Understanding and controlling physical aging below the glass transition temperature (Tg) is very important for the long‐term performance of plastic parts. In this article, the effect of grafted silica nanoparticles on the physical aging of polycarbonate (PC) below the Tg is studied by using the evolution of the enthalpy relaxation and the yield stress. The nanocomposites were found to reach a thermodynamic equilibrium faster than unfilled PC, implying that physical aging is accelerated in presence of grafted nanosilica particles. The Tool‐Narayanaswamy‐Moynihan model shows that the aging is accelerated by the grafted silica nanoparticles, but the molecular mechanism responsible for physical aging remains unaltered. Furthermore, dynamic mechanical analysis shows that the kinetics of physical aging can be related to a free volume distribution or a local attraction‐energy distribution as a result of the change in mobility of the polymer chain. Finally, a qualitative equivalence is observed in the physical aging followed by both the enthalpy relaxation and yield stress. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 2069–2081

Photochromic dyes have restricted use in rigid polycarbonates because of slow coloration and decoloration kinetics. In this study, it is shown that the decoloration kinetics of two photochromic dyes can be controlled by tuning the chain stiffness and free volume of the host matrix. The introduction of flexible moieties in rigid BPA-based polycarbonate chain accelerates the decoloration of these dyes whereas a rigid comonomer delays the decoloration kinetics. Although T g might be used as a parameter to improve photochromism in polymer matrices, dynamic mechanical analysis demonstrates that the decoloration kinetics of the dyes in host polymer matrices having similar T g depends primarily on the secondary relaxations and, thus, on the polymer architecture. The effect of the comonomer type on the characteristic ratio is also discussed underlining the potential relationship between the free volume and chain stiffness. These results open the possibility to develop transparent or semitransparent photochromic materials based on tailor-made co-polycarbonates.

Viscosity controls an important issue in polymer processing. This paper reports on the terminal viscosity behavior of a polymer melt containing grafted nanosilica particles. The melt viscosity behavior of the nanocomposites was found to depend on the interaction between the polymer matrix and the nanoparticle surface. In the case of polycarbonate (PC) nanocomposites, the viscosity decreases by approximately 25% at concentrations below 0.7 vol% of nanosilica, followed by an increase at higher concentrations. Chemical analysis shows that the decrease in viscosity can be attributed to in situ grafting of PC on the nanosilica surface, leading to a lower entanglement density around the nanoparticle. The thickness of the graft layer was found to be of the order of the tube diameter, with the disentangled zone being approximately equal to the radius of gyration (Rg) polymer chain. Furthermore, it is shown that the grafting has an effect on the motion of the PC chains at all timescales. Finally, the viscosity behavior in the PC nanocomposites was found to be independent of the molar mass of PC. The PC data are compared with polystyrene nanocomposites, for which the interaction between the polymer and nanoparticles is absent. The results outlined in this paper can be utilized for applications with low shear processing conditions, e.g., rotomolding, 3D printing, and multilayer co-extrusion.