Bisphenol A-based Epoxy Research Articles

Degradation of epoxy resin by partial discharges

Epoxy resins are used in the production of high-voltage insulation components. Partial discharges, inherent in high-voltage installations, degenerate the resinous material and cause degradation of the insulation thus reducing the working life of the component, An understanding of the nature of the chemical changes taking place under partial discharge stressing should allow the production of improved insulation systems and/or identification of diagnostic methods for monitoring the state of existing equipment. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) microspectroscopy is used to determine the chemical changes to the surface of a bisphenol-A based epoxy resin resulting from partial discharge stressing in an air environment. Differences in stressed resin surface chemistry are found to be dependent upon the humidity of the stressed air. The variation in degradation products occurring in dry and in moist air are discussed and possible reactions to explain these differences are presented.

Brillouin scattering study of epoxy adhesive layers during cure

The isothermal curing process of thin epoxy adhesive layers (mixture of a bisphenol A-based epoxy prepolymer and an aliphatic diamine curing agent) has been investigated. The Brillouin scattering technique with 90°A scattering geometry enables simultaneous measurements of longitudinal and shear wave properties in the GHz range. Observed longitudinal and shear wave velocities showed similar changes during cure. They rapidly increased and gradually became constant, reflecting the elastic changes of the epoxy layer. The final velocities, however, clearly depended on the curing temperature. Taking the glass transition process of epoxy resins into consideration, these curing behaviors in thin layers are discussed.

Microstructure of copolymers obtained from chemical modification of phenoxy resin: a13C NMR study

The microstructure of a series of copolymers obtained from the chemical modification of poly(hydroxy ether of bisphenol-A) (phenoxy resin) with different degrees of modification has been investigated by 1H and 13C NMR spectroscopy. In the 13C spectra, the resonance due to all quaternary carbons of bisphenol-A unit appear to be sensitive to the compositional sequence distribution of the copolymer and exhibit clear diad splitting. The experimentally determined average sequence length is found to be in accord with ideal random distribution statistics with randomness close to unity. These results could be useful in the study of the microstructure of other phenoxy modifications, in polymer blends based on phenoxy and epoxy resins where trans reactions can occur. They could also be useful in the determination of the branching microstructure of bisphenol-A based epoxy resins. © 2000 Society of Chemical Industry

Estimation of conformational characteristics of bisphenol-A based poly(hydroxyethers)

Two samples of bisphenol-A based epoxy resins (poly(hydroxy ethers)) were fractionated by precipitation. The fractions were characterized by the weight-average molecular weight (1.3< M w×10 −3<40) and the intrinsic viscosity in tetrahydrofuran and chloroform. Theories based on the worm-like touched-bead model were used to treat the molecular-weight dependence of the intrinsic viscosity and to estimate the conformational characteristics (Kuhn statistical segment length l K, Flory characteristic ratio C ∞, and steric factor σ). Low values of these characteristics indicating rather high flexibility of the chain are discussed.

Characterization of bisphenol A-based epoxy resins by HPLC, GPC, GPC-MALLS, VPO, viscometry, and end group analysis: On the identification of 2,3-dihydroxypropyl-containing compounds, determination of molar mass distribution, and branching

Reversed-phase high performance liquid chromatography (HPLC), conventional gel permeation chromatography (GPC), and gel permeation chromatography coupled with a multiangle laser light scattering photometer (GPC–MALLS) were used for the analysis of epoxy resins based on bisphenol A. Compounds containing 2,3-dihydroxypropyl group were identified in HPLC chromatograms by means of the derivatization of sample by acetone. The presence of branched molecules was proved by GPC–MALLS using a molar mass versus root mean square (RMS) radius plot or molar mass versus elution volume plot. The molar mass distribution determined by HPLC was compared with that obtained by GPC–MALLS. Molar mass averages measured by means of GPC, GPC–MALLS, vapor pressure osmometry (VPO), and end group analysis (EG) were compared and the differences of results obtained by particular methods were discussed. An appropriate GPC calibration was found on the basis of literature data and the comparison of molar mass averages measured by GPC, VPO, and GPC–MALLS. The refractive index increment of epoxy resins was determined. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2432–2438, 1999

