1,4-Benzenedicarboxylic acid, polymer with 1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxylic acid, .alpha.,.alpha.'-[(1-methylethylidene)di-4,1-phenylene] bis[.omega.-hydroxypoly(oxy-1,2-ethanediyl)] and,.alpha.'-[(1-methylethylidene)di-4,1-phenylene]