The polyphenylene ether resins are a family of engineering thermoplastics that are well known to the polymer art. These polymers may be made by a variety of catalytic and non-catalytic processes from the corresponding phenols or reactive derivatives thereof. By way of illustration, certain of the polyphenylene ethers are disclosed in Hay, U.S. Pat. Nos. 3,306,874 and 3,306,875, and in Stamatoff, U.S. Pat. Nos. 3,257,357 and 3,257,358. In the Hay patents, the polyphenylene ethers are prepared by an oxidative coupling reaction comprising passing an oxygen-containing gas through a reaction solution of a phenol and a metal-amine complex catalyst. Other disclosures relating to processes for preparing polyphenylene ether resins, including graft copolymers of polyphenylene ethers with styrene type compounds, are found in Fox, U.S. Pat. No. 3,356,761; Sumitomo, U.K. Pat. No. 1,291,609; Bussink et al. U.S. Pat. No. 3,337,499; Blanchard et al. U.S. Pat. No. 3,219,626; Laakso et al. U.S. Pat. No. 3,342,892; Borman, U.S. Pat. No. 3,344,166; Hori et al. U.S. Pat. No. 3,384,619; Faurote et al. U.S. Pat. No. 3,440,217; and disclosures relating to metal based catalysts which do not include amines, are known from patents such as Wieden et al., U.S. Pat. No. 3,442,885 (copper-amidines); Nakashio et al., U.S. Pat. No. 3,573,257 (metal-alcoholate or -phenolate); Kobayashi et al. U.S. Pat. No. 3,455,880 (cobalt chelates); and the like. In the Stamatoff patents, the polyphenylene ethers are produced by reacting the corresponding phenolate ion with an initiator, such as peroxy acid salt, an acid peroxide, a hypohalite, and the like, in the presence of a complexing agent. Disclosures relating to non-catalytic processes, such as oxidation with lead dioxide, silver oxide, etc. are described in Price et al., U.S. Pat. No. 3,382,212. Cizek, U.S. Pat. No. 3,383,435 discloses polyphenylene ether-styrene resin compositions. All of the above-mentioned disclosures are incorporated by reference.
The term "polystyrene resin" includes polymers and copolymers of styrene, alpha methyl styrene, chlorostyrene, and the like.
The term "EPDM" includes rubbery interpolymers of a mixture of mono-olefins and a polyene. Preferred types are those rubbery interpolymers of ethylene, an alpha-olefin, and a polyene. Rubbery interpolymers of ethylene, propylene, and a polyene are especially preferred.
The term "EPDM-silicone rubber" includes graft copolymers of EPDM with silicone rubber. An example of an EPDM-silicone rubber employed in the present invention is that commercially manufactured and sold by Shinetsu Chemical Industry, under the name SEP-172U.
In the prior art, rubber-modified styrene resins have been admixed with polyphenylene ether resins to form compositions that have modified properties. The Cizek patent, U.S. Pat. No. 3,383,435, discloses rubber-modified styrene resin-polyphenylene ether resin compositions wherein the rubber component is of the unsaturated type such as polymers and copolymers of butadiene. The physical properties of these compositions are such that it appears that many of the properties of the styrene resins have been upgraded, while the moldability of the polyphenylene ethers are improved.
Nakashio et al. U.S. Pat. No. 3,658,945 discloses that from 0.5 to 15% by weight of an EPDM-modified styrene resin may be used to upgrade the impact strength of polyethylene ether resins. In Cooper et al., U.S. Pat. No. 3,943,191 it is disclosed that when the highly unsaturated rubber used in compositions of the type disclosed by Cizek, is replaced with EPDM rubber that has a low degree of residual unsaturation, the thermal oxidative stability and color stability are improved. The EPDM rubber in the Cooper et al. compositions is comprised substantially of particles in the range of 3-8 microns.
The impact strength of the Cooper et al. compositions is superior to that of a polypropylene ether resin alone or that of similar compositions comprised of unmodified polystyrene; however, the impact strength of the Cooper et al. compositions is inferior to that of similar compositions comprised of polystyrene modified with polybutadiene rubber, such as a composition known as FG-834 available from Foster-Grant Co. As is disclosed in U.S. Pat. No. 3,981,841, the impact strength of the Cooper et al. compositions can be improved by incorporating therein impact modifiers such as an emulsion-grafted EPDM polystyrene copolymer. U.S. Pat. No. 4,152,316 incorporated herein by reference, discloses that a composition of a polyphenylene ether resin and an alkenyl aromatic resin modified with an EPDM rubber comprised of particles having a median diameter less than about two microns, preferably about 0.5 to 1.5 microns, is a very useful thermoplastic molding material having good thermal oxidative stability and good room temperature impact strength but inferior low temperature impact strength.
In U.S. Pat. No. 4,102,850 it is disclosed that the addition of small amounts of mineral oil to the polymerizing mixture of styrene and EPDM rubber produces EPDM-modified polystyrene which yields blends with polyphenylene oxide having significantly better low-temperature impact strength than blends made from EPDM-polystyrene made without the mineral oil.
In U.S. Pat. No. 3,737,479 it is disclosed that the addition of a silicone such as a polyorganosiloxane, which is fluid, to polyphenylene oxide or to polyphenylene oxide-polystyrene blends improves Gardner impact strength but not Izod impact strength (see Col. 1, lines 54-57 of U.S. Pat. No. 3,737,479).
It has now been found when small amounts of a graft copolymer of EPDM with silicone rubber is blended with a polyphenylene oxide resin, and optionally with a polystyrene resin, blends can be obtained which are substantially improved in ductility and Izod impact strength both at room temperature and at low temperatures.