Copolymerization of β-butyrolactone and β-benzyl malolactone with aluminoxane catalysts

Abstract

Poly (β-hydroxylbutyrate-co-benzyl β-malolactonate), (P-HB-co-BML) copolymers, were prepared by the ring-opening copolymerizations of β-butyrolactone (BL) and benzyl β-malolactone (BML) with several alkyl aluminoxane catalysts, including ethylaluminoxane (EAO), methylaluminoxane (MAO), and isobutylaluminoxane (IBAO). The copolymers had very broad molecular weight distributions with weight average molecular weights, Mw, greater than 200,000. The products were fractionated by solubility into acetone-soluble and insoluble copolymers. The former were random, atactic copolymers while the latter were stereoblock copolymers. Random, atactic copolyesters of these two monomers were also obtained with the diethylzinc-water, ZnEt2-H2O (0.6:1), and the (5,10,15,20-tetraphenylporphinato)aluminium chloride, TPPAlCl, catalysts. The copolymerization reactions with the latter two catalysts gave much higher yields (up to 98%) and better control of both the copolymer compositions and the molecular weight distributions, but these copolymers had Mw values of only 20,000 or less. The copolymer tacticities and comonomer sequences were determined by 13C NMR spectroscopy.