CARBOXYLATED PHENYLENE ETHER RESINS

Abstract: Melt-processing a mixture of a polyphenylene ether (PPE) and an ethylenically unsaturated carboxylic compound, in the absence of an added free radical initiator such as a peroxide, serves to introduce carboxyl functionality into the PPE resin. The resulting carboxylated PPE resins are useful in forming alloys with more polar resins such as polyamides.

Description: This invention relates to phenylene ether resins having carboxyl functionality. Polyphenylene ether resins (PPE) have long been known for use as high temperature thermoplastics. For example, PPO, or poly(2,6-dimethyl-1,4-phenylene ether), was disclosed and described in U.S. Patent Nos. 3,134,753 and 3,306,874. More recently, in U.S. Patent No. 4,011,200, phenylene ether copolymer resins having improved thermal stability were described. These resins have achieved a high degree of acceptance, particularly for use in further blends with other polymers such as styrenic resins, described for example in U.s. Patent Nos. 3,356,761; 3,383,435 and 4,038,543. Polyphenylene ethers are substantially non-polar in character, and are therefore difficult to blend with a great many of the more polar resins such as polyamides and polyesters. Moreover, the adhesion of PPE resins to a variety of conventional reinforcing materials such as glass fiber is often poor, and modification of the surfaces of such materials may be required in order to achieve adequate reinforcement of PPE resins. Methods for modifying the non-polar character of PPE resins are known. The use of functional comonomers, as well as the use of metalation, sulfonation, chloromethylation and similar processes have been described for introducing reactive functionality into such resins. Treating preformed polyphenylene ethers with a combination of a styrenic monomer and maleic anhydride in the presence of a free-radical initiator is shown in U.S. 4,097,556 to provide polyphenylene ether-styrene-maleic anhydride graft copolymers which are said to be useful in blends with polyamides. Processes for directly attaching maleic anhydride to phenylene ether resins in the presence of a peroxide are shown in published Japanese applications 59/66452 and 59/59724. Blends of these maleated phenylene ether resins with polyamides are also disclosed therein, and the carboxylated resins are said to have improved affinity for glass. In EP-A- 121 974 a method for preparing polymer mixtures is described, which the decrease of the molecular weight of polyphenylene ethers under extrusion conditions can be suppressed by melt-mixing the phenylene ethers with 0,5 to 4 pbw of N-methylmaleimide or 1 pbw of Maleic acid anhydride and 1 pbw of propylamine. Although the methods available for carboxylating phenylene ether resins and polyamides appear to be successful, further improvements are needed. Chemical modification of phenylene ether resins, either by use of functional comonomers or in a post-reaction, requires additional and costly process steps. The methods presently known for directly modifying phenylene ether resins generally require extended mixing times at melt processing temperatures and/or the use of free-radical compounds, conditions which tend to promote crosslinking and/or deterioration of the resin. Extended mixing at high temperatures also increases energy consumption and adds to production costs. An improved method for directly carboxylating phenylene ether resins which substantially reduces processing times and minimizes resin cross-linking and degradation is needed. The process of this invention is an improved method for the carboxylation of phenylene ether resins, the process comprising melt-processing a mixture of 100 parts by weight of a phenylene ether resin and 0.05 to 1.0 parts by weight of itaconic acid. The phenylene ether resins (or PPE resins) useful for the purposes of this invention include both the homopolymers prepared by the oxidative coupling of a 2,6-dialkylphenol as disclosed for example in U.S. Pat. No. 3,306,874, as well as the copolymers of 2,6-dialkylphenols and 2,3,6-trialkylphenols described in U.S. Pat. No. 4,011,200. In general, these resins are prepared by oxidative coupling of a 2,6-dialkylphenol such as 2,6-dimethylphenol or a mixture of a 2,6-dialkylphenol and a 2,3,6-trialkylphenol such as 2,3,6-trimethylphenol. In forming copolymers suitable for the practice of this invention, the proportion of 2,3,6-trialkylphenol will lie in the range of from about 2 to about 50 wt% based on total polyphenylene ether. However, the preferred copolymers will comprise from about 2 to 20 wt%, more preferably from about 2 to 10 wt% 2,3,6-trialkylphenol, and, correspondingly from about 98 to about 80, more preferably from about 98 to about 90 wt% 2,6-dialkylphenol. The synthesis of these homopolymers and copolymers by a variety of oxidative coupling processes is well known in the art, and such polymers have become available to the art from commercial sources. Carboxylation of the phenylene ether resin is carried out by