Macrocycles. 3. Telechelic polylactones via macrocyclic polymerization

epsilon-Caprolactone (epsilon-CL) was polymerized with 2,2-dibutyl-2-stanna-1,3-dioxepane or 2,2-dibutyl-2-stanna-1,3,6-trioxocane as initiator. All polymerizations were conducted in bulk at monomer/ initiator (M/I) ratios of 10/1, 20/1, 35/1, or 50/1 and yielded macrocyclic poly(epsilon-CL) with quantitative conversion. These macrocycles were reacted in situ with 4-nitrobenzoyl chloride or with thiocresyl 4-nitrobenzoate yielding the 4-nitrobenzoyl-functionalized telechelics. The completion of these ring-opening reactions was checked by Sn-119 NMR spectroscopy of the reaction mixture and by H-1 NMR spectroscopy of the isolated oligo(epsilon-CL). Analogous quantitative functionalizations of the macrocyclic oligo(epsilon-CL) were obtained with 4-bromobenzoyl chloride, 6-propargyloxynaphthoyl chloride, 3- or 4-maleimidobenzoyl chloride, cinnamoyl chloride, undecenoyl chloride, and methacrylic anhydride. The hydrogenation of the nitro groups and the thermal cross-linking of the propargyl ether groups were conducted as examples of the great versatility of the telechelic oligo(epsilon-CL)s in modification and chain extension reactions.