Reinforced Plastic Comprising Fibrous Reinforcement Treated With Poly(arylene Sulfide Sulfone) Polymer Containing Ether Groups

This invention relates to poly(arylene sulfide sulfone) polymers, PASS. In another of its aspects this invention relates to a process for the production of poly(arylene sulfide sulfone) polymers containing ether groups. In accordance with a further aspect this invention relates to reinforced plastics comprising a matrix prepared from poly(arylene sulfide sulfone) polymers containing ether groups and reinforcing material which consists essentially of continuous long fibers which have been precontacted with a poly(arylene sulfide sulfone) polymer containing ether groups prior to contacting the fiber with the matrix polymer.

A wide variety of high polymers have been prepared from aromatic compounds, many of which are currently produced and marketed on a moderate to large scale. While such polymers are useful in many areas, one property of high polymers, particularly those of the thermoplastic type, which needs to be improved is the ability to withstand high use temperatures. Thermoplastic high polymers frequently form a continuous matrix for reinforcing agents and fillers which are added to alter the properties of the polymers before they are shaped into useful articles such as electrical and automotive parts. Although the properties of such compositions are desirable, it would add to the usefulness of such compositions if improvement could be made in the strength of bonding between the reinforcing agents and the matrix polymer. High polymers that will withstand high use temperatures alone or in combination with other ingredients are desirable; and compositions exhibiting increased bonding strength between the reinforcement and the continuous matrix are also desirable.

Accordingly, an object of this invention is to provide a process for producing poly(arylene sulfide sulfone) polymers containing ether groups exhibiting good high temperature properties and increased molecular weight. It is a further objective of this invention to provide a process for the preparation of reinforced plastics, wherein the reinforcement is contacted with a poly(arylene sulfide sulfone) polymer containing ether groups prior to contacting the polymer used as the continuous matrix.

In accordance with this invention reinforced plastics are provided which comprise a poly(arylene sulfide sulfone) polymer as the matrix. The reinforcing material consists essentially of continuous long fibers which are treated with a poly(arylene sulfide sulfone) polymer containing ether groups prior to contacting the polymer matrix. The treating polymer is prepared in a two step process. In a first step a prepolymer comprising essentially dihalo-terminated polyethersulfone oligomers can be prepared by reacting an aromatic diphenol with a substantial excess of a dihalo aromatic sulfone, in the presence of a polar organic compound and an alkali metal base, and optionally in the presence of an alkali metal carboxylate. During this first step, the reaction mixture can be vented when the reactor temperature is in the range of 100.degree. to 150.degree. C. in order to increase molecular weight. Molecular weight can also be increased by limiting the first step reaction to a period in the range of 1 minute to 2 hours. Subsequently, in a second step a sulfur source, an alkali metal carboxylate and water are added to the reaction mixture and the polymerization reaction is continued, resulting in a modified poly(arylene sulfide sulfone) polymer of improved glass transition temperature and softening temperature.

As used herein, the term "irregular polymer" is meant to represent a polymer whose molecules cannot be described by only one species of repeating unit in a single sequential arrangement. The polymers produced by the invention process include aromatic (arylene), sulfide, sulfone and ether groups in the backbone. These groups can be alternating in any sequence and in sequences such that blocks of a constitutional repeating unit are present.

Dihaloaromatic sulfones that can be employed in the process of the invention are bis(halophenyl)sulfones, optionally having each phenyl ring substituted with one to four R groups, wherein each R group is individually and independently selected from the group consisting of hydrogen and alkyl groups having 1 to about 4 carbon atoms, and the total number of carbon atoms in each molecule is within the range of 12 to about 44. The presently preferred bis(halophenyl)sulfone is bis(p-chlorophenyl)sulfone.

