Robust POSS-PEG networks. Nanostructure, viscoelasticity and shape memory behavior

A detailed angstrom- and nm-scale analysis was carried out on polyhedral oligomeric silsesquioxane (POSS) photocrosslinked with polyethylene glycol (PEG) at 10:90 wt% ratio. POSS increased up to two orders of magnitude the shear mechanical modulus thus producing robust molecular networks with one-way shape memory (SM) behavior. The mechanical reinforcement was driven by POSS nanoclusters which were revealed by highresolution transmission electron microscopy (TEM). On the other hand, PEG molecular weight tuned POSS dispersion, i.e., average single or three units POSS dispersion was achieved by varying PEG molecular weight. This resulted in the shear elastic modulus increasing over one and two orders of magnitude, respectively. X-ray scattering wide- and small-angle showed that the robust mechanical reinforcement is unique to POSS as crystallinity and crystal size were not the relevant factors. The one-way SM behavior was thermally activated by the melting the PEG crystals and a temporary shape was fixed by the recrystallization of PEG. That is, the network locked in a temporary shape by PEG crystallization and soft actuation resulted from the crystals melting freeing the stresses that extended through the crystalline phase. These versatile and mechanically robust networks broaden the scope of applications in actuators, sensors, and responsive materials.

Automated summary

A detailed analysis at the angstrom and nm scale was conducted on the photocrosslinked mixture of polyhedral oligomeric silsesquioxane (POSS) and polyethylene glycol (PEG). The study found that POSS significantly increased the shear mechanical modulus, generating robust molecular networks with one-way shape memory behavior. The mechanical reinforcement was attributed to POSS nanoclusters. Additionally, the dispersion of POSS was affected by the molecular weight of PEG. These versatile and mechanically strong networks have important implications for actuators, sensors, and responsive materials.