Synthesis,characterization, and thermal properties of alkyl‐functional naphthoxazines

A series of alkyl‐functional naphthoxazine resins having various alkyl chain lengths from C1 to C18 are synthesized with a high yield and high purity by the reactions of 1,5‐dihydroxynaphthalene, formaldehyde, and aliphatic amines. The proposed chemical structures of the naphthoxazines are confirmed by high‐resolution mass spectrometry, ¹H nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, and pyrolysis mass spectrometry studies. The alkyl‐functional naphthoxazines have shown low polymerization temperature characteristics where polymerization of these monomers is achieved in the range of 150–170°C yielding cross‐linked polynaphthoxazines. The low‐temperature polymerization characteristics and the associated thermal degradation behaviors are studied. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Flame‐retardant properties and mechanisms of epoxy thermosets modified with two phosphorus‐containing phenolic amines

Two phosphorus‐containing phenolic amines, a 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO)‐based derivative (DAP) by covalently bonding DOPO and imine (SB) obtained from the condensation of p‐phenylenediamine with salicylaldehyde, and its analog (AP) via the addition reaction between diethyl phosphite and SB, were used to prepare flame‐retardant epoxy resins. The burning behaviors and dynamic mechanical properties of epoxy thermosets were studied by limited oxygen index (LOI) measurement, UL‐94 test, and dynamic mechanical analysis. The flame‐retardant mechanisms of modified thermosets were investigated by thermogravimetric analysis, Py‐GC/MS, Fourier transform infrared, SEM, elemental analysis, and laser Raman spectroscopy. The results revealed that epoxy thermoset modified with DAP displayed the blowing‐out effect during UL‐94 test. With the incorporation of 10 wt % DAP, the modified thermoset showed an LOI value of 36.1% and V‐0 rating in UL‐94 test. The flame‐retardant mechanism was ascribed to the quenching and diluting effect in the gas phase and the formation of phosphorus‐rich char layers in the condensed phase. However, the thermoset modified with 10 wt % AP only showed an LOI value of 25.7% and no rating in UL‐94 test, which was possibly ascribed to the mismatching of charring process with gas emission process during combustion. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43953.     

Synthesis,polymerization, and properties of the allyl‐functional phthalonitrile

A novel bisphthalonitrile monomer containing allyl groups (DBPA‐Ph) had been synthesized via the reaction of diallyl bisphenol A (DBPA) and 4‐nitrophthalonitrile. The chemical structure of DBPA‐Ph was confirmed by ¹HNMR, ¹³CNMR, and FTIR spectroscopy. The curing behaviors and processability of DBPA‐Ph were studied by differential scanning calorimetry (DSC) and dynamic rheological analysis. The monomer manifested a two‐stage thermal polymerization pattern. The first stage was attributed to the polymerization of allyl groups and the second to the ring‐form polymerization of cyano groups. The result of dynamic rheological analysis indicated the monomer had wide curing window and the self‐catalyzed curing behavior. DBPA‐Ph polymers were prepared from the thermal polymerization with short curing time, showing high glass transition temperature (>350°C) and attractive thermal decomposition temperature (>430°C). The outstanding glass transition temperature, desirable thermo‐oxidative stabilities, good processability and sound process conditions could provide more applications to the DBPA‐Ph polymers. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41203.     

Preparation and properties of novel hybrid resins based on acetylene‐functional benzoxazine and polyvinylsilazane

A serial of addition‐curable hybrid resins for resin matrix of advanced composites are prepared by thermal prepolymerization between acetylene‐functional benzoxazine(BZ) and polyvinylsilazane(PSN) with various weight ratios. Processing capability of BZ‐PSN resin is investigated by measuring viscosity. Cure behavior is investigated by differential scanning calorimetry (DSC) and Fourier transform infrared (FT‐IR) spectra. Thermal property of cured BZ‐PSN resin is investigated by Thermogravimetric analysis (TGA) and Dynamic mechanical analysis (DMA). BZ‐PSN resin shows a low viscosity of 40–180 mPa·s between 60 and 90°C, and maintains the low viscosity for 6 h, indicating that the resin is suitable for resin transfer molding (RTM) process to fabricate composites. DSC results show that BZ‐PSN resin can be cured completely at about 250°C without adding any other curing additives. FT‐IR shows the reaction between BZ and PSN take place. TGA shows that thermal stability of cured BZ‐PSN resin is increased with the content of polyvinylsilazane increasing both in nitrogen and in air. DMA shows cured hybrid resins have excellent thermal properties. The excellent processability and thermal properties suggest that BZ‐PSN resin is a promising candidate for resin matrix of advanced composites. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3794–3799, 2013     

