The bacterium Pseudomonas oleovorans was utilized to produce a novel natural-synthetic hybrid block copolymer. This hybrid biomaterial consists of the natural hydrophobic polymer polyhydroxyoctanoate (PHO) end-capped with hydrophilic synthetic diethylene glycol (DEG). The addition of the synthetic component, in the form of PEG106, to the bioprocessing stage significantly affected polymer yield and properties compared to its non-hybridized counterpart. Compared to PHO polymer, the PHO-DEG hybrid possessed a significantly higher C8 component and reduced molecular mass. In contrast, thermal and crystalline properties were similar in both polymer types. While the molecular weight ratio of the natural and synthetic blocks is approximately 1000: 1, the small hydrophilic component exerted a powerful influence during polymer processing. Under conditions of high humidity, solvent cast films of the PHO-DEG hybrid self-assembled into ordered microporous arrays. Thus, a novel natural-synthetic hybrid comprized of biocompatible components has been produced. (c) 2005 Elsevier Ltd. All rights reserved.