Examples of suitable bis(halophenyl)sulfones that can be employed in the process of this invention include bis(p-chlorophenyl)sulfone, bis(fluorophenyl)sulfone, bis(p-bromophenyl)sulfone, bis(iodophenyl)sulfone, bis(2-methyl-4-chlorophenyl)sulfone, bis(2,5-dimethyl-4-chlorophenyl)sulfone, p-chlorophenyl p-bromophenyl sulfone, bis(3-isopropyl-4-iodophenyl)sulfone, bis(2,5-dipropyl-4-chlorophenyl)sulfone, bis(2-butyl-4-fluorophenyl)sulfone, bis(2,3,5,6-tetramethyl-4-chlorophenyl)sulfone, and the like, and mixtures thereof.

One type of aromatic diphenol that can be employed in the process of this invention is bis(alkylhydroxyphenyl) derivatives having the generalized structure ##STR1## where X is --S--, --SO--, --SO.sub.2 --, --O--, a bond or an alkylene radical, and wherein each R is individually and independently selected from the group consisting of hydrogen and alkyl groups having 1 to about 4 carbon atoms. Examples of aromatic diphenols where X is --S-- or --SO.sub.2 -- include bis(4-hydroxyphenyl)sulfide (Bisphenol T), and bis(4-hydroxyphenyl)sulfone (Bisphenol S).

When X is an alkylene radical, the aromatic diphenols are bis(alkylhydroxyphenyl) alkanes which are characterized by having an alkylene radical link between two phenolic groups as represented by the formula (1) ##STR2## where each R.sub.1 is individually and independently selected from the group consisting of hydrogen and alkyl groups having 1 to about 4 carbon atoms, and each R.sub.2 and R.sub.3 are individually and independently selected from the group consisting of hydrogen and unsubstituted and substituted alkyl groups having 1 to about 11 carbon atoms where the sum of the carbon atoms represented by R.sub.2 plus R.sub.3 is less than 12 carbon atoms, and the sum of the carbon atoms in R.sub.1, R.sub.2, and R.sub.3 groups do not exceed 43; thus the total number of carbon atoms in each molecule is within the range of 13 to about 55.

Examples of suitable aromatic diphenols having this structure that can be employed in the process of this invention include, among others: bis(4-hydroxyphenyl)-methane, bis(2-hydroxyphenyl)methane, 1,1-bis(4-hydroxyphenyl)ethane, 2,2-bis(4-hydroxyphenyl)propane, 2,2-bis(4-hydroxyphenyl)butane, 2,2-bis(3-methyl-4-hydroxyphenyl)propane, 2,2-bis(2-isopropyl-4-hydroxyphenyl)propane, 2,2-bis(3-butyl-4-hydroxyphenyl)propane, 2,2-bis(4-hydroxyphenyl) 1,1,1,3,3,3-hexafluoropropane, and the like, and mixtures thereof. Preferred are 2,2-bis(4-hydroxyphenyl)propane, commonly known as Bisphenol A, and 2,2-bis(4-hydroxyphenyl) 1,1,1,3,3,3-hexafluoropropane, commonly known as Hexafluorobisphenol A.

Examples of other types of aromatic diphenols include hydroquinone(s), biphenol(s), dihydroxynaphthalene(s), bis(hydroxyphenyl)ketone(s), dihydroxyphenylphenylketone(s), dihydroxyfluorenone(s) and alkyl and aryl ring-substituted derivatives thereof.

Polymerizable sulfur sources that can be employed in the process of this invention include hydrogen sulfide, alkali metal hydrosulfides such as sodium hydrosulfide, potassium hydrosulfide, alkali metal sulfides such as sodium sulfide or potassium sulfide, and mixtures thereof. Additional sulfur sources include, among others, those cited in U.S. Pat. No. 3,919,177 such as the acyclic and cyclic thioamides exemplified by N-methyl-2-pyrrolidinethione.

Alkali metal bases that can be employed in the process of this invention include lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide, lithium carbonate, sodium carbonate, potassium carbonate and mixtures thereof. In one embodiment an alkali metal hydroxide is added in the second step as the anhydrous solid. In a preferred embodiment sodium carbonate is added in the first step in an amount required for both steps.

