Model reactions and formation of epoxy networks with the phenylbenzoate mesogen

The phenylbenzoate mesogen was introduced into epoxy networks by the crosslinker 4-hydroxyphenyl-4-hydroxybenzoate and by the diglycidylether of 4-hydroxyphenyl-4-hydroxybenzoate, respectively. Rigid networks were synthesized on the basis of 4-hydroxyphenyl-4-hydroxybenzoate and the diglycidylether of bisphenol A, and flexible networks were prepared by reaction of the diglycidylether of butanediol-1.4 with the same dihydroxy compound. Model investigations were used to obtain information about the reactivity differences of the phenolic hydroxyl groups of the bisphenol used for network formation. Furthermore, the thermal properties of the main products isolated from the model reactions are strongly influenced by the substituents at the phenylbenzoate structure. Some of these model substances demonstrate structures that can be also found in the networks. In addition, photoinduced cationic crosslinking of the diglycidylether of 4-hydroxyphenyl-4-hydroxybenzoate results in networks with different thermal properties that are dependent on the temperature of network formation. Moreover, the temperature used during crosslinking influences the formation of ordered structures in the networks. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 2653–2688, 1997     

Preparation and thermal properties of diglycidylether sulfone epoxy

A diglycidylether sulfone monomer (sulfone type epoxy monomer, SEP) was prepared from bis(4-hydroxyphenyl) sulfone (SDOL) and epichlorohydrin without any NaOH or KOH as basic catalyst. FT-IR, ¹H NMR, ¹³C NMR and mass spectroscopic instruments were utilized to determine the structure of the SEP monomer. The cured SEP epoxy material exhibited not only a higher T_g (163.81 °C) but also a higher T_g than pristine DGEBA (from 111.25 °C to 139.17 °C) when the SEP monomer moiety had been introduced into the DGEBA system. The thermal stability of cured epoxy herein was investigated by thermogravimetric analysis (TGA). The results demonstrated that the sulfone group of the cured SEP material decomposed at lower temperatures and formed thermally stable sulfate compounds, improving char yield and enhancing resistance against thermal oxidation. Additionally, the IPDT and char yield of the cured SEP epoxy (IPDT = 1455.75, char yield = 39.67%) exceeded those of conventional DGEBA epoxy (IPDT = 667.27, char yield = 16.25%).     

The POSS side chain epoxy nanocomposite: Synthesis and thermal properties

The IPI‐POSS‐modified epoxy resin (IPEP) was prepared from isocyanato‐propyldinethylsilyl‐isobutyl‐POSS (IPI‐POSS) and diglycidyl ether of bisphenol A epoxy resin. The steric hindrance of the IPEP bulky POSS side chain improved the curing activation energies. The POSS particles sizes were about 2–3 nm and dispersed uniformly. At lower IPEP concentration (POSS < 12 wt %), the glass transition temperatures (T_gs) of the IPEP nanocomposites increased from 118 to 170 °C. The char yield increased from 15 to 20 wt %, and the LOI values increased from 22 to 28. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 643–652, 2010     

Kinetic features of the formation of poly(epoxy isocyanurate) networks

A new method is developed for the synthesis of branched and network polymers that give rise to poly(epoxy isocyanurate) matrices during thermal curing. Matrix polymers are prepared on the basis of polyethers (poly(propylene glycol) or poly(tetramethylene glycol)), diisocyanate, and an epoxy oligomer. The chemistry of formation of networks is studied by NMR and IR spectroscopy. Formation of structures with different topologies is analyzed, and optimum conditions for the formation of gradient networks that are complex structural organizations are ascertained. It is shown that, during microphase separation of a three-component system whose components differ appreciably in surface energy and other parameters, the composition of microphases may be estimated. Optimum conditions of the curing process that provide formation of the perfect structure of networks are found, and their chemical structure is investigated.     

Dielectric properties of a filled epoxy resin: Effect of thermal treatments

Dielectric measurements have been performed at several frequencies on samples of a cycloaliphatic epoxy resin filled with aluminum hydroxide. The samples were thermally treated at three different temperatures for times up to 2,000 hours. At low aging temperatures and times an improvement of the characteristics is observed due perhaps to an assessment of the bulk of the polymer and more precisely to a change in the free volume. At high temperatures and times a thermo-oxidation involving layers deeper and deeper becomes the predominant mechanism responsible of the decrease in the properties with respect to the virgin material. T _g, tan and versust _a, generalized curves are finally presented useful to predict the behaviour for aging times not easily experienced.Thanks are due to Magrini-Galileo, Italy, for supplying the samples and to C.N.R., Italy, for financial support.     

