Dynamic mechanical and dielectric relaxations of poly(2-tert-butylcyclohexyl methacrylate) (P2tBCHM) and poly(4-tert-butylcyclohexyl methacrylate) (P4tBCHM) have been measured. The tert-butyl group inhibits the chair-to-chair motions in the cyclohexyl ring. However, small motions of the cyclohexyl group are still possible giving rise to subglass relaxations in both polymers. The dielectric response is more sensitive than the mechanical one to the corresponding applied force fields (C) 2000 Elsevier Science Ltd. All rights reserved.