Thermal and mechanical properties of tetra‐functional mesogenic type epoxy resin cured with aromatic amine

A novel tetra‐functional epoxy monomer with mesogenic groups was synthesized and characterized by ¹H‐NMR and FTIR. The synthesized epoxy monomer was cured with aromatic amine to improve the thermal property of epoxy/amine cured system. The glass transition temperature (T_g) and coefficient of thermal expansion (CTE) of the cured system were investigated by dynamic mechanical analysis and thermal mechanical analysis. The properties of the cured system were compared with the conventional bisphenol‐A type epoxy and mesogenic type epoxy system. The storage modulus of the tetra‐functional mesogenic epoxy cured systems showed the value of 0.96 GPa at 250 °C, and T_g‐less behavior was clearly observed. The cured system also showed a low CTE at temperatures above 150 °C without incorporation of inorganic components. These phenomena were achieved by suppression of the thermal motion of network chains by introduction of both mesogenic groups and branched structure to increase the cross linking density. The temperature dependency of the tensile property and thermal conductivity of the cured system was also investigated. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46181.     

Synthesis,cure kinetics,and thermal properties of the Bis(3‐allyl‐2‐cyanatophenyl)sulphoxide/BMI blends

A novel allyl functionalized dicyanate ester resin bearing sulfoxide linkage was synthesized. The monomer was characterized by Fourier Transform Infrared (FT‐IR) Spectroscopy, ¹H‐, and ¹³C Nuclear Magnetic Resonance (NMR) spectroscopy and elemental analysis. The monomer was blended with bismaleimide (BMI) at various ratios in the absence of catalyst. The cure kinetics of one of the blends was studied using differential scanning calorimetry [nonisothermal] and the kinetic parameters like activation energy (E), pre‐exponential factor (A), and the order of the reaction (n) were calculated by Coats‐Redfern method and compared with those calculated using the experimental Borchardt‐Daniels method. The thermal stability of the cured dicyanate, BMI, and the blends was studied using thermogravimetric analyzer. The initial weight loss temperature of dicyanate ester is above 380°C with char yield of about 54% at 800°C. Thermal degradation of BMI starts above 463°C with the char yield of about 68%. Inclusion of BMI in cyanate ester increases the thermal stability from 419 to 441°C. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Low dielectric thermoset. I. Synthesis and properties of novel 2,6‐dimethyl phenol‐dicyclopentadiene epoxy

A 2,6‐dimethyl phenol‐dicyclopentadiene novolac was synthesized from dicyclopentadiene and 2,6‐dimethyl phenol, and the resultant 2,6‐dimethyl phenol‐dicyclopentadiene novolac was epoxidized to 2,6‐dimethyl phenol‐dicyclopentadiene epoxy. The structures of novolac and epoxy were confirmed by Fourier transform infrared spectroscopy (FTIR), elemental analysis, mass spectroscopy (MS), nuclear magnetic resonance spectroscopy (NMR), and epoxy equivalent weight titration. The synthesized 2,6‐dimethyl phenol‐dicyclopentadiene epoxy was then cured with 4,4‐diaminodiphenyl methane (DDM), phenol novolac (PN), 4,4‐diaminodiphenyl sulfone (DDS), and 4,4‐diaminodiphenyl ether (DDE). Thermal properties of cured epoxy resins were studied by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), dielectric analysis (DEA), and thermal gravimetric analysis (TGA). These data were compared with those of the commercial bisphenol A epoxy system. Compared with the bisphenol A epoxy system, the cured 2,6‐dimethyl phenol‐ dicyclopentadiene epoxy resins exhibited lower dielectric constants (～3.0 at 1 MHz and 2.8 at 1 GHz), dissipation factors (～0.007 at 1 MHz and 0.004 at 1 GHz), glass transition temperatures (140–188°C), thermal stability (5% degradation temperature at 382–404°C), thermal expansion coefficients [50–60 ppm/°C before glass‐transition temperature (T_g)], and moisture absorption (0.9–1.1%), but higher modulus (～2 Gpa at 60°C). © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2607–2613, 2003     

High‐performance thermosets with tailored properties derived from methacrylated eugenol and epoxy‐based vinyl ester

