Chemical Composition and Mechanical Deformation Define Lamellar Sizes in Aliphatic Triblock-Based Polyurethane Elastomers

A new set of statistical triblock thermoplastic polyurethane elastomers (TPUs) were synthesized to mimic the complexity of silks and understand the contribution of each block to the properties of the materials obtained. The urethane-rich crystalline phase comprised 1,6-hexamethylene diisocyanate (HDI) and 1,4-butanediol (BD). The intercalation of HDI-BD segments with more amorphous urethane-rich segments based on HDI and N-methyl diethanolamine (MDEA) leads to TPUs with thinner crystalline lamella. A flexible amorphous macrodiol based on poly(trimethylene) ether glycol (PO3G) was used as a mechanically compliant phase. Adding MDEA led to more amorphous materials that were more soluble in organic solvents. The predrawing of materials provoked increased interdomain distances, as observed by SAXS, and was accompanied by a reduction of melting enthalpies, which can be ascribed to the disruption of the HDI-BD crystalline segments. In addition, predrawing reduced the material's elastic modulus while significantly improving the yield strength of all TPUs.