Phosphorus-containing epoxy resin for an electronic application

A phosphorus-containing epoxy resin, 6-H-dibenz[c,e][1,2] oxaphosphorin-6-[2,5-bis(oxiranylmethoxy)phenyl]-6-oxide (DOPO epoxy resin), was synthesized and cured with phenolic novolac (Ph Nov), 4,4′-diaminodiphenylsulfone (DDS), or dicyandiamide (DICY). The reactivity of these three curing agents toward DOPO epoxy resin was found in the order of DICY > DDS > Ph Nov. Thermal stability and the weight loss behavior of the cured polymers were studied by TGA. The phosphorus-containing epoxy resin showed lower weight loss temperature and higher char yield than that of bisphenol-A based epoxy resin. The high char yields and limiting oxygen index (LOI) values as well as excellent UL-94 vertical burn test results of DOPO epoxy resin indicated the flame-retardant effectiveness of phosphorus-containing epoxy resins. The DOPO epoxy resin was investigated as a reactive flame-retardant additive in an electronic encapsulation application. Owing to the rigid structure of DOPO and the pendant P group, the resulting phosphorus-containing encapsulant exhibited better flame retardancy, higher glass transition temperature, and thermal stability than the regular encapsulant containing a brominated epoxy resin. High LOI value and UL-94 V-0 rating could be achieved with a phosphorus content of as low as 1.03% (comparable to bromine content of 7.24%) in the cured epoxy, and no fume and toxic gas emission were observed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 353–361, 1999

The Effect of Polymer Substrate Surface Basicity on the Adsorption of a Cationic Polyacrylamide

The adsorption of a cationic polyacrylamide onto polytetrafluoroethylene, bisphenol-A based epoxy resins, and acrylate substrates was characterized with X-ray photoelectron spectroscopy (XPS) and dynamic contact angle measurement in water. Surface acidity–basicity was quantified via dynamic contact angle measurement in water, ethylene glycol, and diiodomethane. The epoxy resins exhibited intermediate surface basicity and adsorbed the most polyelectrolyte, suggesting that specific substrate–adsorbate acid–base interactions govern adsorption of the cationic polyacrylamide onto surfaces of low to intermediate basicity. In general polar interactions appear to dominate the adsorption process. Advancing contact angle measurements have yielded quantitative fractional surface coverage information for polymer-on-polymer adsorption comparable to that obtained via XPS.

High-performance liquid chromatography-mass spectrometry of epoxy resins

The application of liquid chromatography coupled to mass spectrometry (LC-MS) for the analysis of epoxy resins is shown in two examples. Electro spray (ESI) and atmospheric pressure chemical ionization (APCI) are compared with respect to the ionization of diglycidylether of bisphenol A-based (DGEBA) epoxy resins. By-products in a typical modified solid DGEBA-based epoxy resin and in a new weatherable crosslinker for powder coating applications are characterized and discussed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 913–925, 1999