Alkali metal carboxylates that can be employed in the process of this invention can be represented by the formula R'COOM, where R' is a hydrocarbyl radical selected from alkyl, cycloalkyl, and aryl, and combinations thereof such as alkylaryl, arylalkyl, and the like, the number of carbon atoms in R' being within the range of 1 to about 20, and M is an alkali metal selected from the group consisting of lithium, sodium, potassium, rubidium and cesium. Preferably, R' is an alkyl radical having 1 to about 6 carbon atoms or a phenyl radical, and M is sodium. If desired, the alkali metal carboxylate can be employed as a hydrate or as a solution or dispersion in a liquid. In a preferred embodiment the alkali metal carboxylate is added as the anhydrous salt.

Examples of some alkali metal carboxylates that can be employed in the process of this invention include lithium acetate, sodium acetate, potassium acetate, lithium propionate, sodium propionate, rubidium butyrate, lithium valerate, sodium valerate, cesium hexanoate, lithium cyclohexane carboxylate, potassium benzoate, sodium benzoate, lithium benzoate, and the like, and mixtures thereof. Sodium acetate is the preferred alkali metal carboxylate.

The polar organic compounds that can be used in the method of this invention should be substantially liquid at the reaction temperatures and pressures employed. It is preferred to use organic amides. Suitable amides can be cyclic or acyclic and can have 1 to about 10 carbon atoms per molecule. Examples of suitable amides include formamide, acetamide, N-methylformamide, N,N-dimethylformamide, N,N-dimethylacetamide, N-ethylpropionamide, N,N-dipropylbutyramide, 2-pyrrolidone, N-methyl-2-pyrrolidone, epsilon-caprolactam, dimethyl-benzamide and the like, and mixtures thereof. N-methyl-2-pyrrolidone (NMP) is the presently preferred polar organic compound.

Other suitable polar organic compounds include 1,3-dimethyl-2-imidazolidinone, dimethylsulfoxide, sulfolane, tetramethylurea, and hexamethylphosphoramide and mixtures thereof with an organic amide such as exemplified in the preceding paragraph.

The preferred poly(arylene sulfide sulfone) polymers produced by the process of this invention can be characterized as irregular polymers, the molecules of which cannot be described by only one species of unit in a single sequential arrangement. The irregular polymers can be characterized as having at least the units of (a) -(thio-1,4-phenylenesulfonyl-1,4-phenylene)-, illustrated by the formula (2) ##STR3## where each R" is individually and independently selected from the group consisting of hydrogen and alkyl groups having 1 to about 4 carbon atoms, wherein the total number of carbon atoms in each unit is within the range of 12 to about 44, and (b) -(oxy-1,4-phenylene-alkylene-1,4-phenyleneoxy-1,4-phenylenesulfonyl-1,4-ph enylene) illustrated by the formula (3) ##STR4## where R.sub.1, R.sub.2, and R.sub.3 can be defined as in formula (1) and where R" can be defined as in formula (2) above, and wherein units (b) are randomly dispersed among sequences of variable length of units (a).

A wide variety of reaction conditions can be employed in the practice of the invention. Similarly, any proportions of reactants which will react with each other to produce the irregular polymers of the invention are within the scope of the invention.

In the first step of the inventive process the aromatic diphenol is reacted with an excess of the dihaloaromatic sulfone, the excess conveniently being expressed as the ratio of moles dihaloaromatic sulfone to moles aromatic diphenol. This molar ratio can vary from about 1000/1 to about 1.001/1 as a broad range, preferably from about 100/1 to about 1.01/1, and most preferably from about 10/1 to about 4/1.

In the first step of the preferred inventive process, for example, the mole ratio of reactants can be chosen such that the dihalo-terminated polyethersulfone oligomers formed are characterized as predominantly comprising the oligomer resulting from the reaction of two moles of the dihaloaromatic sulfone with one mole of aromatic diphenol.

Such oligomers are achieved by conducting the reaction at a molar ratio of dihaloaromatic sulfone to aromatic diphenol within the range of about 8/1 to about 20/1 in the first step. The mole ratio of alkali metal base to aromatic diphenol can vary but generally will be within the range of about 2/1 to about 25/1, preferably about 10/1 to about 20/1. The amount of polar organic compound can vary greatly, generally being within the range of about 5 moles to about 15 moles per mole of the dihaloaromatic sulfone, preferably about 6 to about 10 moles. When the optional alkali metal carboxylate is added in the first step, the mole ratio of alkali metal carboxylate to dihaloaromatic sulfone can vary over a wide range but generally will be within the range of about 0.5/1 to about 3/1, preferably about 1/1 to about 2/1.

