| 摘要 |
PROBLEM TO BE SOLVED: To produce the subject polymer having good spinning properties heat resistance, etc., scarcely causing discoloration, etc., and excellent in spinning operation efficiency while having sufficient easy eluting properties with an aqueous alkali by specifying terminal carboxy groups of a copolymerized polyethylene terephthalate prepared by copolymerizing a metal sulfonate-containing isophthalic acid with a polyalkylene glycol in a specific proportion. SOLUTION: This copolyester contains ethylene terephthalate unit as a main recurring unit and further (A) a metal sulfonate group-containing isophthalic acid (SIP) and (B) a polyalkylene glycol having 1,000-10,00 average molecular weight as copolymerization components in a state simultaneously satisfying the formulae 2.0<=M(S)<=3.0; 10.0<=W(P)<=13.0 and 26.0<=M(S)×W(P)<=30.0 [M(S) is the amount (mol.%) of the copolymerized component A; W(P) is the content (wt.%) of the component B]. The amount of the terminal carboxy groups is <=25 equiv./ton. A methyl ester of the SIP is preferred as the component A.
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