Structure tensile properties of polyurethanes

A series of hydroxyl terminated polybutadiene-(HTPB) based polyurethanes (PUs) were synthesized by solution polymerization with different types of diisocyanates, hard segment contents, NCO/OH ratio and polymerization methods. Spectroscopic and stress-strain studies were carried out to elucidate the structure-property relationships existing in these polymers. It was found that the binding of the hard segment and the flexibility of soft segments had subtle effects on the properties of stress-strain at break. The segregation between hard and soft segments was manifested by incompatibility between hard and soft segments, steric hindrance of urethane groups and the extent of interchain hydrogen bonding. The hydrogen bonding index (HBI) measured by FTIR was employed to show the extent of interchain hydrogen bonding, which affects the segregation and hence the stress-strain property of the prepared films. Films with higher hard segment content and NCO/OH ratio, 4,4'-diphenylmethane diisocyanate (MDI) and the one-stage polymerization method exhibit higher stress at break and lower strain at break. The measurement of FTIR was used to identify the degree of phase segregation and to correlate the stress-strain properties of PUs with different compositions. (C) 1997 Elsevier Science Ltd.