Ring-opening polymerization of γ-bromo-ε-caprolactone:: A novel route to functionalized aliphatic polyesters

The synthesis, characterization, and polymerization of a new cyclic ester, gamma-bromo-epsilon-caprolactone (gamma BrCL), are reported. The ring-opening polymerization (ROP) of this new monomer initiated from Al(O(i)Pr)(3) as initiator in toluene at 0 degrees C was found to be living and proceeds by a coordination-insertion mechanism. Random and block copolymerizations of this gamma BrCL with epsilon-caprolactone (epsilon CL) were also found to be living as evidenced by the experimental molecular weight which is consistent with that expected from the monomer to initiator molar ratio, the narrow polydispersity, and the good agreement between the comonomers molar fraction in the comonomer feed and the copolymer. The thermal transitions (T(g) and T(m)) in the epsilon CL/gamma BrCL random copolymers depend strongly on the gamma BrCL content. Increasing the gamma BrCL content in the copolymer (F(BrCL)) increased the T(g) of the copolymer from -61 degrees C for poly(epsilon-caprolactone) to -16.5 degrees C for the P gamma BrCL homopolymer but decreased the T(m) of the PCL to contents of similar to 30 mol % of gamma BrCL (F(BrCL) = 0 3) Beyond this value, the copolymers were found to be amorphous and exist as viscous liquids.