This review focuses on the factors that determine the molecular weight of polyhydroxyalkanoate (PHA), an aliphatic polyester synthesized by bacteria for carbon and energy storage. Because the mechanical strength of PHA increases with its molecular weight, high-molecular weight PHA polymers are preferred. The synthesis of high-molecular weight PHA should consider the following factors: the concentration of PHA synthase, occurrence of chain transfer reaction, catalytic activity of PHA synthase and simultaneous degradation of PHA during biosynthesis. These factors have a direct impact on the molecular weight of PHA.
