Effect of the silsesquioxane structure on the mechanical properties of the silsesquioxane-reinforced polymer composite films

Abstract

As additives for reinforcing the physical properties of polymer coating materials, silicone-based silsesquioxanes (SQs) have received considerable attention owing to their excellent mechanical and thermal robustness. To understand the effect of the SQ structure on the mechanical properties of SQ-reinforced polymer composite films, a series of SQs with different siloxane structures, i.e., randomly branched SQ (RSQ), cage-like SQ (POSS) and ladder-like SQs (LPSQs), were incorporated into the poly(urethane acrylate) (PUA) polymer. Regardless of the SQ structure and loading, all the SQ-reinforced PUA (SQ-PUA) composite films exhibited excellent optical transparency and high colorlessness. Moreover, the incorporation of the SQs increased the hardness and scratch resistance, but decreased the elastic modulus of the PUA film for all the SQs due to the strong and compliant nature of the SQ network. Importantly, at the same SQ loading, the SQ-PUA films exhibited the increasing hardness, scratch resistance and modulus in the order of RSQ < POSS < LPSQ (4 K) < LPSQ (7 K). The results suggested that the highly ordered and one-dimensional LPSQ with a higher aspect ratio is desirable for effectively reinforcing the mechanical properties of polymers with guaranteeing their excellent optical transparency.