Polymer crystallinity is known to be dependent upon backbone stereochemistry, and this concept has emerged as an effective means of altering bulk material properties. Herein we describe a simple, step-growth polymerization to synthesize unsaturated poly(ester-urethane)s using the thiol-Michael addition reaction. The absolute control of alkene stereochemistry (0-100% trans content) in the polymer backbone was achieved by varying the cis/trans double bond content of the monomer feedstock. In turn, the crystallinity of the polymer was systematically varied which manifested in control over the resultant tensile properties such as Young's modulus, ultimate tensile strength, and elongation at break. Generally, the crystallinity and tensile strength were positively correlated with increasing trans double bond content within the polymer.