Takao Iijima

Effect of cross-link density on modification of epoxy resins with reactive acrylic elastomers

Abstract The effect of cross-link density on the toughness of modified resins was investigated for modification of epoxy resins with acrylic elastomers with pendant epoxy groups. The elastomers were prepared by terpolymerization of butyl acrylate (BA), glycidyl methacrylate (GMA) and acrylonitrile (AN). The cross-link density of the epoxy matrix was controlled using hybrid hardeners composed of p,p′-diaminodiphenyl sulphone (DDS) as a primary diamine and p,p′-(N,N′-dimethyl)-diaminodiphenyl sulphone (MDS) as a secondary diamine. The terpolymers were effective as modifiers for toughening of difunctional epoxy resins (bisphenol A diglycidyl ether). The addition of 20 wt% of the terpolymer (62 mol% BA, 25 mol% GMA and 13 mol% AN, M n 7900 ) led to a 100% increase in the fractural toughness of the resin cured with the hybrid hardener (DDS/MDS, 48:52 mol ratio, 65:35 NH ratio). The lower the cross-link density, the larger was the fracture toughness and the lower was the glass transition temperature. On the other hand, the terpolymers were less effective in the modification of trifunctional epoxy resins of higher cross-link density (triglycidyl aminocresol) even when using the hybrid hardener (DDS/MDS, 48:52 mol ratio). Both modified systems afforded cured resins with two-phase morphologies. The toughening mechanism is discussed in terms of the morphological and dynamic mechanical behaviours of the modified epoxy resin systems. It is concluded that the ductility of the epoxy matrix contributes greatly to toughening of epoxy resins with acrylic elastomers.

Effect of cross-link density on modification of epoxy resins by N-phenylmaleimide-styrene copolymers

Abstract The effect of cross-link density on the toughening of modified resins was investigated for the modification of epoxy resins with N-phenylmaleimide-styrene alternating copolymers (PMS). The cross-link density of the epoxy matrix was controlled by a combination of two kinds of epoxy resins [diglycidyl ether of bisphenol-A (DGEBA) or triglycidyl aminocresol (TGAC)] and hybrid hardeners composed of p,p′-diaminodiphenyl sulphone (DDS) and p,p′-(N,N′-dimethyl)-diaminodiphenyl sulphone (MDS). The addition of 10 wt% of PMS ( M w 214,000 ) led to 120% increase in the fracture toughness (K1C) of the DGEBA resin cured with the hybrid hardener (DDS: MDS, 67:33 mol ratio). On addition of 15 wt% of PMS ( M w 214,000 ), K1C for the modified resin increased 110% in the TGAC/hybrid hardener (DDS: MDS, 67:33 mol ratio) system. Morphologies of the modified resins depended on PMS molecular weight and concentration, and the cross-link density of the matrix. The toughening of epoxies could be explained by the cocontinuous phase structure in every case.

Toughening of epoxy resins by modification with reactive elastomers composed of butyl acrylate and glycidyl (meth)acrylate

Acrylic elastomers with pendant epoxy groups were used to reduce the brittleness of bisphenol-A diglycidyl ether epoxy resin cured with p,p′-diaminodiphenyl sulphone. The elastomers were prepared by copolymerization of butyl acrylate (BA) with glycidyl acrylate (GA) or methacrylate. These copolymers were effective for toughening of the epoxy resin system. The addition of 20 wt% of copolymer (74 mol% BA and 26 mol% GA) led to 60% increase in the fracture toughness of the cured resin at slight expense of its mechanical properties. The glass transition temperatures of cured resins were comparable to that of the parent epoxy resin. The toughening mechanism is discussed in terms of the morphological and dynamic viscoelastic behaviour of the modified epoxy resin system.

Toughening of aromatic diamine-cured epoxy resins by modification with N-phenylmaleimide-styrene-p-hydroxystyrene terpolymers

Abstract N-phenylmaleimide-styrene-p-hydroxystyrene terpolymers (PMSH), containing pendant p-hydroxyphenyl groups as functionalities, were prepared and used to improve the toughness of bisphenol-A diglycidyl ether epoxy resin cured with p,p′-diaminodiphenyl sulphone. The terpolymers were effective as modifiers for toughening the epoxy resin. When using more than 10 wt% of PMSH with K IC ) for the modified resins increased > 100% with a medium loss of flexural strength and with a retention in flexural modulus and the glass transition temperature. For example, inclusion of 12.5 wt% of PMSH (1.0 mol.% HSt unit, M w 291,000) led to a 130% increase in K IC . The most effective modification for the modified resins could be attained because of the co-continuous structure of the modified resins. The toughening mechanism is discussed in terms of the morphological behaviours of the modified epoxy resin systems.

Effect of matrix compositions on modification of bismaleimide resin by N-phenylmaleimide–styrene copolymers

The effect of matrix compositions on the toughening of bismaleimide resin by modification with N-phenylmaleimide–styrene copolymers (PMS) were examined. The bis-maleimide resin was composed of 4,4′-bismaleimidediphenyl methane (BMI), o,o′-diallyl bisphenol A (DBA), and triallyl isocyanurate (TAIC). The matrix structure was controlled by changing the equivalent ratio of the two allyl components (DBA and TAIC). Morphologies of the modified resins changed from particulate to cocontinuous and to inverted phase structures, depending on the modifier content. The most effective modification for the cured resins could be attained because of the cocontinuous structure of the modified resins. Inclusion of TAIC led to a decrease in the extent of dispersion of the cocontinuous phase, and the optimum matrix structure to improve the toughness was obtained on 20 eq % addition of TAIC. For example, when using 20 eq % of TAIC and 5 wt % of PMS (Mw 303,000), the fracture toughness (Kic) for the modified resins increased 100% at a moderate loss of flexural strength and with retention in flexural modulus and the glass transition temperature, compared to those of the unmodified cured Matrimid resin.