Sucrose-based epoxy monomers and their reactions with diethylenetriamine

Two sets of sucrose-based epoxy monomers, namely, epoxy allyl sucroses (EAS), and epoxy crotyl sucroses (ECS), were prepared by epoxidation of octa-O-allyl and octa-O-crotyl sucroses (OAS and OCS, respectively). Synthetic and structural characterization studies showed that the new epoxy monomers were mixtures of structural isomers and diastereoisomers that contained varying numbers of epoxy groups per sucrose. EAS and ECS can be tailored to contain an average of one to eight epoxy groups per sucrose. Quantitative 13C-NMR spectrometry and titrimetry were used independently to confirm the average number of epoxy groups per sucrose. Sucrose-based epoxy monomers were cured with diethylenetriamine (DETA) in a differential scanning calorimeter (DSC), and their curing characteristics were compared with those of diglycidyl ether of bisphenol A (DGEBA) and diepoxycrotyl ether of bisphenol A (DECEBA). EAS and DGEBA cured at 100 to 125°C and exhibited a heat of cure of about 108.8 kJ per mol epoxy. ECS and DECEBA cured at 150 and 171°C, respectively, and exhibited a heat of cure of about 83.7 kJ per mol epoxy. Depending upon the degree of epoxidation (average number of epoxy groups per sucrose) and the concentration of DETA, glass transition temperatures (Tgs) of cured EAS varied from −17 to 72°C. DETA-cured ECS containing an average of 7.3 epoxy groups per sucrose (ECS-7.3) showed no DSC glass transition between −140 and 220°C when the ratio of amine (NH) to epoxy group was 1:1 and 1.5:1. Maximum Tgs obtained for DETA-cured DGEBA and DECEBA polymers were 134 and 106°C, respectively. DETA-cured bisphenol A-based epoxy polymers degraded at about 340°C, as observed by thermogravimetric analysis (TGA). DETA-cured sucrose-based epoxy polymers degraded at about 320°C. Sucrose-based epoxies cured with DETA were found to bind aluminum, glass, and steel. Comparative lap shear tests (ASTM D1002–94) showed that DETA-cured epoxy allyl sucroses with an average of 3.2 epoxy groups per sucrose (EAS-3.2) generated a flexible adhesive comparable in bond strength to DGEBA. However, DETA-cured ECS-7.3 outperformed the bonding characteristics of both DGEBA and EAS-3.2. All sucrose-based epoxy polymers were crosslinked and insoluble in water, N,N-dimethylformamide, tetrahydrofuran, acetone, and dichloromethane. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2397–2413, 1998

Fracture Behavior of Epoxy-Based, Hybrid Particulate Composites

ABSTRACTEpoxy-based, particulate composites are commonly used in packaging applications for the microelectronics industry. For example molding compounds, die attach adhesives, and encapsulant resins are all polymer matrix, particulate-reinforced composites. The mechanical behavior of these materials is a function of the type of resin, the shape and size of the reinforcing particles, the filler content, etc. In this paper, we will examine the interactions of the toughening mechanisms between rubber particles and the reinforcing particles. Hybrid-particulate composites are prepared by compounding both rubber particles and disc-shaped boron nitride particles in a bisphenol A-based epoxy cured with piperidine. Interestingly, there are combinations of rubber and reinforcing particles that lead to synergistic toughening. The underlying causes for synergistic toughening will be discussed.

Polycarbonate-epoxy semi-interpenetrating polymer network: 2. Phase separation and morphology

Bisphenol A-based epoxy resin (DGEBA) was modified with bisphenol A polycarbonate (PC), by either a physical or chemical process, and thermally cured with 4,4′-diaminodiphenyl sulfone, tetraethylenepentamine, and anhydride. The phase separation in the PC/epoxy blends was controlled by varying the composition, and the PC-epoxy reaction, and utilizing curing agents of different reactivity. A single phase morphology was achieved by accelerating the curing reaction, or introducing PC-epoxy reaction, or eliminating crystallization of PC. Under certain conditions, PC spherulites are able to form, in company with the formation of epoxy networks. Curing of the epoxy resin modified the crystallization mechanism, the melting behaviour and the morphology. The nuclei are likely to be pre-existing high molecular weight PC chains and are formed by the special interaction between PC molecules and the primary network. Low molecular weight epoxy resins increase the crystallization rate. The internal fractionation changes by PC chain scission during the melt blending process has an important influence on the crystallization. The spherulite morphology fixed by semi-IPN structure subjected a loss of order by annealing. It is suggested that hydrogen bonding and graft reaction in this kind of PC/epoxy semi-IPN is the key to controlling phase separation and morphology.

