Enhancement to the rate-dependent mechanical behavior of polycarbonate by incorporation of triptycenes

Abstract

The tensile and compressive properties of triptycene-polycarbonates were tested over 6 orders of magnitude in strain rate. Initially we studied a low molecular weight, low triptycene content PC blended with Iupilon® PC and then a series of higher molecular weight, higher triptycene content polymers. The PC blend with only 1.9wt% triptycene displayed up to 20% increase in modulus and up to 17% increase in yield strength with elongations over 80% as compared to the Iupilon® PC. The higher molecular weight T-PCs (up to 26wt% triptycene) exhibited improvements in modulus by over 20% and improvements in compressive strengths by nearly 50% at both low and high strain rates without any apparent sacrifice to ductility, as compared to Iupilon® PC. All samples containing triptycene units retained transparency and exhibited no signs of crystallinity or phase separation. Moreover, both the blends and triptycene-PC copolymers displayed significantly altered dynamic mechanical spectra, specifically, the emergence of a pronounced, new β′ relaxation approximately 75°C above the traditionally observed β relaxation in PC (approximately −100°C). The enhancement of the mechanical properties observed provides valuable insights into the unique packing and interactions during plastic flow induced by the presence of triptycene units.