The Effect of Hard Sequence Ordering on the Mechanical Behavior of Polyurethane Elastomers

Polyurethane elastomers (PUs) with similar chemical structures based on hard segments of 4,4 '-dibenzyl diisocyanate and soft segment poly(ethylene adipate) and extended with a low-molecular-weight diol diethyelene glycol were synthesized by three different polymerization methods: (a) the "one-shot" technique, (b) the conventional prepolymer route, and (c) an inverse step-by-step synthesis that started with the construction of the hard ordered reactive intermediate followed by reaction with the macrodiol, resulting in an increased hard sequence ordering. The effects of the preparation method and of the hard sequence ordering on PU elastomeric performance were studied by means of tensile tests and thermomechanical analysis. The PUs with a more regular structure obtained by method (c) exhibited a more rigid network, which resulted in higher strain energies but lower tensile strength along with higher residual elongation. An enhanced hard sequence ordering leads to a moderate decrease of PU performance as an elastomer.