Copolymerizing glutaraldehyde with tetraols such as diglycerol, meso‐erythritol, and pentaerythritol is particularly effective for forming very high molecular weight polycycloacetals (Mn up to 65,000 g/mol) with elastomeric properties and up to 70% biorenewable content by weight. Altering the tetraol monomer feed ratio provides control over the polycycloacetal's tensile properties. The polymerizations are high‐yielding, readily scalable, and employ commercially available starting materials that are used without further purification. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48780.