The synthesis of primary hydroxyl-telechelic polyisobutylene, HOCH2-PIB-CH2OH, often yields product the number average terminal functionality (fn,CH2OH) of which is less than theoretical 2.0, typically fn,CH2OH = 1.75-1.95. Polyurethane (PU) prepared with such low-cost imperfect PIB-diols, unsurprisingly, exhibit poor overall properties. Herein we report that mechanical, rheological, and thermal properties of polyisobutylene-based polyurethane (PIB-PU) and PIB-PU reinforced with organically modified montmorillonite (OmMMT) prepared with PIB-diol of fn,CH2OH = 1.85 are significantly enhanced by glycerol. Specifically, we document that calculated minor amounts of glycerol substantially improves tensile strength, ultimate elongation, elastic modulus, toughness, rubbery plateau, flow temperature, creep, permanent set, rate of recovery after loading, and thermal properties of PIB-PU and OmMMT-reinforced PIB-PU prepared with PIB-diol of fn,CH2OH = 1.85. The observations are summarized and discussed in terms of chemistry, micromorphology, and viscoelasticity. (c) 2019 Wiley Periodicals, Inc.