Polyphenylene ethers of improved stability

Abstract: Polyphenylene ethers containing aminoalkyl­ substituted end groups are sometimes undesirably reactive and unstable, especially at high temperatures. This problem is solved by reacting them, at temperatures within the range of about 200-300°C, with nitrogen compounds containing at least one N-H moiety, such as ε-caprolactam.

Description: This invention relates to a method for converting a phenylene ether having amino-alkyl-substituted and groups to derivatives of increased stability and to compositions such derivatives of increased stability. Polyphenylene ethers (also known as polyphenylene oxides) are a well known class of polymers. They are widely used in industry, especially as engineering plastics in applications requiring toughness and heat resistance. Since their discovery, they have given rise to numerous variations and modifications, including those described hereinafter. The polyphenylene ethers comprise a plurality of structural units having the formula In each of said units independently, each Q¹ is independently halogen, primary or secondary lower alkyl having up to 7 carbon atoms , phenyl, haloalkyl, aminoalkyl, hydrocarbonoxy, or halohydrocarbonoxy wherein at least two carbon atoms separate the halogen and oxygen atoms; and each Q² is independently hydrogen, or as defined for Q¹. Examples of suitable primary lower alkyl groups are methyl, ethyl, n-propyl, n-butyl, isobutyl, n-amyl, isoamyl, 2-methylbutyl, n-hexyl, 2,3-dimethylbutyl, 2-, 3- or 4-methylpentyl and the corresponding heptyl groups. Examples of secondary lower alkyl groups are isopropyl, sec-butyl and 3-pentyl. Preferably, any alkyl radicals are straight chain rather than branched. Most often, each Q¹ is alkyl or phenyl, especially C₁₋₄ alkyl, and each Q² is hydrogen. Both homopolymer and copolymer polyphenylene ethers are known. The homopolymers include those containing, for example, 2,6-dimethyl-1,4-phenylene ether units. The copolymers include random copolymers containing such units in combination with (for example) 2,3,6-trimethyl-1,4-phenylene ether units. Many suitable random copolymers, as well as homopolymers, are disclosed in the patent literature. Also known are polyphenylene ethers containing moieties which modify properties such as molecular weight; melt viscosity and/or impact strength. Such polymers are described in the patent literature and may be prepared by grafting onto the polyphenylene ether in known manner such vinyl monomers as acrylonitrile and vinylaromatic compounds (e.g., styrene), or such polymers as polystyrenes and elastomers. The product typically contains both grafted and ungrafted moieties. Other polyphenylene ethers are coupled polymers in which the coupling agent is reacted in known manner with the hydroxy groups of two polyphenylene ether chains to produce a higher molecular weight polymer containing the reaction product of the hydroxy groups and the coupling agent. Illustrative coupling agents are low molecular weight polycarbonates, quinones, heterocycles and formals. Polyphenylene ethers are typically prepared by the oxidative coupling of at least one corresponding monohydroxyaromatic compound. Particularly useful and readily available monohydroxyaromatic compounds are 2,6-xylenol (wherein each Q¹ is methyl and each Q² is hydrogen), whereupon the polymer may be characterized as a poly(2,6-dimethyl-1,4-phenylene ether), and 2,3,6-trimethylphenol (wherein each Q¹ and one Q² is methyl and the other Q² is hydrogen). A variety of catalyst systems are known for the preparation of polyphenylene ethers by oxidative coupling. For the most part, they contain at least one heavy metal compound such as a copper, manganese or cobalt compound, usually in combination with various other materials. Catalyst systems containing a copper compound are disclosed, for example, in U.S-A-3,306,874. 