Gregory S. Pollock’s scientific contributions

Segmented polyurethane elastomers containing additional ordered structures within the hard or soft domains were developed to mimic the hierarchical structure and superior properties observed in spider silk fibers. The silk's toughness is related to a fiber morphology that includes P-pleated crystalline sheets within an amorphous matrix, as well as an additional interphase with an orientation and mobility between that of the two microphases. In the polyurethane mimics, bulky aromatic diisocyanates were incorporated between aliphatic hexamethylene diisocyanate (HDI) hard segments and poly(tetramethylene oxide) (PTMO) soft segments, to enhance the size and orientation of the interphase. The mixture of diisocyanates reduces the crystallinity of the HDI hard segments, allowing the polyurethane to form more well-organized domains observed by AFM imaging. The more interconnected hard domains allow the elastomers to deform to higher elongations and absorb more energy without a decrease of initial modulus. Shearing of the hydrogen-bonded hard domains orients the hard blocks at a preferred tilt angle of ±20⁰ from the strain direction during tensile deformation.