Phosphorus‐containing terephthaldialdehyde adducts—Structure determination and their application as flame retardants in epoxy resins

Abstract

Two novel phosphorus-rich prepolymers based on epoxy novolac and terephthaldialdehyde and potential flame retardants, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and 2,8-dimethyl-phenoxaphosphin-10-oxide (DPPO) were synthesised. The resultant flame-retardant epoxy resins were cured with 4,4 0 -diaminodiphenylmethane (DDM) and 4,4 0 -diamino-dicyclohexylmethane (PACM). Their flammability and burning behavior were characterised by UL 94 and LOI and compared with analogue prepolymers based on diethylphosphite (DEPP). The glass transition temperatures were determined by DSC measurements. Furthermore, the structures of two exemplary molecules based on p-tolylaldehyde adducts were examined by XRD and NMR analysis to determine the possibilities of linking the two novel DOPO and DPPO derivatives to the backbone of the epoxy resin. Additionally, the char yields were determined by TG analysis and thermal desorption mass spectroscopy of the thermosets used and compared with each other to obtain more information about the possible mode of flame-retardant action of the different phosphorus compounds.

Recent Developments in Halogen Free Flame Retardants for Epoxy Resins for Electrical and Electronic Applications

“…The introduction of flame retardant molecules in the polymer backbone was also reported by Seibold et al who reacted phosphorus-rich molecules DOPO and DPPO with terphathaldialdehyde to form new bifunctional flame retardants for PWB (Figure 18) [78]. The novolac epoxy resins cured with DDM and the bifunctional phosphorus molecules reached UL 94-V0 rating with 1.02 and 1.45% phosphorus for the DOPO and DPPO derivatives respectively.…”

Flame retardant epoxy resin for electrical and electronic applications

“…PWB are low Tg, metal-resin adhesion, fabricating properties, dimensional stability, long-term reliability, and increased cost [5]. There are copious reports available based on DOPO and its derivatives [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24], whereas little work has been presented on the basis of Fyrol PMP and aluminum diethylphosphinate-filled epoxies. Wu et al have studied the curing kinetics of epoxy cured with a stoichiometric amount of Fyrol PMP and showed that in the presence of a catalyst, the epoxy curing is completed at 150°C after 70 min [25].…”

2,8-Dimethyl-10-p-tolyl-10H-phenoxaphosphine

“…The title compound was synthesised by a modified literature method (Bronger et al, 2004). For other structurally related ligands, see: Levy et al (1965); Seibold et al (2008); Shau et al (2002).…”