A stereoregular poly(ether ester), poly(trans-2-oxycyclohexyl butanoate) (-[trans-2-OCHB](n)-) (II). was obtained by cationic polymerization of cis-2,3-tetramethylene-1,4,6-trioxaspiro[4,4]nonane (I) initiated by the 9-phenyl-9,10-dihydroanthracen-10-ylium cation (PDAC) obtained by exposing a mixture of (4-octylphenyl)phenyliodonium hexa fluoroantimonate (OPIA) and anthracene (A) to UV light at 254 urn. The structure of II, the polymerization mechanism or I, and the relationship between volume changes during polymerization and polymer structure were studied. The polymerization mechanism of I proceeded in a regiospecific manner and was determined in terms of the relation among the polymer structure, the steric hindrance sensitized PDAC, and the only intermediate, 1,3-dioxolan-2-ylium carbocation (DOLC). Polymer II exhibited high volume expansion (2.09 +/- 0.25%) during polymerization compared to that of -[cis-2-OCHB](n)- (III), obtained by polymerization of I using SnCl4 as an initiator, which demonstrated high volume shrinkage (-2.49 +/- 0.13%) during polymerization. The volume expansion of II is caused by the conversion of cis substitution at C-2 and C-3 in I to the trans form during polymerization.