Proof of a disentanglement process of aliphatic polyesters via transesterification by evaluation of the growth rate of spherulites

In order to proof the existence of a disentangling pathway of condensation polymers via transesterification, we measured the growth rate of spherulites (G) of poly(L-lactic acid) (PLLA) and poly(e-caprolactone) (PCL) as a function of melt annealing time (At) before isothermal crystallization. We prepared three PLLA samples by means of reaction induced crystallization of oligomers during polymerization. For the sample with unclear crystal habit, we found that G was almost constant at δt < 30 min, and then monotonically decreased with increasing δt. On the other hand, for the sample with clear crystal habit, we found that G monotonically decreased with increasing δt. For PCL prepared by bulk polymerization, we found that G shows a plateau at δt < 30 min for the samples with a melt annealing temperature of r _max= 100 and 130°C. However, it was found that G monotonically decreased at T _max= S0°C. From GPC measurements of PLLA and PCL after melt annealing, we confirmed that the molecular weight did not change and molecular weight distribution became broad. These imply that PLLA and PCL have a pathway of disentanglement within the melt via transesterification.