Synthesis and positive-imaging photosensitivity of soluble polyimides having pendant carboxyl groups

Polyimides having pendant carboxyl groups were prepared by a direct one-pot polycondensation of 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) with 3,5-diaminobenzoic acid (DABz) and bis[4-(3-aminophenoxy)phenyl]sulfone (m-BAPS) in the presence of a γ-valerolactone/pyridine catalyst system using N-methyl-2-pyrrolidone (NMP)/toluene mixture as a solvent at 180 °C. The obtained polyimides were soluble in dipolar aprotic solvents such as dimethylformamide, dimethyl sulfoxide, and NMP as well as in tetrahydrofuran and aqueous basic solution. The solubility of the polyimides was dependent on the diamine composition. Photosensitve polyimide (PSPI) systems composed of the polyimides and diazonaphthoquinone compound as a photosensitive material gave positive-tone behavior by UV irradiation, followed by development with aqueous tetramethylammonium hydroxide (TMAH) solution. The scanning electron microscopic photograph of the resulting image showed 10-μm line/space resolution with about 15 μm of film thickness. The PSPIs baked at 350 °C for a short time had excellent thermal resistance comparable to the original polyimides.

Modification of cyanate ester resin by poly(ethylene phthalate) and related copolyesters

Aromatic polyesters were prepared and used to improve the brittleness of the cyanate ester resin. The aromatic polyesters include poly(ethylene phthalate) (PEP) and poly(ethylene phthalate-co-1,4-phenylene phthalate). The polyesters were effective modifiers for improving the brittleness of the cyanate ester resin. For example, inclusion of 20 wt % PEP (MW 19,800) led to a 120% increase in the fracture toughness (KIC) with retention in flexural properties and a slight loss of the glass transition temperature compared to the mechanical and thermal properties of the unmodified cured cyanate ester resin. The microstructures of the modified resins were examined by scanning electron microscopy and dynamic viscoelastic analysis. The thermal stability of the modified resins was lower than that of the unmodified resin as determined by thermogravimetric analysis. The water absorptivity of the modified resin increased significantly, compared to that of the unmodified cured cyanate ester resin. The toughening mechanism was discussed in terms of the morphological and dynamic viscoelastic behaviors of the modified cyanate ester resin system.

Toughening of epoxy resins by N-phenylmaleimide-styrene copolymers

Abstract N -Phenylmaleimide (PMI)-styrene (St) alternating copolymers were used to improve the toughness of bisphenol-A diglycidyl ether epoxy resin cured with p , p ′-diaminodiphenyl sulphone (DDS). The most suitable composition for the modification was inclusion of 10 wt% of the copolymer ( M w 345,000 ) which led to a 130% increase in the fracture toughness ( K IC ) of the cured resin with a medium decrease of its mechanical properties. The glass transition temperatures of the modified resins were equal to or higher than that of the parent epoxy resin. The morphologies of the modified resins were dependent on the copolymer molecular weight and concentration. On addition of up to 7 wt% of the copolymer ( M w 345,000 ) the modified resins had two-phase morphologies with the copolymer-rich dispersed particles in the epoxy matrix. On addition of 8 wt% of the copolymer, the morphologies of the cured resins changed drastically and showed a tendency to form co-continuous phases. The toughening mechanism is discussed in terms of the morphological characteristics of the modified epoxy resin systems.

Modification of bismaleimide resin by N-phenylmaleimide-styrene copolymers

Abstract N -Phenylmaleimide-styrene alternating copolymers were used to improve the toughness of the bismaleimide resin composed of bis(4-maleimidediphenyl) methane and o , o ′-diallyl bisphenol A. The most suitable composition for modification of the bismaleimide resin was inclusion of 5 wt% of the copolymer ( M W 231,000) which led to a 50% increase in the fracture toughness ( K IC ) of the cured resin with a medium expense of its flexural strength. The glass transition temperatures of the modified resins were equal to or slightly less than that of the unmodified bismaleimide resin. The modified resins had different phase separation morphologies, depending on the copolymer molecular weight and concentration. The toughening mechanism was discussed in terms of the morphological characteristics of the modified bismaleimide resin systems.

Toughening of epoxy resins by modification with acrylic elastomers containing pendant epoxy groups

Abstract New acrylic elastomers with pendant epoxy groups were used to reduce the brittleness of bisphenol-A diglycidyl ether epoxy resin cured with p , p ′-diaminodiphenyl sulphone. The elastomers were prepared by copolymerization of butyl acrylate (BA), vinylbenzyl glycidyl ether (VBGE) and styrene (St) or acrylonitrile (AN). These terpolymers were effective for toughening of the epoxy resin system. The addition of 20 wt% of the terpolymer (74 mol% BA, 18 mol% VBGE and 8 mol% St) resulted in an 80% increase in the fracture toughness ( K 1c ) of the cured resin at the slight expense of its mechanical properties. The modified epoxy resins had two-phase morphology in which the volume fraction and average diameter of the dispersed elastomer particles were dependent on the structure and concentration of the terpolymer. The toughening mechanism is discussed in terms of the morphological and dynamic mechanical behaviour of the modified epoxy resin system.