Blended hybrids based on silsesquioxane–OH and epoxy resins

Blended hybrids based on silsesquioxane cyclohexyl trisilanol [STOH; i.e., (c‐C₆H₁₁)₇Si₇O₉(OH)₃] and epoxy resin 4,5‐epoxyhexyl‐1,2‐dimethyl acid diglycidyl ester (TDE‐85) were prepared with good compatibility of STOH up to 5 wt % with TDE‐85. The blended hybrid resins, with various STOH additions, were cured by 4,4′‐diaminodiphenylsulfone, and the curing reactions were investigated with differential scanning calorimetry. The incorporation of STOH increased the curing reaction of TDE‐85 for three active hydrogens existing in the STOH molecule. The storage moduli and glass‐transition temperatures of the cured hybrid resins were studied with dynamic mechanical analysis. The cured hybrids had higher storage moduli than the pure epoxy resins at lower temperatures and increased slightly even when the temperature was above the glass‐transition temperature. Two peaks appearing in tan δ curves indicated the block copolymer structure and two different glass‐transition temperatures of the cured hybrid resins. The thermal stability and flame retardancy of the cured hybrid resins were investigated with thermogravimetric analysis and limited oxygen index values, respectively. The results showed that introducing silsesquioxane–OH units into epoxy resins could improve the thermal stability and flame retardancy of the resins. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Molecular weight controlled poly(amic acid) resins end‐capped with phenylethynyl groups for manufacturing advanced polyimide films

To investigate the effect of reactive end‐capping groups on film‐forming quality and processability, a series of molecular weight‐controlled aromatic poly(amic acid) (PAA) resins functionalized with phenylethynyl end groups were prepared via the polycondensation of 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA), para ‐phenylenediamine (PDA), and 4‐phenylethynyl phthalic anhydride (PEPA) served as molecular‐weight‐controlling and reactive end capping agent. The PAA resins with relatively high concentrations endow enhanced wetting/spreading ability to form PAA gel films by solution‐cast method which were thermally converted to the fully‐cured polyimide (PI) films. The mechanical and thermal properties of PI films were investigated as a function of PAA molecular weights (M_n ) and thermal‐curing parameters. Mechanical property, dimensional stability and heat resistance of the fully‐cured PI films with PAA M_n > 20 ×10³ g mol^?1 are found to be better than that of their unreactive phthalic end‐capped counterparts. The covalent incorporation of chain‐extension structures in the backbones, induced by thermal curing of phenylethynyl groups, might facilitate yielding a higher degree of polymer chain order and consequently improved resistance strength and elongation at break to tensile plastic deformation. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45168.     

Studies on syntheses and properties of episulfide‐type optical resins with high refractive index

A series of novel high refractive index episulfide‐type optical resins were prepared by ring‐opening copolymerization of bis(β‐epithiopropylthioethyl) sulfide (BEPTES) with episulfide derivative of diglydicyl ether of bisphenol A (ESDGEBA) and 2,4‐tolylene diisocyanate (TDI), respectively, in the presence of triethylamine as a curing catalyst. The episulfide monomers, BEPTES and ESDGEBA, were synthesized from their corresponding epoxy compounds, respectively. The cured transparent resins exhibit high refractive index (n_d > 1.63) and relatively low dispersion. The refractive index (n_d) and Abbe's number (ν_d) of the BEPTES/ESDGEBA curing system increased linearly with the weight content of BEPTES monomer in the range from 1.633 and 34.0 for the copolymer with 10 wt % of BEPTES to 1.697 and 38.1 for the homopolymer of pure BEPTES. For the BEPTES/TDI curing system, the refractive index and Abbe's number varied linearly with the molar ratio of BEPTES to TDI from 1.652 and 28.7 to 1.669 and 34.6. High glass‐transition temperatures (T_g > 130°C) of the cured BEPTES/TDI resins were observed, which indicate that the cured BEPTES/TDI resins possess a good heat resistance. The optical, physical, and thermal properties of the episulfide‐type cured optical resins were also discussed in this study. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2426–2430, 2003     

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.     

