Poly (arylene sulfide) and production process thereof

A poly(arylene sulfide) having the following properties (a) to (f):

• (a) melt viscosity being 3 Pa·s to 2,000 Pa·s as measured under conditions of a temperature of 310° C. and a shear rate of 1,216 sec−1;
• (b) pH being 7.5 to 11.5 as measured in a mixed solvent of water/acetone (volume ratio=2/1);
• (c) crystallization temperature being 165° C. to 220° C. as measured in the course of lowering the temperature of the polymer at a rate of 10° C./min from a molten state at a temperature of 340° C.;
• (d) whiteness degree being 70 to 85, wherein the whiteness degree indicates a color tone of a sample of a crystallized sheet of the poly(arylene sulfide) in accordance with a reflected light measuring method under conditions of standard light C;
• (e) a ratio MV2/MV1 being 0.85 to 1.0, wherein MV2 is a melt viscosity value measured at a shear rate of 1,216 sec−1 after held for 30 minutes at 310° C. and MV1 is a melt viscosity value measured at a shear rate of 1,216 sec−1 after held for 5 minutes at 310° C.;
• and
• (f) content of a low-molecular weight component extracted by Soxhlet extraction with chloroform being 1.0% to 4.0% by weight,
• wherein the poly(arylene sulfide) is produced by a production process comprising:
• (1) a dehydration step comprising heating and reacting a mixture containing an organic amide solvent, an alkali metal hydrosulfide and an alkali metal hydroxide in a proportion of 0.95 to 1.05 mol per mol of the alkali metal hydrosulfide at a temperature of 100 to 300° C. to discharge at least a part of a distillate containing water from the interior of the system containing the mixture to the exterior of the system;
• (2) a charging step comprising adding an alkali metal hydroxide and water to the mixture remaining in the system after the dehydration step, as needed, in such a manner that the alkali metal hydroxide and water are present in proportions of 1.00 to 1.09 mol and 0.5 to 2.0 mol, respectively, per mol of a sulfur source (charged sulfur source) including the alkali metal hydrosulfide and alkali metal sulfide, wherein the amount of the charged sulfur source is calculated in accordance with an equation:
• (Charged sulfur source)=(Total moles of sulfur charged)−(Moles of sulfur volatilized off after dehydration);
• (3) a polymerization step comprising a first-stage polymerization step of adding a dihalo-aromatic compound to the mixture to subject the sulfur source and the dihalo-aromatic compound to a polymerization reaction at a temperature of 170 to 270° C., thereby forming a prepolymer, wherein conversion of the dihalo-aromatic compound is 50 to 98%, and a second-stage polymerization step of controlling the amount of water in the reaction system after the first-stage polymerization step so water is present in a proportion of 2.0 to 10 mol per mol of the charged sulfur source, and heating the reaction system to 245 to 290° C., thereby continuing the polymerization reaction;
• (4) a washing step comprising washing a polymer formed in the polymerization step after the polymerization step repeatedly at least twice with a washing liquid composed of water, a hydrophilic organic solvent or a mixed liquid thereof, and at this time, washing the polymer with water or the mixed liquid at a final washing stage, and controlling washing conditions in such a manner that the pH of the washing liquid after the washing falls within a range of 8.5 to 10.7;
• and
• (5) a collecting step comprising separating the polymer from the washing liquid after the washing step.