Solid-state NMR and TEM were used to quantitatively examine the evolution of clay morphology upon equibiaxial stretching of polypropylene/montmorillonite (PP-MMT) nanocomposites tip to a stretch ratio (lambda = final length/initial length) of 3.5. H-1 spin-lattice relaxation times were measured by the saturation-recovery sequence. For the nanocomposites, initial portions of the magnetization recovery Curves (<=similar to 20 ms) were found to depend on root t, indicative of diffusion-limited relaxation and in agreement with calculations based on estimates of the spin-diffusion barrier radius surrounding the paramagnetic centers in the clay, the electron-nucleus coupling constant, and the spin-diffusion coefficient. Initial slopes of these magnetization recovery curves directly correlated with the fraction of clay/polymer interface. New clay surface was exposed as a near linear function of strain. Long-time portions of the magnetization recovery curves yielded information oil the average interparticle separations, which decreased slowly before reaching a plateau at lambda = similar to 2.5 as particles aligned. TEM images supported these findings and were used to define and quantify degrees of exfoliation and homogeneity from the NMR data. Exfoliation, defined as (platelets/stack)(-1), increased from 0.38 (unstretched) to 0.80 at lambda = 3.5 for PP-MMT nanocomposites stretched at 150 degrees C and 16 s(-1). A lower stretch temperature, 145 degrees C, which is slightly below melting onset, led to an exfoliation degree of 0.87 at lambda = 2.8, consistent with the ability of higher melt viscosities to allow for higher shear stress transfer. Exposure of new clay surface is attributed to aggregate breakup and orientation at low strains (lambda <= similar to 2) and to platelets sliding apart at higher strains.