Surface functionalized boehmite sheets filled epoxy composites with enhanced mechanical and thermal properties

Boehmite (AlOOH) sheets were synthesized via a hydrothermal method and then successfully functionalized with a bi‐functional coupling agent, γ‐aminopropyl‐ triethoxysilane (APTES), through a facile neutral solvent method. Scanning electron microscope and transmission electron microscopy images showed a uniform morphology of AlOOH sheets. APTES was found to be covalently bound with AlOOH sheets. The linked APTES can be combined with an epoxy oligomer through a ring opening addition reaction. The modified AlOOH was used as reinforcing agent to reinforce the epoxy resin cured by 4,4‐diaminodiphenylsulfone. The results of tensile and differential scanning calorimetric test revealed the tensile strength and glass transition temperature (Tg) firstly increase and then decrease with the increase of functionalized AlOOH sheets loading. When the loading of functionalized AlOOH sheets increased to 5 parts per hundred resin, the highest tensile strength and Tg were obtained. They are 100.8 MPa and 174.5 °C. Microscopic examinations revealed the presence of large plastic deformations at the micronscale in the formed composites in agreement with the observed strengthening effect of functionalized AlOOH sheets. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis and properties of miscible epoxy/acrylic interpenetrating polymer networks

Three series of epoxy/acrylic interpenetrating polymer networks were prepared by the simultaneous polymerization of diglycidyl ether of bisphenol A, crosslinked with an aliphatic diamine, diglycidyl ether of bisphenol A dimethacrylate, bisphenol A dimethacrylate, and diethoxy bisphenol A dimethacrylate. Under the conditions provided it is believed that the two networks form simultaneously but independently. Differential scanning calorimetry and dielectric measurements indicate that these polymer networks are miscible because they exhibit a single, sharp glass transition temperature, the values of which, however, are lower than predicted by the law of mixture. This decrease may be due in part to the dilution of one network by the other and to the resulting breakage of intramolecular interactions. It is also due, in part or in whole, to the presence of solvent and/or monomer impurities that act as plasticizers.     

Fluorene-bridged polyphenylquinoxalines with high solubility and good thermal stability: Synthesis and properties

<正>A novel fluorene-bridged tetraketone monomer,9,9-bis[(4-benzilyloxy)phenyl]fluorene(FLTK) was synthesized and characterized.The tetraketone was polymerized with various aromatic tetraamines to afford a series of polyphenylquinoxalines(PPQs).The obtained polymers were found to be soluble in common organic solvents such as N-methyl-2-pyrrolidone(NMP),chloroform and m-cresol.Flexible and tough PPQ films obtained by spin-casting their NMP solutions exhibited tensile strengths higher than 60 MPa.The films also demonstrated good thermal stability up to 500℃in nitrogen and glass transition temperatures higher than 280℃.In addition,the PPQ films exhibited good hydrolytic stability. High surface and volume resistivity retentions were achieved for the films after immersion or boiling in water for 24 h.     

Mechanical and thermal properties of epoxy/silicon carbide nanofiber composites

The silicon carbide (SiC) nanofibers (0.1, 0.25, and 0.5 phr), produced by self‐propagating high‐temperature synthesis (SHS), are used to reinforce the epoxy matrix cured with an anhydride hardener. Morphological studies reveal a better dispersion of SiC nanofibers and a good level of adhesion between nanofiber and the matrix in composites with lower (0.1 and 0.25 phr) nanofiber loading. The flexural studies show that a maximum increase in flexural properties is obtained for composites with 0.25 phr SiC nanofiber. The fracture toughness of epoxy is found to increase with the incorporation of SiC nanofibers, and 0.25 phr SiC nanofiber loading shows maximum fracture toughness value. The possible fracture mechanisms that exist in epoxy/SiC nanofiber composites have been investigated in detail. Thermogravimetric analysis reveals that SiC nanofibers are effective fillers to improve the thermal stability of epoxy matrix. Copyright © 2014 John Wiley & Sons, Ltd.     

Functionalized reduced graphene oxide/epoxy composites with enhanced mechanical properties and thermal stability

One-pot hydrothermal reduction of graphene oxide (GO) in N-methyl-2-pyrrolidone (NMP) suspension was performed, wherein GO surface were functionalized by free radicals generated from NMP molecules. The NMP functionalized reduced GO (NMPG) nanosheets were then incorporated into epoxy matrix to prepare epoxy composites. The significant improvement of 100 and 240% in fracture toughness (critical intensity factor, K_IC) and fracture energy (critical strain energy release rate, G_IC) achieved from single edge notched bending (SENB) test revealed the excellent toughening ability of NMPG. The improved compatibility and interfacial interaction between the epoxy matrix and NMPG yielded∼28, 19 and 51% improvement in tensile strength, Young's and storage modulus, respectively. Thermal stability of pure epoxy and its composites was determined at 5, 10 and 50% weight loss, which showed 30, 27.5 and 29 °C improvement with 0.2 wt% NMPG loading. The work provides a simple method to prepare graphene-based epoxy composites with improved performance.     

