Collect. Czech. Chem. Commun. 1995, 60, 1925-1934

Effect of Molecular Weight on Mechanical Behaviour of Segmented Polyurethanes

Michal Ilavskýa,b, Jaromír Fähnrichb, Tadeusz Pakulac and Christopher Lantmand

a Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, 162 06 Prague 6, Czech Republic
b Faculty of Mathematics and Physics, Charles University, 180 00 Prague 8, Czech Republic
c Max-Planck-Institut für Polymerforschung, D-6500 Mainz, Germany
d Mobay Corporation, Pittsburgh, PA 15205-9741, U.S.A.


The effect of molecular weight of polyurethanes on their dynamic mechanical and ultimate behaviour was investigated in wide frequency and temperature ranges. The polyurethanes were prepared from α,ω-dihydroxy-poly(oxypropylene), 1,4-butanediol, 1-butanol and 4,4'-dicyclohexylmethane diisocyanate at constant stoichiometric molar ratio of OH and NCO groups. Molecular weight (MW) of the copolymers was varied by replacing partly the butanediol by equivalent amounts of butanol; the calculated values of MW ranged from 6 000 to infinity. In all samples the constant soft-segment concentrations (~50 wt.%) were obtained. Two transition regions located around -30 °C and 70 °C, corresponding to the soft polyether and hard polyurethane domains, respectively, were observed with all samples in the temperature dependences of both components of the dynamic modulus measured at 1 Hz. Due to high miscibility of the phases, both transitions overlap; the two-phase character of the structure increases with decreasing MW. At T > 120 °C the samples are homogeneous and the frequency-temperature superposition could be applied. Quenching of the samples from 150 °C down to -80 °C preserves quasi-homogeneous structure; the rate of re-establishment of the two-phase structure increases with decreasing MW. The ultimate properties, strain-at-break and tensile strength measured at room temperature decrease with decreasing MW.