A renewable chemical, eugenol, is methacrylated to produce methacrylated eugenol (ME) employing the Steglich esterification reaction without any solvent. The resulting ME is used as a low‐viscosity co‐monomer to replace styrene in a commercial epoxy‐based vinyl ester resin (VE). The volatility and viscosity of ME and styrene are compared. The effect of ME loading and temperature on the viscosity of the VE–ME resin is investigated. Moreover, the thermomechanical properties, curing extent and thermal stability of the fully cured VE–ME thermosets are systematically examined. The results indicate that ME is a monomer with low volatility and low viscosity, and therefore the incorporation of ME monomer in VE resins allows significant reduction of viscosity. Moreover, the viscosity of the VE–ME resin can be tailored by adjusting the ME loadings and processing temperature to meet commercial liquid molding technology requirements. The glass transition temperatures of VE–ME thermosets range from 139 to 199 °C. In addition, more than 95% of the monomer is incorporated and fixed in the crosslinked network structure of VE–ME thermosets. Overall, the developed ME monomer exhibits promising potential for replacing styrene as an effective low‐viscosity co‐monomer. The VE–ME resins show great advantages for use in polymer matrices for high‐performance fiber‐reinforced composites. This work is of great significance to the vinyl ester industry by providing detailed experimental support. © 2018 Society of Chemical Industry     

Influence of the introduction of flexible alkyl chains on the thermal behavior and mechanical properties of mesogenic epoxy thermosets

A mesogenic epoxy resin (DGETAM) was cured with a series of curing agents having different lengths of long alkyl chain (nBAB, n = 4, 8, 12). Properties of the curings were compared with those of the DGEBA cured with the same curing agents revealing the achievement of a balance between certain levels of thermal properties and excellent mechanical properties. Moreover, some curing systems were prepared with twin mesogenic type epoxy resins (DGEnMA, n = 4, 6, 8, 10, 12) having different lengths of alkyl chain as a flexible spacer and the same curing agents (n′BABs). Combinations of the same concentrations of chemical structures in the basic units of the network structure were applied, and the thermal and mechanical properties of their curing systems were investigated. The fracture energy of each system increased considerably with the increase of the alkyl chain length that adjoins the two mesogenic groups in the epoxy resins. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44244.     

Thermal and mechanical properties of acrylated expoxidized‐soybean oil‐based thermosets

A series of epoxidized‐soybean oil (ESO) with different epoxyl content were synthesized by in situ epoxidation of soybean oil (SBO). The acrylated epoxidized‐soybean oil (AESO) was obtained by the reaction of ring opening of ESO using acrylic acid as ring opener. The acrylated expoxidized‐soybean oil‐based thermosets have been synthesized by bulk radical polymerization of these AESOs and styrene. The thermal properties of the resins were characterized by differential scanning calorimetry (DSC) and thermo‐gravimetric analysis (TG). The results showed that these resins possess high thermal stability. There were two glass transition temperature of each resin due to the triglycerides structure of the resins. The tensile strength and impact strength of the resins were also recorded, and the tensile strength and impact strength increased as the iodine value of ESO decreased. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis and properties of novel benzocyclobutene‐functionalized siloxane thermosets

Two kinds of novel benzocyclobutene (BCB) functionalized monomers were synthesized through imidization of siloxane‐containing dianhydride with 4‐aminobenzocyclobutene. The BCB monomers obtained exhibited good solubility in various organic solvents. They were converted into crosslinked polymer via ring opening and the following Diels–Alder reaction at proper temperature. The curing kinetics were studied by non‐isothermal differential scanning calorimetry. The BCB polymers showed good thermal stability, excellent dielectric properties, low water absorption and good planarization. Moreover, the thermal and mechanical properties of the BCB resins could be adjusted by the length of the siloxane unit. The BCB resins with a shorter siloxane chain exhibited higher glass transition temperature, higher modulus and lower coefficient of thermal expansion than BCB resins with longer chains. © 2013 Society of Chemical Industry     

Mechanical and thermal properties of bio‐based CaCO3/soybean‐based hybrid unsaturated polyester nanocomposites

