End group modified polyphenylene sulfide and modification method

Abstract

The invention discloses a modification method of end-group-modified polyphenylene sulfide, which comprises the following steps: mixing polyphenylene sulfide prepared by a sodium sulfide method, an organic solvent, a sulfydryl modifier and an organic tin catalyst, and reacting for 1-4 hours at the temperature of 200-300 DEG C to obtain the end-group-modified polyphenylene sulfide, the chemical structural formula of the end group modified polyphenylene sulfide is shown as a formula I, wherein n is greater than 0. According to the invention, isocyanate and a terminal group react under the catalysis of dibutyltin dilaurate to generate thiocarbamate, and the terminal group of polyphenylene sulfide is accurately regulated and modified from the molecular level, so that the solution fluidity of polyphenylene sulfide is improved, and the processability is obviously improved.

Description

Technical Field

[0001] The present invention relates to the field of polyphenylene sulfide modification, and in particular to an end-group-modified polyphenylene sulfide and a modification method. Background Art

[0002] Polyphenylene sulfide (PPS) is a white crystalline polymer that has become the sixth most popular engineering plastic due to its outstanding performance. Its main chain has a repeating structure of (-S-Ar-), and it possesses many excellent properties, including high-temperature resistance, excellent mechanical properties, flame retardancy, chemical resistance, and electrical insulation. PPS can be processed into plastic products through injection molding and extrusion, films through biaxial stretching, and fibers through spinning. It can also be made into composite materials through modification methods such as filling and reinforcement. Therefore, it has broad development prospects in the fields of electronic and electrical equipment, automotive equipment, and other fields.

[0003] Common methods for producing polyphenylene sulfide include the sodium sulfide method, sulfur solution method, hydrogen sulfide method, oxidative polymerization method, and para-halogenated benzenethiophenolate melt or solution polycondensation method. The sodium sulfide method was first proposed by Phillips Company in the United States in 1967, and industrial production of polyphenylene sulfide was achieved in 1973. Currently, the sodium sulfide method is the predominant method for industrial synthesis. This method offers high yield, good results, strong reproducibility, and simple operation, making it suitable for industrial production. Furthermore, the polyphenylene sulfide synthesized by this method exhibits superior properties unmatched by other methods.

[0004] Due to its high density and brittleness, polyphenylene sulfide cannot be used to produce high-toughness products. Furthermore, its high melting point reduces its fluidity during melt processing. Therefore, practical applications require modification. Common modification methods include inorganic filler reinforcement, fiber reinforcement, copolymerization, blending, and changes to the main chain structure and end groups.

[0005] Patent CN116082840A discloses a modified polyphenylene sulfide resin and its preparation method. By compounding glass fiber with polyphenylene sulfide, the impact toughness of the polyphenylene sulfide resin is enhanced, reducing the brittleness of the polyphenylene sulfide resin composite. The addition of glass fiber also significantly improves the fluidity of the polyphenylene sulfide resin during injection molding, making it easier to process and shape. The use of ethylene-glycidyl methacrylate copolymer as a toughening agent enhances the compatibility between the glass fiber and the polyphenylene sulfide resin, thereby increasing the rigidity and toughness of the polyphenylene sulfide resin product.

[0006] Patent CN116462968A describes the preparation and application of a modified graphene oxide / polyvinylidene fluoride / carboxymethyl polyphenylene sulfide composite material. The modified graphene oxide and polyvinylidene fluoride are evenly distributed on the surface of carboxylated polyphenylene sulfide, improving the surface morphology of pure polyphenylene sulfide, which often exhibits numerous micropores due to uneven high-temperature curing when used as a coating. This results in a denser surface structure, effectively blocking the diffusion of corrosive media. Furthermore, the modified graphene oxide exhibits higher heat resistance, lower corrosion current density, and superior corrosion resistance compared to graphene oxide, resulting in a higher impedance modulus and significantly improved corrosion resistance.

[0007] Patent CN116516515A discloses a method for preparing boron nitride-modified polyphenylene sulfide fibers and the resulting products, belonging to the field of specialty fiber manufacturing technology. This patent utilizes fiber-grade polyphenylene sulfide resin and boron nitride as raw materials, producing the modified polyphenylene sulfide fibers through a melt-drawing process without harsh reaction conditions. Boron nitride exhibits excellent resistance to chemical corrosion and oxidation. Leveraging its unique advantages, the patent enhances the antioxidant capacity of polyphenylene sulfide fibers.

