Polyurethane-ductilized epoxy resins

Amine-cured epoxy resins were modified to improve their impact properties. Urethane prepolymers (PUs), in which terminal isocyanate groups were blocked with nonylphenol (NP) for easy handling, were used as modifiers. The synthesis of the elastomers were carried out at different NCO : OH ratios: 1 : 1, 2 : 1, and 3 : 1 (PU1, PU2, and PU3). Characterization of these materials by GPC and FTIR indicated that PU1 has a negligible amount of NCO-terminated chains and no unreacted toluenediisocyanate (TDI). PU2 and PU3 have free-blocked TDI in the mixture, even after distillation under a vacuum. The molecular weight and polydispersity of the prepolymer increases as PU3 < PU2 < PU1. Copolymerization was carried out by crosslinking with a mixture of cycloaliphatic amines, which react with the epoxy ring and with the NCO groups by deblocking and urea formation. Dynamic mechanical tests were used to measure the glass transition temperatures (T_g) of the copolymers. Two T_g were found if PU1 was the epoxy modifier, indicating that phase separation took place. This was correlated with a structure of PU1 of linear chains with a negligible amount of reactive groups. Flexural and compression properties showed negligible changes for PU2- and PU3-modified epoxy, but the critical strain energy release rate (G_1C) was improved if PU2 was the modifier. This behavior was explained by the linkage of elastomeric chains into the epoxy network. The PU1–epoxy copolymer showed a completely different behavior, with the bending modulus (E_b) reduced to almost one-half with respect to that of the epoxy matrix and with largely improved impact properties. This difference was attributed to the separation of an elastomeric phase, which favors the formation of shear bands in the epoxy matrix. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1781–1789, 1998     

Multifunctional epoxy resins

The curing behavior of epoxy resins prepared by reacting epichlorohydrin with 4,4′-diaminodiphenyl methane (DADPM)/4,4′-diaminodiphenyl ether (DADPE) or 4,4′-diaminodiphenyl sulfone (DDS) was investigated using DDS and tris-(m-aminophenyl)phosphine oxide (TAP) as curing agents. A broad exothermic transition with two maxima were observed in the temperature range of 100–315°C when TAP was used as the curing agent. The effect of varying DDS concentration on curing behavior of epoxy resin was also investigated. Peak exotherm temperature (T_exo) decreased with increasing concentration of DDS, whereas heat of curing (ΔH) increased with an increase in amine concentration up to an optimum value and then decreased. Thermal stability of the resins, cured isothermally at 200°C for 3 h, was investigated using thermogravimetric analysis in a nitrogen atmosphere. Glass fiber-reinforced multifunctional epoxy resin laminates were fabricated and the mechanical properties were evaluated. © 1993 John Wiley & Sons, Inc.     

Deoxybenzoin-based epoxy resins

The diepoxide of bishydroxydeoxybenzoin, termed BEDB, was prepared and used as a diepoxide in adhesive formulations with various aromatic diamine cross-linkers. These novel epoxy resins were characterized and compared to the properties of bisphenol A (BPA)- and 3,3′,5,5′-tetrabromobisphenol A (TBBA)-based epoxies in terms of their thermal and mechanical properties. Cured formulations were characterized to determine glass transition temperatures by differential scanning calorimetry (DSC). The char residue, heat release capacity, dynamic mechanical properties, fracture toughness, and adhesion strength of the cured resins were investigated by thermogravimetric analysis (TGA), microscale combustion calorimetry, dynamic mechanical analysis (DMA), plain-strain fracture toughness tests, and lap shear tests. The BEDB-based resins exhibited significantly higher fracture toughness and adhesion strength compared to the BPA-epoxy resins, as well as low heat release properties (i.e., lower flammability) despite the absence of halogen.     

Fracture and mechanical properties of epoxy resins and rubber-modified epoxy resins

Fracture and mechanical property data on a wide range of epoxy resin systems are presented. The extent to which toughening can be induced by heterophase rubber inclusions depends more on the curing agent used than on the resin component. The greatest improvements in toughness were obtained by rubber modification of epoxy resins cured with an anhydride. A preformed ABS polymer can be used to toughen many epoxy resin systems. With one major exception (where a large improvement was found) only small changes in tensile properties occur when small amounts of rubber are present.     

Storage-stable epoxy B-stage resins

N-Substituted β-aminopropionhydrazides, RNHC₂h₄CONHNH₂, were prepared by the Michael addition of primary amines to acrylic esters. The adducts were converted to the corresponding hydrazides. The aminohydrazides react readily with terminal epoxides at moderate temperatures yeilding B-stage resins of excellent storage stability. When powdered B-stage resins are sprayed on hot metal (150-230°C.), a smooth cross-linked coating is formed in less than 3 min. The coatings have unusually high elasticity, they pass the Olson button test. For best performance the amine used should have the primary amino group attached to either a primary carbon atom or directly to an aromatic nucleus. Aminohydrazides with the following R. Groups have been prepared: methyl, n-butyl, sec-butyl, tert-butyl, phenyl, cyclohexyl, benzyl, octyl, dodecyl, and octadecyl.     

Flammability of epoxy resins

Flammability determinations have been made for epoxy resin formulations. The oxygen index, defined as the volume fraction of oxygen in an oxygen/nitrogen atmosphere that is required just to sustain steady candlelike burning of a stick of the material, has been used as the measure of flammability. The formulations selected for study were those for which the chemical composition of the ingredients was known at least approximately and for which uniform cast slabs (1/8 in. thick) could be readily prepared. They covered a range of compositions of commercial interest. The results have been interpreted in terms of a proposed model for candlelike burning. Effects due to resin composition, cure conditions, fillers, and flame-retardant additives are discussed.     

