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((OPr)-Pr-i)(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 (Tg and Tm) in the epsilon-CL/gamma-Br-CL random copolymers depend strongly on the gamma-BrCL content. Increasing the gamma BrCL content in the copolymer [F(BrCL)] increased the Tg of the copolymer from -61 degrees C for poly(epsilon-caprolactone) to -16.5 degrees C for the poly( gamma-BrCL) homopolymer but decreased the Tm 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.