[0008] Patent CN116589858A discloses a silicone resin-modified polyphenylene sulfide composite material and methods for its preparation and use. By adjusting the ratio of added silicone monomer to polyphenylene sulfide resin powder, a polymer gel with excellent transparency, solvent resistance, and bonding properties is prepared. The synthesized silicone resin-modified flame-retardant polyphenylene sulfide is then stirred and mixed with the inorganic thermally conductive filler boron nitride to form a thermally conductive composite material. At room temperature, cross-linking and curing occur between the silicone resin segments to achieve solar cell encapsulation. This silicone resin-modified polyphenylene sulfide composite material is flame-retardant, thermally conductive, aging-resistant, and has excellent sealing properties. This encapsulation process can meet the requirements of the commercial production process of photovoltaic devices and help to increase the service life of solar cells.

[0009] Among the above patents, although they all carry out relevant work around the theme of polyphenylene sulfide modification. However, in terms of the methods used for modification, most of these patents only use relatively simple physical methods to achieve the modification of polyphenylene sulfide, such as the common method of blending, and methods such as fiber reinforcement. These physical methods are relatively direct and basic in terms of operating principles and implementation methods. In sharp contrast, among the numerous existing patents, few patents mention the use of chemical modification methods to modify polyphenylene sulfide. Chemical modification methods often have unique reaction mechanisms and potential advantages, and can change and optimize the properties of polyphenylene sulfide from different angles such as the molecular level, but they are rarely involved in these existing patents. Among them, there are fewer studies on the modification of polyphenylene sulfide end groups, mainly due to the difficulty in detecting the number and type of end groups. In view of the fact that the end group is one of the important factors affecting the performance of polyphenylene sulfide, the present invention discloses a method for modifying the end groups of polyphenylene sulfide. Summary of the Invention

[0010] In view of the above-mentioned defects of the prior art, the purpose of the present invention is to provide a mercapto-terminated polyphenylene sulfide and a modification method, which utilizes isocyanate to react with the end group under the catalysis of dibutyltin dilaurate to form thiocarbamate, and accurately controls and modifies the end group of polyphenylene sulfide at the molecular level, thereby improving the melt fluidity of polyphenylene sulfide and significantly improving the processing performance.

[0011] The objective of the present invention is achieved through such technical solution:

[0012] A method for modifying end-group-modified polyphenylene sulfide comprises the following steps:

[0013] The polyphenylene sulfide prepared by the sodium sulfide method, an organic solvent, a thiol modifier, and an organic tin catalyst are mixed and reacted at a temperature of 200 to 300 degrees Celsius for 1 to 4 hours to obtain end-group-modified polyphenylene sulfide. The chemical structure of the end-group-modified polyphenylene sulfide is shown in Formula I.

[0014]

[0015] Wherein, n is greater than 0.

[0016] Furthermore, the organic solvent is an ultra-dry high-boiling point organic solvent, including one or more of ultra-dry N,N-dimethylamide and ultra-dry dimethyl sulfoxide.

[0017] Furthermore, the mercapto modifier is one or more compounds containing an isocyanate group.

[0018] Furthermore, the organotin catalyst includes dibutyltin dilaurate.

[0019] Furthermore, the weight ratio of the polyphenylene sulfide, the ultra-dry high-boiling point organic solvent, the compound containing an isocyanate group, and the organic tin catalyst is 2.6-3.5:17-25:0.13-0.17:0.14-0.18.

[0020] Furthermore, the reaction temperature is 220 to 270 degrees Celsius, and the reaction time is 2 to 3 hours.

[0021] Furthermore, the method further comprises the following steps:

[0022] After the reaction is completed, the temperature is naturally cooled to room temperature and filtered to obtain a solid product;

[0023] The solid product is washed with deionized water at 75 to 95 degrees Celsius, and dried at 95 to 115 degrees Celsius for 2 to 3 hours to obtain end-group-modified polyphenylene sulfide.

