Abstract Prior work has shown that nanoparticle (NP) organization within the interlamellar regions of semicrystalline polymers can be achieved below a critical crystallization rate defined by an appropriate Péclet number, Pe = aG/D, where a is the characteristic NP transport distance, G is the crystal growth rate, and D is the NP diffusivity. NPs can redistribute ahead of the advancing crystallization front and become organized within the interlamellar regions with the most pronounced NP ordering occurring when Pe ≈ 1. We demonstrate, using small-angle X-ray scattering (SAXS) and electron microscopy, that the application of an external acoustic field increases the temperature range (i.e., the supercooling) over which NPs can be ordered by crystallization thereby shifting the kinetic boundary for crystallization-induced ordering and expanding the accessible processing window. Analysis using the Péclet-number framework indicates that acoustic excitation enhances effective NP transport relative to the advancing crystallization front. Acoustic excitation therefore provides a means of controlling NP morphology without substantially altering the bulk crystalline fraction or melting temperature of the polymer matrix.
Abstract Visible-light photoiniferter RAFT polymerization enables highly controlled block copolymer synthesis with low dead chain formation; however, distinguishing living from dead chains remains challenging. Here, an α,ω-dihydroxyl-functionalized trithiocarbonate was used as a photoiniferter to synthesize poly(benzyl acrylate) (pBzA) and poly(benzyl acrylate-b-tert-butyl acrylate) (p(BzA-b-tBA)) under blue-light irradiation. Solvent-gradient HPLC (SG-HPLC) using a bare silica column then separated RAFT agent-derived living chains from dead chains through end-group polarity contrast installed by the dihydroxyl iniferter design. Living fractions accounted for ∼96% of the integrated 260 nm signal and 94.9 wt % of the recovered block copolymer, with chain-end fidelity enriched from ∼95% to >99% upon SG-HPLC isolation. MALDI–TOF MS of the isolated fractions gave apparent dispersities (ĐMALDI = 1.02–1.03), close to 1 + 1/DPn, supporting a near-ideal single population. This study demonstrates SG-HPLC as a practical route to separate and quantify living and dead chains in photoiniferter-mediated acrylic block copolymers.
Abstract In conventional ABA triblock copolymers, hard domains (A) often act as physical cross-links connected by a soft midblock (B), leading ABA architecture to be commonly associated with better mechanical performance than BAB analogues. Here, we propose a new design principle using triblock ionomers in which charged A blocks self-assemble into spherical ionic micelles dispersed within a polymer matrix. Surprisingly, BAB triblock ionomer exhibits higher modulus and markedly slower stress relaxation than compositionally analogous ABA triblock. Small-angle X-ray scattering and atomic force microscopy reveal that the BAB architecture produces a much higher density of smaller ionic micelles with substantially reduced intermicellar spacing. With both ABA and BAB show little-to-no intermicellar connectivity, the enhanced mechanical performance cannot be explained by conventional thermoplastic elastomer (TPE) theory. Instead, the dense micellar packing and the resulting cooperative structural relaxation play a critical role in governing the mechanical response. More broadly, this work demonstrates that self-assembled ionic domains can fundamentally alter the structure–property relationships of triblock copolymers and identifies micellar organization as an important design parameter for controlling the mechanics and thermomechanical stability of ionomer materials.
Abstract Random copolymers intrinsically possess chain-by-chain composition distributions that originate from sequence heterogeneity. Yet they can form macroscopically homogeneous materials and develop intriguing, higher-order self-assembled structures at microscopic levels. Here, we investigate the miscibility and self-assembly behaviors of model amphiphilic random copolymer mixtures in water as a function of composition distributions. We systematically vary the compositional distribution width (σ) and the fraction of the central composition (wR55) by mixing presynthesized random copolymers with different weight ratios. Increasing σ drives a phase transition from homogeneously coassembled, bilayer-folded lamellar mesophases to macrophase-separated, self-sorted states. Introducing a central composition to broadly distributed multinary blends restores macroscopic homogeneity and ordered coassembly, effectively mediating compatibility between compositionally disparate chains. While alternating copolymers with uniform composition distribution do not undergo bilayer folding, the lyotropic mesophase can persist in a ternary blend even under strong shear, suggesting opportunities to use composition distributions as a design parameter of soft matter.
Abstract Fabrication of chiral microgels through in situ cross-linking polymerization of thermally aggregated chiral dendronized phenylacetylene (PA) macromonomers is reported. These macromonomers bear either ethoxyl- (more hydrophobic) or methoxyl-terminated (more hydrophilic) dendritic oligo(ethylene glycol)s (OEGs), affording tunable thermoresponsive properties with distinct cloud points (Tcps). Systematic optimization of polymerization parameters─including macromonomer hydrophilicity and concentration, temperature, stirring rate, and cross-linker loading─enables the convenient one-pot synthesis of cross-linked chiral microgels with uniform spherical morphology and stable helicity from the thermally aggregated monomeric mesoglobules. Notably, this surfactant-free strategy offers a significant advantage over conventional microgel preparation methods. Moreover, the approach is versatile and readily extendable to the one-pot fabrication of other nano-objects via polymerization from aggregated monomers.
