Compositions of P4HB and processes to injection mold these compositions have been developed. These compositions are prepared from P4HB polymers and blends having intrinsic viscosities less than 3.2 dl/g but greater than 0.8 dl/g, moisture contents of less than 0.5% by weight, and more preferably less than 0.05% by weight, and using a polymer melt temperature during molding of at least 150° C. A preferred embodiment comprises a P4HB molding with an intrinsic viscosity of less than 3.2 dl/g that degrades rapidly in vivo.