Effect of microencapsulation on thermal properties and flammability performance of epoxy composite

The influence of microencapsulated ammonium polyphosphate (MFAPP) on flame retardancy, thermal properties and water resistance of epoxy (EP) composite were investigated by LOI, UL-94, DSC, TG, microscale combustion calorimeter (MCC) and TG-FTIR. The results of DSC show that the shell outside MFAPP can increase its compatibility in EP. EP/MFAPP containing only 9 wt% MFAPP can pass V-0 in the UL-94 test, while neat EP cannot pass any rating. Due to the presence of shell, water treatment show few effects on the flame retardancy of EP/MFAPP, while LIO values of EP/APP decrease remarkably after treatment. The presence of MFAPP can reduce the heat release rate and total heat release of EP significantly in MCC test. The reason is that MFAPP can stimulate the dehydration of EP at low temperature and retard the release of pyrolysis gas at high temperature. Moreover, a char formed via the reaction of EP and MFAPP has excellent thermal stability and can prevent underlying materials from further combustion during a fire.     

Influence of POSS structure on the fire retardant properties of epoxy hybrid networks

Monofunctional Polyhedral Oligomeric Silsesquioxanes (POSS), differing in chemical structure, were introduced into an epoxy-amine formulation in order to obtain hybrid organic/inorganic epoxy networks. The process developed allows the POSS to be either covalently bonded to the network and organized in small amorphous domains, or completely dispersed in larger crystalline domains. Morphology, thermal and fire retardant properties were studied through electron microscopy, DSC, TGA, cone calorimeter experiments and UL94 tests. It was demonstrated that POSS nanoclusters induced an effective fire retardant effect, which was controlled by several factors. It was shown that POSS bearing phenyl ligands were far more effective than POSS with isobutyl ligands, and that the presence of a chemical linkage between the phenyl-based POSS clusters and the matrix favoured the dispersion of the nanoclusters, resulting in enhanced fire retardancy. The fire retardant effect was only slightly enhanced by increasing the amount of POSS nanoclusters.     

Combustion and thermal properties of epoxy/phenyltrisilanol polyhedral oligomeric silsesquioxane nanocomposites

Organic–inorganic hybrid composites of epoxy and phenyltrisilanol polyhedral oligomeric silsesquioxane (Ph₇Si₇O₉(OH)₃, POSS-triol) were prepared via in situ polymerization of epoxy monomers. The nanocomposites of epoxy with POSS-triol can be prepared in the presence of metal complex latent catalyst, aluminum triacetylacetonate ([Al]) for the reaction between POSS-triol and diglycidyl ether of bisphenol A (DGEBA). The dispersion morphology of organic–inorganic hybrid was characterized by scanning electronic microscopy (SEM). The thermostability of composites was evaluated by thermal gravimetric (TG) analysis. The flammability was evaluated by cone calorimeter test. The presence of [Al] latent catalyst leads to a decrease in combustion rate with respect to epoxy and epoxy/POSS composites as well as reduction in smoke, CO and CO₂ production rate. The effect of [Al] is to reduce the size of spherical POSS particles from 3–5 μm in epoxy/POSS to 0.5 μm in epoxy/POSS[Al]. Furthermore, POSS with smaller size may form compact and continue char layer on the surface of composites more efficiently.     

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

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

Effect of the network structure on thermal and mechanical properties of mesogenic epoxy resin cured with aromatic amine

The epoxy resin containing a typical mesogenic group such as biphenol was cured with catechol novolak and aromatic diamines which have neighboring active hydrogens. In the biphenol-type epoxy resin cured with catechol novolak, 4,4′ diaminodiphenylmethane, and p-phenylenediamine (PPD), the glass-rubber transition almost disappeared, and thus a very high elastic modulus was obtained in the high temperature region. It is clear that the thermal motion of the network chains is significantly suppressed in these cured systems. In addition, in the PPD-cured system, a characteristic pattern like a schlieren texture was clearly observed under the crossed polarized optical microscope. Thus we conclude that the mesogenic group contained in the epoxy molecule is oriented in the networks when the mesogenic epoxy resin is cured with phenols and diamines which have neighboring active hydrogens. On the other hand, the biphenol-type resin cured with 3,3′,5,5′-tetraethyl-4,4′-diamino diphenylmethane (TEDDM) showed a well-defined glass-rubber transition and, thus, a low rubbery modulus. In this cured system, no characteristic pattern was observed under the crossed polarized light. These results show that the large branches, such as ethyl groups on the network chains, prevent the orientation of network chains which contain the mesogenic group. © 1997 John Wiley & Sons, Inc.     