3,306,875, 3,914,266 and 4,028,341. They are usually combinations of cuprous or cupric ions, halide (i.e., chloride, bromide or iodide) ions and at least one amine. Other catalyst systems contain manganese compounds. They are generally alkaline systems in which divalent manganese is combined with such anions as halide, alkoxide or phenoxide. Most often, the manganese is present as a complex with one or more complexing and/or chelating agents such as dialkylamines, alkanolamines, alkylenediamines, o-hydroxyaromatic aldehydes, o-hydroxyazo compounds, ω-hydroxyoximes (monomeric and polymeric), o-hydroxyaryl oximes and β-diketones. Also known are cobalt-containing catalyst systems. Suitable manganese and cobalt-containing catalyst systems for polyphenylene ether preparation are known in the art by reason of disclosure in numerous patents and publications. The present invention relates specifically to a method for converting into derivatives of increased stability; polyphenylene ethers comprising molecules having end groups of the formula: (hereinafter "aminoalkyl end groups"), wherein Q¹ and Q² are as previously defined; each R¹ is independently hydrogen or alkyl, with the proviso that the total number of carbon atoms in both R¹ radicals is 6 or less; and each R² is independently hydrogen or a C₁₋₆ primary alkyl radical. Preferably, each R¹ is hydrogen and each R² is alkyl, especially methyl or n-butyl. Such polymers are typically obtained by incorporating an appropriate primary or secondary monoamine as one of the constituents of the oxidative coupling reaction mixture, especially when a copper- or manganese-containing catalyst is used. Such amines, especially the dialkylamines and preferably di-n-butylamine and dimethylamine, frequently become chemically bound to the polyphenylene ether, most often by replacing one of the α-hydrogen atoms on one or more Q¹ radicals. The principal site of reaction is the Q¹ radical adjacent to the hydroxy group on the terminal unit of the polymer chain. During further processing and/or blending, the aminoalkyl end groups may undergo various reactions, probably involving a quinone methide-type intermediate of the formula These aminoalkyl end groups have numerous effects on the chemistry of the polyphenylene ether. Many of these effects are beneficial, often including an increase in impact strength and compatibilization with other blend components. Reference is made to U.S-A-4,054,553, 4,092,294, 4,477,649, 4,477,651 and 4,517,341. Other effects of the aminoalkyl end groups, however, may be detrimental under certain circumstances. For example, substantial increases in the molecular weight of the polyphenylene ether can occur as a result of deamination to a quinone methide of formula III followed by coupling of two molecules of the deaminated polymer. Such molecular weight increases may be undesirable when close control of the molecular weight of the polyphenylene ether is necessary. Also, block copolymers formed by reactions involving the aminoalkyl end groups may be relatively unstable at high temperatures. A principal object of the present invention, therefore, is to prepare polyphenylene ethers having improved stability, particularly at high temperatures. A further object is to improve the stability of polyphenylene ethers by chemical treatment of aminoalkyl end groups thereon. Other objects will in part be obvious and will in part appear hereinafter. The present invention is based on the discovery that aminoalkyl end groups in polyphenylene ethers react with various nitrogen compounds to form derivatives which are, for the most part, characterized by improved thermal stability. The nitrogen compounds which react in this way include amides, amidines, imides, sulfonamides and amino acids, which may be acyclic, carbocyclic or heterocyclic. Accordingly, an aspect of this invention is a method for converting a polyphenylene ether having amino-alkyl-substituted end groups of formula II, to derivatives of increased stability which comprises reacting said polyphenylene ether, at a temperature within the range of 200-300°C, with at least one nitrogen-containing compound, wherein at least one NH moiety forms part of an amide, imide, amidine, 2-aminocarboxylic acid or sulfonamide group, in the absence of materials which catalyze polymerization of said nitrogen-containing compound. The polyphenylene ethers having amino-alkyl-substituted end groups useful in this invention are those previously described, particularly the poly(2,6-dimethyl-1,4-phenylene)ethers. Although the molecular weight of the polyphenylene ether having amino-alkyl substituted end groups is not critical for the purposes of the invention, polymers having a number average molecular weight within the range of 3,000-40,000 and a weight average molecular weight within the range of 20,000-80,000, as determined by gel permeation chromatography, are readily available commercially and are therefore particularly contemplated. The