Melt polycondensation was utilized to chain extend polytrimethylene terephthalate with 1,3-propanediol based fluorinated isophthalic oligomers, resulting in copolymers with retained microstructure. Our findings point toward the formation of a blocky type copolymer. In general, formation of block or segmented copolymers from melt derived polycondensation is a very challenging task due to the propensity for adverse randomization reactions. Supported by size exclusion chromatography, our copolymers are fully chain extended, with no presence of the initial components. Furthermore, thermal differential scanning calorimetry has confirmed that the melt characteristics of the starting components are retained. In addition, interaction polymer chromatography and sequence distribution analysis using C-13 NMR supports a blocky backbone microstructure. Seemingly, intermolecular chain end condensation occurs, whereas transesterification is dormant. While these findings open up new doors for polymer/materials development, we are particularly interested in these structures as melt additives to address oil repellency of polyester blends. When used in blends these blocky additives show an improvement in oil repellency compared with random additives of identical molar composition, i.e., they are more fluorine efficient.