Aromatic Cyclolinear Phosphazene Polyimides Based on a Novel Bis-Spiro-Substituted Cyclotriphosphazene Diamine

Abstract

A new class of aromatic cyclolinear phosphazene polyimides has been synthesized from a novel bisspiro(arylenedioxy)cyclotriphosphazenediamine. The geminal diamine, 2,2-bis(4'-aminophenoxy)-4,4,6,6-bis[spiro(2',2''-dioxy-1',1''-biphenylyl)]cyclotriphosphazene (5) was polymerized by two-stage condensation polymerization with 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA, 7) and 4,4'-hexafluoroisopropylidenediphthalic anhydride (6FDA, 8), respectively. The obtained poly(amic acid)s 9 and 10 were spread on soda-lime glass plates with a doctor blade and left in a low-humidity chamber. The tack-free film of poly(amic acid) 9 was cyclodehydrated to a light-yellow polyimide (11) film by heating 1 h each at 100, 200, and 300 °C in a nitrogen atmosphere. The poly(amic acid) 10 on thermal cyclodehydration at 160 °C for 0.5 h, 235 °C for 1.5 h, and 280 °C for 0.5 h gave almost a colorless polyimide (12) film. The polyimide films showed good thermal stability and are noteworthy for their high char yield in air, viz., 58-50% at 800 °C. A simple and useful procedure was developed for the synthesis of polymer-grade monomer diamine (5). This involved substitution of 2,2-dichloro-4,4,6,6-bis [spiro(2',2''-dioxy-1',1''-biphenylyl)]cyclotriphosphazene (3) with a potassium salt of 4-nitrophenol followed by catalytic reduction of the formed 2,2-bis(4'-nitrophenoxy)-4,4,6,6-bis[spiro(2',2''-dioxy-1',1''-biphenylyl)]cyclotriphosphazene (4). The acetylation of diamine (5) gave 2,2-bis(4'-acetamidophenoxy)-4,4,6,6-bis[spiro(2',2''-dioxy-1',1''-biphenylyl)]cyclotriphosphazene (6) in 95% yield. The structures of these cyclic phosphazene precursors and monomer diamine were confirmed by FT IR, 1 H-NMR, 31 P-NMR and differential scanning calorimetry (DSC).