I Barakat

Stereocomplexation of polylactide enhanced by poly(methyl methacrylate): improved processability and thermomechanical properties of stereocomplexable polylactide-based materials.

Stereocomplexable polylactides (PLAs) with improved processability and thermomechanical properties have been prepared by one-step melt blending of high-molecular-weight poly(l-lactide) (PLLA), poly(d-lactide) (PDLA), and poly(methyl methacrylate) (PMMA). Crystallization of PLA stereocomplexes occurred during cooling from the melt, and, surprisingly, PMMA enhanced the amount of stereocomplex formation, especially with the addition of 30-40 % PMMA. The prepared ternary blends were found to be miscible, and such miscibility is likely a key factor to the role of PMMA in enhancing stereocomplexation. In addition, the incorporation of PMMA during compounding substantially raised the melt viscosity at 230 °C. Therefore, to some extent, the use of PMMA could also overcome processing difficulties associated with low viscosities of stereocomplexable PLA-based materials. Semicrystalline miscible blends with good transparency were recovered after injection molding, and in a first approach, the thermomechanical properties could be tuned by the PMMA content. Superior storage modulus and thermal resistance to deformation were thereby found for semicrystalline ternary blends compared to binary PLLA/PMMA blends. The amount of PLA stereocomplexes could be significantly increased with an additional thermal treatment, without compromising transparency. This could result in a remarkable thermal resistance to deformation at much higher temperatures than with conventional PLA. Consequently, stereocomplex crystallization into miscible PLLA/PDLA/PMMA blends represents a relevant approach to developing transparent, heat-resistant, and partly biobased polymers using conventional injection-molding processes.

Macromolecular engineering of polylactones and polylactides. XXV. Synthesis and characterization of bioerodible amphiphilic networks and their use as controlled drug delivery systems

Well-defined α,ω-methacryloyl poly-e-caprolactone (PCL) and poly(d,l)-lactide P(D,L)LA dimacromonomers have been synthesized by living ring-opening polymerization of the parent monomers initiated by diethylaluminum 2-hydroxyethylmethacrylate (Et2AlO(CH2)2OC(O)C(CH3)CH2) and terminated by reaction of the propagating Al alkoxide groups with methacryloyl chloride. These dimacromonomers have been copolymerized with a hydrophilic comonomer, i.e., 2-hydroxyethylmethacrylate, in bulk at 65°C by using benzoyl peroxide as a free-radical initiator. The swelling ability of the amphiphilic PHEMA/PCL or P(D,L)LA networks has been investigated in both aqueous and organic media. Effect of network composition and molecular weight of the dimacromonomer on the swelling kinetics and the equilibrium solvent uptake has been studied. Lipophilic dexamethasone acetate and the hydrophilic sodium phosphate counterpart have been incorporated into the amphiphilic gels and their release has been studied in relation to the gel characteristics.

Poly(?-caprolactone-b-glycolide) and poly(D,L-lactide-b-glycolide) diblock copolyesters: Controlled synthesis, characterization, and colloidal dispersions

Living ω-aluminum alkoxide poly-ϵ-caprolactone and poly-D,L-lactide chains were synthesized by the ring-opening polymerization of ϵ-caprolactone (ϵ-CL) and D,L-lactide (D,L-LA), respectively, and were used as macroinitiators for glycolide (GA) polymerization in tetrahydrofuran at 40 °C. The P(CL-b-GA) and P(LA-b-GA) diblock copolymers that formed were fractionated by the use of a selective solvent for each block and were characterized by 1H NMR spectroscopy and differential scanning calorimetry analysis. The livingness of the operative coordination–insertion mechanism is responsible for the control of the copolyester composition, the length of the blocks, and, ultimately, the thermal behavior. Because of the inherent insolubility of the polyglycolide blocks, microphase separation occurs during the course of the sequential polymerization, resulting in a stable, colloidal, nonaqueous copolymer dispersion, as confirmed by photon correlation spectroscopy.

SAXS analysis of the morphology of biocompatible and biodegradable poly(ε-caprolactone-b-glycolide) copolymers☆

Abstract Poly(e-caprolacrone-b-glycolide) diblock copolyesters have been synthesized by the sequential polymerization of e-caprolactone and glycolide as initiated by aluminium alkoxides. Copolymerization is typically “living” and yields copolyesters of perfectly controlled molecular weight and composition. Diblock molecular weight (MnPGA + MnPCL) ranges from 5700 to 42000 and the ϱ = Mn PCL Mn PGA ratio varies from 1.5 to 13.1. Due to the inherent insolubility of the polyglycolide (PGA) segment in common organic solvent, the diblock copolyesters form stable non-aqueous colloidal dispersions e.g., in toluene, the stability of which results from the soluble poly(e-caprolactone) (PCL) block. Combining all the experimental observations (PCS, TEM, WAXS, SAXS, AFM), a micelle model has been proposed which consists of a polyglycolide core surrounded with a corona of polycaprolactone (PCL). Both constituents are semi crystalline. From SAXS observations, the PGA core is better described by two concentric spheres. The internal sphere of a 5–6.7 nm diameter would essentially contain crystalline PGA. The diameter of the external sphere, DPGA, is in the range from 6.2 to 9.6 nm, at least for the investigated diblock copolymers. As a rule, this diameter increases as ϱ decreases at constant molecular weight and as the diblock molecular weight increases at constant ϱ. A scattering peak (weak) is observed in the range from 10.8 to 15.5 nm and the Bragg distance is close μDPGA, where μ is equal to (1+ 3 ϱ 2 ) 1 3 . From steric considerations, μ is the ratio between the diameter of the micelle and the diameter of the PGA core, so that this peak has been assigned to the characteristic intermicellar distance. At very small angles, several additional peaks are the signature of a hyperstructure which is possibly lamellar.

Synthesis of Oligo(butylene succinate)-based Polyurethanes

Biobased oligo(butylene succinate)-based thermoplastic polyurethanes (TPUs) were prepared following a two-step polymerization process: condensation of succinic acid and butanediol and the chain extension of resulting hydroxyl-terminated butylene succinate oligomers (OBS) in the presence of butanediol as chain extender and isophorone diisocyanate (IPDI) as coupling agent. Mechanical and thermal properties of the elaborated TPUs were evaluated in terms of hard segment and compared with those of commercial polybutylene succinate (PBS), Bionolle 1001. Whatever the compositions, the ultimate tensile properties of OBS-based TPUs and Bionolle 1001 were found to exhibit similar values (e ≈400%, σ ≈40 MPa), which can be explained by their close molecular weight (60000 g.mol-1 equiv. PS). Interestingly, a higher content of hard segments within OBS-based TPUs leads to materials exhibiting higher rigidity, smaller degree of crystallization, lower melting temperature and weaker stability of the materials with temperature. Such a trend was attributed to the presence of urethane functions and their ability to set up strong H-bonding interchain interactions.