The polyphenylene ether resins and blends prepared from such polymers have become well known in the art of engineering plastics. These materials can be fabricated, as by molding, into a wide variety of consumer and industrial products which are characterized by good electrical, mechanical, chemical and physical properties. The polyphenylene ether resins and methods of their preparation are described extensively in the patent literature, including Hay, U.S. Pat. Nos. 3,306,874 and 3,306,875 and Stamatoff, U.S. Pat. Nos. 3,257,357 and 3,257,358.
The prior art discloses various additives for affecting the properties of polyphenylene ether resin blends. These include aromatic phosphates, e.g., triphenyl phosphate, which is often employed in such compositions to impart flame retardancy and, in larger amounts, to provide a plasticizing function as well. Haaf and Lee, Jr. in U.S. Pat. No. 4,313,864 describe thermoplastic compositions of a polyphenylene ether resin, a plasticizer, such as an aromatic phosphate, and a minor amount of a hydrogenated radial teleblock copolymer.
Another development is the use of certain cyclic phosphates, for example, diphenyl pentaerythritol diphosphate, as a flame retardant agent for polyphenylene ether resins, as is described by Axelrod in U.S. Pat. No. 4,254,775.
Other known additives are stabilizers for increasing the resistance of polyphenylene ether resins against color formation due to the degradative effects of heat or light. Many such stabilizers are founded on the chemical element phosphorus. Holoch, U.S. Pat. No. 3,639,334 discloses various phosphite compounds which serve to reduce color formation where the polyphenylene ether resin is exposed to an oxidizing atmosphere at an elevated temperature. Yonemitsu et al. in U.S. Pat. No. 3,952,072 discloses polyphenylene ether blends stabilized with higher molecular weight phosphorus esters, alone or in combination with sterically hindered phenols. Katchman et al., U.S. Pat. No. 3,761,541 describes polyphenylene ether compositions stabilized by the addition of a combination of alkanolamines and organic phosphites. Cyclic phosphites which function as thermal oxidative stabilizers for such polymers are disclosed by Kinson in U.S. Pat. No. 4,405,739.