Cationic ring-opening polymerizations of 5-alkyl- or 5,7-dialkyl-1,3-dehydroadamantanes, such as 5-hexyl- (4), 5-octyl- (5), 5-butyl-7-isobutyl- (6), 5-ethyl-7-hexyl- (7), and 5-butyl-7-hexyl-1,3-dehydroadamantane (8), were carried out with super BrOnsted acids, such as trifluoromethanesulfonic acid or trifluoromethanesulfonimide in CH2Cl2 or n-heptane. The ring-opening polymerizations of inverted carbon-carbon bonds in 4-8 proceeded to afford corresponding poly(1,3-adamantane)s in good to quantitative yields. Poly(4-8)s possessing alkyl substituents were soluble in 1,2-dichlorobenzene, although a nonsubstituted poly(1,3-adamantane) was not soluble in any organic solvent. In particular, poly(8) exhibited the highest molecular weight at around 7500 g mol(-1) and showed excellent solubility in common organic solvents, such as THF, CHCl3, benzene, and hexane. The resulting poly(4-8)s containing adamantane-1,3-diyl linkages showed good thermal stability, and 10% weight loss temperatures (T-10) were observed over 400 degrees C. (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4111-4124