[0024] Furthermore, the preparation method of polyphenylene sulfide prepared by the sodium sulfide method comprises the following steps:

[0025] Step 1: After adding a sulfur-containing compound, an alkaline auxiliary agent and a catalyst to a solvent, dehydration treatment is performed, and the dehydration rate is 83-87%; the solvent is an organic solvent with a high boiling point, and the amount of the organic solvent is 3-6 mol based on 1 mol of total sulfur; the sulfur-containing compound is one or more of Na2S·9H2O and Na2S·5H2O, and the water content of the sulfur-containing compound is 0.9-1.1 mol / L of total sulfur content; the alkaline auxiliary agent is one or more of an alkali metal hydroxide or carbonate thereof, and the amount of the alkaline substance is 0.02-0.05 mol based on 1 mol of total sulfur; the catalyst is an organic or inorganic compound containing lithium, and the amount of the catalyst is 0.3-0.6 mol based on 1 mol of total sulfur;

[0026] Step 2: adding p-dichlorobenzene to the mixed system obtained in step 1, adding a solvent, and conducting a polycondensation reaction; the added solvent is an organic solvent with a higher boiling point, and the amount used is 1.5 to 3 mol based on 1 mol of total sulfur; the purity of the selected p-dichlorobenzene is not less than 99%, and the amount of the p-dichlorobenzene used is 1.03 to 1.06 mol based on 1 mol of total sulfur;

[0027] Step 3: After the reaction in step 2 is completed, the polyphenylene sulfide prepared by the sodium sulfide method is obtained by filtering, washing, and drying.

[0028] Furthermore, the dehydration treatment in step 1 includes placing the mixture into an autoclave, introducing nitrogen into the autoclave and maintaining a certain flow rate of nitrogen, and raising and maintaining the temperature in the autoclave at 220 to 240 degrees Celsius until the dehydration rate reaches 83 to 87%;

[0029] The solvent in step 1 and step 2 is NMP; the alkaline auxiliary agent is one or more of NaOH and Na2CO3;

[0030] The catalyst in step 1 is one or more of lithium benzoate, LiCl, and LiOH;

[0031] The polycondensation reaction in step 2 includes two stages: in the first stage, the reactants are heated to 210-230 degrees Celsius and kept reacting for 2-3 hours; in the second stage, the reactants are heated to 270 degrees Celsius and kept reacting for 2.5-3.5 hours;

[0032] In step 3, after the reaction in step 2 is completed, deionized water is added to prepare the slurry when the temperature of the reactant drops to 90 to 110 degrees Celsius, and the reactant is filtered to obtain a filter cake when the temperature drops to 55 to 65 degrees Celsius; the filter cake is washed with boiled deionized water until the filtrate contains no chloride ions, and then the filter cake is washed with ethanol 3 to 4 times and then dried at 150 degrees Celsius for 6 hours to obtain polyphenylene sulfide prepared by the sodium sulfide method.

[0033] A compound of formula I

[0034]

[0035] Wherein, n is greater than 0.

[0036] Due to the adoption of the above technical solution, the present invention has the following advantages:

[0037] 1. The terminal groups of polyphenylene sulfide are precisely controlled and modified at the molecular level. Under the catalysis of dibutyltin dilaurate, p-methoxyphenyl isocyanate reacts with the terminal group -SH (thiol) without affecting the terminal group -Cl.

[0038] 2. Due to the presence of polar sulfur atoms in the polyphenylene sulfide molecular chain, strong polar interactions and hydrogen bonds exist between the molecular chains. When capped with the non-polar 4-methoxyphenyl group, the non-polar group is located at the end of the molecular chain, which acts as an "isolation" between the molecular chains, reducing the polar interactions and the number of hydrogen bonds between the molecular chains. This weakens the binding force between the molecular chains, making them relatively easier to slide and shift, which manifests itself as improved melt fluidity on a macro scale, significantly improving the processing properties of the modified polyphenylene sulfide.

[0039] 3. When polyphenylene sulfide is exposed to high temperatures (>300°C) and oxygen (such as air contact during injection molding and extrusion), the -SH (thiol) groups at the ends of the molecular chains are easily oxidized, generating free radicals and initiating cross-linking reactions, which affect the processing properties of the material and the performance of the final product. Through molecular-level modification, the thiol groups are capped with non-polar 4-methoxyphenyl groups to reduce thermal oxidative cross-linking reactions during processing, making polyphenylene sulfide easier to flow and form in the molten state, thereby improving processing properties.

