Molecular engineering of elastic and strong supertough polyurethanes

Spider silk is an icon of supertough energy absorbing polymeric material which its macromolecular multiblock composition has been attributed to be responsible for such remarkable properties. As in spider silk, polyurethanes can be synthesized with two distinct block which can differ in nature, combining properties like deformability and relatively high strengths. Here we synthesized and studied four different block polyurethanes with two different soft segments (SS) and two different hard segments (HS), with the aim of discovering the best molecular architecture to develop best mechanical performance after macromolecular alignment. The difference between soft segments is the crystalline nature, one in the rubbery state (T _{g, SS} < T _room) and the other in the semicrystalline state at room temperature (T _room < T _m,SS). In parallel one hard segment was amorphous in the glassy state (T _room < T _g,HS) and the other semicrystalline (T _{g, HS} < T _room < T _{m, HS}). Results indicate that polyurethane with crystalline soft segments produce stronger materials after drawing than polyurethanes with rubbery soft segments, but the most exciting finding is the influence that hard segment has on the mechanical performance of predrawn materials, having polyurethanes prepared with semicrystalline hard segments more capability to undergo macromolecular alignment than materials with glassy segments, developing stiffer, stronger, and tougher materials.