Cationic Polyacrylamide Adsorption on Epoxy Surfaces

The adsorption of a cationic polyacrylamide (acrylamide/β-methacryloxyethyltrimethylammonium methyl sulfate copolymer) onto an imidazole catalyzed bisphenol-A based epoxy resin surface was examined by surface wetting. The work of adhesion of diodomethane, ethylene glycol and water was measured on microscopically smooth epoxy surfaces using a Wilhemy plate method, in both advancing and receding modes. The cationic polyacrylamide was adsorbed from aqueous solutions as a function of the pH of the solution. In addition to the cationic quaternary amine groups along the polymer chain, there were carboxylate groups from amide hydrolysis, which had a pKaof 10.73. The surface wetting of neither diodomethane nor ethylene glycol was sensitive to the adsorbed polyacrylamide. Wetting of the surface by water was very sensitive to the presence of adsorbed polyacrylamide. Polyacrylamides in solutions below pH 9 adsorbed onto the epoxy surface resulting in increased water adhesion to the surface. When the polyacrylamide solution was greater than pH 9 carboxylate groups ionized and the anions inhibited adsorption of the polyacrylamide. The water wetting measurements were shown to correlate with the adsorption of Pd/Sn colloidal particles used for electroless deposition of copper circuit lines on printed circuit boards.

Characterization of the particle–matrix interface in rubber‐modified epoxy by atomic force microscopy

AbstractAtomic force microscopy (AFM) was used to study the interphase regions in rubber‐toughened epoxy polymers. The nature of the interphase region was varied by either the adducting of reactive oligomers or by crosslinking the shell polymer on core/shell latex particles. The adducted reactive oligomers were comprised of carboxyl‐terminated, butadiene‐actrylonitrile copolymers (CTBN) prereacted with either (1) a low molecular weight diglycidyl ether of bisphenol A‐based epoxy, which results in an interphase with increased crosslink density, or (2) a high molecular weight epoxy based on the diglycidyl ether of propylene glycol (DEGP), which results in an interphase with decreased crosslink density. The second type of rubber particles is custom‐made submicron core/shell latex particles of a poly(butadiene‐co‐styrene)[P(BS)] core with an acrylate shell. Two acrylate shells were (1) PMMA/AN shell containing 25% acrylonitile and (2) a similar PMMA/AN with 5% divinyl benzene. The toughness of these blends was characterized using linear elastic fracture mechanics. The features on the fracture surfaces were examined using both AFM and FESEM (field emission scanning electron microscopy). AFM was able to detect features not observed in SEM and also to quantify all of the fracture surface features. In particular, the height‐to‐width ratio of the rim surrounding cavitated particles provided a useful means for determining the ductility of the interphase region. Attempts were made to determine the size of the interphase region using the frictional mode and the tip‐adhesion forces. Unfortunately, the results of both approaches are inconclusive at the present time; this is most likely due to the deformation surrounding the rubber particles detected in the fast fracture regions. © 1995 John Wiley &amp; Sons, Inc.

Partially miscible blends of epoxy resin and epoxidized rubber: Structural characterization of the epoxidized rubber and mechanical properties of the blends

AbstractThe cure process and the mechanical properties of blends of diglycidyl ether of bisphenol‐A–based epoxy resin and hydroxyl terminated, internally epoxidized polybutadiene rubber have been studied. Internal oxirane groups are characterized by a main absorption at 885 cm−1 in the infrared spectrum while the terminal oxirane groups of the diepoxide monomer absorb at 913 cm−1. In the absence of prereaction of the rubber, gelation of the epoxy matrix occurs much faster than any reaction involving the internal oxirane groups or the terminal hydroxyl groups. Therefore, only weak chemical bonding between the rubber particles and the epoxy matrix exists and the fracture toughness of the blends does not show any significant improvement. Upon prereaction of the rubber with an excess diepoxide monomers, a 40% improvement in the value of the critical stress intensity factor is obtained. However, dynamic mechanical spectra of these blends acquired in the rubbery plateau region uniquely demonstrate that this improvement is due to the incorporation of the rubber into the epoxy network rather than to the presence of phase‐separated rubber particles. © 1994 John Wiley &amp; Sons, Inc.

