Controlled shrinkage polymers: Characterization of epoxy resins cured with spirobislactones

The diglycidyl ether of bisphenol A (DGEBA) was cured with either an aliphatic or an aromatic spirobislactone using a tertiary amine catalyst. The products were characterized by FTIR, TGA, DSC, dilatometry, and single-fiber adhesion measurements, and their performance was compared to that of DGEBA cured with acid anhydrides. Both aliphatic and aromatic bislactones are effective curing agents for DGEBA. FTIR and dilatometry confirm that both lactone rings open early in the curing reaction and initially offset shrinkage caused by polymerization. After the bislactone has been consumed, oxirane reactions proceed in a normal fashion. The final shrinkage of cured DGEBA polymers, with or without addition of bislactones, is 3.0–3.5%. Bislactone-modified materials possess superior thermal properties, when compared to those of anhydride-cured materials.     

Properties of epoxy polymers filled with nanopowders

The complex character of the effect of aluminum oxide and zirconium dioxide nanopowders that differ in their thermal prehistory, the specific surface value of particle sizes, phase composition, and the content of alloying additive of yttrium oxide on the stress-strain, thermophysical, tribotechnical, and adhesion properties of epoxy polymers is revealed. The effect depends on the chemical nature of the fillers, the sizes and specific surfaces of their particles, and the presence of alloying additive and other factors.     

Investigation of epoxide adhesive compositions cured with polyoxypropylene triamine

The results of investigations of the effect of Jeffamine-type curing agents on the adhesion and physicomechanical properties of epoxide compositions modified with rubber are presented. It was shown that epoxy-rnbber oligomers cured with polyoxypropylene tria mine are characterized by high elasticity with good cohesion and adhesion strength, which allows one to obtain adhesive compositions with small quantities of internal stresses on their basis that can be used at negative temperatures under the conditions of dynamic loads and thermal cycles.     

Adjustment of properties of epoxide compositions cured with polyoxypropylene triamine

The effect of the temperature for mixing epoxy-diane resin ED-20 with a curing agent, specifically polyoxypropylene triamine, the ratio of the components, and the introduction of diluting agents and fillers on the strength properties and water absorption of cured compositions is investigated. It was shown that, by using these methods, one can affect the parameters of characteristics of epoxide compositions.     

Properties of methyltetrahydrophthalic anhydride‐cured epoxy resin modified with MITU

Methylimidazole‐terminated chain‐extended urea (MITU) containing polypropylene oxide spacer was synthesized and employed to modify epoxies composed of a diglycidyl ether of bisphenol‐A (E‐51) and methyltetrahydrophthalic anhydride (MTHPA). The curing behavior, viscoelastic property, impact response, and fracture surface morphology of the curing systems were systematically investigated. Differential scanning calorimeter (DSC) analysis reveals that the curing reactivity of the epoxy system is greatly enhanced with the addition of MITU. From the dynamic mechanical analysis, besides the low‐temperature β relaxation, shoulder at higher temperature side appears for the MITU‐modified systems. Meanwhile, the addition of MITU leads to the increase of loss factor (tan δ) over the temperature range of 0–75°C. Impact tests show that the modifier can be effective in toughening the epoxy resin at relatively low loading, and the scanning electron microscope (SEM) images of the fracture surface for the modified systems display signs of ductility. Copyright © 2008 John Wiley & Sons, Ltd.     

Tough epoxy resins cured with aminimides

Aminimide compounds ( 1–4 ) thermally generating isocyanates and tertiary amines were found to be excellent curing agents for epoxy resin. Tensile behavior, glass transition temperature, and degree of curing for the combination of EPIKOTE 828 prepolymer with a series of curing agents ( 1–4 ) are reported. The resins exhibit a large elongation at breakage and a high fracture energy per unit volume. The epoxy resins (EP-AI) cured with 3 or 4 containing no hydroxyl group showed larger ultimate elongations (up to 15%) and higher fracture energies (ca. 8 J/cm³) than the resins (EP–AI_OH) cured with 1 or 2 . The curing reaction depends on the structure of aminimide (presence of hydroxyl group and generation of mono- or bisisocyanates). The origin of toughness and dependence of physical properties on the curing condition and the structure of aminimides were discussed. It was concluded that relatively slow curing at elevated temperature controlled by thermal decomposition of aminimides was a reason for the toughness.     

