Gadolinium methacrylate containing poly(methyl methacrylate) ionomers (GMA-PMMA) and gadolinium octanoate containing poly(methyl methacrylate) (GOA-PMMA) have been synthesized. The investigation of their glass transitions was performed by the internal friction method. Although the internal friction at about 110 degrees C for both samples showed a reduction when the Gd3+ content increased, differences have been found between the change tendencies, T-g and Delta E-a, of GMA-PMMA and GOA-PMMA as the concentration of Gd3+ increased. The behaviour of GMA-PMMA is similar to that of PMMA ionomers and the rates of change of T-g with ion concentration was found to be 15.6 degrees C and 18.9 degrees C per mol% of Gd3+ content at 0.7 and 0.1 Hz, respectively. A maximum T-g of GOA-PMMA appears at a 0.3 mol% concentration of Gd3+ and 0.7 Hz. Explanations are given in terms of structure differences, plastification of GOA and interactions between ions and PMMA chains, and a new model of multiplets is given for the GOA-PMMA sample based on this.