Separation of poly(ethylene glycols) into fractions by sequential liquid–liquid extraction

PLA-PEG forming worm-like nanoparticles despite unfavorable packing parameter: Formation mechanism, thermal stability and potential for cell internalization

Most nanoparticles produced for drug delivery purposes are spherical. However, the literature suggests that elongated particles are advantageous, notably in terms of cellular uptake. Thus, we synthesized biocompatible polylactide-b-poly(ethylene glycol) (PLA-PEG) polymers bearing carboxylate moieties, and used them to formulate worm-like nanoparticles by a simple emulsion-evaporation process. Worm-like nanoparticles with variable aspect ratio were obtained by simply adjusting the molar mass of the PLA block: the shorter the molar mass of the PLA block, the more elongated the particles. As PLA molar mass decreased from 80,000 g/mol to 13,000 g/mol, the proportion of worm-like nanoparticles increased from 0 to 46%, in contradiction with the usual behavior of block polymers based on their packing parameter. To explain this unusual phenomenon, we hypothesized the shape arises from a combination of steric and electrostatic repulsions between PEG chains bearing a carboxylate moiety present at the dichloromethane-water interface during the evaporation process. Worm-like particles turned out to be unstable when incubated at 37 °C, above polymer glass transition temperature. Indeed, above Tg, a Plateau-Rayleigh instability occurs, leading to the division of the worm-like particles into spheres. However, this instability was slow enough to assess worm-like particles uptake by murine macrophages. A slight but significant increase of internalization was observed for worm-like particles, compared to their spherical counterparts, confirming the interest of developing biocompatible anisotropic nanoparticles for pharmaceutical applications such as drug delivery.

Aerobic biodegradation of alkylphenol ethoxylates

Primary aerobic biodegradation of alkylphenol ethoxylates (APEOs) was studied using a new simple and fast porphyrin method, which did not require the extraction step. Extent of primary biodegradation of a nonylphenol ethoxylates (NP-10) was excess of 92% after 1.5 days, and reached 99% after 2 days, which was similar to the results obtained using modified CTAS (thiocyanate active substances) method. Degradation of benzene ring of NP-10 was studied using UV-absorbance at 277 nm in chloroform. Results showed that only little of benzene ring was degraded.

Interfacial properties of adsorbed films made of a PEG2000 and PLA50 mixture or a copolymer at the dichloromethane–water interface

Adsorption kinetics of films of poly(ethylene glycol) (PEG2000) studied by the dynamic pendant drop method showed that PEG2000 was more tensioactive at the dichloromethane (DCM)-water interface than at the air-water interface. When initially solubilized into DCM, PEG2000 segments would form an adsorbed layer with hydrophobic segments buried into the polymer chains turned toward the organic phase. Compression of this layer, accompanied by viscoelastic effects, led to expulsion of some hydrophilic tails toward the water phase. When initially dissolved in water, adsorption of PEG2000 segments led to an elastic PEG2000 layer organized on both sides of the interface. Results showed that when the PEG2000-PLA50 (poly(D,L-lactide)) copolymer film was adsorbed at the DCM-water interface, it resulted in a mixed layer exclusively turned toward DCM and its rheological properties were governed by PLA50. When adsorption at the DCM-water interface resulted from a physical mixture of PEG2000 and PLA50, rheological properties of the film were influenced by the initial localization of PEG2000 in the bulk phases. In the case of a mixed film formed by the adsorption of PLA50 from DCM and PEG2000 from water, results showed that PEG2000 segments totally pushed those of PLA50 away from the interface and exclusively influenced the behavior of the mixed film.