Novel phosphorus‐containing hardeners with tailored chemical structures for epoxy resins: Synthesis and cured resin properties

Abstract

A comparative evaluation of systematically tailored chemical structures of various phosphorus-containing aminic hardeners for epoxy resins was carried out. In particular, the effect of the oxidation state of the phosphorus in the hardener molecule on the curing behavior, the mechanical, thermomechanical, and hot-wet properties of a cured bifunctional bisphenol-A based thermoset is discussed. Particular attention is paid to the comparative pyrolysis of neat cured epoxy resins containing phosphine oxide, phosphinate, phosphonate, and phosphate (with a phosphorus content of about 2.6 wt %) and of the fire behavior of their corresponding carbon fiber-reinforced composites. Comparatively faster curing thermosetting system with an enhanced flame retardancy and adequate processing behavior can be formulated by taking advantage of the higher reactivity of the phosphorus-modified hardeners. For example, a combination of the high reactivity and of induced secondary crosslinking reactions leads to a comparatively high T g when curing the epoxy using a substoichiometric amount of the phosphinate-based hardener. The overall mechanical performance of the materials cured with the phosphorus-containing hardeners is comparable to that of a 4,4 0 -DDS-cured reference system. While the various phosphorus-containing hardeners in general provide the epoxy-based matrix with enhanced flame retardancy properties, it is the flame inhibition in the gas phase especially that determines the improvement in fire retardancy of carbon fiber-reinforced composites. In summary, the present study provides an important contribution towards developing a better understanding of the potential use of such phosphorus-containing compounds to provide the composite matrix with sufficient flame retardancy while simultaneously maintaining its overall mechanical performance on a suitable level.

Synthesis of a novel PEPA-substituted polyphosphoramide with high char residues and its performance as an intumescent flame retardant for epoxy resins

“…The chemical incorporation of phosphorus into the backbones of EP are more preferred because they show less negative effects on physical properties and glass transition temperature (T g ) [18,19]. For instance, Schartel [20,21] have compared various phosphorus-containing hardeners incorporated in both epoxy resins and composites, and observed clear tendencies according to the oxidation state. Liu [22,23] and D€ oring [24,25] synthesized several effective DOPO-based epoxide and hardeners; nevertheless, the presence of phosphorus in the macromolecule could also lead to detrimental changes: undesirable modification of T g s and lower crosslinking.…”

Synthesis of charring agent and its derivatives of dipentaerythritol polycyclicphosphonates flame retardants

“…Phosphonate-and phosphinate-based reactive flame retardants (Braun et al 2006;Ebdon et al 2000;Hergenrother et al 2005;Perez et al 2007) have been hot topics because of high thermal stability. The incorporation of phosphates, through covalent linkages in the DPER biphosphite, should improve the FR properties.…”

Dioxaheteroatom Cyclics as Initiators for Radical Polymerization

“…[3][4][5] In particular, new organophosphorus compounds have been developed to replace tetrabromobisphenol A for flame reatarding epoxy resins. [6,7] In this instance, strained five-membered dioxaheterocyclic compounds have been utilized as vehicles by which flame-retarding moieties may be incorporated into vinyl polymers. One of these, 2,4,4,5,5-pentaphenyl-1,3,2-dioxaphospholane, undergoes smooth thermal rearrangement to a new compound presumed to be the corresponding linear polymer.…”