melt-blending a mixture of the phenylene ether resin with itaconic acid, having both a reactive ethylenic carboncarbon double bond and two reactive carboxylic functional groups. The phenylene ether resin and the itaconic acid will be combined and melt-processed in conventional melt compounding equipment such as a compounding extruder. The most practical and convenient processing method will be to dry blend the components thoroughly as powders and/or pellets to obtain a well-mixed and complete dispersion of the components and then meltmixing the dry blend. The application of high shearing forces together with external heating achieves a further thorough mixing of the components and melting of the resinous component and provides the conditions necessary to achieve the interaction of the itaconic acid with the resin. In carrying out the carboxylation step for the purposes of this invention, prolonged mixing times are to be avoided. Phenylene ether resins are high melt temperature materials and are difficult to melt mix thoroughly; high stock temperatures in the range of from 600-750°F (301-385°C) are commonly used in PPE compounding operations. High shear mixing devices such as for example single or twin screw compounding extruders, are therefore generally preferred for successful melt-processing. Such devices, and particularly twin-screw compounding extruders, can rapidly melt process PPE resins with high shear and thorough mixing, permitting shortened residence times and thus reducing the extent of exposure to severe heat conditions; ie., the heat history of the resin is minimized. The use of heated roll mills and Banbury mixers for compounding these resins may require extended mixing times, which increases the heat history of the resin and may cross link, gel and/or oxidize the phenylene ether resin; hence although these devices may be employed for the purposes of this invention when care is used to avoid such detrimental results, these devices are not preferred. The carboxylated phenylene ether resin produced in this process step may be used directly, as for example in preparing alloys with polyamides. However, the interaction of the itaconic acid with the PPE resin may be incomplete, and the carboxylated polyphenylene ether may thus contain a substantial portion of unattached carboxylic compound, either as unreacted itaconic acid or as a low-molecular weight reaction by-product. Low molecular weight carboxylic compounds may interact deleteriously with condensation polymers such as polyesters or polyamides under melt blending conditions and, depending on the chemical nature of the carboxylic compound, may cross link such polymers and/or alter the molecular weight of the polyamide by chain scission or graft-linking reactions. Low molecular weight carboxylic compounds, if present, may also interact with plasticizers, antioxidants and other additives conventionally used with such resins, thereby reducing or even destroying their effectiveness. It may therefore be desirable to remove any remaining low molecular weight carboxylic compounds. In as much as the unattached low molecular weight compounds are volatile at the temperatures required for melt processing, these compounds may be readily removed by devolatilizing the melt during or after the carboxylation step preferably by means of a vented or vacuum-vented extruder. Alternatively the unattached carboxylic compounds, if present, may be removed from the carboxylated phenylene ether resin in a separate process step, such as by extraction with a suitable solvent, or by dissolving the resin in a suitable solvent and then re-precipitating the resin. The amount of itaconic acid employed will thus depend upon the melt processing conditions and equipment used in the carboxylation step. In general, the level of attached to the phenylene ether resin lies in the range of from about 0.05 to about 1.0 wt. % and preferably, from 0.1 to about 0.5 wt. %, based on phenylene ether resin. At levels below this range, little if any effect will be seen, while at levels much above 0.75 wt. % and particularly above 1.0 wt. %, a substantial reduction occurs in the physical properties of polyamide alloys prepared from the product, and some deterioration of the PPE resin may be seen. Where the melt processing conditions employed are highly effective in promoting the carboxylation, the level of itaconic acid charged will approximate that desired in the carboxylated PPE. Where less efficient carboxylation processing conditions are used, and particularly where a devolatilization or other process step will be employed, thus removing any unattached low molecular weight carboxylic compound that results, higher levels of itaconic acid may be charged. It may also be a desirable alternative method for some purposes to effect an even higher level of PPE carboxylation, then melt-blend the resulting carboxylated resin with sufficient un-carboxylated PPE resin to provide resin with the desired degree of carboxylation for further blending. The carboxylated