Composition of the continuous phase in partially miscible blends of epoxy resin and epoxidized rubber by dynamic mechanical analysis

The dynamic mechanical properties of blends of diglycidyl ether of bisphenol-A based epoxy resin and internally epoxidized polybutadiene rubber have been studied as a function of initial rubber content, stoichiometry and cure cycle of the epoxy resin. It is shown that both the glass transition temperature of the epoxy-rich continuous phase, T g E (r) . and the apparent enthalpy of activation associated with this transition, ΔH a E(r) , are sensitive to the state of the rubber in the sample. Specifically, dynamic mechanical analysis can be used to distinguish between rubber dissolved in the matrix (plasticizer), incorporated into the network (flexibilizer) or phase separated (toughener). Furthermore, it is demonstrated that the Gordon-Taylor equation rather than the more commonly used Fox equation should be used to model the effect of dissolved rubber on T g E (r) and that the Gordon-Taylor equation can also be extended to describe the variations of ΔH a E(r) . Ultimately this equation can be generalized to predict the glass transition temperature of a sample containing both dissolved and phase separated rubber.

Synthesis and manufacture of bisphenol-A based epoxy resins – a review of papers and patents from the period of 1986-1990

Synthesis and manufacture of bisphenol-A based epoxy resins – a review of papers and patents from the period of 1986-1990

Ultrasonic Study of Sub β Relaxation in Epoxides Cured with Aliphatic Diamines

In the bisphenol A-based epoxy resin made from different length prepolymers and Aliphatic Diamines, sub β relaxation were investigated. Low frequency dynamic and ultrasonic results suggest that the relaxation seems to follow Arrhenius type behavior. In addition, the β relaxation is observed separately from the main α relaxation in the MHz range. The strength of β relaxation depends on the molecular length of prepolymer and the amount of curing agent used. This indicates that the relaxation arises from motion within an internal side group containing crosslinks.

Chemical modification of matrix resin networks with engineering thermoplastics: 1. Synthesis, morphology, physical behaviour and toughening mechanisms of poly(arylene ether sulphone) modified epoxy networks

Bisphenol A-based epoxy resins were modified with either phenolic hydroxyl or aromatic amine functionally-terminated poly(arylene ether sulphone) oligomers and thermally cured with 4,4′ diaminodiphenyl sulphone. The resulting networks displayed significantly improved fracture toughness, with little sacrifice in modulus. The bisphenol A-based polysulphones were molecularly miscible with the epoxy precursors over the entire range of compositions and molecular weights investigated, but developed a two phase structure upon network formation. The molecular weights and composition of polysulphone chemically incorporated into the network were varied and their effect on several important physical properties was investigated. The dynamic mechanical analysis and scanning electron microscopy (SEM) studies showed that it is possible to generate a two-phase morphology in the cured networks wherein polysulphone composite particles are dispersed in the epoxy matrix. Despite the two-phase structure, the modified crosslinked systems are nearly transparent, due to a similarity in component refractive index values. The fracture toughness of these modified networks under plane strain conditions improved significantly with minimal sacrifice of the flexural modulus.

An infrared spectroscopic investigation of the curing reactions of the EPON 828/meta-phenylenediamine system

Mid- and near-infrared (IR) spectroscopy has been used to study the curing of a bisphenol-A based epoxy resin (EPON-828) with a tetrafunctional curing agent, viz., meta-phenylenediamine (MPDA). Three different cure cycles were used in the study. Primary amine functionality was observed to react relatively rapidly; none remained after curing for 2 h at 75°C. Secondary amine functionality was exhausted in epoxy rich samples subjected to the standard cure cycle (2 h at 75°C followed by 2 h at 125°C). In samples with stoichiometric amount or higher MPDA, complete reaction of secondary amine or epoxy groups was not observed. In amine-rich samples subjected to post curing (6 h at 175°C), evidence was seen for the reaction of hydroxyl and epoxy groups, resulting in a considerable increase in the crosslink density of these samples.

107—IMPROVEMENTS IN EPOXY-AMINO POLYAMIDE FINISHES FOR EASY-CARE WOOL FABRICS

This paper describes significantly improved finishes for control of felting shrinkage in wool apparel fabrics obtained with blends of glycerol-based and bisphenol A-based epoxy resins with an amino polyamide resin. Oxidative pretreatment of the fabric improves the shrinkage-resistance. Much of the stiffness imparted to the fabric by the resin treatment is removed by mechanical methods. Successful application of a typical resin formulation to full-size woollen fabrics is described.