from the A and B series are weak and tend to flow under stress. Comparing
maximum values, one can conclude that they are not significantly different. This
means that in this range of segment lengths, high tensile strength can be achieved
by using any one of the three polyols, but at different SSC.
The strengths are given usually in the form of engineering stresses at break.
In order to obtain the true stress at break, tensile strengths should be multiplied
by extension ratio 2(= 1/Io), where I and l0 are extended and original sample
lengths. Since elongation at break, e (e = 2 + 1) increases with increasing of
SSC, the maxima on the true stress at break-SSC curves are expected to move
to higher SSC values, as compared to tensile strength-SSC maxima. In a series
of polyurethane elastomeric fibers based on Adiprene L-100, piperazine and
MDI, a maximum on the true stress at break vs extension diagram 2°7 was found
at about 60% SSC, Fig. 37. Adiprene L-100 is the prepolymer obtained from
two moles of PTMO and three moles of TDI, having a nominal molecular
weight of about 2000.