In the second step of the inventive process, the amount of sulfur source added is chosen such that the ratio of the moles of dihaloaromatic sulfone minus the moles of aromatic diphenol to the moles sulfur source, can be within the range of about 2/1 to about 0.8/1, preferably about 1.25/1 to about 0.9/1, and most preferably about 1.05/1 to about 0.95/1. The molar ratio of alkali metal base to sulfur source added in the second step can be within the range of about 0.5/1 to about 3/1, preferably about 1.1/1 to about 2.2/1. When the alkali metal carboxylate is added totally in the second step, the molar ratio of alkali metal carboxylate to dihaloaromatic sulfone charged can vary over a wide range, but generally will be within the range of about 0.5/1 to 2/1.

A polar organic compound is used as a transfer medium during the addition of sulfur source and alkali metal carboxylate. Water is also added to bring the total water, including water of hydration, present in the polymerization system to an amount of at least about 3.5 moles water per mole of sulfur source and an amount greater than about 0.5 moles per mole of polar organic compound. Water of hydration can be contained in the sulfur source and the alkali metal base and must be taken into account.

When N-methyl-2-pyrrolidone (NMP) is used as the polar organic compound, the NMP and water are added in amounts such that the ratio of the moles total water including water of hydration to the moles total NMP is greater than about 0.5, preferably in the range from about 0.8 to about 1.5.

It is to be understood that the process of this invention can be carried out by mixing the dihaloaromatic sulfone, the aromatic diphenol, the alkali metal base, the polar organic compound and optionally, the alkali metal carboxylate in any order in a first process step. Then, in a second process step the sulfur source, the alkali metal carboxylate and, if required, the remaining quantity of the alkali metal base and polar organic compound are added. The alkali metal carboxylate must be added in this step when it is not present in the first step.

Although the temperature at which reaction in the first process step is conducted can vary over a considerable range, generally it is within the range of about 150.degree. to about 250.degree. C., preferably about 160.degree. to about 225.degree. C., and most preferably about 175.degree. to about 200.degree. C.

It has been discovered that poly(arylene sulfide sulfone) polymers containing ether groups which have high molecular weight can be prepared by venting the reactor during the first step. The venting procedure is preferably performed in the range of 100.degree.-150.degree. C., preferably about 120.degree. C. The venting procedure is performed until all or at least a portion of the water has been removed. The amount of time during which the venting is continued is generally governed by process and economic limitations and can be determined by one of ordinary skill in the art without undue experimentation.

The reaction temperature in a second process step generally is within the range of about 175.degree. to about 235.degree. C., preferably about 190.degree. to about 215.degree. C., and most preferably about 195.degree. to about 205.degree. C.

The reaction time of each of the two process steps can vary widely, depending in part on the reaction temperature, but generally will be within the range of about 1 minute to about 24 hours, preferably about 5 minutes to about 8 hours. It has also been discovered that the molecular weight of the polymer can be increased by limiting the first step reaction time to a period in the range of 1 minute to 2 hours, more preferably 5 minutes to 1 hour. The pressure should be sufficient to maintain the dihaloaromatic sulfone and the polar organic compound substantially in the liquid phase.

After the second step of the reaction has proceeded for the desired time, the reaction mixture is cooled. The mixture can be cooled slowly by discontinuation of the heating, or alternately, more rapidly by introduction of a coolant through internal or external coils. In a preferred embodiment a fluid is added to the reaction mixture after the heating is discontinued to cool it more rapidly and in some cases aid in the separation of the polymer from the remainder of the reaction mixture. Water, N-methyl-2-pyrrolidone or mixtures thereof can be added during a time period which is shorter than the second step reaction time. For example, liquid NMP in an amount equivalent to about 1/3 to 1/4 of the total NMP used in the two-step reaction process is added to the reaction mixture over a five minute period after the heat is discontinued. The reaction mixture is allowed to cool further before the polymeric solids are recovered. Use of a fluid improves the recovery of polymeric solids in that particles easily recovered by filtration are formed.

