We investigated the linear viscoelasticity of bottlebrush polystyrenes (PSs) with total molar masses ranging from 132 to 769 kg/mol, bearing short side chains (with molar masses of 5 and 7 kg/mol, well below the entanglement limit of PS). Their estimated length to diameter ratio was smaller than 1, corresponding to a globular conformation and conforming to the molar mass dependence of the radii and to recent computer simulation results. The master curves were constructed by means of time− temperature superposition and featured a hierarchical relaxation (glassy, side-chain, intermediate, and terminal regimes) along with the absence of a rubbery plateau, indicating that the entire macromolecules behaved as unentangled polymers, though with some distinct features. The analysis of the dependence of storage and loss moduli on oscillatory frequency revealed cooperative side-chain dynamics at intermediate frequencies because of their mutual repulsion and Rouse-like dynamics at low frequencies. The zero-shear viscosity scaled with the total molar mass of the bottlebrush as η 0 ≈ M w,bottlebrush like Rouse chains; however, the respective dependence of the terminal flow time appeared to be stronger. The estimated values of the fragility index suggested that these unentangled bottlebrushes became stiffer with increasing length of the side chains but remained less stiff compared to linear PSs of the same total mass. These results are compared with and contrasted against bottlebrush data from the literature, suggesting universalities and distinct features likely attributed to chemical differences and calling for further investigations.

The negative environmental effects of conventional polymeric materials have intensified the research toward the production of biobased counterparts. Vanillic acid (VA), a vanillin oxidation product, is a relatively new and most promising aromatic monomer for the synthesis of biobased polyesters. In this work, the synthesis of a new, high molecular weight alipharomatic polyester, poly­(hexylene vanillate) (PHV), using 4-(6-hydroxyethoxy)-3-methoxybenzoic acid via a two-stage melt polycondensation method is reported. The success of the polymerization was confirmed using nuclear magnetic resonance spectroscopy (NMR) and Fourier-transformed infrared spectroscopy (FTIR), while the number-average molecular weight (Mn) was estimated by size-exclusion chromatography (SEC). Moreover, the thermal behavior of PHV was determined with differential scanning calorimetry (DSC), and insights on the thermal stability and degradation mechanism of PHV were given. The mechanical and thermomechanical properties of the synthesized material were investigated, revealing a thermoplastic elastomer behavior, with elastic recovery at room temperature, associated with the formation of a mesophase status. Finally, rheological tests were applied, indicating that PHV is easily processable and fully recoverable upon yielding and flow cessation.

Materials with increased mechanical strength and toughness bearing mussel-inspired iron–catechol complexes and network architectures exhibit several dynamic features, e.g., high and broad glass-“transition” temperature, not explored so far. By combining differential scanning calorimetry and dielectric spectroscopy, the latter as a function of temperature and pressure, we have explored the increase in the glass temperature, T g, and the concomitant increase in the breath of T g in bioinspired networks bearing one (covalent) or two (covalent and coordination) types of cross-links. Cross-linked networks experience heterogeneous segmental dynamics that are responsible for the broad T g range observed in the thermal measurements. The two distinct dynamics reflect the relaxation of segments in the vicinity versus more distant cross-linked units. The various topologies are shown to have different fragilities and tend to form stronger glasses with increasing network topology. In addition, the ionic conductivity is influenced by the segmental dynamics and the increased T g in the networks. These features (reduced specific heat step, Δc p, at T g and “strong” dynamic behavior) are also found in permanently cross-linked polymers with dynamic network topology known as vitrimers. The similarities in the two network systems are discussed.