intrinsic viscosities of such polymers are most often in the range of 0.35-0.6 dl./g., as measured in chloroform at 25°C. According to the invention, the polyphenylene ether having amino-alkyl-substituted end groups is reacted with at least one nitrogen-containing compound hereinafter sometimes denoted "inactivating agent". The nitrogen compound contains at least on NH moiety which forms part of an amide, imide, amidine, 2-aminocarboxylic acid or sulfonamide group. A wide variety of nitrogen-containing compounds are useful as inactivating agents. For the most part, they may be represented by the formula wherein: R³ is hydrogen, hydroxy, amino, alkyl, aryl or aralkyl; R⁴ is hydrogen, alkyl, aryl or aralkyl; or R³ and R⁴ together form an alkylene, ketoalkylene, ketoarylene or -aza- -ketoalkylene group; Y is carbon or Z¹ is O or when Z¹ and R⁴ are taken together, compound of formula (IV) is a cyclic amidine; and n is 0 or 1. In particular, Z¹ and R⁴ together may form a substituted or unsubstituted =N-(CH=CH)- or =N-(CH₂)₃- radical. As will be apparent from the formula, the compounds in which Z¹ and R⁴ are taken together are cyclic amidines. The Z¹-R⁴ combination therein is usually unsubstituted but may contain relatively inert substituents such as alkyl (especially C₁₋₃ alkyl), aryl or alkoxy. The compounds in which Z is O may be amides, imides, amino acids or sulfonamides. For the most part, the imides are cyclic (i.e., R³ and R⁴ together are ketoalkylene or ketoarylene); the amides may be acyclic or carbocyclic (R³ is alkyl, aryl, aralkyl or amino and R⁴ is hydrogen, alkyl, aryl or aralkyl) or may be lactams (R³ and R⁴ together are alkylene or α-aza-β-ketoalkylene, the latter being present in such compounds as diketopiperazine, the condensation dimer of glycine). In the amino acids, n is 1; otherwise it is zero. The following inactivating agents are illustrative. Amidines: imidazole, tetrahydropyrimidine. Acyclic and carbocyclic amides: acetamide, N-methylacetamide, acetanilide, benzamide, N-methylbenzamide, N-benzylbenzamide, benzanilide, urea. Cyclic amides: 2-pyrrolidone, ε-caprolactam, diketopiperazine. Imides: succinimide, maleimide, phthalimide. Sulfonamides: benzenesulfonamide. Amino acids: glycine. ε-Caprolactam is a particularly preferred inactivating agent, by reason of the particular stability of the polyphenylene ethers obtained by its use. According to the invention, the inactivating agent is reacted with the polyphenylene ether having amino-alkyl-substituted end groups at a temperature in the range of 200-300°C. It is generally preferred to conduct the reaction in the melt, although it is also contemplated to use solvents which have boiling points high enough to permit their utilization at the temperatures required. Such solvents ordinarily serve only as reaction media and do not contribute to the essential properties of the inactivated polymers. In general, the reaction mixture will consist essentially of the polyphenylene ether having amino-alkyl-substituted end groups and inactivating agent. In any event, it should be free from materials which catalyze polymerization of the inactivating agent, such as water or extraneous acids or bases when said agent is a lactam, since polymerization of the inactivating agent is not desired. The proportion of inactivating agent in the reaction mixture should generally be a large excess, to ensure complete inactivation of the aminoalkyl end groups. In general, a 50-1000% excess and preferably a 100-500% excess is used, based on the molecular weight of the polymer and the proportion of aminoalkyl end groups therein as determined by suitable analysis. Another aspect of the invention is polyphenylene ethers which have been inactivated by the above-described method. As shown by analytical methods such as carbon-13 nuclear magnetic resonance, the polymeric compositions thus obtained comprise polyphenylene ethers containing end groups having the formula wherein Q¹, Q² and R¹ are as previously defined and N=Z² is an amide, imide, amidine, 2-aminocarboxylic acid or sulfonamide group. Most often, N=Z² has the formula wherein R³, R⁴, Z¹ and n are as previously defined. However, the inactivated polymer may also contain other molecular species, the exact structures of which are not presently known with certainty. Therefore, the compositions of this invention are also appropriately defined in terms of the method for their preparation.

