The fourth generation of a hydroxylated dendritic hyperbranched polyester (HBP) was combined with sodium montmorillonite clay (Na+MMT) using water to generate a broad range of polymer clay nanocomposites from 0 to 100% wt/wt Na+MMT. Analysis with differential scanning calorimetry (DSC) showed a deviation in heat capacity, Delta C-p, with clay content at the T-g from a two-phase trend which was attributed to the formation of an immobilized rigid amorphous fraction (RAF) in the interlayer spacing of the intercalated system. This deviation occurred in a step-like fashion which we attributed to 0.5 nm incremental changes in the interlayer spacing, previously observed through X-ray diffraction analysis. A simple series model was utilized to quantify these interlayer spacings based on the Delta C-p values and showed good correspondence with the X-ray results. The RAF was quantified from changes in heat capacity with clay content and was verified by an alternative novel positron annihilation lifetime spectroscopy (PALS) approach. The PALS quantification of the RAF was possible through an analysis of changes in the hole size thermal expansivity of the nanocomposites as a function of clay composition. Results indicated that as much as 32% by weight of the system is made up of the RAF at its maximum. (C) 2017 Elsevier Ltd. All rights reserved.