intercalated structure is predominant with 5 wt% GO. The homogeneous dispersion and the strong interaction of the GO layers and the polymer matrix induced the significant improvement in thermal and mechanical properties of the bionanocomposites. The tensile strength and elastic modulus of the bionanocomposite increased by 133% and 68% respectively with 3 wt% GO loading. The thermal stability of the bionanocomposite improved by 39 °C and T_g is shifted toward higher temperature by 20 °C as compared to the pristine polymer. Incorporation of GO significantly decreases the curing time of the alkyd/epoxy resin blend.     

Effects of adhesive modulus and curing conditions on curing behavior of silicate based ceramic coatings on carbon fiber reinforced resin matrix composites

Sodium silicate based ceramic coatings were prepared on the surface of carbon fiber reinforced epoxy resin matrix composite. The coatings were obtained by curing the mixture of silicate adhesive, SiO₂ or Na₂SiF₆ as curing agent, and YSZ and Al₂O₃ as filler. The effects of adhesive modulus, curing agent, curing temperature and time on curing behavior of the coatings were investigated. The results indicated that the coating obtained from 2.7 modulus of silicate adhesive was dense, cohesiveness, uniform and continuous. As curing agent, SiO₂ could promote curing better than Na₂SiF₆, achieving complete curing of the coating. And the coating containing SiO₂ as curing agent was dense, flat and well adhered to the substrate. The curing behavior of coatings was significantly affected by curing temperature and time. The coatings could be cured completely with the increase of curing temperature. The best curing result was obtained at 100 °C curing temperature. Also the experimental results showed that the characteristics of coatings were improved to a certain extent by prolonging the curing time.     

Studies on the curing behavior,thermal, and mechanical properties of epoxy resin-co-amine-functionalized lead phthalocyanine

A high performance copolymer was prepared by using epoxy (EP) resin as matrix and 3,10,17,24-tetra-aminoethoxy lead phthalocyanine (APbPc) as additive with dicyandiamide as curing agent. Fourier-transform infrared spectroscopy, dynamic mechanical analysis (DMA), differential scanning calorimetric analysis (DSC), and thermogravimetric analysis (TGA) were used to study the curing behavior, curing kinetics, dynamic mechanical properties, impact and tensile strength, and thermal stability of EP/APbPc blends. The experimental results show that APbPc, as a synergistic curing agent, can effectively reduce the curing temperature of epoxy resin. The curing kinetics of the copolymer was investigated by non-isothermal DSC to determine kinetic data and measurement of the activation energy. DMA, impact, and tensile strength tests proved that phthalocyanine can significantly improve the toughness and stiffness of epoxy resin. Highest values were seen on the 20 wt% loading of APbPc in the copolymers, energy storage modulus, and impact strength increased respectively 388.46 MPa and 3.6 kJ/m², T_g decreased 19.46°C. TGA curves indicated that the cured copolymers also exhibit excellent thermal properties.     

Epoxy/imidazolium-based ionic liquid systems: The effect of the hardener on the curing behavior,thermal stability,and microwave absorbing properties

A new transparent microwave absorbing coating was developed by compounding 1-butyl-3-methyl imidazolium tetrafluoroborate (bmim.BF₄) ionic liquid (IL) with diglycidyl ether of bisphenol A-type epoxy resin. The systems were crosslinked with the IL alone or combined with conventional hardeners, as anhydride or aromatic amine. The curing behavior was investigated by thermal and spectroscopic analysis performed at high temperatures. Neat bmim.BF₄ was able to cure epoxy resin, giving rise to networks with outstanding thermal stability compared with the systems cured with anhydride or aromatic amine. bmim.BF₄ accelerated the curing process in the presence of aromatic amine but retarded this event when anhydride was used as an external curing agent. The glass-transition temperature evaluated by dynamic mechanical analysis decreased when the amount of IL increased, which can be attributed to side reactions during the curing process, as well as the plasticizing effect of IL. The epoxy networks cured with bmim.BF₄ alone or in combination with anhydride or aromatic amine were transparent and presented considerable microwave absorbing properties in the X-band frequency range (8–12 GHz), being the best performance observed for the systems cured with bmim.BF4/anhydride curing system, with reflection loss value around −16 dB at 11.3 GHz. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48326.     

High-toughness,environment-friendly solid epoxy resins: Preparation,mechanical performance,curing behavior,and thermal properties

The development of a facile and efficient approach to prepare high-toughness epoxy resin is vital but has remained an enormous challenge. Herein, we have developed a high-performance environment-friendly solid epoxy resin modified with epoxidized hydroxyl-terminated polybutadiene (EHTPB) via one-step melt blending. The characterization, mechanical performance, curing behavior, and thermal properties of EHTPB-modified epoxy resin were investigated. EHTPB-modified epoxy resin exhibited excellent toughness with a 100% increase in elongation at break of tensile than that of neat epoxy resin. The transfer stress and dissipated energy in the rubber phase were predominant mechanisms of toughening. The toughening effect of EHTPB on solid epoxy resin was better than that of some of the previously reported liquid epoxy resins. Meanwhile, at 10 wt % of EHTPB loading, the EHTPB-modified epoxy resin displayed high strength and 22 and 101% improvement of flexural strength and impact strength, respectively. Moreover, at 10 wt % of EHTPB loading, the activation energy of EHTPB-modified epoxy resin for curing reaction decreased from 73.89 to 65.12 kJ·mol⁻¹, which is beneficial for the curing reaction. Furthermore, EHTPB-modified epoxy resin had a good thermal stability and the initial degradation temperature increased from 249 to 313 °C at 10 wt % of EHTPB loading. This work provides a simple-preparation and highly efficient and large-scale approach for the production of high-toughness environment-friendly solid epoxy resins. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48596.