Stereoregular Polymerization of [R,S]-3-Butyrolactone Catalyzed by Alumoxane−Monomer Adducts

The reaction between 2 molar equiv of 3-butyrolactone (BL) and either methylalumoxane (MAO) or isobutylalumoxane (IBAO) yielded an adduct, either MAO−BL or IBAO−BL. Both MAO−BL and IBAO−BL were found to be much more effective catalysts for the ring-opening polymerization of the racemic monomer, [ R, S ]-BL, than either MAO or IBAO alone in having much higher reaction rates and forming higher yields of crystalline polymer. The polymerization of [ R, S ]-BL in bulk catalyzed by 10 mol % MAO−BL at 80 °C went to near completion within 20 min, while use of the equivalent amount of MAO alone as the catalyst required many hours or days to obtain the same results. The crude polymeric products obtained from the polymerization reaction using 10 mol % MAO−BL contained 60 wt % of a crystalline, isotactic polymer, as compared to only 30−40% with MAO alone. The polymers obtained were characterized by GPC, DSC, and NMR. No difference was found between the catalytic behavior of the complex formed between either [ R ]-BL and MAO or [ R, S ]-BL and MAO. The structures of MAO−BL and IBAO−BL could not be determined because of their instability and insolubility. A procedure for removing the catalyst residue from the polymeric products was developed so that nearly complete removal of Al residue could be realized in short contact times without loss of atactic polymers.