A poly(ester-carbonate) copolymer comprises carbonate units of the formula (I); and ester units of the formula (II) wherein: T is a C2-20 alkylene, a C6-20 cycloalkylene, or a C6-20 arylene; and R1 and J are each independently a bisphenol A divalent group and a phthalimidine divalent group, provided that the phthalimidine divalent group is present in an amount of 40 to 50 mol% based on the total moles of the bisphenol A divalent groups and the C½ divalent group, and the ester units are present in an amount of 40 to 60 mol% based on the sum of the moles of the carbonate units and the ester units; and wherein the poly(ester-carbonate) copolymer has a weight average molecular weight of 18,000 to 24,000 Daltons; and the composition has a Tg of 210 to 235 °C and a melt viscosity of less than 1050 Pa- s at 644 sec -1 and 350°C.