The effect of crystallization on the solid state polycondensation of poly(L-lactic acid)

Melt solid polycondensation is an approach to increase the molecular weight of poly (L-lactic acid) (PLLA). For this report, the effect of crystallization time of PLLA prepolymer on the molecular weight of the biomaterial was studied. In this process, PLLA prepolymer with a molecular weight of 18,000 was first prepared by the ordinary melt-polycondensation process. The prepolymer was crystallized at 105 degrees C for various times, and then heated at 135 degrees C for 15-50 h for further solid state polycondensation (SSP). The differential scanning calorimetry (DSC) and viscosity measurements were used to characterize the crystalline properties and molecular weight of the resulting PLLA polymers, respectively. The results showed that the molecular weight of PLLA reached a maximum value under the condition of a crystallization time of 30 min and SSP of 35 h.