Wakichi Fukuda

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 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.

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.

Polymer-Supported Bases. XI. Esterification and Alkylation in the Presence of Polymer-Supported Bicyclic Amidine or Guanidine Moieties

Abstract Polymer-supported 1,5,7-triazabicyclo[4.4.0]deca-5-ene (TBD) was prepared by the reaction of chloromethylated polystyrene resins, cross-linked with 2 mol% of divinylbenzene, with TBD. The reaction of benzoic acid with bromobutane was carried out in toluene or acetonitrile in the presence of polymer-supported TBD or polymer-supported 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). The rate of esterification was dependent on the ring substitution of the supported bases and the solvent. The reduced ring substitution resulted in the increased swellability of the polymeric beads containing benzoate or bromide ions for toluene and thereby in the increased reaction rate. The rate with the high ring-substituted bases increased in acetonitrile, because of the high swellability of the immobilized salts and the high nucleophilicity of benzoate anion in the solvent. The supported bases were also effective for alkylation of an active methylene compound with bromoalkane.

Toughening of aromatic diamine‐cured epoxy resins by poly(butylene phthalate)s and the related copolyesters

Aromatic polyesters, prepared by the reaction of aromatic dicarboxylic acids and 1,4-butanediol, were used to improve the toughness of bisphenol-A diglycidyl ether epoxy resin cured with p,p′-diaminodiphenyl sulfone. These polyesters contained poly(butylene phthalate)s (PBP), poly(butylene phthalate-co-butylene isophthalate)s, poly(butylene phthalate-co-butylene terephthalate)s, and poly(butylene phthalate-co-butylene 2,6-naphthalene dicarboxylate)s. All aromatic polyesters used in this study were soluble in the epoxy resin without solvents and were found to be effective as modifiers for toughening the cured epoxy resin. For example, the inclusion of 20 wt % PBP (MW 16,300) led to a 120% increase in the fracture toughness (KIC) of the cured resin with no loss of mechanical and thermal properties. The toughening mechanism was discussed in terms of the morphological and dynamic viscoelastic behaviors of the modified epoxy resin system.

Toughening of bismaleimide resin by modification with poly(ethylene phthalate) and poly(ethylene phthalate-co-ethylene isophthalate)

Aromatic polyesters were prepared and used to improve the brittleness of the bismaleimide resin composed of 4,4′-bismaleimidediphenyl methane and o,o′-diallyl bisphenol A. The aromatic polyesters contain poly(ethylene phthalate) (PEP) and poly(ethylene phthalate-co-ethylene isophthalate) (10 mol % isophthalate unit) (PEPI). PEP and PEPI were effective modifiers for improving the brittleness of the bismaleimide resin. The most suitable composition for the modification of the bismaleimide was inclusion of 20 wt % PEP (MW 18,200), which led to an 80% increase in the fracture toughness with retention of flexural properties and a slight decrease in the glass transition temperature, compared with the mechanical and thermal properties of the unmodified cured bismaleimide resin (Matrimid resin). Microstructures of the modified resins were examined by scanning electron microscopy and dynamic viscoelastic analysis. The thermal stability of the modified resin was slightly lower than that of the unmodified resin by thermogravimetric analysis. The toughening mechanism is discussed in terms of the morphological and dynamic viscoelastic behavior of the modified bismaleimide resin system.

Modification of bismaleimide resin by poly(phthaloyl diphenyl ether) and the related copolymers

Poly(ether ketone ketone)s were prepared and used to improve the brittleness of the bismaleimide resin. The bismaleimide resin was composed of 4,4′-bismaleimidediphenyl methane (BMI) and o,o′-diallyl bisphenol A (DBA). Poly(ether ketone ketone)s include poly(phthaloyl diphenyl ether) (PPDE), poly(phthaloyl diphenyl ether-co-isophthaloyl diphenyl ether) (PPIDE), and poly(phthaloyl diphenyl ether-co-terephthaloyl diphenyl ether) (PPTDE). PPIDE (50 mol % isophthaloyl unit) was more effective as a modifier for the bismaleimide resin than were PPDE and PPTDE (50 mol % terephthaloyl unit). Morphologies of the modified resins changed from particulate to cocontinuous and to phase-inverted structures, depending on the modifier structure and content. The most effective modification for the cured resins could be attained because of the cocontinuous phase or phase-inverted structure of the modified resins. For example, when using 10 wt % of PPIDE (50 mol % IP unit, MW 349,000), the modified resin had a phase-inverted morphology and the fracture toughness (KIC) for the modified resins increased 75% with retention in flexural properties and the glass transition temperature, compared to those of the unmodified cured bismaleimide resin.