Effect of aromatic substitution on the cure reaction and network properties of anhydride cured triphenyl ether tetraglycidyl epoxy resins

Abstract

A systemic study of the impact of aromatic substitution on the reaction rate and network properties of the isomers of a tetraglycidylaniline triphenyl ether epoxy resin cured with anhydride hardeners is presented here. The epoxy resins synthesized in this work were based upon N,N,N,N‐tetraglycidyl bis(aminophenoxy)benzene (TGAPB), where the glycidyl aniline and ether groups change from being all meta (133 TGAPB), to meta and para (134 TGAPB), and finally to an all para substituted epoxy resin (144 TGAPB). Increasing para substitution increased reaction rate, promoted the onset of vitrification and increased epoxide conversion. Thermal properties such as glass transition temperatures (Tg) and coefficients of thermal expansion (CTE) both increased consistently with increasing para substitution, although thermal stability as measured via thermogravimetric analysis decreased. Mechanical properties also varied systematically with flexural strength and ductility increasing with increased para substitution, while the modulus decreased. Indeed, the ductility almost doubled, as measured by the work of fracture and displacement at failure highlighting the importance of substitution on properties.

Synthesis of tri‐aryl ether epoxy resin isomers and their cure with diamino diphenyl sulphone

“…These results support other findings that indicate that thermal stability is primarily a function of cohesive energies between molecules rather than the subtle variations in network structure. [ 9 ]…”

“…The synthesis of the 133 TGAPB and 144 TGAPB epoxy resins (Figure 1e) were synthesized by epoxidizing the respective tri‐aryl ether amines as described elsewhere. [ 9 ] A generic description of the epoxidation reaction (Figure 4) however is as follows.…”

“…[8] More recently, the epoxy resins used here were cured with anhydride hardeners and increases in strain to failure, coefficients of thermal expansion (CTE), strength, reaction rate, and T g were observed for increasing para substitution along with a reduction in modulus. [9] This study therefore seeks to uncover new insights into the molecular origin of structure property and processing relationships using isomeric tri-aryl epoxy resins of higher and lower crosslink density. Bifunctional and tetra-functional tri-aryl ether epoxy monomers have been synthesized and cured with DDS and compared against similarly cured commercially available epoxy resins, such as di-glycidyl ether of bisphenol F (BisF) and tetra-glycidyl diamino diphenyl methane (TGDDM).…”

“…The bi-functional tri-aryl ether epoxy resins 1,3 bis(3-glycidyloxyphenoxy)benzene (133 BGOPB) and 1,4 bis (4-glycidyloxyphenoxy)benzene (144 BGOPB) have not been reported previously as high-performance epoxy resins, while studies using the tetra functional epoxy resins, N,N,N, N-tetraglycidyl 1,3-bis (3-aminophenoxy) benzene (133 TGAPB) and N,N,N,N-tetraglycidyl 1,4-bis (4-aminophenoxy) benzene (144 TGAPB) are extremely limited. [9,10] Cure reactions were investigated using isothermal differential scanning calorimetry (DSC), thermal properties such as the glass transition temperature, CTE, and degradation temperatures were measured using DSC, dynamic mechanical thermal analysis (DMTA), thermomechanical analysis (TMA, and thermogravimetric analysis (TGA), respectively, and mechanical properties were determined using compression. The physical properties of the network such as density and moisture ingress were measured while near infrared spectroscopy (NIR) was used to characterize the chemical structure of the network after cure.…”

“…[ 8 ] More recently, the epoxy resins used here were cured with anhydride hardeners and increases in strain to failure, coefficients of thermal expansion (CTE), strength, reaction rate, and T g were observed for increasing para substitution along with a reduction in modulus. [ 9 ]…”