New ether dimer (ED-Od) and diester (ODE) derivatives of alpha-bydroxymethylacrylate, each having two octadecyl side chains, were synthesized and (co)polymerized to evaluate the effects of differences in the structures of the monomers on final (co)polymer properties, particularly glass transition temperature. The free radical polymerizations of both monomers yielded high-molecular weight polymers. Cyclopolymer formation of ED-Od was confirmed by C-13 NMR analysis and the cyclization efficiency (0.95 or greater) was found to be as high as the cyclization efficiencies of the cyclopolymerizations of ether dimers of various alkyl alpha-bydroxymethylacrylates synthesized previously. Copolymers of both ED-Od and ODE with methyl methacrylate (MMA) showed significant T-g decreases over PMMA due to octadecyl side groups causing "internal" plasticization. Comparison of the T-g's of the copolymers of octadecyl methacrylate, ED-Od and ODE with MMA revealed that the impacts of these monomers on depression of T-g's are identical. That is, the magnitude of decrease in Tg's was quantitatively related to the number of the octadecyl side groups in the copolymers rather than their placement on the same or randomly incorporated repeat units. (C) 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46:7785-7793,2008