. "The linear, partially crystalline polyesters, component (IIa), have the following basic formula (III): ##STR1## where R is a divalent, branched or unbranched, aliphatic and/or cycloaliphatic radical having 2 to 12, preferably 2 to 8, carbon atoms in the carbon chain, and R' is a divalent aromatic radical having 6 to 20, preferably 8 to 12, carbon atoms in the carbon structure." . . .