Single crystals of the poly(l-lactide) (PLLA) block and the poly(ethylene glycol) (PEG) block in poly(l-lactide)−poly(ethylene glycol) diblock copolymer were obtained by melt crystallization. The morphology, structure, and evolution process of the single crystals were investigated using transmission electron microscopy (TEM), selected-area electron diffraction (SAED), and real-time atomic force microscopy (AFM). Two types of crystal morphology were obtained. One was the regular morphology of a single crystal:  lozenge-spiral dislocation, lozenge multilayer, and hexagonal (or truncated-lozenge) multilayer, which was layer-by-layer structure. The foregoing crystallization of the PLLA block determined the regular morphology of single crystal. The other type of crystal morphology was that the layer-dendritic crystal, which was affirmed to be the PEG crystal by real-time AFM, formed at the edge of the regular single crystal and grew along some certain directions on the crystal surface of the PLLA block. The forming of layer-dendritic crystal was through the reorganization of metastable phase crystal of the PEG block. The SAED results indicated that the (001) plane of the PLLA crystal was parallel to the (10−4) plane of the PEG crystal and the substrate. The foregoing crystallization of the PLLA block had an effect on the crystal orientation of the PEG block.

The confined crystallization behavior, melting behavior, and nonisothermal crystallization kinetics of the poly(ethylene glycol) block (PEG) in poly(L-lactide)poly(ethylene glycol) (PLLA-PEG) diblock copolymers were investigated with wideangle X-ray diffraction and differential scanning calorimetry. The analysis showed that the nonisothermal crystallization behavior changed from fitting the Ozawa equation and the Avrami equation modified by Jeziorny to deviating from them with the molecular weight of the poly(L-lactide) (PLLA) block increasing. This resulted from the gradual strengthening of the confined effect, which was imposed by the crystallization of the PLLA block. The nucleation mechanism of the PEG block of PLLA15000-PEG5000 at a larger degree of supercooling was different from that of PLLA2500-PEG5000, PLLA5000-PEG5000, and PEG5000 (the numbers after PEG and PLLA denote the molecular weights of the PEG and PLLA blocks, respectively). They were homogeneous nucleation and heterogeneous nucleation, respectively. The PLLA block bonded chemically with the PEG block and increased the crystallization activation energy, but it provided nucleating sites for the crystallization of the PEG block, and the crystallization rate rose when it was heterogeneous nucleation. The number of melting peaks was three and one for the PEG homopolymer and the PEG block of the diblock copolymers, respectively. V V C 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: [3215][3216][3217][3218][3219][3220][3221][3222][3223][3224][3225][3226] 2006