Synthesis and characterization of a novel rac-PHB derivative containing α-malate units

The ring-opening copolymerization of [RS]-β-butyrolactone (βBL) and 3-(S)-[(benzyloxycarbonyl)methyl]-1,4-dioxane-2,5-dione (BMD) was conducted in the bulk at relatively low BMD/ BL ratios with a distannoxane as the catalyst. The resulting copolymer was a terpolymer consisting of 3-hydroxybutyrate (3HB), glycolate (G), and benzyl-L-α-malate (M) repeating units, with a copolymer composition being almost identical to the monomer feed ratio. It was then subjected to hydrogenolysis at atmospheric pressure in the presence of a palladium on charcoal catalyst to remove the pendant benzyl group of the M unit quantitatively. The deprotected copolymer, having carboxyl functionalities as pendants, was reacted with 1,4-dibromobutane for its crosslinking through the pendant carboxyl group of the malate units. These results revealed that this malate-containing [RS]-PHB has high potential for use as biodegradable elastomer that can be crosslinkable.