[0040] 4. The introduction of the non-polar end group 4-methoxyphenyl disrupts the regularity of the polyphenylene sulfide molecular chain. Regular polyphenylene sulfide molecular chains tend to be tightly packed, forming crystalline regions, which restricts molecular chain movement and increases melt viscosity. However, after capping with non-polar end groups, the regularity of the molecular chain decreases, the crystallinity decreases, and the amorphous region increases. In the amorphous region, the molecular chain moves more freely and is more susceptible to flow under external forces, which helps improve the fluidity of the polyphenylene sulfide and significantly enhances the processing properties of the modified polyphenylene sulfide.

[0041] Other advantages, objects and features of the present invention will be described in part in the following description and, in part, will be apparent to those skilled in the art based on an examination of the following or may be learned from the practice of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a dot plot of water content and refractive index of aqueous NMP solutions of different concentrations.

[0043] Figure 2 This is a comparison chart of infrared measurements of polyphenylene sulfide prepared by the sodium sulfide method and the modified polyphenylene sulfide. DETAILED DESCRIPTION

[0044] The present invention will be further described below with reference to the embodiments.

[0045] Example:

[0046] The first step is to prepare polyphenylene sulfide raw materials using the sodium sulfide method. The sodium sulfide method used in this example differs significantly from the conventional sodium sulfide method in terms of preparation steps and process parameters. This allows the polyphenylene sulfide prepared in this example to be used as a raw material in subsequent modification to increase the modification yield and the average molecular weight of the modified polyphenylene sulfide. The preparation reaction process is as follows:

[0047]

[0048] Specifically, the following steps are included:

[0049] Step 1: After adding a sulfur-containing compound, an alkaline auxiliary agent and a catalyst to a solvent, a dehydration treatment is performed, and the dehydration rate is 83-87%;

[0050] Specifically, the solvent is an organic solvent with a higher boiling point, and NMP is selected. Based on 1 mol of total sulfur, the amount of NMP used is 3-6 mol;

[0051] The sulfur-containing compound is Na2S·9H2O, and the water content of Na2S·9H2O is 1 mol / L of total sulfur content;

[0052] The alkaline auxiliary agent is an alkali metal hydroxide, and the amount of the hydroxide is 0.02-0.05 mol based on 1 mol of total sulfur;

[0053] The catalyst is an organic or inorganic compound containing lithium, preferably LiCl in this embodiment, and the amount of the catalyst used is 0.3-0.6 mol based on 1 mol of total sulfur;

[0054] The dehydration rate is controlled at 83-87%, which is achieved as follows:

[0055] First, since different substances have different refractive indices, the determination of the refractive index can be used to assist in identifying the type of substance, detecting the purity of the compound, determining the concentration of the solution, etc. In step 1, the water content in the system is mainly determined by calculating the refractive index of the desorbed aqueous solution. The Abbe refractometer is a classic refractometer with high precision and stability, and is widely used in scientific research and industrial production. It can calculate the refractive index by measuring the deflection angle of light after passing through a substance. Abbe refractometers are divided into monocular and binocular types, and there are different models such as digital display and optical reading to meet different experimental needs. In the present invention, a monocular Abbe refractometer is mainly used to determine the water content of the desorbed aqueous solution. First, at 25°C, a series of aqueous NMP solutions of different concentrations are prepared, and the refractive index of the aqueous NMP solutions of corresponding concentrations is detected. The results are shown in Table 1 below.

[0056] Table 1 Comparison of water content and refractive index in aqueous NMP solution

[0057]

[0058] Secondly, when specifically controlling the dehydration rate, all raw materials are placed in an autoclave, nitrogen is introduced into the autoclave and a certain nitrogen flow rate is maintained, and the temperature in the autoclave is raised and maintained at 220-240 degrees Celsius (preferably 230 degrees Celsius in this embodiment) until the dehydration rate reaches 83-87% (preferably 85% in this embodiment).

