Structure–property relationships for polycaprolactone-based polyurethane elastomers

A study on a number of different polyurethane (PUR) elastomer materials based on different polyester soft segments has been carried out. The soft segments (Mn = 2000) were varied, both in terms of chemical structure and content. The emphasis of the study has been put on polycaprolactone (PCL) soft segments based on seven different initiator diols, but a homologous series of polyadipate soft segments was also investigated (based on ethyleneglycol, butanediol and hexanediol). The materials were characterised by means of DSC, DMTA, WAXD, SAXS, density and tear strength measurements and tensile testing. Additionally, the morphology of one material was characterised by means of TEM and PFM (Pulsed Force Microscopy). The most significant difference between the soft segments is a more or less strong tendency towards soft segment crystallisation. Soft segment crystallinity influences hardness, translucency, tear strength and other tensile properties. In general, polyadipate-based PURs exhibit much more soft segment crystallinity than PCL-based PURs. They also crystallise significantly faster. [Continues.]