“Smart” polyesters for nanoparticles synthesis and stabilization
Advancing the chemical engineering fundamentals
Particulate Systems (T2-3)
Keywords: invertible polyesters, nanoparticles, stabilization
Respond and conform to local changes in pH, temperature and solvent quality are well known for flexible polymer chains. Surface modification with polymers which provides possibilities for control and change of surface compositions thus allowing for demanded properties is significant for practical applications. Amphiphilic block copolymers recently gained a great interest, for example for biomedical applications. We synthesized a new class of amphiphilic polyesters forming stimuli responsive architectures. They offer adaptive properties, do not require a complex multistep synthesis and are accessible on larger scale. These polyesters are soluble in aqueous and organic media where they reveal inverse behaviour which could be correlated to their chemical structure. Polymers with such properties can find use in applications such as stimuli-responsive release, stabilization of colloidal nanoparticles and nanoreactors for the nanoparticles synthesis.
We developed and characterized the invertible polyesters based on poly(ethylene glycol) (PEG) of various molecular weights and aliphatic dicarboxylic acids. Obtained copolymers have been synthesized via polycondensation in solution. We believe that the possibility of conformational switching for polyester architectures can be reached with a controllable presence of oxygen atoms in a polymers main backbone. Our structural hypothesis suggests that the hydrophilic PEG and the hydrophobic aliphatic acid residues can change the polymeric micelle architecture in solvents of different polarities.
As it has been shown, the amphiphilic polyesters are able to form invertible architectures in media differing by polarity. These polymer architectures have been employed as nanoreactors for the synthesis of noble metal colloids (silver, gold, and palladium). The amphiphilic polyester architectures, which have hydrodynamic radii in toluene between 14 ± 1.4 and 18 ± 1.2 nm, possess a hydrophilic interior and a hydrophobic shell. Dispersed in organic solvents such as toluene or benzene, it has been achieved to transfer hydrophilic metal precursors through the solvent into the nanoreactors by liquid–liquid phase transfer. The precursors trapped into polymeric nanoreactors and are reduced by their hydrophilic poly(ethylene glycol) blocks. Nanoparticles stabilization occurs due to presence of hydrophobic (polymethylene) fragments outside of the micelle structure. Subsequently, reduction of the metal precursor led to the formation of 8 – 20 nm sized metal colloids stable both in a polar and nonpolar medium.
A new approach to building up self-adjustable invertible polyester coatings at solid surfaces was proposed recently. It was based on the functionalization of the solid surface with the reactive anchor copolymer poly(styrene-alt-maleic anhydride) due to the physical adsorption and on grafting the chains of developed amphiphilic polyester to the modified solid surface through a reaction between the functional groups of the anchor and the polyester. An essential increase in colloidal stability has been observed for the titania particles after their modification with the invertible polyester chains. Redispersion cycles show the ability of the modified titanium dioxide particles to be redispersed in media differing in polarity from the previous medium.
Presented Monday 17, 16:20 to 16:40, in session Particulate Systems (T2-3).
