Cholesterol-Based Molecular Glasses: Attempts to Control Their Thermal Stability and Mechanical Properties

Driven by environmental concerns regarding conventional polymer-based materials, biomolecule-derived bulk solids, such as glasses and plastics, are attracting increasing attention. Here, we report molecular glasses consisting of a hydrophobic cholesterol scaffold. By designing intermolecular hydrogen bonding, crystallization was suppressed; however, the glassy state was kinetically unstable. We explored a simple strategy of mixing two cholesterol derivatives in the expectation that this would produce a greater diversity in intermolecular interactions and thereby enhance the glass-forming ability. Gratifyingly, we obtained stable, humidity-resistant, transparent glasses with tunable mechanical properties in a scalable manner. The optimized glass exhibited a hardness of H = 88 MPa and a reduced modulus of Er = 3.1 GPa (nanoindentation analysis), values comparable to those of known molecular glasses and approaching those of conventional polycarbonate glass. This study highlights a promising strategy for developing sustainable hydrophobic organic glassy materials.