US Patent 7750111 Polyarylene sulfide and its production method

A polyarylene sulfide has a narrow molecular weight distribution and a high molecular weight and high purity which is industrially useful, wherein the polyarylene sulfide has a weight average molecular weight of 10,000 or more, and weight loss when heated, ΔWr=(W1−W2)/W1 × 100≦0.18(%) (wherein ΔWr is weight loss ratio (%), W1 is sample weight when arrived at 100° C. and W2 is sample weight when arrived at 330° C.). Its production method includes a polyarylene sulfide prepolymer which contains a cyclic polyarylene sulfide at least 50 wt % or more, and of which weight average molecular weight is less than 10,000 is heated to be converted to a high polymer of which weight average molecular weight is 10,000 or more.