In this study, we quantified the thermal and solid-state mechanical and viscoelastic properties of isotactic polypropylene (i-PP) homopolymer and poly(propylene-1-butene) copolymer films having a 1-butene ratio of 8, 12, and 14 wt %, depending on the comonomer content. The uniaxial tensile creep and stress-relaxation behaviors of the samples were studied in a dynamic mechanical analyzer at different temperatures. The creep behaviors of the samples were modeled with the four-element Burger equation, and the long-term creep strains were predicted with the time-temperature superposition method. The short-term mechanical properties of the samples were also determined with tensile and impact testing at room temperature. We found that the Young's modulus and ultimate strength values of the samples decreased with increasing amount of 1-butene in the copolymer structure. On the other hand, the strain at break and impact strength values of the samples improved with increasing amount of 1-butene. Creep analysis showed that i-PP exhibited a relatively lower creep strain than the poly(propylene-co-1-butene)s at 30 degrees C. However, interestingly, we discovered that the temperature increase resulted in different effects on the creep behaviors. We also found that short-chain branching improved the creep resistance of polypropylene at relatively high temperatures. (c) 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46350.