High-performance poly(methylsilane arylether arylacetylene) resins with low curing temperatures and weak secondary relaxations

A series of poly(methylsilane arylether arylacetylene) (PSEA-H) resins were synthesized from methyldichlorosilane and isomeric arylether arylacetylenes, and characterized by ¹H-NMR and FT-IR spectroscopies. The effect of reactive Si-H groups and the linking positions of benzene rings in the arylether arylacetylene units on the properties of the resins were investigated. The results show that PSEA-H resins possess good processability with processing windows of over 80°C. The introduction of Si-H groups reduces the curing temperatures for PSEA-H resins and weakens the secondary relaxation for the cured PSEA-H resins. The cured resins and T300 carbon fiber (T300CF) reinforced composites display high mechanical properties. The flexural strengths of a cured PSEA-H resin and its T300CF composite at room temperature reach 64.2 and 426.5 MPa, respectively. The flexural properties depend on the linking positions of benzene rings. The cured PSEA-H resins show excellent heat resistance with a temperature of 5% weight loss (T_d5) above 500°C.     

Kinetic rate equation combining ultraviolet‐induced curing and thermal curing. I. Bismaleimide system

A novel and general kinetic rate equation combining ultraviolet‐induced (UV‐induced) curing and thermal curing was successfully derived from the conventional thermal‐kinetic rate equation. This proposed novel kinetic rate equation can be applicable to the curing system either simultaneously or individually by UV‐induced and thermal cure methods. This general kinetic rate equation is composed of the reaction order n, activation energy E_a, curing temperature T, energy barrier of photoinitiation E_Q, intensity of UV radiation Q, concentration of photoinitiator [I], and a few other parameters. The proposed equation was supported by experimental data based on the curing systems of 4,4′‐bismaleimidodiphenylmethane (BMI) and 2,2‐bis(4‐(4 maleimido phenoxy) phenyl propane (BMIP). The BMI and BMIP systems were isothermally cured at various temperatures, or simultaneously cured with varying intensity of UV radiation (wavelength 365 nm). Conversion levels for the various cured samples were subsequently measured with a FTIR spectrometer. The reaction order n = 1.2, activation energy E_a = 40,800 J/mol, and E_Q = 7.5 mW/cm² were obtained for curing BMI system. The reaction order n = 1.3, activation energy E_a = 53,000 J/mol, and E_Q = 9.1 mW/cm² were obtained for curing BMIP system. The values of n and E_a in the same curing system (BMI or BMIP) are irrespective of the curing method (either simultaneously or individually by UV‐induced and thermal cure methods). The salient results of this study show that UV radiation only enhances the initiation rate and UV ration do not influence the activation energy E_a. The experimental results are reasonably well represented by these semi‐empirical expressions.© 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis of rosin‐based flexible anhydride‐type curing agents and properties of the cured epoxy

BACKGROUND: Although rosin acid derivatives have received attention in polymer synthesis in recent years, to the best of our knowledge, they have rarely been employed as epoxy curing agents. The objective of the study reported here was to synthesize rosin‐based flexible anhydride‐type curing agents and demonstrate that the flexibility of a cured epoxy resin can be manipulated by selection of rosin‐based anhydride‐type curing agents with appropriate molecular rigidity/flexibility. RESULTS: Maleopimarate‐terminated low molecular weight polycaprolactones (PCLs) were synthesized and studied as anhydride‐type curing agents for epoxy curing. The chemical structures of the products were confirmed using ¹H NMR spectroscopy and Fourier transform infrared spectroscopy. Mechanical and thermal properties of the cured epoxy resins were studied. The results indicate that both the epoxy/anhydride equivalent ratio and the molecular weight of PCL diol play important roles in the properties of cured resins. CONCLUSION: Rosin‐based anhydride‐terminated polyesters could be used as bio‐based epoxy curing agents. A broad spectrum of mechanical and thermal properties of the cured epoxy resins can be obtained by varying the molecular length of the polyester segment and the epoxy/curing agent ratio. Copyright © 2009 Society of Chemical Industry     

Synthesis and characterization of diphenylsilanediol modified epoxy resin and curing agent

A series of diphenylsilanediol modified epoxy resins and novel curing agents were synthesized. The modified epoxy resins were cured with regular curing agent diethylenetriamine (DETA); the curing agents were applied to cure unmodified diglycidyl ether of bisphenol A epoxy resin (DGEBA). The heat resistance, mechanical property, and toughness of all the curing products were investigated. The results showed that the application of modified resin and newly synthesized curing agents leads to curing products with lower thermal decomposition rate and only slightly decreased glass transition temperature (T_g), as well as improved tensile modulus and tensile strength. In particular, products cured with newly synthesized curing agents showed higher corresponding temperature to the maximum thermal decomposition rate, comparing with products of DGEBA cured by DETA. Scanning electron microscopy micro images proved that a ductile fracture happened on the cross sections of curing products obtained from modified epoxy resins and newly synthesized curing agents, indicating an effective toughening effect of silicon–oxygen bond.     

