| 摘要 |
PURPOSE:To obtain a copolyester which can given an optical material having good transparency and excellent moldability, heat resistance, dimensional stability and chemical resistance and being economically profitable. CONSTITUTION:A substantially linear copolyester is produced from a mixture comprising 2,6-naphthalenedicarboxylic acid or its esterifiable derivative and isophthalic acid or its esterifiable derivative, a dihydroxy compound having aromatic rings in the main chain and side chains and represented by the formula wherein R1 is 2-4C alkylene; R2 is hydrogen, 1-7C alkyl, allyl or aralkyl; R3, R4 and R5 may be the same or different from each other and are each 1-4C alkyl; and l, m and n are each an integer of 1 or 2, and a 2-4C aliphatic glycol. |
