Copolymerized polymer

A polyester obtainable by copolymerizing a dicarboxylic acid component (A) comprising: (a) 10 to 90 mol% of isophthalic acid or an ester forming derivative thereof;(b) 10 to 60 mol% of a phenylenedi(oxyacetic acid) of formula [I]: wherein R¹, R², R³ and R⁴ each independently represents a hydrogen atom, an alkyl group of 1 to 6 carbon atoms, an alkoxy group of 1 to 6 carbon atoms, a phenyl group, a chlorine atom, a bromine atom or a fluorine atom, or an ester forming derivative thereof; and(c) 0 to 45 mol% of a naphthalenedicarboxylic acid or an ester forming derivative thereof; and a diol component (B).