In our recent paper, 17 a 1 H NMR methodology to quantitatively measure the cross-linked density in the individual phases of NR/SBR blend subjected to thermo-oxidative aging was demonstrated. Phase-distinction was achieved by spinning the sample at the magic-angle and using a homonuclear double-quantum (DQ) dipolar recoupling pulse sequence. In the present paper, the role of artificial weathering in the dissimilar aging of NR and SBR phases in their blend is addressed. NR and SBR react differently to oxygen and ozone. SBR itself is composed of randomly bonded aromatic and aliphatic segments. Brown et al. have conducted extensive studies by thermo-oxidative aging and weathering, which show different effects with respect to the aging of NR and SBR in the blend. During weathering the high energy UV radiation has been recognized to promote various reactions. Thus, due to their markedly different characteristics, one may expect unique changes in the blend phases that could lead to a distribution of cross-link densities.