| Abstract: | We studied segmented polyurethanes (SPU) from poly(diethylene glycol adipate) with molar masses MSFT = 780, 1365, 1780 and 3200 g/mol (soft fragments, SFT), 2,4-toluene diisocyanate and 2,4-toluene diamine (stiff fragments, STF) with essentially monodisperse molar mass distribution of STF. They were characterized by WAXS, SAXS, heat capacity measurements, mainly from 150–450 K, and enthalpies of solution in dimethyl formamide at room temperature, ΔHsol. The experimental results may be summarized as follows. - The glass transition temperatures of SFT decrease with an increase of MSFT, but remain essentially composition-invariant at fixed MSFT, whatever the STF volume fraction φ.
- The surface-to-volume ratio of STF domains exhibits sudden, jump-like transitions at volume fractions φ* = 0.23 and φ** = 0.40, respectively.
- Exothermic (i.e., negative) values of ΔHSOl exhibit a jump-like decrease at φ* = 0.23.
It has been shown that the main cause of the latter effect is the transition of SFT from a somewhat extended to an essentially unperturbed conformation. |