Bio‐based calcium carbonate nanoparticles (CaCO₃) were synthesized via size reduction of eggshell powder using mechanical attrition followed by high intensity ultrasonic irradiation. The transmission electron microscopic (TEM) and BET surface area measurements show that these particles are less than 10 nm in size and a surface area of ～44 m²/g. Bio‐based nanocomposites were fabricated by infusion of different weight fractions of as‐prepared CaCO₃ nanoparticles into Polylite® 31325‐00 resin system using a non‐contact Thinky® mixing method. As‐prepared bio‐nanocomposites were characterized for their thermal and mechanical properties. TEM studies showed that the particles were well dispersed over the entire volume of the matrix. Thermal analyses indicated that the bio‐nanocomposites are thermally more stable than the corresponding neat systems. Nanocomposite with 2% by weight loading of bio‐CaCO₃ nanoparticles exhibited an 18°C increase in the glass transition temperature over the neat Polylite 31325 system. Mechanical tests have been carried out for both bio‐nanocomposites and neat resin systems. The compression test results of the 2% Bio‐CaCO₃/Polylite 31325 nanocomposite showed an improvement of 14% and 27% in compressive strength and modulus respectively compared with the neat system. Details of the fabrication procedure and thermal and mechanical characterizations are presented in this article. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1442–1452, 2013     

Trehalose‐based thermosetting resins. I. Synthesis and thermal properties of trehalose vinylbenzyl ether

Trehalose vinylbenzyl ether was synthesized from trehalose and p‐chloromethylstyrene (CMS) in DMSO in the presence of powdered NaOH. The structure of the product was characterized by IR and ¹H NMR spectroscopy. Degree of substitution (DS) on a trehalose unit calculated from the ¹H NMR spectrum varied from 2.4 to 3.2 by changing the feed ratio of p‐chloromethylstyrene to trehalose. Thermal properties of the resin were analyzed by differential scanning calorimetry (DSC). DSC analysis revealed that the resin DS 2.4 has one exothermal peak at 132°C, whereas the resins DS 2.8 and 3.0 have two exothermal peaks. Furthermore, the resin DS 3.2 was found to have only one exothermal peak at 191°C. Dynamic mechanical analysis (DMA) and thermomechanical analysis (TMA) revealed that the cured resin has one transition, implying a glass transition. Biodegradability was assayed by the BOD method, and several percent of the cured resin was found to be degraded with activated sludge for 50 days. Further degradation, however, was not observed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 46–51, 2004     

High-performance thermosets with tailored properties derived from multi-arm stared vanillin and carbon fiber composites

Vanillin, a rigid compound can be separated from lignin, is a promising sustainable candidate for industrial and high performance polymers, while synthesis of hexa-epoxies is challenging. Meanwhile, carbon fiber reinforced bio-based polymers combining high performance are more difficult to be achieved because of the contradictions of liquidity and high rigidity in the polymer structure and performance. In this paper, a novel hexa-epoxy functionalized bio-based epoxy resin (HPVIGEP) with a multi-arm star structure, which simultaneously reduced the viscosity and improved thermo-mechanical properties. The rheological behavior analysis results of HPVIGEP indicated that the viscosity was 3406.9 mPa·s at 25°C, which dramatically decreased by 75.8% compared to DGEBA (14,096 mPa·s), leading to excellent processability and adaptability. At the same time, the study on mechanical properties revealed that the cured HPVIGEP manifested 30.6%, 33.7% and 49.0% in higher tensile strength, tensile modulus and storage modulus (30°C) than of cured commercial epoxy, respectively. The tensile strength and flexural strength of carbon fiber composites which were applied HPVIGEP were increased by 9.3% and 10.9%, respectively. In a word, this work provides the promise for the application of environmentally friendly bio-based composite materials.     

Processing and mechanical properties of bio‐derived vinyl ester resin‐based composites

A “green” vinyl ester resin (GVER) is investigated for use in structural applications. The GVER was formulated using a monodisperse vinyl ester created via a novel synthetic route capable of using bio‐waste material from paper and biodiesel industries. The GVER was used either as a neat resin or as blended with a commercial vinyl ester resin. The processing viscosity and gel times are investigated. The GVER reaches a similar viscosity as the commercial resin with only half the styrene monomer content, thereby reducing the volatile organic compounds associated with manufacturing. Composites of the GVER matrix reinforced by carbon fabric were tested for their tensile and flexural properties. The mechanical performance of the GVER compares favorably with commercial resin and provide a route for composites manufacturing from sustainably sourced vinyl ester matrix. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44642.     

