Synthesis and characterization of biodegradable homopolymers and block copolymers based on adipic anhydride

Homopolymers of adipic anhydride (AA) and block copolymers of -caprolactone (-CL) and AA have been synthesized with aluminum triisopropoxide as an initiator. Homopolymerization was studied at 20°C in toluene and methylene chloride (CH2Cl2). The end-group analysis agrees with a coordination insertion mechanism based on the acyl-oxygen cleavage of the AA ring. Living poly(-caprolactone) (PCL) chains are very efficient macro-initiators for the polymerization of AA, with formation of diblock copolymers of a narrow molecular weight distribution. At our best knowledge, low molecular weight -aluminum alkoxide PCL macroinitiators (M¯n < 1000) allow the first valuable synthesis of PAA with a molecular weight as high as 58,000 and a quite narrow polydispersity (M¯w/M¯n = 1.2). Size-exclusion chromatography (SEC) and 13C NMR confirm the blocky structure of the copolymers, in agreement with DSC that shows two melting endotherms and two glass transitions characteristic of the crystalline and amorphous phases of PCL and PAA, respectively. Block copolymers of c-CL and AA are also sensitive to hydrolysis, which makes them possible candidates for biomedical applications. Initiation of the AA polymerization in bulk with aluminum triisopropoxide in the presence of various ligands is also discussed.