Curing Characteristics and Thermal Properties of Epoxidized Soybean Oil Based Thermosetting Resin

Epoxidized soybean oil (ESO) was thermally cured using methylhexahydrophthalic anhydride (MHHPA) curing agent in the presence of 2-ethyl-4-methylimidazole (EMI) catalyst. The curing characteristics of ESO/MHHPA/EMI systems were characterized using Fourier transform infrared spectroscopy (FTIR), a dynamic mechanical analyzer (DMA) and a differential scanning calorimeter (DSC). FTIR spectra showed that the polyesterification rate in ESO/MHHPA/EMI systems increased with increasing of the catalyst concentration. DSC thermograms indicated that EMI-catalyzed ESO/MHHPA systems experienced enthalpy relaxation at low EMI concentration whereas the extent decreased with increasing of the EMI concentration. There is a direct relationship between the degree of conversion and crosslink density of the thermal cured ESO/MHHPA/EMI systems with EMI concentration. The curing characteristics of thermal curable ESO thermosetting resins were found to have influence on the thermal properties of the ESO systems. It was determined that the glass transition temperature (T _g) and storage modulus (E′) of cured ESO increased with increasing the EMI concentration whereas the damping properties of the ESO/MHHPA/EMI systems exhibited the reverse trend. It was found that the thermally curable ESO thermosetting resins experienced a two-stage thermal decomposition process.     

Synthesis,phase behaviors,and mechanical properties of biphenyl‐type epoxy resins and composites

Diglycidyl ether of 3,3′,5,5′‐tetramethyl‐4,4′‐biphenyl (TMBPDGE) which has been found great applications in semiconductor packaging was synthesized. The liquid crystalline phases of diglycidyl ether of 4,4′‐dihydroxybiphenol (BPDGE) cured with phenol novolac (PN) were studied by wide angle X‐ray diffraction (WAXD) and polarized optical microscopy (POM). BPDGE was in situ copolymerized with TMBPDGE to improve its thermal and mechanical properties by means of the LC domains retained in the crosslinked networks. The results indicated that a nematic phase was formed and fixed with proper curing schedule when BPDGE was cured with PN that had no neighboring active hydrogens and the LC domains could also be efficiently embedded into the composite systems. Dynamic mechanical properties showed that epoxy networks containing LC domains displayed higher α‐relaxation temperature and linear elastic modulus traces. The impact toughness and T_g were improved with the addition of BPDGE. Scanning electron microscope observation of the fracture surfaces showed that there was a change in failure mechanism in the composite systems. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Synthesis and properties of bismaleimide resins containing ether bonds

New bismaleimides containing ether bonds were prepared. The thermal properties of the bismaleimides were investigated by differential scanning calorimetry (DSC). The effects of structure of the bismaleimides and curing conditions on the thermal and mechanical properties of the cured resins such as initial decomposition temperature (T_d), glass transition temperature (T_g), and flexural strength were studied. The introduction of ether bonds to bismaleimide resins decreased the brittleness of the resins without reductions in their heat-resistant properties.     

Amino‐capped aniline trimer/epoxy resin intercrosslinked networks

An amino‐capped aniline trimer (ACAT) in emeraldine base form was reacted with an epoxy resin to produce intercrosslinked networks. The quinoid structure of the ACAT was able to crosslink on curing and, thus, led to a very high glass‐transition temperature of the cured resin. The epoxy resin cured with the ACAT showed superior thermal properties over the resins cured with p‐phenylenediamine and 4,4′‐diamino diphenylamine. These findings were based on differential scanning calorimetry, IR, dynamic mechanical analysis, and thermogravimetric analysis data. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 222–226, 2006     

Phenolic‐epoxy matrix curable by click chemistry—synthesis,curing, and syntactic foam composite properties

Alkyne functional phenolic resin was cured by azide functional epoxy resins making use of alkyne‐azide click reaction. For this, propargylated novolac (PN) was reacted with bisphenol A bisazide (BABA) and azido hydroxy propyloxy novolac (AHPN) leading to triazole‐linked phenolic‐epoxy networks. The click cure reaction was initiated at 40–65°C in presence of Cu₂I₂. Glass transition temperature (Tg) of the cured networks varied from 70°C to 75°C in the case of BABA‐PN and 75°C to 80°C in the case of AHPN‐PN. DSC and rheological studies revealed a single stage curing pattern for both the systems. The cured BABA‐PN and AHPN‐PN blends showed mass loss above 300°C because of decomposition of the triazole rings and the novolac backbone. Silica fiber‐reinforced syntactic foam composites derived from these resins possessed comparable mechanical properties and superior impact resistance vis‐a‐vis their phenolic resin analogues. The mechanical properties could be tuned by regulating the reactant stoichiometry. These low temperature addition curable resins are suited for light weight polymer composite for related applications. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41254.     

