Free Volume and Local Dynamics in Modulus-Enhanced Polycarbonate under Addition of Low-Mass Molecules

Abstract

We investigated the relation between modulus enhancement and reduction of free volume of polycarbonate (PC) by addition of low-mass molecules (LMs) with various sizes and concentrations. The modulus enhancement of PC, which is called “antiplasticization”, is due to the restriction of local chain motion of PC by the LM additives. For PC and antiplasticized PC, the free volume was evaluated at various temperatures below the glass transition temperature through positron annihilation lifetime spectroscopy. The results showed that the free volume decreased in the presence of LMs at all the temperatures in the glassy region, but the free volume of antiplasticized PC became close to that of pure PC at the rotational relaxation temperature for LMs. This result indicated that the LM dynamics strongly affected the PC free volume, which determined the degree of modulus enhancement. Furthermore, storage moduli of PC blends were compared for various LMs at different concentrations. The comparison showed a universal relation between the PC storage modulus at 25 °C and the LM molar concentration. This result suggests that each LM restricts the local motion of PC to the same degree independently of the molecular size.