Small-angle x-ray scattering experiments conducted with compositionally asymmetric low molar mass poly(isoprene)--poly(lactide) diblock copolymers reveal an extraordinary thermal history dependence. The development of distinct periodic crystalline or aperiodic quasicrystalline states depends on how specimens are cooled from the disordered state to temperatures below the order-disorder transition temperature. Whereas direct cooling leads to the formation of documented morphologies, rapidly quenched samples that are then heated from low temperature form the hexagonal C14 and cubic C15 Laves phases commonly found in metal alloys. Self-consistent mean-field theory calculations show that these, and other associated Frank-Kasper phases, have nearly degenerate free energies, suggesting that processing history drives the material into long-lived metastable states defined by self-assembled particles with discrete populations of volumes and polyhedral shapes.

The primary challenge in solid-state polymer electrolyte membranes (PEMs) is to enhance properties, such as modulus, toughness, and high temperature stability, without sacrificing ionic conductivity. We report a remarkably facile one-pot synthetic strategy based on polymerization-induced phase separation (PIPS) to generate nanostructured PEMs that exhibit an unprecedented combination of high modulus and ionic conductivity. Simple heating of a poly(ethylene oxide) macromolecular chain transfer agent dissolved in a mixture of ionic liquid, styrene and divinylbenzene, leads to a bicontinuous PEM comprising interpenetrating nanodomains of highly cross-linked polystyrene and poly(ethylene oxide)/ionic liquid. Ionic conductivities higher than the 1 mS/cm benchmark were achieved in samples with an elastic modulus approaching 1 GPa at room temperature. Crucially, these samples are robust solids above 100 °C, where the conductivity is significantly higher. This strategy holds tremendous potential to advance lithium-ion battery technology by enabling the use of lithium metal anodes or to serve as membranes in high-temperature fuel cells.

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.

Using the synthetic approach of polymerization-induced microphase separation (PIMS), we prepared cocontinuous and cross-linked nanostructured monoliths from bulk polymerizations of styrene and divinylbenzene (DVB) in the presence of polylactide macro-chain-transfer agents (PLA-CTAs). The resulting monolithic precursors were converted to cross-linked mesoporous materials following hydrolytic degradation of the PLA domain, the morphology and porosity of which were characterized through a combination of small-angle X-ray scattering, scanning electron microscopy, and nitrogen sorption experiments. This report highlights the concept, functionality, and limitations of PIMS for the generation of mesoporous materials through variation of reaction parameters found to strongly influence the porous properties of the matrix: the cross-linker-to-monomer ratio, reaction temperature, molar mass and mass fraction of PLA-CTA, and the reactivity of the DVB isomer. Increases in the cross-linker-to-monomer ratio (≥40 mol % DVB) induced formation of smaller mesopores within the matrix in addition to the principal pore mode largely defined by the molar mass and mass fraction of the PLA-CTA. Higher reaction temperatures and the increased relative reactivity of the p-DVB isomer are shown to influence the matrix integrity, ultimately achieving surface areas as high as 796 m2 g–1 using 8 kg mol–1 PLA-CTA. In combination, these parameters suggest methods to circumvent limitations of pore collapse associated with concomitant reductions in the molar mass of PLA-CTA.

Polymer electrolytes are alternatives to liquid electrolytes traditionally used in electrochemical devices such as lithium-ion batteries and fuel cells. In particular, block polymer electrolytes are promising candidates because they self-assemble into well-defined microstructures, in which orthogonal properties can be integrated into a single material (e.g., high modulus in domain A, fast ion transport in domain B). However, the performance of block polymer electrolytes often falls short, due to the lack of long-range continuity of both domains and relatively low strength. We recently reported a simple, one-pot synthetic strategy to prepare polymer electrolytes with the highest reported combination of modulus and ionic conductivity, attributes enabled by a co-continuous, cross-linked network morphology. In this work we aim to understand the mechanism by which this nanoscale morphology is formed by performing a series of in situ, time-resolved experimentssmall-angle X-ray scattering, conductivity, rheology, and reaction kineticsto monitor the electrolyte as it transitions from a macroscopically homogeneous liquid to a microphase-separated solid. The results suggest that the chain connectivity of the diblock gives rise to isotropic concentration fluctuations that increase in amplitude and coherence such that the network morphology is ultimately produced. The kinetic trapping of this network morphology by chemical cross-linking prior to the ordering transition is shown to be critically important to the resulting advantageous bulk electrolyte properties.