The melt rheol. behavior of two highly stereo irregular chain configurations of PLA is compared to stereo regular PLLA using small amplitude dynamic frequency response in parallel plate flow geometry.The degree of heterotactic bonds along the polymer backbone is related to changes in the critical mol. weight, entanglement mol. weight, plateau modulus, and characteristic ratio.The melt rheol. of PMLA was further characterized for temperature and frequency response.The mole fraction of syndiotactic lactic acid monomer transitions was estimated to be 0.01, 0.22, and 0.79 for PLLA, PRLA, and PMLA resp.The highly disrupted stereo configuration of PMLA led to a more flexible chain in the melt than PLLA, with PMLA C = 5.9 vs. that of PLLA where C = 7.5.PRLA exhibited chain flexibility behavior between that of PMLA and PLLA, with C = 6.9.The greater chain flexibility of PMLA in the melt resulted in lower flow activation energy temperature dependence, lower zero shear viscosity for a given mol. weight, and lower frequency at the onset of shear thinning than PLLA.The critical mol. weight and entanglement mol. weight of PMLA were estimated to be 1.75x and 2.05x that of PLLA.Plateau moduli of PMLA and PRLA were estimated from the crossover frequency using models of Wu and Nobile-Cocchini to enable direct comparison to PLLA and calculation of entanglement characteristics, packing length, and characteristic ratio.Frequency dependences of the dynamic moduli and complex viscosity were modeled using generalized Maxwell, Bird-Carreau, and Havriliak-Negami models.