Core-shell particles designed for toughening the epoxy resins. II. Core-shell-particle-toughened epoxy resins

The diglycidyl ether of bisphenol A–m-phenylene diamine (DGEBA–MPDA) epoxy resin was toughened with various sizes and amounts of reactive core-shell particles (CSP) with butyl acrylate (BA) as a core and methyl methacrylate (MMA) copolymerized with various concentration of glycidyl methacrylate (GMA) as a shell. Ethylene glycol dimethacrylate (EGDMA) was used to crosslink either core or shell. Among the variables of incorporated CSP indicated above, the optimal design was to obtain the maximum plastic flow of epoxy matrix surrounding the cavitated CSP during the fracture test. It could be achieved by maximizing the content of GMA in a shell-crosslinked CSP, the particle size, and the content of CSP in the epoxy resin without causing the large-scale coagulations. The incorporation of reactive CSP could also accelerate the curing reaction of epoxy resins. Besides, it was able to increase the glass transition temperature of epoxy resins if the particle size ≤0.25 μm and the dispersion was globally uniform. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2313–2322, 1998     

Heat resistance of epoxy resins

A torsion pendulum has been found to be a sensitive tool to detect the first steps of pyrolysis. It has been shown that some primary bonds break at elevated temperatures, but in the presence of oxygen, new crosslinks can form simultaneously. In resin heated in air, embrittlement due to these crosslinks starts on the surface of the resin and progresses inwards with time.     

Nodular structure in epoxy resins

Nodular morphology is observed on free surfaces, fracture surfaces, and etched surfaces of epoxy resins of widely different cure and chemistry. The influence of high- and low-energy substrates on nodule size is illustrated. Fine structure or “dimples” exist on several individual nodules, and various states of agglomeration of nodules are depicted. The possible relations between nodular morphology and adhesion phenomena are discussed.     

高性能环氧树脂基体的发展

综述了高性能环氧树脂的制备方法和性能。介绍了几种高性能的环氧树脂固化体系 ,新型的耐湿热性的环氧树脂 ,氰酸酯改性环氧树脂 ,液晶环氧树脂 ,双马来酰亚胺改性环氧树脂等     

含磷阻燃环氧树脂体系研究进展

简要介绍了磷系阻燃剂作为一类新型无卤阻燃剂的特点和阻燃机理,重点综述了含磷阻燃环氧树脂体系的含磷固化剂、含磷环氧化合物及含磷环氧半固化物和添加磷型阻燃的进展,并通过热稳定性、成炭率和极限氧指数（LOI）等阻燃性能参数揭示了各类方法的阻燃效果,最后对含磷阻燃环氧树脂体系研究的未来进行了展望。     

环氧树脂的水性化

对环氧树脂水性化的主要进展进行了综述,侧重对水性环氧乳化技术、成膜机理及一些相关问题进行了简单分析.     

Electrochemical curing of epoxy resins

An electrochemical method has been developed for bonding electrically-conductive adherends. The procedure is based on the electrochemical generation of a curing agent from an otherwise chemically-unreactive precursor mixed with an epoxy resin sandwiched between the bonding members. The one-part epoxy resin is storage stable and cured rapidly on passage of current.     

Toughening epoxy resins with polyepichlorohydrin

Polyepichlorohydrin (PECH) rubbers were found to toughen epoxy resins based on the diglycidyl ether of bisphenol A (DGEBA) and cured with piperidine. The degree of toughening depends on the molecular weight of the PECH and on the curing temperature. Best toughening was achieved with PECH of the highest nominal molecular weight of 3400 (Hydrin 10 × 2). Hydrin 10 × 1 (nominal molecular weight 1700) did not toughen the epoxy resin unless bisphenol A was also added, whereas Hydrin 10 × 2 toughened it in the absence of bisphenol A. Curing resins containing bisphenol A and Hydrin 10 × 1 at 160°C resulted in a slightly more brittle resin than when cured at 120°C. The effect of PECH rubbers on the T_g, modulus, and hot/wet properties is similar to that of carboxy-terminated butadiene-acrylonitrile rubbers (CTBN). Dynamic mechanical thermal analysis (DMTA) and scanning electron micrographs (SEM) of fractured surfaces show that the PECH separates as a discrete phase during curing. © 1993 John Wiley & Sons, Inc.     

Chromatographic studies of epoxy resins

Methods are given for the‘derivatisation’ of various of the components of epoxy resins: after fractionation by g.p.c. but before further analysis by h.p.l.c. or g.p.c. This paper describes the use of the following reagents for this purpose: concentrated HCl (to convert epoxy groups into chlorohydrin units); solid NaOH (to convert 1, 2-chlorohydrin groups into epoxy units); phenol (to open epoxy rings); N-methylaniline (to open epoxy rings); and KMnO₄ (to oxidise —CH₂ — and — OCH₂CHOHCH₂O — bridging units).     

Multifunctional formaldehyde resins as curing agent for epoxy resins

Formaldehyde resins (FR) at 1/1/2 molar ratios of monomers (Cl‐phenol/amino monomers/p‐formaldehyde) were synthesized under acid catalysis. The obtained resins were characterized using elemental analysis, FTIR and RMN spectroscopic methods, being used as crosslinking agents for epoxy resin formulations. The curing of epoxy resins with FR were investigated. The glass transition temperature (T_g) and decomposition behavior of crosslinked resins were studied by differential scanning calorimetry (DSC) and thermogravimetric (TGA) techniques. All DSC scans show two exothermic peaks, which implied the occurrence of cure reactions between epoxy ring and amine or carboxylic protons, in function of chemical structures of FR. The crosslinked products showed good thermal properties, high glass transitions, and low water absorption. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010