Curing and thermal behaviour of diamide–diimide–diamines based on l-phenylalanine with epoxy blends containing phosphorus/silicon

Abstract

A series of diamide–diimide–diamines (DADIDAs) were synthesized by reacting diacid N,N’-(3,3’,4,4’-benzophenone tetracarboxylic)-3,3’4,4’ diimido-bis-l-phenylalanine (I) with different aromatic diamines viz. 1,4-phenylene diamine (PD), 1,5-diamino naphthalene (N), 4,4’-(9-fluorenyllidene)-dianiline (F), 4,4’-diaminodiphenyl sulphide (DS) and 3,4’-oxydianiline (O). The diacid (I) was synthesized by the condensation of 3,3’,4,4’-benzophenone tetracarboxylic dianhydride (BTDA) with l-phenylalanine (PA) in a solution of glacial acetic acid and pyridine (3:2 v/v) at refluxing temperature. The resulting DADIDAs so synthesized were characterized with the help of elemental analysis (EA) and spectroscopic techniques, and were used as epoxy curing agents. Two epoxy blends (EP and ES) were prepared, each by mixing in an equivalent ratio of 2:3 of tris(glycidyloxy)phosphine oxide (TGPO) with diglycidyl ether of bisphenol-A (DGEBA) and 1,3-bis(3-glycidyloxypropyl)tetramethyl disiloxane (BGPTMSO) with diglycidyl ether of bisphenol-A (DGEBA), respectively. A series of new epoxy thermosets with good thermal stability were prepared by reacting EP/ES with synthesized DADIDAs stoichiometrically. Thermal properties of these epoxy resins were observed using the techniques viz. Differential scanning calorimeter (DSC) for curing behaviour and Thermogravimetric analysis (TGA) to study the thermal stability and mass loss behaviour. All the samples showed good thermal stabilities in terms of char yield (24.8–52.7) and calculated LOI (27.4–38.6), thereby demonstrate their effective use as flame retardant systems.