[0059] Step 2: adding p-dichlorobenzene and NMP to the dehydrated mixture to carry out a polycondensation reaction; the amount of NMP used is 1.5 to 3 mol based on 1 mol of total sulfur; the purity of the selected p-dichlorobenzene is not less than 99%, and the amount of p-dichlorobenzene used is 1.03 to 1.06 mol based on 1 mol of total sulfur;

[0060] The specific polycondensation reaction includes two stages. In the first stage, the reactants are heated to 210-230 degrees Celsius (preferably 220 degrees Celsius in this embodiment) and kept reacting for 2-3 hours. In the second stage, the reactants are heated to 270 degrees Celsius and kept reacting for 2.5-3.5 hours (preferably 3 hours in this embodiment).

[0061] Step 3: After the reaction in step 2 is completed, deionized water is added to the reactant to prepare the slurry when the temperature drops to 90-110 degrees Celsius (preferably 100 degrees Celsius in this embodiment), and the reactant is filtered to obtain a filter cake when the temperature drops to 55-65 degrees Celsius (preferably 60 degrees Celsius in this embodiment); the filter cake is washed with boiled deionized water until the filtrate contains no chloride ions, and then the filter cake is washed with ethanol 3-4 times, and then dried at 150 degrees Celsius for 6 hours to obtain polyphenylene sulfide prepared by the sodium sulfide method.

[0062] In the second step, the polyphenylene sulfide prepared in the first step is modified. The modification reaction process is as follows:

[0063]

[0064] Specifically, the polyphenylene sulfide prepared in the first step, an organic solvent, a thiol modifier, and an organic tin catalyst are mixed and reacted at a temperature of 200 to 300 degrees Celsius for 1 to 4 hours to prepare end-group-modified polyphenylene sulfide. The chemical structure of the end-group-modified polyphenylene sulfide is shown in Formula I.

[0065]

[0066] Wherein, n is greater than 0.

[0067] Among them, the organic solvent is an ultra-dry high-boiling point organic solvent, including one or more of ultra-dry N,N-dimethylamide and ultra-dry dimethyl sulfoxide, and NMP is selected in this embodiment; the thiol modifier is one or more compounds containing an isocyanate group, and methoxyphenyl isocyanate is selected in this embodiment; the organic tin catalyst includes dibutyltin dilaurate.

[0068] The weight ratio of the polyphenylene sulfide, the ultra-dry high-boiling point organic solvent, the compound containing an isocyanate group, and the organic tin catalyst is 2.6-3.5:17-25:0.13-0.17:0.14-0.18. In this embodiment, the preferred raw material ratio is 3:20:0.15:0.15.

[0069] In this embodiment, the reaction temperature is preferably 220 to 270 degrees Celsius, and the reaction time is preferably 2 to 3 hours.

[0070] In the third step, after the second step reaction is completed, the reactants are naturally cooled to room temperature and filtered to obtain a solid product; the solid product is then washed with deionized water at 75 to 95 degrees Celsius (preferably 85 degrees Celsius in this embodiment) and dried at 95 to 115 degrees Celsius (preferably 105 degrees Celsius in this embodiment) for 2 to 3 hours to obtain end-group modified polyphenylene sulfide.

[0071] The infrared determination of polyphenylene sulfide prepared by sodium sulfide method and modified polyphenylene sulfide was carried out, such as Figure 2 As shown, the dotted line is polyphenylene sulfide, and the solid line is modified polyphenylene sulfide. Figure 2 Transmittance and wave velocity of modified polyphenylene sulfide (cm -1 ) relationship curve, in the wave speed (cm -1 )1270, the absorption peak of ether bond was detected at the wave velocity (cm -1 )The absorption peak of amide was detected near 1515.

[0072] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for modifying end-group-modified polyphenylene sulfide, characterized in that: The following steps are involved: The polyphenylene sulfide prepared by the sodium sulfide method, an organic solvent, a thiol modifier, and an organic tin catalyst are mixed and reacted at a temperature of 200 to 300 degrees Celsius for 1 to 4 hours to obtain end-group-modified polyphenylene sulfide. The chemical structure of the end-group-modified polyphenylene sulfide is shown in Formula I. Wherein, n is greater than 0.

2. The method for modifying end-group-modified polyphenylene sulfide according to claim 1, wherein: The organic solvent is an ultra-dry high-boiling point organic solvent, including one or more of ultra-dry N,N-dimethylamide and ultra-dry dimethyl sulfoxide.

