Distribution of Phenols in Thermoresponsive Hydrogels

Temperature-driven self-assembly of self-limiting uniform supraparticles from non-uniform unimolecular micelles

In this work, the self-assembly of non-uniform unimolecular micelles constituted of a hyperbranched polyester core decorated with a corona of thermoresponsive poly(N-isopropylacrylamide) (PNIPAm) chains has been studied. As revealed by dynamic light scattering (DLS), transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS), these unimicelles form uniform supraparticles through a thermally-induced self-limited process, as well as exhibit molecular features commonly observed in PNIPAm-based gels. We believe that these results provide new insights into the application of stimuli-responsive polymeric materials as versatile building blocks to build up soft supraparticles displaying well-defined dimensional characteristics.

Phase transition behaviors of poly(N-isopropylacrylamide) microgels induced by tannic acid

Effects of tannic acid (TA) on the phase transition behaviors of monodisperse poly(N-isopropylacrylamide) (PNIPAM) microgels in aqueous solutions are systematically investigated. Monodisperse PNIPAM microgels are prepared through a microfluidic approach. The isothermal phase transition behaviors of PNIPAM microgels induced by TA in aqueous solutions are studied at 25 degrees C. The results show that there exist significant isothermal phase transition phenomena for PNIPAM microgels induced by TA, and the dynamic phase transition rate and the equilibrium shrinking degree of PNIPAM microgels in TA solutions are dependent on the TA concentration. The higher the TA concentration, the faster the isothermal shrinking rate of PNIPAM microgels induced by TA. There exists a critical TA concentration for the isothermal phase transition behavior, below which the equilibrium shrinking degree of PNIPAM microgels becomes larger with increasing the TA concentration, while above which the equilibrium shrinking degrees of PNIPAM microgels remain almost the same. The adsorption of TA molecules to PNIPAM polymer networks leads to slight shift of the low critical solution temperature to higher temperatures when the TA concentration in solution is lower than 10(-5) mol/L.

Bioresorbable and nonresorbable macroporous thermosensitive hydrogels prepared by cryopolymerization. Role of the cross-linking agent

Macroporous poly( N-isopropylacrylamide) (pNIPA) gels (so-called cryogels), cross-linked with different bis-acrylic compounds, N,N'-methylenebisacrylamide (MBAAm) and dimethacrylate-tyrosine-lysine-tyrosine (DMTLT), were prepared through free-radical polymerization at subzero temperature in dioxane/water media. DMTLT is a hydrolytically degradable cross-linker with relatively hydrophobic character. The effects of different synthesis conditions, namely the concentration of monomers, the cross-linker, and the initiator in the reaction mixture, on the structure of the pNIPA-cryogels have been studied. The equilibrium swelling ratio of the DMTLT cross-linked pNIPA cryogels at temperatures below lower critical solution temperature (LCST) of pNIPA, was over ten times higher than that of the gels synthesized at room temperature from the same feed composition. The MBAAm cross-linked pNIPA cryogels synthesized in water exhibited the highest equilibrium swelling and the fastest response. The critical transition temperature, T c, was lower ( T c approximately 31 degrees C) for pNIPA-cryogels synthesized in dioxane/water media or cross-linked with DMTLT as compared to MBAAm cross-linked pNIPA cryogels synthesized in water (T c approximately 33 degrees C). Scanning electron microscopy (SEM) revealed different porous structure and pore surface morphology depending on the cross-linker (MBAAm or DMTLT) and the solvent (water or dioxane/water) used. Gels and cryogels were also characterized by SAXS, showing that the nanostructure of the samples is related to swelling.