Poly(l,l-lactide) Microspheres by Ring-Opening Polymerization

Abstract

Poly(l,l-lactide) microspheres were synthesized directly during the ring-opening precipitation polymerizations of l,l-lactide. The polymerizations were carried out in heptane−1,4-dioxane (4:1 v/v) mixed solvent in the presence of various poly(dodecyl acrylate)-g-poly(ε-caprolactone) copolymers (poly(DA−CL)) used as surface active agents. Copolymers with different molecular weights, different average number of poly(ε-caprolactone) grafts per macromolecule, and different molecular weights of these grafts were used. Poly(l,l-lactide) microspheres with number-average diameters (D̄ n) from 2.46 to 4.07 μm and with polydispersity parameters (D̄ v/D̄ n, where D̄ v denotes the volume-average diameter) from 1.08 to 1.45 were obtained. The dependence of D̄ n and D̄ v/D̄ n on the structure and on the concentration of poly(DA−CL) was investigated. The narrow diameter polydispersity (D̄ v/D̄ n = 1.08) was obtained when poly(DA−CL), containing an average of 1.3 poly(ε-caprolactone) grafts (with M̄ n = 4700 g/mol) per copolymer macromolecule, was used at a concentration of 1.6 g/L, i.e., below the critical concentration of micellization of this surface active agent (ccm = 5.1 g/L). Poly(l,l-lactide) microspheres contained from 1.5 to 6.6 wt % of the unreacted lactide. The optical purity of monomer (95.4%) and of the corresponding polylactide from microspheres (from 91.0% to 94.9%) indicated that polymerization in the investigated heterogeneous system proceeds with retention of configuration on the chiral carbon atom. The DSC studies revealed that the crystallinity of the poly(l,l-lactide) microspheres was strongly dependent on the thermal history of these materials and on the concentration of the surface active agent used for the polymerization. Microspheres partly composed of crystalline and/or amorphous poly(l,l-lactide) were obtained.

Influence of melt processing conditions on poly(lactic acid) degradation: Molar mass distribution and crystallization

“…In the literature, the differential refractive index increment (dn/dc) of PLA was determined at 0.042 mL g À1 [28], 0.049 mL g À1 [29] and 0.0558 mL g À1 [30]. In the case of the studied PLA, it was obtained by determining the refractive index of six solutions at different concentrations of PLA in THF using the Optilab refractometer (laser wavelength: 658 nm).…”

Functionalization of Poly(divinylbenzene) Microspheres by Combination of Hydrobromination and Click Chemistry Processes: A Model Study

“…A number of methods including water-based emulsion, seeded suspension, non-aqueous dispersion polymerization and precipitation polymerization were successfully employed for preparation of such monodisperse microspheres [1][2][3][4]. Among them, precipitation polymerization, which can be performed in the absence of any added surfactant or stabilizer [5][6][7][8][9][10][11][12], appeared to be an attractive route to obtain microspheres with uniform size and shape. Typically, monodisperse and highly cross-linked poly(divinylbenzene) (PDVB) surfactantfree microspheres (with diameters between 2 and 5 µm) were prepared by us-512 B.…”

Biodegradable Polyesters for Tissue Engineering

“…At these conditions particles with D w /D n ¼ 1.03 were obtained. [39] It has been found also that addition of new monomer portions does not lead to formation of new particles but to an increase of size of the already existing ones. Increase of particle volume was proportional to amount of added monomer.…”