Phosphorus-containing diamine for flame retardancy of high functionality epoxy resins. Part II. The thermal and mechanical properties of mixed amine systems Weichang Liu a , Russell J. Varley b , George P. Simon a, * a Department of Materials Engineering, Monash University, Clayton 3800, Vic., Australia b CSIRO Molecular Science, Clayton 3168, Vic., Australia Received 20 August 2005; received in revised form 14 December 2005; accepted 29 December 2005 Abstract Bis(4-aminophenoxy)phenyl phosphonate (BAPP) was used in various ratios in combination with diethyltoluenediamine (DETDA) to investigate the effect of increasing phosphorous addition upon the thermal and mechanical properties of diglycidyl ether of bisphenol A (DGEBA) and tetra glycidyl dimethylenedianiline (TGDDM) based epoxy networks. Increasing phosphorous content was shown to decrease the temperature of the initial onset of degradation, while the char yield at 540 8C increased in both the nitrogen and air atmosphere. At 700 8C, however, the char formation was shown to be dependent upon the atmosphere with an oxidative environment promoting further chain scission, while a non-oxidative environment promoted char formation through crosslinking reactions. Increasing phosphorous content was found to produce only modest decreases in the glass transition temperatures, while no significant deleterious effects upon the mechanical and physical properties such as flexural properties and CTE were observed. q 2006 Elsevier Ltd. All rights reserved. Keywords: Epoxy resin; Phosphorous; Flammability 1. Introduction In the modern polymer industry, epoxy resins are widely used as encapsulating materials in the electronic/electrical industries and advanced composite matrices for structural laminates, owing to their high tensile strength and modulus, good chemical and corrosion resistance and excellent dimensional stability [1,2]. The main drawback of epoxy resins, like other organic polymer materials, is their flamm- ability. Although brominated compounds can be blended into epoxy resins to improve their flame retardancy, the generation of toxic, corrosive gases produced during combustion is increasingly an area of concern to environmental legislators. As a result of this there is a need to develop more environmentally benign, halogen-free fire retardants [3,4]. As an alternative to simply adding or blending high levels of a non-reactive fire retardant to a polymer, lower levels of fire retardant can be used by incorporating them into the polymer backbone if they have reactive species, which allow this to occur. This enables lower levels of fire retardant to be used, which generally will have less of a deleterious effect upon the physical and mechanical properties of epoxy resins [5,6]. Of this class of additive, reactive organo-phosphorus compounds have been shown to have a powerful flame retardant effect and, in the case of epoxy resins, can be incorporated into the backbone of the network either through being part of the amine hardener or the epoxy itself [7–18]. When compared to phosphorus-free epoxy resins, phos- phorus-containing epoxy resins show a lower thermal stability, with a reduced initial decomposition temperature, but exhibit a multi-step degradation with a higher final char yield. During the first degradation step, a thermally stable char is formed and serves as an outer layer to prevent the further degradation of the bulk and thus improve the flame retardancy. Recent work in the literature for systems where the phosphorous species was incorporated into the network via a pre-reaction step with a commercial epoxy resin, substantial decreases in T g compared to the non-phosphorous species were observed [7–11,16] due to an inevitable decrease in crosslink density as a result of attaching the phosphorous species to a reactive epoxide functional group. Other systems which reported the use of Polymer 47 (2006) 2091–2098 www.elsevier.com/locate/polymer 0032-3861/$ - see front matter q 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymer.2005.12.083 * Corresponding author. Tel.: C61 39 9054936; fax: C61 39 9054940. E-mail address: george.simon@eng.monash.edu.au (G.P. Simon).