The poly(arylene sulfide sulfone) polymers produced by the inventive process can be separated from the reaction mixture by conventional procedures such as by filtration, followed by washing the recovered solids with water, or by dilution of the reaction mixture with a suitable diluent such as N-methyl-2-pyrrolidone and/or water followed by filtration and water washing of the recovered solids.

The poly(arylene sulfide sulfone) polymers recovered are characterized by having a polymer melt temperature in excess of about 250.degree. C., preferably in excess of about 275.degree. C., and even more preferably in excess of about 290.degree. C., and a measurable melt flow rate using ASTM D 1238 condition 317/5.0 (modified employ a 5 minute preheat time) of less than about 5000 g/10 minutes, preferably less than about 1000 g/10 minutes, and even more preferred less than about 100 g/10 minutes. Polymers prepared according to this invention generally exhibit an inherent viscosity (0.5 g/100 mL NMP at 30.degree. /C.) greater than about 0.30 dL/g, more preferably from about 0.30 to about 0.60 dL/g.

Optionally, treatment of the dried polymeric solids with a aqueous solution containing 0.01 to 5 wt % zinc acetate based on dry polymer in 5 to 50 fold amounts of water (relative to dry polymer) for about 0.5 to about 2 hours at about 150 to about 200.degree. C. can yield treated-polymeric solids having an improved melt stability.

Melt stability of a polymeric solid can be characterized as the ratio of the melt flow rates measured after 5 and 15 minutes holding time of the molten polymeric solids in the barrel of the apparatus described in ASTM D 1238, condition 317/5.0. A melt stable polymeric solid demonstrates only a small difference in the two measured melt flow rates. Therefore, the ratio of the two melt flow rates does not vary appreciably from 1, preferably in the range from about 0.80 to about 1.2. Unless otherwise noted herein, melt flow rates are measured using a 5 minute hold time and reported in units of grams/10 minutes in accordance with ASTM D 1238, condition 317/5.0. The poly(arylene sulfide sulfone) polymers produced by the inventive process can be blended with fillers, pigments, extenders, other polymers, and the like.

The poly(arylene sulfide sulfone) polymers containing ether groups can be employed as the continuous matrix in fiber reinforced compositions such as prepregs, laminates and pultruded shapes. Typically the matrix is present in an amount in the range of 25 to 50 wt. % of the fully consolidated composition.

Such fiber reinforced compositions can be prepared by any method known to those of ordinary skill in the art. Examples of such methods are those described in U.S. Pat. Nos. 4,680,224 and 4,792,481, which patents are hereby incorporated by reference herein.

Although the poly(arylene sulfide sulfone) polymers containing ether groups can be employed as the continuous matrix in reinforced compositions, it has been discovered that a composition which exhibits good mechanical properties can be prepared by employing poly(arylene sulfide sulfone) polymers as the continuous matrix and employing a fibrous reinforcement which has been pre-contacted with a poly(arylene sulfide sulfone) polymer containing ether groups.

The treatment of the fibrous reinforcement with the poly(arylene sulfide sulfone) polymer containing ether groups can be performed by any method known to those of ordinary skill in the art, for example, by passing such fibers through a solution bath of the polymer.

The amount of poly(arylene sulfide sulfone) polymer containing ether groups that is employed in the treatment of the fiber reinforcement is governed by economic and process limitations and can be determined by one of ordinary skill in the art without undue experimentation. Generally, the amount used is in the range of 0.1 wt. % to about 5 wt. % of the weight of the fiber.

It is preferred to use poly(arylene sulfide sulfone) polymers containing ether groups which contain lower levels of ether groups to pretreat the fibers.

