Chemical synthesis of poly(β-hydroxybutyrate) by the polymerization of (R,S)-β-butyrolactone with aluminoxane catalysts

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Abstract
Racemic β-butyrolactone can be polymerized to crystalline polymers of reasonably high molecular weight by the use of aluminoxane catalysts. Investigations in this and other laboratories have shown that these polymers can be fairly highly isotactic, and in that form they are closely related in structure and physical properties to a reserve polyester produced by many bacteria: poly(β-hydroxybutyrate). In the present investigation, Ziegler–Natta type aluminoxane catalyst systems and a new aluminoxane derivative, tert-butylaluminoxane, were evaluated in attempts to polymerize racemic β-butyrolactone in higher yields to polymers of higher molecular weight and higher stereoregularity. The addition of group 4 metallocenes as cocatalysts for both methylaluminoxane and iso-butylaluminoxane catalysts gave higher yields of the isotactic polymer than those obtained with these catalysts alone, but surprisingly, the tert-butylaluminoxane catalysts produced predominantly syndiotactic rather than isotactic polymers.Key words: poly(β-hydroxybutyrate), β-butyrolactone, aluminoxane catalysts, isotactic poly(β-hydroxybutyrate), syndiotactic poly(β-hydroxybutyrate).