phenylene ether resins prepared by the process of this invention are particularly useful in preparing alloys with polyamides. These alloys may be prepared by further compounding the carboxylated phenylene ether resin with a polyamide resin. The polyamides useful for preparing such alloys include the conventional injection-moldable polyamide resins known widely as nylon resins, including both aliphatic polylactams such as polycaprolactam (Nylon 6) and higher analogs such as Nylon 11 and Nylon 12, and polyamides formed from aliphatic diamines and aliphatic dicarboxylic acids such as polyhexamethylene sebacamide (Nylon 6,10) and polyhexamethylene adipamide (Nylon 6,6). Further examples of useful polyamides include the amorphous as well as the crystalline versions, the toughened polyamides, and the aromatic-aliphatic copolymers, terpolymers and tetrapolymers. A great variety of these nylon resins are well-known and widely available commercially. Combining the carboxylated phenylene ether resin with the polyamide may be accomplished by any of the common melt blending processes, including the use of compounding extruders, Banbury mixers and roll mills. The powdered or pelletized resins may be dry blended, then fed to the processing equipment, or, alternatively, one of the resinous components may be fluxed in the melt processing equipment, then combined by adding the remaining resinous component, together with impact modifiers, additional pigments, dyes, fillers, stabilizers, antioxidants, lubricants and plasticizers as may be desired, and according to the practices commonly employed in the thermoplastic compounding art. The resulting alloy is a readily melt-processible thermoplastic exhibiting no significant delamination. These compositions are thus not highly-crosslinked, and yet do not exhibit any of the characteristics of the incompatible mixtures attained by a simple mixing and molding of phenylene ether resins and nylons. Whether this composition is an alloy of now highly compatible components or is a graft resin comprising a graft of nylon and polyphenylene components is not known. These compositions are useful thermoplastics, and may be further modified by the addition of fillers, reinforcing fibers, dyes, pigments, flame retardants, antioxidants, stabilizers, plasticizers and processing aids, as is well-known and practiced in the molding art. Particularly useful are compositions further modified by the addition of suitable impact modifiers, and particularly those well-known and commonly used for the impact modification of polyphenylene ether resins, such as impact modified styrenic resins, block copolymer elastomer resins and olefin polymers. The compositions may also be extended by further compounding with suitable resins, such as styrenic resins, as well as by the further addition of polyamides and polyphenylene ethers. The invention will be better understood by consideration of the following examples, which are obtained by way of illustration of the invention and not in limitation thereof. In the examples, the following abbreviations and terms are employed: PEC= copolymer of 2,6-dimethylphenol (95%)and 2,3,6-trimethylphenol (5%), prepared substantially by the process of U.S. 4,011,200 Impact= Izod impact, ft lbs/in notch, ASTM D-256 A (at room temperature). Lubricant= Pluronic® F88 ethylene oxide/propylene-oxide copolymer, obtained from Wyandotte Chemical Co. Example 1 PEC resin (100 pbw) and 1.0 pbw of itaconic acid were dry blended and melt-compounded in a 1 3/4" (44,5 mm) single screw extruder. The resulting carboxylated PEC resin (50 pbw) was then melt-blended with 50 pbw Nylon 6,6 in a compounding extruder, providing a smooth, ductile extrudate. The extrudate, on injection molding, gave test specimens having a 0.50 ft lbs/in notch Izod Impact value. Control Example The proceedure of Example 18 was repeated using 1.0 pbw succinic anhydride in place of the itaconic acid. The blend of carboxylated PEC resin with Nylon 6,6 gave only a poorly compatibilized mixture when compounded on a single screw extruder, which could not be molded. Compounding in a 28mm twin screw extruder afforded only slight improvement, giving test specimens having a 0.21 ft lbs/in notch. The proceedure was repeated, using 1.0 pbw succinic anhydride and 0.5 pbw dicumyl peroxide per 100 pbw PEC. The blend of this material with Nylon 6,6 gave very rough, brittle extrudate when compounded on the twin screw extruder. It will therefore be apparent that itaconic acid is effective in the carboxylation of PPE resins. The saturated analogs such as succinic anhydride are ineffective, even when employed together with a free-radical generator such as a peroxide compound.

Claims: Carboxylated phenylene ether resins, obtainable by melt-mixing a mixture consisting of 100 parts by weight phenylene ether resin and from 0.05 to 1.0 pbw of itaconic acid.

Inventors: GRANT, THOMAS STANLEY, JALBERT, RONALD LOUIS
Applicants: GE CHEMICALS, INC.
Application year: 1986
Main classification: C08G65
IPC codes: C08L71, C08G65