Small angle x-ray scattering experiments on three model low molar mass diblock copolymer systems containing minority polylactide and majority hydrocarbon blocks demonstrate that conformational asymmetry stabilizes the Frank-Kasper σ phase. Differences in block flexibility compete with space filling at constant density inducing the formation of polyhedral shaped particles that assemble into this low symmetry ordered state with local tetrahedral coordination. These results confirm predictions from self-consistent field theory that establish the origins of symmetry breaking in the ordering of block polymer melts subjected to compositional and conformational asymmetry.

Dynamic covalent networks comprised of tunable thia-Michael bonds result in phase separated networks with tailorable mechanical and adaptive properties.

Polymer-grafted nanoparticle (PGN) films were prepared from polystyrene (PS) grafted to rodlike cellulose nanocrystals (MxG-CNC-g-PS) with a controllable grafting density (0.03−0.25 chains/nm 2 ) and molecular weight (5−60 kg/mol). These nanorod-based PGNs are solution-and melt-processible, permitting access to one-component composite films with high nanofiller loadings (with up to 55 wt %). The impact of both grafted polymer density and molecular weight on the mechanical properties of the films was investigated and related to the polymer brush conformation: concentrated polymer brush (CPB), semidilute polymer brush (SDPB), or CPB core with SDPB corona (CPB/ SDPB). The rubbery regime storage modulus (above T g ) showed 2 orders of magnitude increase, maximizing at a low degree of polymerization (N) and low grafting density (σ). Fracture toughness was maximized in samples with the grafted polymer in the SDPB or CPD/SDPB (higher N and relatively low σ) regime and showed enhancement relative to PS of molecular weight similar to the graft. In line with prior computation predictions, optimizing for both rubbery modulus and fracture toughness in such nanorodbased PGN films requires the polymers in the SDPB regime and CNC loading levels (ca. 50−60 wt %) that are difficult to attain in more traditional two-component CNC composites.

Mechanically robust, thermoresponsive, ion-conducting nanocomposite films are prepared from poly­(2-phenylethyl methacrylate)-grafted cellulose nanocrystals ( MxG -CNC- g -PPMA). One-component nanocomposite films of the polymer-grafted nanoparticle (PGN) MxG -CNC- g -PPMA are imbibed with 30 wt % imidazolium-based ionic liquid to produce flexible ion-conducting films. These films with 1-hexyl-3-methylimidazolium bis­(trifluoromethylsulfonyl)­imide ( MxG -CNC-g-PPMA/[H]) not only display remarkable improvements in toughness (>25 times) and tensile strength (>70 times) relative to the corresponding films consisting of the ionic liquid imbibed in the two-component CNC/PPMA nanocomposite but also show higher ionic conductivity than the corresponding neat PPMA with the same weight percent of ionic liquid. Notably, the one-component film containing 1-ethyl-3-methylimidazolium bis­(trifluoromethylsulfonyl)­imide ( MxG-CNC-g-PPMA/[E]) exhibits temperature-responsive ionic conduction. The ionic conductivity decreases at around 60 °C as a consequence of the lower critical solution temperature phase transition of the grafted polymer in the ionic liquid, which leads to phase separation. Moreover, holding the MxG -CNC- g -PPMA/[E] film at room temperature for 24 h returns the film to its original homogenous state. These materials exhibit properties relevant to thermal cutoff safety devices (e.g., thermal fuse) where a reduction in conductivity above a critical temperature is needed.