Claims: A method for converting a polyphenylene ether having amino-alkyl-substituted end groups of the formula wherein, Q¹ is halogen, primary or secondary alkyl containing up to 7 carbon atoms, phenyl, haloalkyl, aminoalkyl, hydrocarbonoxy or halohydrocarbonoxy wherein at least two carbon atoms separate the halogen and oxygen atoms, each Q² is independently hydrogen or as defined for Q¹, each R¹ is independently hydrogen or alkyl, with the proviso that the total number of carbon atoms in both R¹ radicals is 6 or less, and each R² is independently hydrogen or a C₁₋₆ primary alkyl radical to derivatives of increased stability which comprises reacting said polyphenylene ether, at a temperature within the range of 200-300°C, with at least one nitrogen containing compound wherein at least one NH moiety forms part of an amide, imide, amidine, 2-aminocarboxylic acid or sulfonamide group, in the absence of materials which catalyze polymerization of said nitrogen-containing compound. A method according to claim 1 wherein the polyphenylene ether having amino-alkyl-substituted end groups is a poly(2,6-dimethyl-1,4-phenylene) ether. A method according to claim 2 wherein the mixture which undergoes reaction consists essentially of said polyphenylene ether and nitrogen-containing compound. A method according to claim 3 wherein the nitrogen-containing compound has the formula wherein: R³ is hydrogen, hydroxy, amino, alkyl, aryl or aralkyl; R⁴ is hydrogen, alkyl, aryl or aralkyl; or R³ and R⁴ together form an alkylene, ketoalkylene, ketoarylene or α-aza-β-ketoalkylene group; Y is carbon or Z¹ is 0; or when Z¹ and R⁴ are taken together compound of formula (IV) is a cyclic amidine; and n is 0 or 1. A method according to claim 4 wherein the aminoalkyl-substituted end groups have the formula wherein each R² is independently hydrogen or a C₁₋₆ primary alkyl radical. A method according to claim 4 wherein the nitrogen-containing compound is at least one compound selected from the group consisting of imidazole, tetrahydropyrimidine, acetamide, N-methylacetamide, acetanilide, benzamide, N-methylbenzamide, N-benzylbenzamide, benzanilide, urea, 2-pyrrolidone, ε-caprolactam, diketopiperazine, succinimide, maleimide, phthalimide, benzenesulfonamide and glycine. A method according to claim 6 wherein the nitrogen-containing compound is ε-caprolactam. A composition comprising polyphenylene ethers containing end groups having the formula wherein: each Q¹ is independently halogen, primary or secondary alkyl containing up to 7 carbon atoms, phenyl, haloalkyl, aminoalkyl, hydrocarbonoxy or halohydrocarbonoxy wherein at least two carbon atoms separate the halogen and oxygen atoms; each Q² is independently hydrogen, or as defined for Q¹; each R¹ is independently hydrogen or alkyl, with the proviso that the total number of carbon atoms in both R¹ radicals is 6 or less: and N=Z² is an amide, imide, amidine, 2-aminocarboxylic acid or sulfonamide group. A composition according to claim 8 wherein the polyphenylene ether is a poly(2,6-dimethyl-1,4-phenylene) ether, Q¹ is methyl, and each Q² and each R¹ is hydrogen. A composition according to claim 9 wherein N=Z² has the formula wherein: R³ is hydrogen, hydroxy, amino, alkyl, aryl or aralkyl; R⁴ is hydrogen, alkyl, aryl or aralkyl; or R³ and R⁴ together form an alkylene, ketoalkylene, ketoarylene or α-aza-β-ketoalkylene group; Y is carbon or Z¹ is O; or when Z¹ and R⁴ are taken together, radical of formula (VI) is a cyclic amidine; and n is 0 or 1. A composition according to claim 10 wherein N=Z² is derived from at least one compound selected from the group consisting of imidazole, tetrahydropyrimidine, acetamide, N-methylacetamide, acetanilide, benzamide, N-methylbenzamide, N-benzylbenzamide, benzanilide, urea, 2-pyrrolidone, ε-caprolactam, diketopiperazine, succinimide, maleimide, phthalimide, benzenesulfonamide, and glycine. A method according to claim 11 wherein N=Z² is derived from ε-caprolactam.

Inventors: WHITE DWAIN MONTGOMERY, WHITE, DWAIN MONTGOMERY
Applicants: GEN ELECTRIC, GENERAL ELECTRIC COMPANY
Application year: 1987
Main classification: C08G65
IPC codes: C08G65