Relationship between polyurethane composition and viscoelastic properties of model urethane systems

Abstract

A study was performed to determine the relationship between polyurethane composition and viscoelastic properties in a series of model urethane compounds. The compositional variables studied included the nature of the soft segment, amount of hard segment, and cure stochiometry. Model urethanes were prepared using the aliphatic diisocyanate, metatetramethylene diisocyanate (m‐TMXDI). This aliphatic isocyanate is less reactive than commonly used aromatic isocyanates and does not undergo the secondary cross‐linking reactions commonly observed with aromatic isocyanates. The urethanes chosen for this study contained soft segments based on hydroxy‐terminated polybutadiene (HTPBD) or polycaprolactone (PCL), which is a highly polar material in which extensive phase mixing should occur. In contrast, polyurethanes based on HTPBD should undergo more complete phase separation. Prepolymers were prepared with both of these soft segments and with available isocyanate contents varying from 3.7% to 5.7%. Diethyltoluene diamine (DETDA) was used to cure these prepolymers over a range of cure stochiometries. Thermal transitions attributed to the hard and soft segments were observed in these urethanes using a Perkin‐Elmer DSC‐4. Dynamic mechancial behavior was measured using both a Polymer Labs dynamic mechanical thermal analyzer (DMTA) and a resonance apparatus developed at the NRL‐USRD. [Sponsored by ONT.]