Structure and properties of novel epoxy resins containing naphthalene units and aliphatic chains

Two novel epoxy resins; namely, R1 and R2 were synthesized and characterized. These two resins were isomers and both contained naphthalene units and two symmetric flexible aliphatic ester chains terminated by epoxy groups. To investigate the influence of different structural isomers on the performance of these epoxy resins, they were both cured with various curing agents which results in the choosing of 4,4′-diaminodiphenylmethane (DDM) as the optimized curing agent. The curing technical temperature was obtained from extrapolated plots of T–β curve at different heating rates. The kinetic parameters, the activation energy (E _a) and the reaction order (n) were deduced by Kissnger’s isoconversional method and Crane equation. The moisture absorption and mechanical and thermal properties of the cured epoxy resins were investigated. Experimental results indicated that the R1/DDM and R2/DDM epoxy resins displayed improved mechanical performance without significant decrease in their important inherent properties, e.g., temperature of glass transition (T _g), moisture absorption and thermal properties when compared with the corresponding commercial biphenyl-type epoxy resins. The average inter-segment distances in R1/DDM and R2/DDM systems were 4.46 and 4.88 Å, respectively, which were measured by wide-angle X-ray diffraction. The result showed R1/DDM (1,5-di-substituted) was strongly hindered in comparison with R2/DDM (2,7-di-substituted) and E _a and T _g values of the R1/DDM were slightly higher than those of R2/DDM. Furthermore, mechanical properties and moisture absorption of the R1/DDM were lower than those of R2/DDM. Nevertheless, the position of the substituent only weakly affected the thermal properties and the reaction order (n).     

Synthesis,thermal properties,and flame retardance of the epoxy‐silsesquioxane hybrid resins

Epoxy/silsesquioxane‐OH (EP‐SDOH, ED) hybrid resins were prepared from cyclohexyl‐disilanol silsesquioxane (SDOH) and diglycidyl ether of bisphenol A via the reaction between silanol and the oxirane group, with the cobalt naphthanate as a catalyst. It was found that incorporation of SDOH allows the reaction between oxirane ring and Si? OH, and the silsesquioxane cage structure can be the main chain or as the side chain of the hybrid resin. The EP‐SDOH hybrid resins with various SDOH contents were cured by 4,4′‐diaminodiphenylsulphone, and the curing reaction was investigated by differential scanning calorimetry. The curing characteristics of EP‐SDOH hybrids had been observed to be influenced by the content of SDOH in the hybrid. The differential scanning calorimetry thermograms indicated that the EP‐SDOH hybrid exhibited a higher initial temperature, peak temperature, as well as final temperature than those of the pure epoxy resin when cured by the same curing agent 4,4′‐diaminodiphenylsulphone. The curing kinetic parameters were calculated by using the Ozawa method and the results indicated that EP‐SDOH hybrids possess the same curing mechanism as the pure epoxy resin. The properties of the cured EP‐SDOH hybrid resins such as the glass transition temperature (T_g), dynamic mechanical analysis, thermal stability, as well as the flame retardance were also investigated, and the results showed that introducing silsesquioxane‐OH unit into epoxy resin successfully modified the local structure, made the chain stiffness, restrict the chain mobility, and eventually improved thermal stability and flame retardance of epoxy resin. POLYM. ENG. SCI., 47:225–234, 2007. © 2007 Society of Plastics Engineers.     

Synthesis and properties of copolymer epoxy resins prepared from copolymerization of bisphenol A,epichlorohydrin, and liquefied Dendrocalamus latiflorus

Dendrocalamus latiflorus Munro (ma bamboo) was liquefied in phenol and polyhydric alcohol (polyethylene glycol/glycerol cosolvent) with H₂SO₄ as catalyst. Liquefied bamboos reacted with bisphenol A and epichlorohydrin were then employed to prepare copolymer epoxy resins. The curing property and thermal property of copolymer epoxy resins were investigated. The results showed that copolymer epoxy resins could cure at room temperature after the hardener was added, and its curing process was an exothermic reaction. Comparison showed that copolymer epoxy resins prepared with phenol‐liquefied bamboo as raw material had higher heat released than those prepared with polyhydric alcohol‐liquefied bamboo during curing. The DSC analysis showed that heat treatment could enhance the crosslinking of copolymer epoxy resins cured at room temperature. However, resins prepared with polyhydric alcohol‐liquefied bamboo had a lower glass transition temperature. The TGA analysis showed that resins prepared with phenol‐liquefied bamboo had better thermal stability. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effects of curing program on mechanical behavior and water absorption of DGEBA/TETa epoxy network