The poly(arylene sulfide sulfone) polymers containing ether groups can be cured through crosslinking and/or chain extension to provide cured products having high thermal stability and good chemical resistance. They are useful in the production of coatings, film, molded objects and fibers. The polymers exhibit improved properties, especially the melting temperature and the glass transition temperature.

Polymer melt temperature, PMT, is expressed in degrees Celsius, and is determined by observing where the polymeric solids melt on a temperature gradient bar. The glass transition temperature, Tg, is measured using Perkin-Elmer Differential Scanning Calorimeter, Model DSC-2C. The inherent viscosity of the polymeric solids is measured at 30.degree. C. using as solvent either a 3:2 mixture (by weight) of phenol:1,1,2,2-tetrachloroethane or N-methyl-2-pyrrolidone at a solids concentration of 0.5 grams per 100 mL. The units of inherent viscosity (I.V.) are deciliters per gram, dL/g.

Into a 1 liter stainless steel autoclave 0.375 moles bis(4-chlorophenyl)sulfone (107.7 grams), 0.75 moles sodium carbonate (79.5 grams), 1.5 moles N-methyl-2-pyrrolidone (148.7 grams), and 0.0375 moles hexafluorobisphenol A (12.6 grams) were introduced. The autoclave was closed and purged with nitrogen simultaneously with heating and stirring at 600 rpm. The temperature was increased to 200.degree. C. and held for 3 hours. The autoclave was cooled to less than 80.degree. C. Subsequently, the reactants of the second step were introduced: 0.375 moles sodium acetate (30.8 grams), 0.341 moles sodium hydrosulfide (31.73 grams as a 60 wt. % aqueous solution, 1.5 moles N-methyl-2-pyrrolidone (148.7 g), and 2.83 moles water (51.0 grams). The autoclave temperature was increased to 200.degree. C. and maintained at that temperature for 3 hours. The autoclave was then cooled to room temperature, employing NMP as a cooling fluid, and opened to remove the polymer slurry.

The dried product (designated Polymer 1) was characterized as having large particle size, a MF of 44.1 at 317.degree. C., a PMT of 290.degree. C. and an I.V. of 0.31. A total of 88.6 grams of dried polymeric solids was recovered.

A second polymerization was conducted in a manner very similar to that of Example 1. The same types of reactants were added as in Example 1. The amounts differed only in that 0.1875 moles (63.04 g) of the hexafluorobisphenol A was used, 0.19 moles (17.63 g) sodium hydrosulfide was used, and 2.95 moles (53.1 g) water was added. The autoclave was closed and purged with nitrogen simultaneously with heating and stirring at 600 rpm. The temperature was increased to 200.degree. C. and held for 3 hours. Then the reactor was cooled to less than 80.degree. C. Subsequently, the reactants of the second step were introduced in amounts as specified. The polymer was recovered as in Example 1.

The dried product (designated Polymer 2) was characterized as having a fine particle form, a PMT of 125.degree. C. and an I.V. of 0.05. A total of 141.0 grams of dried polymeric solids was recovered.

One more polymerization was conducted. Polymer 3 was prepared in a manner similar to that of Example 1 and 2, except that Bisphenol A was employed and the amounts of the reactants were changed. 1.5 moles of bis(4-chlorophenyl)sulfone (430.7 g), 3 moles sodium carbonate (318.0 g), 0.15 moles Bisphenol A (34.2 g) and 6 moles NMP (594.8 g) were introduced into a 2-gallon autoclave. The first step polymerization was conducted at 200.degree. C. for 3 hours, then the reactor was cooled to less than 80.degree. C. and the second step reactants were introduced: 1.5 moles sodium acetate (123.1 g), 1.36 moles sodium hydrosulfide (as a 60% aqueous solution), 6 moles NMP and 11.3 moles water (203.6 g). The autoclave temperature was raised to 200.degree. C. and maintained at that temperature for 3 hours. The autoclave was then cooled to room temperature, employing NMP as a cooling liquid, and opened to remove the polymer slurry.

The dried product (designated as Polymer 3) was chacterized as having a large particle size, a MF of 105.1 at 317.degree. C. and an I.V. of 0.31. A total of 359.0 g of dried polymeric solids was recovered.

A poly(phenylene sulfide sulfone) polymer (PPSS) sample was prepared according to the method described in U.S. Pat. No. 4,808,698. The polymer was treated with zinc acetate in the manner described in U.S. Pat. No. 4,774,276. This polymer sample was used as the matrix to prepare composites in Examples 4 and 5, with or without the addition of the PG,16 invention poly(arylene sulfide sulfone) polymer containing ether groups which can be used to treat the fiber reinforcement according to this invention.

This example compares PPSS composites made with and without carbon fiber sizings. In all runs, the PPSS samples were ground to a fine powder with a particle size of about 20 microns.

In Run A, a slurry bath was prepared from 50 g of the PPSS sample, 1200 g distilled water, and 2 mL of an ethoxylated nonylphenol (Triton X-100) surfactant. Two tows of continuous carbon fiber reinforcement (12K Hercules AS-4) were passed through the aqueous PPSS slurry bath at a rate of about 130 cm per minute. The wet, impregnated continuous carbon fiber strands were pulled through a guide mechanism, a drying section at a temperature of about 396.degree. C., and a heated (about 366.degree. C.), 50.8 mm wide shaping die. The product was unidirectional tape A containing about 66 weight percent carbon fiber.

Run B was carried out in a manner similar to that described in Run A except for the addition of a sizing bath for the carbon fibers before the slurry bath. The sizing bath contained 2 g of Polymer 2 (I.V.=0.05 dL/g) in 398 g of NMP (0.5 weight percent polymer sizing). Polymer 2 contained about 50 mole percent of the ether sulfone segment derived from hexafluorobisphenol A (FBPA). Unidirectional tape B was produced with a drying section temperature of about 380.degree. C. and a shaping die temperature of about 370.degree. C.

Run C was carried out in a manner similar to that described in Run B except the polymer in the sizing bath was Polymer 1, which had an I.V. of 0.31 dL/g and contained 10 mole percent of the ether sulfone segment derived from FBPA. Tape C was produced with a dryer temperature of about 411.degree. C. and the shaping die at about 369.degree. C.

The continuous prepreg tapes A, B, and C were cut into segments about 25 cm long and plied for compression molding into unidirectional laminates for testing. Test specimens were cut from the laminates. The results are shown in Table 1.

Table 1 shows that the application of sizing from a 0.5 weight percent sizing bath to the carbon fibers using the lower I.V. copolymer (sample B) results in improved longitudinal and transverse tensile strengths compared with control sample A.

This example compares several more runs using carbon fiber sizings for PPSS-carbon fiber composites. Run D was a control run made without a sizing bath. It used the PPSS sample and similar conditions to those of Run A except for a carbon fiber strand rate of about 127 cm per minute, dryer temperature of 398.degree. C., and die temperature of 368.degree. C.

Run E used a sizing bath containing 2.5 weight percent (12.5 g of the copolymer in 487.5 g of NMP) of Polymer 2 (with an I.V. ov 00.5 dL/g and 50 mole percent of the ether sulfone segment derived from FBPA). The dryer temperature was about 405.degree. C. and the die temperature was about 366.degree. C.

Run F used Polymer 1 (with an I.V. of 0.31 dL/g and 10 mole percent of the ether sulfone segment derived from FBPA) in the sizing bath at a level of 0.5 weight percent. Runs G and H used Polymer 3 (with an I.V. of 0.31 dL/g and 10 mole percent of the ether sulfone segment derived from BPA) at sizing bath levels of 0.5 weight percent in Run G and 2.5 weight percent in Run H. The dryer temperature in Run G was about 395.degree. C. and in Run H was about 389.degree. C., while the die temperature was about 366.degree. C. in both runs.

The five continuous tapes were cut into segments about 25 cm long and plied for compression molding ito unidirectional laminates for testing. Table 2 depicts the results.

Table 2 shows that the best transverse tensile strengths were obtained with samples F and H, which used the preferred higher levels of sizing in the sizing bath and lower level of ether units in the copolymer. All four tapes made with the sizing bath had improved longitudinal tensile strengths compared with the control D.