A series of dendronized polymers carrying oligo(ethyleneoxy) peripheral branches have been prepared by postpolymerization functionalization of multiallylic dendronized polymers using a radical addition of mercaptans, namely 2-methoxy(ethoxy)ethanethiol (EO2) and {2-(2-methoxyethoxy)ethoxy)}ethanethiol (EO3). The functionalization proved to be quite efficient, leading to up to 6 or 9 EO chains per monomer repeating unit. A constant T g value was observed independently of the material characteristics, indicating that T g is ruled by the sole presence of EO chains. According to the hydrophilic and hydrophobic balance, some polymers exhibited a thermoresponsive behavior in water solution, characterized by a sharp lower critical solution temperature (LCST) transition and a small hysteresis. These LCST showed an unusual increase with DP, which might be correlated to a dilution effect and an increase of polymer hydrophilicity by densification of the dendritic coverage. By SAXS investigations and using a spherocylinder shape model, the polymers in solution (below the LCST) could be satisfactorily described. By increasing the DP, the shape of the macromolecule was found to evolve from a spherical to a spherocylinder shape with a constant cross section of ca. 40 Å.

By employing rheological experiments, mode coupling theory, and computer simulations based on realistic coarse-grained models, we investigate the effects of small, hard colloids on the glassy states formed by large, soft colloids. Multiarm star polymers mimic hard and soft colloids by appropriately varying the number and size of their arms. The addition of hard colloids leads, depending on their concentration, to either melting of the soft glass or the emergence of two distinct glassy states. We explain our findings by depletion of the colloids adjacent to the stars, which leads to an arrested phase separation when the repulsive glass line meets the demixing binodal. The parameter-free agreement between experiment, theory, and simulations suggests the generic nature of our results and opens the route for designing soft-hard colloidal composites with tunable rheology.

We present extensive experimental and theoretical investigations on the structure, phase behavior, dynamics and rheology of model soft-hard colloidal mixtures realized with large, multiarm star polymers as the soft component and smaller, compact stars as the hard one. The number and length of the arms in star polymers control their softness, whereas the size ratio, the overall density and the composition are additional parameters varied for the mixtures. A coarse-grained theoretical strategy is employed to predict the structure of the systems as well as their ergodicity properties on the basis of mode coupling theory, for comparison with rheological measurements on the samples. We discovered that dynamically arrested star-polymer solutions recover their ergodicity upon addition of colloidal additives. At the same time the system displays demixing instability, and the binodal of the latter meets the glass line in a way that leads, upon addition of a sufficient amount of colloidal particles, to an arrested phase separation and reentrant solidification. We present evidence for a subsequent solid-to-solid transition well within the region of arrested phase separation, attributed to a hard-sphere-mixture type of glass, due to osmotic shrinkage of the stars at high colloidal particle concentrations. We systematically investigated the interplay of star functionality and size ratio with glass melting and demixing, and rationalized our findings by the depletion of the big stars due to the smaller colloids. This new depletion potential in which, contrary to the classic colloid-polymer case, the hard component depletes the soft one, has unique and novel characteristics and allows the calculation of phase diagrams for such mixtures. This work covers a broad range of soft-hard colloidal mixture compositions in which the soft component exceeds the hard one in size and provides general guidelines for controlling the properties of such complex mixtures.