The nature of irregularities and end-groups in poly(styrene oxide) samples prepared using Maghnite-H+ as a cationic catalyst were studied by H-1- and C-13- NMR at 200 MHz. Head-to-head (H-H) and tail-to-tail (TT) irregularities are detected in all the samples studied. Secondary hydroxyl terminal groups are identified in polymers prepared with Maghnite-H+. Poly(styrene oxide) was found to undergo chain scission by aging at 25 degrees C. It was confirmed that oxidation of this type of polymers results from the important sensitivity of the polyether soft segment to oxidative degradation. For this reason, the scissions due to the oxidation of the material lead to notable quantities of low molecular weight photoproducts. Among the various structures produced by the oxidative degradation process, benzoate and secondary hydroxyl groups are identified by MALDI-TOF-MS. (C) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 110: 3195-3202, 2008