A novel metal-organic network with high thermal stability: nonlinear optical and photoluminescent properties

A novel zinc(II) 4-(5H-tetrazol)benzoic coordination polymer with an in situ generated tetrazole ligand exhibits the gsi (gamma-silicon) topology and high thermal stability; this compound possesses second-order nonlinear optical and interesting heat-induced photoluminescent properties.     

Preparation, thermal properties and flame retardancy of phosphorus- and silicon-containing epoxy resins

Phosphorus- and silicon-containing epoxy resins were prepared from (2,5-dihydroxyphenyl)diphenyl phosphine oxide (Gly-HPO), diglycidyloxy methylphenyl silane (DGMPS) and 1,4-bis(glycidyloxydimethyl silyl)-benzene (BGDMSB) as epoxy monomers and diaminodiphenylmethane (DDM), bis(3-aminophenyl)methyl phosphine oxide (BAMPO) and bis(4-aminophenoxy)dimethyl silane (APDS) as curing agents. Epoxy resins with different phosphorus and silicon content were obtained. Their thermal, dynamic mechanical and flame retardant properties were evaluated. The high LOI values confirmed that epoxy resins containing hetero-atoms are effective flame retardants, but a synergistic efficiency of phosphorus and silicon on flame retardation was not observed.     

Lanthanide complexes of D-penicillamine: formation constants,spectral and thermal properties

The complex-formation of lanthanide(III) elements with D-penicillamine have been investigated in acidic and neutral media. The macroscopic protonation constants of the ligand and the formation constants of [Ln.Pen]⁺, [Ln.Pen₂]^?, [Ln.Pen.OH] and [Ln.Pen.(OH)₂]^? complexes were determined from pH-metric data using the BEST computer program. Elemental analyses of the solid complexes indicate formation of 1?:?1 metal?:?ligand species. The binding sites in the complexes with the possible role of –COO^?, –NH₂ and –SH groups in the coordination have been discussed using infrared data. The complexes decompose in four steps as shown by their t.g. and d.t.a. analyses. A mechanism of decomposition is proposed which is supported by mass spectral data.     

Morphology, flexural, and thermal properties of sepiolite modified epoxy resins with different curing agents

A bisphenol A-based epoxy resin was modified with 5 wt% organically modified sepiolite (Pangel B40) and thermally cured using two different curing agents: an aliphatic diamine (Jeffamine D230, D230) and a cycloaliphatic diamine (3DCM). The morphology of the cured materials was established by scanning and transmission electron microscopy analysis. The thermal stability, thermo-mechanical properties, and flexural behaviour of the sepiolite-modified matrices were evaluated and compared with the corresponding neat matrix. The initial thermal decomposition temperature did not change with the addition of sepiolite. The flexural modulus of the epoxy matrix slightly increases by the incorporation of the organophilic sepiolite. The flexural strength of the sepiolite modified resin cured with D230 increased by a 10% while the sepiolite modified resin cured with 3DCM resulted in a lower flexural strength compared with the unmodified resin. The reduced flexural strength was attributed to the stress concentrations caused by the sepiolite modifier, which rendered the resins more brittle.     

Phosphonium‐based polyelectrolyte networks with high thermal stability,high alkaline stability,and high surface areas

Phosphonium‐containing polyelectrolyte networks (PENs) ( P1 – P4 ) were prepared by cyclotrimerization of bis(4‐acetylphenyl)diphenylphosphonium bromide ( M1 ) and 1,4‐diacetylbenzene ( M2 ) with p‐toluene sulfonic acid in various M1:M2 ratios (1,0, 1:1, 1:2, and 1:4). The relative abundance of the PAr₄⁺ units in each PEN was demonstrated to influence thermal stability, alkaline stability, water uptake, surface area, and CO₂ uptake in predictable ways. Impressively, PENs with NTf₂^? counterions (Tf = CF₃SO₃) did not exhibit 5% mass loss until heating above 400 °C. Alkaline stability, tested by challenging a PEN with 6 M NaOH(aq) at 65 °C for 120 h, increased with increasing PAr₄⁺ content, which reflected the enhanced reactivity of the HO^? anion in more hydrophobic materials (i.e., PENs with lower M1:M2 ratios). The specific surface areas estimated by Brunauer‐Emmett‐Teller (BET) analysis for these PENs were above 60 m²/g under N₂ and nearly 90 m²/g under CO₂. Notably, P3 (in which 33% of monomers comprise a phosphonium moiety) exhibited a CO₂ uptake affinity of one CO₂ molecule adsorbed for every phosphonium site. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 598–604