Preparation and properties of novel oligo(phenylene oxide)-branched cyclophosphazenes

Abstract

Novel oligo(phenylene oxide)-branched cyclophosphazenes (POPZs) were synthesised by a redistribution reaction of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) with 4-hydroxyphenoxycyclotriphosphazenes in the presence of benzoyl peroxide (BPO) as a free-radical initiator. The redistribution yielded benzoyl moiety-substituted cyclotriphosphazenes in addition to cyclotriphosphazene-branched oxy-2,6-dimethyl-1,4-phenylene (ODMP) repeating units in the hydroxyphenoxy group. The benzoyl moieties originated from the BPO and attached to the methyl side group and the terminal hydroxy group of a constitutional ODMP unit. The benzoyl moiety in the cyclophosphazenes was eliminated completely via hydrolysis with NaOMe, followed by chlorination with SOCl₂ and reduction with LiAlH₄. Both the redistribution and elimination reactions were observed using FT-IR, LC-MS, ¹H NMR, ¹³C NMR, ³¹P NMR, MALDI-TOF mass spectroscopy, and size exclusion chromatography (SEC). The resulting POPZs were evaluated for their thermal and electrical properties and their flame retardancy. The benzoyl moiety-free POPZs exhibited high thermal stability up to 300 °C and electrical properties such as dielectric constants of 2.56–2.67 and dissipation factors of 0.0044–0.0049.