Two diols, 2,2-bis(4-[hydroxyethoxy]phenyl)propane (Dianol 220 (R)) and bis(2-hydroxyethyl)terephthalate (BHET), were incorporated into poly(butylene terephthalate) (PBT) by solid-state polymerization (SSP) and melt polymerization (MP). Different PBT/diol ratios were used to obtain copolymers with different compositions. C-13 NMR spectroscopy was used to analyze the sequence distribution and the data analysis was discussed in detail. Both Dianol and BHET were randomly incorporated in the MP copolymers. For both PBT-Dianol and PBT-BHET copolymers obtained via SSP, a non-random, blocky microstructure was obtained. For the PBT-Dianol copolymers, the randomness increased for increased fractions of incorporated Dianol. For the PBT-BHET copolymers, the randomness continuously decreased with increased fractions of incorporated BHET.