Lactic acids melt/solid polycondensation

Moon, S. I., Lee, C. W., Taniguchi, I., Mi5 moto, M., Kimura, Y. Melt/ solid polycondensation of L-lactic acid An alternative route to poly(L-lactic acid) with high molecular weight. Polvm. Commun.. 2001,42, 5059-5062. 

S.l. Moon, I. Taniguchi, M. Miyamoto, Y. Kimura, C.W. Lee, Synthesis and properties of high-molecular-weight poly (L-lactic acid) by melt/solid polycondensation under different reaction conditions. High Perform. Polym. 13 (2) (2001) S189-S196. 

Moreover, the molecular weight remained around 100 000 Da, being much lower than that of the PLLA obtained by the ring-opening polymerization of Z-lactide. Therefore, they examined the melt/solid polycondensation of lactic acid in which the melt polycondensation of Z,-lactic acid was subjected to solid-state polycondensation below Tm of PLLA [8]. In solid state, the polymerization reaction can be favored over the depolymerization or other side reactions. Particularly, in the process of crystallization of the resultant polymer, both monomer and catalyst can be segregated and concentrated in the noncrystalline part to allow the polymer formation to reach 100% [9]. Figure 3.2 shows the whole process of this melt/solid polycondensation of Z-lactic acid. In this process, a polycondensation with a molecular weight of 20 000 Da is first prepared by... 

Figure 3.2 The whole process of the melt/solid polycondensation of L-lactic acid...

The concentration of the remaining monomer decreases to zero at 120 and 140 °C where the polymerization systems turn to solid state, whereas at 160 °C the monomer consumption reaches a plateau with the melt-state retained. The same technique is utilized to increase the molecular weight of PLA in the solid-state polycondensation of lactic acid vide infra). 

The synthesis of high-molar-mass PLA and PGA by two-step polycondensations of lactic and glycolic acids, respectively, has recently been reported.374,375 It involves the formation of a low-molar-mass oligomer followed by a polycondensation step either in the solid state374 or in the melt under vacuum.375 The procedures are detailed in Section 2.4.1.5.2. 

---