Polyurethane‐modified epoxy resin: Solventless preparation and properties

A polyurethane‐modified epoxy resin system with potential as an underfill material in electronic packaging and its preparation procedure were studied. The procedure enabled the practical incorporation of an aliphatic polyurethane precursor, synthesized from poly(ethylene glycol) and hexamethylene diisocyanate without a solvent, as a precrosslinking agent into a conventional epoxy resin. With a stoichiometric quantity of the polyurethane precursor added to the epoxy (ca. 5 phr), the polyurethane‐modified epoxy resin, mixed with methylene dianiline, exhibited a 36% reduction in the contact angle with the epoxy–amine surface, a 31% reduction in the cure onset temperature versus the control epoxy system, and a viscosity within the processable range. The resultant amine‐cured thermosets, meanwhile, exhibited enhanced thermal stability, flexural strength, storage modulus, and adhesion strength at the expense of a 5% increase in the coefficient of thermal expansion. Exceeding the stoichiometric quantity of the polyurethane precursor, however, reduced the thermal stability and modulus but further increased the coefficient of thermal expansion. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Use of allyl‐functional benzoxazine monomers as replacement for styrene in vinyl ester resins

New vinyl ester systems are prepared using allyl‐functional benzoxazine monomers, 3‐allyl‐6‐methyl‐3,4‐dihydro‐2H‐benzo[e][1,3]oxazine (pC‐ala) or bis(3‐allyl‐3,4‐dihydro‐2H‐benzo[e][1,3]oxazin‐6‐yl)methane (BF‐ala), as reactive diluents for vinyl ester resins derived from an epoxy resin, diglycidyl ether of bisphenol A, instead of using styrene. Different initiators are used to investigate the copolymerization of allyl function from pC‐ala with vinyl function from vinyl ester resin prepolymer. The temperature dependence of viscosity is studied to demonstrate the retention of processability of the new vinyl ester resins. Dynamic mechanical and thermogravimetric analyses are used to investigate the dynamic mechanical properties and thermal stability of the new resins. Copyright © 2012 Society of Chemical Industry     

Addition‐curable propargyl‐containing novolac‐type phenolic resin: Its synthesis,characterization, cure,and thermal properties

In this article, propargyl functionalized novolac resins (PN resins), with varying propargyl contents and varying molecular weights, were synthesized conveniently. The structural characteristics were determined by ¹HNMR and FTIR methods. Thermal cure studies revealed that the uncatalyzed thermal cure was remarkably affected by propargyl extent, while it was hardly affected by molecular weight. The processability of the as‐prepared PN resins was excellent as matrix of composite materials. The cure mechanism was complicated; postcure at high temperature was required to achieve entire crosslink formation. Both dynamic mechanical analysis and thermogravimetric analysis showed that the cured PN resins had substantially improved thermal mechanical properties and thermal stability in comparison to conventional cured phenolics. High propargyl extent was preferred for high thermal stability. The results show that PN resin is one of the ideal candidates for advanced composites matrices in thermostructural and ablative applications. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1010–1017, 2006     

Influence of partial cross‐linking degree on basic physical properties of RTM6 epoxy resin

Thermo‐physical and mechanical properties of partially and completely cross‐linked RTM6 epoxy resin samples in the glassy state have been investigated. A significant dependence of glass transition temperature, density, and modulus on the curing history and the curing degree is found. Density and modulus decrease with increasing curing degree and show a step‐like irregularity in the so called transition region, which is related to the transition from rubber to glassy state during cross‐linking and the starting of structural relaxation processes. The relationship between the thermo‐physical and mechanical properties, which is important for the development of new processing routes for fiber reinforced polymers, is addressed. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4338–4346, 2013     

Mechanical and thermal properties of novel rubber‐toughened epoxy blend prepared by in situ pre‐crosslinking

A novel method is used for preparing liquid rubber‐toughened epoxy blend, in which an initiator was added to the liquid rubber–epoxy mixture to initiate crosslinking reaction of liquid rubber, and then curing agent was added to form the thermoset. Two epoxy blends with carboxyl‐terminated butadiene‐acrylonitrile copolymers were prepared using traditional and novel methods respectively. Results indicated that the novel rubber‐toughened epoxy blend exhibited much better mechanical properties than its traditional counterpart. The morphologies of the blends were explored by transmission electron microscopy (TEM), it was revealed that the use of the novel method formed a local interpenetrating network structure in the blend, which substantially improved the interfacial adhesion. The impact fracture surfaces of the two blends were observed by scanning electron microscopy (SEM) to explore the toughening mechanism, it was found that crack pinning was the major toughening mechanism for the novel rubber‐toughened epoxy blend. Dynamic mechanical analysis (DMA) was applied to determine the T_g values of the blends, which were found to be close. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41110.