Shear-Induced Lamellae Alignment in Matched Triblock and Pentablock Copolymers

Complete Photonic Band Gaps with Nonfrustrated ABC Bottlebrush Block Polymers

Bottlebrush block polymers are a promising platform for self-assembled photonic materials, yet most work has been limited to one-dimensional photonic crystals based on the lamellar phase. Here we demonstrate with simulation that nonfrustrated ABC bottlebrush block polymers can be used to self-assemble three-dimensional photonic crystals with complete photonic band gaps. To show this, we have developed a computational approach that couples self-consistent field theory (SCFT) simulations to Maxwell's equations, thereby permitting a direct link between molecular design, self-assembly, and photonic band structures. Using this approach, we calculate the phase diagram of nonfrustrated ABC bottlebrush block polymers and identify regions where the alternating gyroid and alternating diamond phases are stable. By computing the photonic band structures of these phases, we demonstrate that complete band gaps can be found in regions of thermodynamic stability, thereby suggesting a route to realize these photonic materials experimentally. Furthermore, we demonstrate that gap size depends on volume fraction, segregation strength, and polymer architecture, and we identify a design strategy based on symmetry breaking that can achieve band gaps for lower values of refractive index contrast. Taken together, the approach presented here provides a powerful and flexible tool for predicting both the self-assembly and photonic band structures of polymeric materials.

Synthetic approaches for multiblock copolymers

Multiblock copolymers (MBCs) are an emerging class of synthetic polymers that exhibit different macromolecular architectures and behaviours to those of homopolymers or di/triblock copolymers.

Influence of Composition Fluctuations on the Linear Viscoelastic Properties of Symmetric Diblock Copolymers near the Order-Disorder Transition

Rheological evidence of composition fluctuations in disordered diblock copolymers near the order-disorder transition (ODT) has been documented in the literature over the past three decades, characterized by a failure of time-temperature superposition (tTS) to reduce linear dynamic mechanical spectroscopy (DMS) data in the terminal viscoelastic regime to a temperature-independent form. However, for some materials, most notably poly(styrene-b-isoprene) (PS-PI), no signature of these rheological features has been found. We present small-angle X-ray scattering (SAXS) results on symmetric poly(cyclohexylethylene-b-ethylene) (PCHE-PE) diblock copolymers that confirm the presence of fluctuations in the disordered state and DMS measurements that also show no sign of the features ascribed to composition fluctuations. Assessment of DMS results published on five different diblock copolymer systems leads us to conclude that the effects of composition fluctuations can be masked by highly asymmetric block dynamics, thereby resolving a long-standing disagreement in the literature and reinforcing the importance of mechanical contrast in understanding the dynamics of ordered and disordered block polymers.

High-modulus, high-conductivity nanostructured polymer electrolyte membranes via polymerization-induced phase separation

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.

Diamino Telechelic Polybutadienes for Solventless Styrene-butadiene-styrene (SBS) Triblock Copolymer Formation

High molecular weight, high functionality diamino telechelic polybutadienes (TPBs) were synthesized by ring-opening metathesis polymerization (ROMP) of 1,5-cyclooctadiene (COD) in the presence of a chain transfer agent, 1,8-dicyano-4-octene, followed by lithium aluminum hydride reduction. Melt coupling of diamino TPB with anhydride-terminated polystyrene (PS-anh) resulted in the formation of styrene-butadiene-styrene (SBS) triblock copolymers; ca. 80% maximum conversion of PS-anh was achieved within 30 seconds. The results from SAXS, TEM, and rheological measurements of the coupling products confirmed the formation of SBS triblock copolymers having lamellar morphology. A fluororesent-labeled PS-anh was used to study the coupling kinetics by diluting the reactants by the addition of non-functional PS.