The influence of hard segment crosslinking on the morphology and mechanical properties of segmented poly(ester-urethanes)

The morphology and mechanical properties of uncrosslinked (PUR-unc) and hard segment crosslinked (PUR-c) segmented polyester-urethanes (PUR) obtained with DABCO catalyst were investigated. The crosslinking was introduced by using 60 wt. % of trimethylol propane (TMP) in the mixture with butanediol. The morphology of bulk samples was studied with the use of AFM. Uncrosslinked PUR was characterized by a morphology in which hard-segment domains were inhomogeneously distributed in the whole sample. They created hard-segment rich aggregates (in the range of 70-380 nm diameter) which were connected to each other. Hard-segment crosslinked PUR showed spherical domains in the range of 20 nm diameter. They were homogeneously distributed in a soft-segment rich matrix and no other aggregates were present. The mechanical properties such as stress at 100 % of elongation, tensile strength, elongation at break, permanent set and tensile hysteresis percent (H-t) were compared. All studied parameters changed clearly after crosslinking excluding H-t, which only changed slightly.