Properties of polymers while hardening epoxy resins with polyam BS-5

Poliam BS-5 (the product of reaction between aniline and formaldehyde) is studied as concerns its use as a hardener of ED-22, UP-643, and ED-BM epoxy resins. Serving as a curing agent, it possesses high reactivity, while the thermal-mechanical and physicomechanical properties of the cured polymers are at a level corresponding to the characteristics of polymers with application of known curing agents such as the aromatic diamines 4,4'-diaminodiphenylmethane and 4,4'-diaminodiphenylsulfone and eutectic mixtures with metaphenylene diamine.     

Polyoxometalate cured epoxy resins with photochromic properties

Novel photochromic thermosetting materials were facilely prepared by polyoxometalate, Keggin-type H₃PW₁₂O₄₀, cured epoxy networks with ethylene oxide blocks. The dual functions of polyoxometalate as both hardener and photochromophore were studied by differential scanning calorimetry, infrared spectroscopy, ultraviolet–visible spectroscopy (UV–vis), and generalized two-dimensional correlation analysis. Polyoxometalate initiates the cationic polymerization of epoxy resin through dissolving in either polyethylene oxide epoxy or organic solvents. When subjected to UV irradiation, the transparent thermosetting materials with ethylene oxide blocks change from colorless to blue, and could be bleached in air at various temperatures to recover its initial state. From the UV–vis measurements, all the resultant thermosetting materials demonstrated similar photochromic behavior after ultraviolet irradiation showing characteristic d–d transition band and intervalence charge transfer band. The 2D correlation analysis of the photochromic spectra clearly revealed the sequence of electron movements in the framework of PW₁₂ anion.     

Properties of materials effect of thiokol on properties of epoxy polymers

The complex character of the effect of the concentration of liquid thiokol of brand, I heat treatment, and water on the complex of physicomechanical, relaxation, and adhesion properties of epoxy polymers was demonstrated.     

Thermal properties and fracture toughness of a liquid‐crystalline epoxy resin cured with an aromatic diamine crosslinker having a mesogenic group

A mesogenic‐type curing agent was synthesized to introduce a mesogenic group not only into epoxy resin backbones but also into the crosslink units. In the mesogenic curing agent system, the domain size became larger, and the network arrangement in each domain existed to a greater extent than that in a system cured with the ordinary diamine curing system according to the evidence from polarized optical micrographs and polarized Fourier transform infrared mapping measurements. Moreover, the fracture toughness of the system was considerably improved. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2486–2494, 2006     

Modification of epoxy polymers with epoxy thiirane derivative of benzimidazolone-2

An epoxy thiirane derivative of benzimidazolone-2 was synthesized. An addition of epoxy thiirane derivative of denzimidazolone-2 to epoxy rubber and epoxy composites was shown to increase their thermal stability, elasticity modulus, and cohesion and adhesion strengths, especially at higher test temperatures. The effect depends on the concentration of additive, hardening temperature, type of rubber, and other factors.     

Thermal stability of epoxy compounds cured with boron trifluoride complexes

The thermal resistances of epoxy resins cured with complexes of boron trifluoride with benzylamine, 2-benzylaminoethanol and 2-anilinoethanol were examined. Thermal analysis data were used to compare the thermal resistances of epoxy compusitions cured with polyamines (aliphatic and aromatic), acid anhydrides and complexes of boron trifluoride with the above amines.

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Zusammenfassung Der WÄrmewiderstand von mit Komplexen von Bortrifluorid mit Benzylamin, 2-Benzylamino-Äthanol und 2-Anilino-Äthanol gehÄrteten Epoxyharzen wurde untersucht. Anhand thermoanalytischer Daten wurden die WÄrmewiderstandswerte von mit (aliphatischen und aromatischen) Polyaminen, SÄureanhydriden und Komplexen von Bortrifluorid mit den oben angeführten Aminen gehÄrteten Epoxy-Kompositionen miteinander verglichen.

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Segmental relaxation of water-aged ambient cured epoxy

The effects of long-term immersion on the viscoelastic characteristics of an ambient-temperature cured epoxy system, typical of systems used in infrastructure rehabilitation, are investigated using dynamic mechanical thermal analysis (DMTA). The study considers specimens aged at temperatures of immersion of 23, 37.8 and 60 °C. Time-temperature superposition principles were used to construct master curves of the storage modulus in the glass-rubber transition region for both wet and rejuvenated specimens. Viscoelastic parameters such as the relaxation time and the distribution parameters (β) were determined using KWW curve fits to the master curves. The free-volume content determined through curve fitting of the WLF is higher by about 0.4% for wet specimens than the rejuvenated specimens. Consequently, the fragility index and the activation energy of the relaxation around T_g are all reduced in the wet state. The viscoelastic properties of the aged epoxy specimens are strongly dependent on the temperatures of immersion although the level of water uptake in all cases is similar. Formation of multi-bound water molecules leads to the broadest glass-rubber relaxation in the wet state for specimens aged at 37.8 °C in deionized water, whereas the 60 °C aged specimens show the broadest relaxation in the rejuvenated state due to the formation of a heterogeneous network structure.     

