Poly(1,5-pentylene-co-2,2,4,4-tetramethyl cyclobutylene terephthalate) (PPecBT) random copolyesters glass transition temperature up to 136 ?C were synthesized through two-step melting polycondensation of dimethyl terephthalate (DMT) or terephthalic acid (TPA), 2,2,4,4-tetramethyl-1,3-cyclobutanediol (CBDO) and 1,5-pentanediol (PeDO). They were characterized and assessed with intrinsic viscosity, 1H NMR, DSC, TGA, tensile and impact testing as well as melt foaming observation. Using PeDO as a diol comonomer was helpful to depress CBDO sublimation and pipeline blocking, and to reduce the composition and cis-trans ratio deviations between monomer and copolymer. The presence of PeT repeat unit in PPecBT was beneficial to improve the thermal stability of PPecBT and to reduce undesired melt foaming and volume expansion during melt processing. The Tg of these amorphous copolymers is determined by intrinsic viscosity, copolymer composition and cis-cB unit 

fraction, and a quantitative relationship among them is established. Futhermore, these PPecBTs showed superior 

tensile ductility as well as strength and modulus.