Disclosed is a composition comprising or produced from poly(trimethylene terephthalate), an ionomer of an ethylene acid copolymer comprising copolymerized units of at least one α,β-ethylenically unsaturated carboxylic acid comonomer, a nucleating agent and optionally an ethylene ester copolymer. Also disclosed are articles prepared from the composition. Also disclosed is a process for preparing the compositions, including methods for controlling the melt viscosity and strain hardening of the compositions.