Structure and properties of epoxy composites cured with new organosilicon amines

The results of the curing of bisphenol A-based epoxy oligomers (ED-20 and NPEL-128) with silicon-containing amines (SCAs) synthesized by the interaction between bifunctional alcohols with different molecular masses and γ-aminopropyltriethoxysilane (AGM-9) are reported. It is shown that, in the case of using SCAs, epoxy oligomer is cured more completely and a higher degree of elasticity in the polymer matrix is achieved without using modifiers, which is impossible in the case when polyethylene polyamines are used.     

Photo-oxidation of epoxy resins cured by non-aromatic amines

The photo-oxidation of epoxy resins based on bisphenol A and cured by non-aromatic amines: diethylene triamine, aminoethyl piperazine and isophorone diamine results in carbonyl and amide formation, decrease of glass transition temperature, and the appearance of a new endotherm at 70–80°C in the DSC traces. The carbonyl and, essentially the amide yield depend strongly on the hardener structure and concentration. The mechanisms of formation of these groups are discussed.     

Low temperature rearrangement of amine cured epoxy resins

Studies are reported on the rearrangements which occur in epoxy resins when heated above 497 K. The nature of the processes which occur in the resin and in model compounds is discussed with reference to changes in the ultraviolet, infra-red and ¹³C and ¹H NMR spectra. Chain scission is preceded by dehydration of the glycidyl segment and occurs at the CN and OC bonds, generating phenoxy radicals in the latter case. The observed coloration of the resin at high temperatures is associated with the formation of a polyenyl structure and the possible generation of quinoid and cyclic conjugated nitrogen-containing aromatic ring structures.     

Network structure and glass transition of epoxy resins cured with active ester

The effect of network structure on the glass transition temperature (T _g) was examined by differential scanning calorimetry, thermomechanical analysis and dynamic thermomechanometry for epoxy resins cured with mixtures of curing agents consisting of an active ester, 1,3,5-triacetoxybenzene (TAB), and a polyfunctional phenol, 1,3,5-trihydroxybenzene (THB). Free hydroxyl groups are formed from THB after curing, whereas acetyl groups are left from TAB. TheT _g value of cured epoxy resins decreased with increasing TAB content in the curing agent, which is attributed to the looser network structure induced by the steric hindrance of acetyl groups from TAB in the curing reaction and also to the weaker intermolecular interaction and the internal plasticization of acetyl groups from TAB.     

Enthalpy relaxation in a partially cured epoxy resin

The enthalpy relaxation of a partially cured (70%) epoxy resin, derived from diglycidyl ether of bisphenol-A cured by methyl-tetrahydrophthalic anhydride with accelerator, has been investigated. The key parameters of the structural relaxation (the apparent activation energy Δh*, the nonlinearity parameter x, and the nonexponentiality parameter β) are compared with those of the fully cured epoxy resin. The aging rates, characterized by the dependences of the enthalpy loss and peak temperature on log(annealing time), are greater in the partially cured epoxy than they are in the fully cured resin at an equivalent aging temperature (T_a = T_g − 20°C). There is a significant reduction in Δh*, from 1100 kJ mol⁻¹ for the fully cured system to 615 kJ mol⁻¹, as the degree of cure is reduced. The parameter x determined by the peak-shift method appears essentially independent of the degree of cure (x = 0.41 ± 0.03 for the partially cured resin compared with 0.42 ± 0.03 obtained previously for the fully cured resin), and does not follow the usually observed correlation of increasing x as Δh* decreases. This invariability of the parameter x seems to indicate that it is determined essentially by the local chemical structure of the backbone chain, and rather little by the supramolecular structure. On the other hand, the estimated nonexponentiality parameter β lies between 0.3 and 0.456, which is significantly lower than in the fully cured epoxy (β ≅ 0.5), indicative of a broadening of the distribution of relaxation times as the degree of cross-linking is reduced. Like the parameter x, this also does not follow the usual correlation with Δh*. These results are discussed in the framework of strong and fragile behavior of glass-forming systems, but it is difficult to reconcile these results in any simple way with the concept of strength and fragility. © 1996 John Wiley & Sons, Inc.