Polyhydroxyalkanoates (PHAs) are bio-based polyesters synthesized by
bacteria as an intracellular storage material. PHAs can be produced from renewable
biomass without using fossil resources, and thus are environmentally friendly plastics.
The most common PHA, poly[(R)-3-hydroxybutyrate] [PHB or P(3HB)], can be
synthesized in large quantities by bacterial fermentation, but has rigid and brittle
properties. Therefore, attempts have been made to improve its material properties. This
chapter focuses on the recent progress in improving two types of PHA, 3HB-based
copolymers and unusual PHA homopolymers, which show improved material
properties and/or cannot be synthesized in nature. 3HB-based copolymers, that not only
includes 3-hydroxyvalerate, 3-hydroxyhexanoate, and long chain 3-hydroxyalkanoatecontaining
copolymers, but also 3-hydroxy-4-methylvalerate, 3-hydroxy-
3-phenylpropionate, 3-hydroxy-2-methylbutyrate, and lactate-containing copolymers
have been reviewed. Additionally, ultrahigh-molecular-weight PHB and mediumchain-
length PHA homopolymers are highlighted as unusual homopolymers. These
polymers have notable characteristics and are expected to expand the range of PHA
applications.
Keywords: Aromatic building blocks, Branched building blocks, Copolymer,
Copolymerization, Homopolymer, Metabolic pathway, Molecular weight, Poly(3-
hydroxybutyrate-co-3-hydroxyhexanoate) P(3HB-co-3HHx), Ultrahigh-molecular
weight.