Water uptake in organic coatings remains an interesting challenge for fundamental and applied researches because chemical, physical, and mechanical properties are concerned. The polymer network, which is affected by the curing program, is a key factor for water absorption. In this work, an epoxy network based on diglycidyl ether of bisphenol A and a hardener triethylentetramine was cured at different temperatures: below T_g (protocol 1) and above T_g (protocol 2). DMA, Differential Scanning Calorimetry (DSC), and FT‐IR measurements showed that both protocols allow to obtain totally cured networks. However, DSC and DMA results revealed that both cured networks present different levels of homogeneity, depending on the different curing conditions, which affect the free volume and the activation volume associated with visco‐elastic properties. The mechanical properties of free films and water sorption behaviors were investigated as function of cured conditions. It was found that protocol 1‐cured networks present higher mechanical properties and was less affected by water ingress than protocol 2‐cured systems, leading to better barrier properties. These results highlight the influence of the curing program onto the heterogeneous distribution of the epoxy network. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Curing behavior,thermal, and mechanical properties of epoxy resins cured with a novel liquid crystalline dicarboxylic acid curing agent

A novel di‐carboxylic acid curing agent (DACA) was successfully synthesized and cured with three different epoxy resins: glycidyl end‐capped poly(bisphenol‐A‐co‐epichlorohydrin) (pDGEBA, M_n = 377), N,N‐diglycidyl‐4‐glycidyloxyaniline (TGAP), and 4,4′‐methylenebis(N,N‐diglycidylaniline) (TGDDM). The cured epoxy exhibited excellent thermal stability, which was indicated by high initial degradation temperature (T_id) and char yield. The T_id values of cured epoxy were in the range of 327–338°C, and the char yields increased with increasing epoxy functionality. The char yields of cured DACA/pDGEPA, DACA/TGAP, and DACA/TGDDM samples were 21.1, 60.4, and 66.9%, respectively. In addition, the cured epoxy samples also showed low coefficients of thermal expansion and high storage moduli (E′), which were around 60 ppm/°C and 2800 MPa, respectively. The failure surfaces were ductile and rough, so the cured epoxy samples are expected to have high fracture toughness and impact strength. POLYM. ENG. SCI., 54:695–703, 2014. © 2013 Society of Plastics Engineers     

Thermally curable adhesive tapes with complex catalyst system for fabricating semiconductor packages

Thermal curing of adhesive films was investigated to facilitate the fabrication of a reliable bonding for semiconductors. The formulated adhesive films contained acrylic polymer, epoxy resins, phenol resin, and an imidazole derivative that was the catalyst for curing the epoxy resins with phenol resin. The solubility, thermally latent characteristics, mechanical and adhesive properties of 2‐methylimidazole/boron trifluoride (2MZ/BF3), and 2MZ/aluminum trisacetylacetonate (AlAC) were investigated. It was found that 2MZ/BF3 and 2MZ/AlAC had excellent solubility in adhesive materials and they had excellent latent characteristics as thermal curing catalysts for epoxy resins, whereas conventional catalysts (2MZ and 2‐phenyl‐4, 5‐dihydroxymethylimidazole (2PHZ)) could not achieve both excellent solubility and thermally latent characteristics. The mechanical and adhesive properties of the post‐thermal‐cured adhesive film that contained 2MZ/BF3 or 2MZ/AlAC were comparable to those of the post‐thermal‐cured adhesive films that contained conventional catalysts. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis,thermal properties,and flame retardance of phosphorus‐containing epoxy‐silica hybrid resins

A novel epoxy resin modifier, phosphorus‐containing epoxide siloxane (DPS) with cyclic phosphorus groups in the Si O network, was prepared from the reaction of 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) with polyhedral‐oligomeric siloxanes, which was synthesized by the sol–gel reaction of 3‐glycidoxypropyltrimethoxysilane. DPS was confirmed by Fourier transform infrared and ²⁹Si NMR measurement, and then was employed to modify epoxy resin at various ratios, with 4,4‐diaminodiphenyl‐methane as a curing agent. In order to make a comparison, DOPO‐containing epoxy resins were also cured under the same conditions. The resulting organic–inorganic hybrid epoxy resins modified with DPS exhibited a high glass transition temperature (T_g), a good thermal stability, and a high limited oxygen index. In addition, the tensile strength of cured products was also rather desirable. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers