In this study

a series of monodispersed poly(L-lactide) (PLLA) were synthesized by the ring-opening polymerization with Schiff base aluminum catalyst

and the effects of the number-average molecular weight (

M

n

) on the crystallization and melting behaviors of PLLA were investigated by differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD). The total crystallization rate of PLLA was

M

n

-dependent

which reached the maximum value for PLLA with

M

n

of 18.6 kg/mol. In addition

when

M

n

of PLLA was 18.6 kg/mol

the melting enthalpy (Δ

H

m

) showed a maximum value (87.1 J/g)

which was the highest reported value till now. The critical temperature for change of crystal formation from

δ

-form to

α

-form crystals increased in the isothermal crystallization process with

M

n

increasing. In the reheating procedure

high-

M

n

PLLA demonstrated a small exothermal peak prior to the dominant melting peak

corresponding to crystal transition from

δ

- to

α

-form

but low-

M

n

PLLA didn’t show the peak of crystal transition. These different crystallization and melting behaviors were attributed to the different chain mobility of PLLA with different

M

n

.