A series of size -controlled, cyclic poly(tetrahydrofuran)s (M,,,NMR of 4 400-8 600) that consist exclusively of the monomer, i.e., oxytetramethylene, unit (1) have been prepared in high yield through the metathesis polymer cyclization of a telechelic precursor having allyl groups, 1, in the presence of a Grubbs catalyst, and the subsequent hydrogenation of the linking, i.e., 2-butenoxy, unit in the presence of an Adams' catalyst 002). A remarkable topology effect has sub sequently been observed upon the isothermal crystallization of these two model polymers, show in distinctive spherulite growth rates and spheru9 lite morphologies in comparison with the relevant linear poly(tetrahydrofuran) counterpart that has ethoxy end groups (II).