Sulfur-containing polyisobutylene (PIB)-based polyurethane nanocomposite (PIBs-PU/NC) was synthesized using HO-CH2CH2-S-PIB-S-CH2CH2-OH for the soft segment, conventional hard segments of MDI and BDO, and organically modified montmorillonite (OmMMT) nanolayers. The properties of PIBs-PU/NC containing 72.5% PIB and 0.5% OmMMT were studied and contrasted with unmodified PIBs-PU. PIBs-PU/NC produces colorless optically clear films exhibiting enhanced tensile strength, elongation, oxidative-hydrolytic stability, and creep resistance relative to that of PIBs-PU. FTIR spectroscopy indicates H bonded S atoms between soft and hard segments, and OmMMT nanolayers. DSC and XRD suggest randomly dispersed low-periodicity crystals and urea groups between galleries. We propose that minute amounts of OmMMT nanolayers become covalently attached to polyurethane chains and beneficially affect properties by acting as co-chain extender/reinforcing filler. (C) 2016 Wiley Periodicals, Inc.