Many kinds of poly-1,3,4-oxadiazoles show excellent thermal proper tie^.'-^ Linear phosphorus-containing poly-1,3,4-oxadiazoles were synthesized by Borisov et al.? who reported the preparation of cardo-poly-l,3,4-oxadiazoles in polyphosphoric acid (PPA) and disclosed that the polymers were composed of heat-resistant materials that exhibited increased flame resistance, and by Yokoyama and co-workers,7 who found that open-chain phosphorus-containing poly-1,3,4-oxadiazoles rapidly degrade in the 300-45OoC range and exhibit self-extinguishing behavior. In our earlier articles the preparation of polyamides* and polyestersg that contained phenoxaphosphine rings was discussed and it was shown that the polymers had thermal stability. This article describes the preparation and some of the properties of phenoxaphosphine-containing poly-1,3,4-oxadiazoles, which are synthesized by cyclodehydration of polyhydrazides obtained from 2,8-dichloroformyl-10-phenylphenoxaphosphine 10-oxide (I) and aliphatic and aromatic dihydrazides.
EXPERIMENTALHexamethylphosphoric triamide (HMPA) and dimethylacetamide (DMA) were purified by vacuum distillation and stored over 4-A molecular sieves. PPA (116%) and dihydrazides were obtained commercially. 2,8-Dichloroformyl-lO-phenylphenoxaphosphine 10-oxide was prepared by a method previously given: and infrared (IR) spectra and thermal analyses were measured as des~r i b e d .~,~ Reduced viscosities were examined at a concentration of 0.2 gldl in concentrated HzSO4 or DMA at 30°C.
Model Compound
2,8-Bis(Benzohydrazidocarbonyl)-lO-Phenylphenoxaphosphme 10-Oxide (11):To a solution of phenylhydrazide (2.1 mmole) in HMPA (5 ml), I (1.0 mmole) was added and stirred at room temperature for 2 days. The solution obtained was poured into a large quantity of water and the white precipitate was collected on a filter. The product was repeatedly washed with water and dried over P205 at 100OC. This compound melted at 307OC, followed by cyclodehydration (DTA method); yield, 89%. IR (cm-l): 1645, 1510 (hydrazide linkage); 1600, 1460 (CeH5); 1380 (P-C&,); 1250 (C-0-C); 1180 (P=O).ANAL. Calcd for C34H25N406P: N, 9.09%; P, 5.03%. Found: N, 9.30%; P, 5.03%. ANAL. Calcd for C34H21N404P: N, 9.66%; P, 5.34%. Found: N, 9.67% P, 4.70%.
Preparation of Polymers Polyhydrazides (IV):The following is an example of polymerization: To a solution of terephthalic dihydrazide (1 mmole) in 20 ml of HMPA, I was added in one portion and stored at room temperature for 3 days. The reaction mixture was poured into a large amount of water to precipitate the white product. The compound was filtered, washed thoroughly with water, and dried under reduced pressure over P205 at 100OC.Poly-l,3,4-Oxadiazoles (V): The corresponding polyhydrazide (0.25 g) was added to PPA (25 g) and cyclodehydrated for 19 hr at 180°C in Nz. After cooling the mixture was poured into water and the precipitate was collected by filtration. The compound was saturated in aqueous sodium carbonate Overnight. The product was washed repeatedly with water and acetone and d...
