title: Formation of flower- or cake-shaped stereocomplex particles from the stereo multiblock copoly(rac-lactide)s.
abstract: Flower- or cake-shaped particles with uniform particle size ranging from nanometers to micrometers were prepared from the stereo multiblock copoly(rac-lactide)s (smb-PLAs) by precipitating the polymer from its solution in methylene chloride/ethanol via three different methods: slowly lowering the solution temperature, slowly evaporating the solvent, and slowly adding a nonsolvent. Under the same condition, sheet-shaped crystals in 10 mum size but not particles were obtained from the pure PLLA with almost the same molecular weight. Electron diffraction and WAXD data demonstrated that the stereocomplex particles belonged to the monoclinic system. All three methods resulted in particles with identical morphology and almost the same particle size. At a given stereoregularity of 88%, as the molecular weight of the polymer increased from 8700 to 23,200 Da, the crystallinity decreased, the particle morphology changed from flower-shaped to cake-shaped, and the diameter and height of the particles increased from 0.8 and 0.45 to 3.6 microm and 2.0 microm, respectively. The initial concentration of the polymer solution influenced the particle size slightly but affected the morphology markedly. On the basis of the above experimental observations, it was proposed that the smb-PLA particles of flower- or cake-shape were formed in four steps: (1) complexation in solution of the smb-PLA chains; (2) particle nucleation; (3) particle growth in the width direction; and (4) particle growth in the height direction. The curvature of the paired smb-PLA chains and the inner stress governed the particle size, and the interconnection between the neighboring particles determined the layered structure and the package density of the particles formed.
authors.affiliation: State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, China.
authors.forename: Junli
authors.initials: J
authors.lastname: Hu
authors.forename: Zhaohui
authors.initials: Z
authors.lastname: Tang
authors.forename: Xueyu
authors.initials: X
authors.lastname: Qiu
authors.forename: Xuan
authors.initials: X
authors.lastname: Pang
authors.forename: Yongkun
authors.initials: Y
authors.lastname: Yang
authors.forename: Xuesi
authors.initials: X
authors.lastname: Chen
authors.forename: Xiabin
authors.initials: X
authors.lastname: Jing
mesh_terms: D001704:Biopolymers / Q000737:chemistry*; D002152:Calorimetry, Differential Scanning; D016503:Drug Delivery Systems; D004583:Electrons; D000431:Ethanol / Q000737:chemistry; D019344:Lactic Acid / Q000737:chemistry; D046911:Macromolecular Substances / Q000737:chemistry; D008752:Methylene Chloride / Q000737:chemistry; D008863:Microspheres; D008956:Models, Chemical; D008970:Molecular Weight; D049329:Nanostructures; D036103:Nanotechnology / Q000379:methods*; D010316:Particle Size; D011091:Polyesters / Q000737:chemistry*; D011100:Polyglycolic Acid / Q000737:chemistry; D011108:Polymers / Q000737:chemistry; D012997:Solvents / Q000737:chemistry; D013237:Stereoisomerism; D013696:Temperature; D013997:Time Factors; D014961:X-Ray Diffraction
chemical_list: D001704:Biopolymers; D046911:Macromolecular Substances; D011091:Polyesters; D011108:Polymers; D012997:Solvents; D011100:Polyglycolic Acid; D019344:Lactic Acid; D000431:Ethanol; C033616:poly(lactide); D008752:Methylene Chloride