Disclosed are polymeric compositions comprising polyhydroxyalkanoates. These compostions can comprise a blend comprising a polyhydroxyalkanoate (PHA) polymer, and a rubber polymer. The blend can comprise a biphasic mixture comprising a first phase comprising the PHA polymer, and a second phase comprising the rubber polymer dispersed with the first phase. The rubber polymer can be crosslinked, for example, through reaction with a free radical initiator. By incorporating the dynamically crosslinked rubber polymer, the polymer composition can exhibit one or more improved characteristics relative to PHA alone, including improved thermal stability, improved melt strength, improved flexibility, improved toughness, or a combination thereof. Also provided are articles formed at least in part from these polymeric compositions, as well as methods of making these polymeric compositions.