Molecular mobility and hydration properties of segmented polyurethanes with varying structure of soft- and hard-chain segments

✍ Scribed by A. Kanapitsas; P. Pissis; J. L. Gomez Ribelles; M. Monleon Pradas; E. G. Privalko; V. P. Privalko

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 232 KB
• Volume: 71
• Category: Article
• ISSN: 0021-8995
• DOI: 10.1002/(sici)1097-4628(19990222)71:8<1209::aid-app1>3.0.co;2-5

✦ Synopsis

The molecular mobility and hydration properties of model segmented polyurethanes from either poly(propylene glycol) (PPG) or poly(butylene adipate) (PBAD), both of molecular weight 2000 (soft segments), and three different diisocyanates (all-trans 4,4Јdicyclohexylmethane diisocyanate, 100% t,t HMDI; HMDI with 20% of trans isomers, 20% t,t HMDI; and 4,4Ј-diphenylmethane diisocyanate, MDI) (hard segments) were investigated using differential scanning calorimetry (DSC), thermally stimulated depolarization currents (TSDC) measurements, ac dielectric relaxation spectroscopy (ac DRS), equilibrium water-sorption isotherms (ESI), and dynamic water-sorption isotherms (DSI). No effects of the structure and of the amount of the soft segments on the overall degree of microphase separation (DMS) into microphases rich in soft and hard segments, respectively, were observed. On the contrary, DMS depends on the composition of the diisocyanates used and systematically increases in the order MDI, 20% t,t HMDI, 100% t,t HMDI as indicated by DSC, TSDC, and ac DRS. The PPG-based polyurethanes are characterized by larger values of water content at saturation, h, and smaller values of the diffusion coefficient of water, D. h increases with temperature, indicating that the sorption process is endothermic.