3. The method for modifying end-group-modified polyphenylene sulfide according to claim 1, wherein: The mercapto modifier is one or more compounds containing an isocyanate group.

4. The method for modifying end-group-modified polyphenylene sulfide according to claim 1, wherein: The organotin catalyst includes dibutyltin dilaurate.

5. The method for modifying end-group-modified polyphenylene sulfide according to claim 1, wherein: The weight ratio of the polyphenylene sulfide, the ultra-dry high-boiling point organic solvent, the compound containing an isocyanate group, and the organic tin catalyst is 2.6-3.5:17-25:0.13-0.17:0.14-0.

18.

6. The method for modifying end-group-modified polyphenylene sulfide according to claim 1, wherein: The reaction temperature is 220-270 degrees Celsius, and the reaction time is 2-3 hours.

7. The method for modifying end-group-modified polyphenylene sulfide according to claim 1, wherein: The following steps are also included: After the reaction is completed, the temperature is naturally cooled to room temperature and filtered to obtain a solid product; The solid product is washed with deionized water at 75 to 95 degrees Celsius, and dried at 95 to 115 degrees Celsius for 2 to 3 hours to obtain end-group-modified polyphenylene sulfide.

8. The method for modifying end-group-modified polyphenylene sulfide according to claim 1, wherein: The preparation method of polyphenylene sulfide prepared by the sodium sulfide method comprises the following steps: Step 1: After adding a sulfur-containing compound, an alkaline auxiliary agent and a catalyst to a solvent, dehydration treatment is performed, and the dehydration rate is 83-87%; the solvent is an organic solvent with a high boiling point, and the amount of the organic solvent is 3-6 mol based on 1 mol of total sulfur; the sulfur-containing compound is one or more of Na2S·9H2O and Na2S·5H2O, and the water content of the sulfur-containing compound is 0.9-1.1 mol / L of total sulfur content; the alkaline auxiliary agent is one or more of an alkali metal hydroxide or carbonate thereof, and the amount of the alkaline substance is 0.02-0.05 mol based on 1 mol of total sulfur; the catalyst is an organic or inorganic compound containing lithium, and the amount of the catalyst is 0.3-0.6 mol based on 1 mol of total sulfur; Step 2: adding p-dichlorobenzene to the mixed system obtained in step 1, adding a solvent, and conducting a polycondensation reaction; the added solvent is an organic solvent with a higher boiling point, and the amount used is 1.5 to 3 mol based on 1 mol of total sulfur; the purity of the selected p-dichlorobenzene is not less than 99%, and the amount of the p-dichlorobenzene used is 1.03 to 1.06 mol based on 1 mol of total sulfur; Step 3: After the reaction in step 2 is completed, the polyphenylene sulfide prepared by the sodium sulfide method is obtained by filtering, washing, and drying.

9. The method for modifying end-group-modified polyphenylene sulfide according to claim 8, wherein: The dehydration treatment in step 1 includes placing the mixture into an autoclave, introducing nitrogen into the autoclave at a constant flow rate, and raising and maintaining the temperature in the autoclave at 220 to 240 degrees Celsius until the dehydration rate reaches 83 to 87%; The solvent in step 1 and step 2 is NMP; the alkaline auxiliary agent is one or more of NaOH and Na2CO3; The catalyst in step 1 is one or more of lithium benzoate, LiCl, and LiOH; The polycondensation reaction in step 2 includes two stages: in the first stage, the reactants are heated to 210-230 degrees Celsius and kept reacting for 2-3 hours; in the second stage, the reactants are heated to 270 degrees Celsius and kept reacting for 2.5-3.5 hours; In step 3, after the reaction in step 2 is completed, deionized water is added to prepare the slurry when the temperature of the reactant drops to 90 to 110 degrees Celsius, and the reactant is filtered to obtain a filter cake when the temperature drops to 55 to 65 degrees Celsius; the filter cake is washed with boiled deionized water until the filtrate contains no chloride ions, and then the filter cake is washed with ethanol 3 to 4 times and then dried at 150 degrees Celsius for 6 hours to obtain polyphenylene sulfide prepared by the sodium sulfide method.

10. A compound having the structural formula I in, n is greater than 0.

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