Deciphering the Complex Phase Behavior during Polymerization-Induced Nanostructural Transitions of a Block Polymer/Monomer Blend

Abstract

The simultaneous use of nonequilibrium reaction processing and complex macromolecular architecture is an exciting way to achieve nanostructures that are not easily accessible via standard static block polymer self-assembly. Previous work has shown that the polymerization of styrene in the presence of a poly(styrene)-block-poly(butadiene) (PS-PBD) diblock copolymer induces a nanostructural transition from a lamellar (LAM) to a hexagonally packed cylinder (HEX) morphology. The transition was found to be driven by in situ PS grafting from the PBD block, which transforms the PS-PBD coil−coil diblock copolymer to a poly(styrene)-block-[poly(butadiene)-graf t-poly(styrene)] (PS-b-PBD-g-PS) coil−comb block polymer. In situ small-angle X-ray scattering and oscillatory shear dynamic mechanical spectroscopy measurements show that the order−order transition is not a simple epitaxial transition seen in prototypical block polymers, but undergoes a complex phase path in which the starting LAM phase at room temperature before polymerization initially disorders at elevated temperatures, evolves from a disordered phase to what is presumed to be a hexagonally perforated lamellae phase during the polymerization, and then transitions to a HEX phase on cooling to room temperature. The high-temperature phase persists for extended periods of time during the polymerization process, which allows for both the trapping and the characterization of the structure at room temperature. By utilizing nonequilibrium reactive processing to convert linear block copolymers to comb−coil type polymers, the creation of polymers with complex molecular topologies can be synthetically simplified while simultaneously allowing for the development of new processing modalities.

Controlling nanostructure and mechanical properties in triblock copolymer/monomer blends via reaction-induced phase transitions

“…Although synthetic improvements for controlling polymer topology and chemical composition have led to TPE advances, there are a wealth of opportunities in utilizing in situ reaction and processing modalities to tune macromolecular structures and nanoscale phases not easily accessible via traditional methods. [8][9][10][11] The molecular architecture of TPEs is based on a block polymer framework in which covalent bonds chemically link distinct repeat segments or ''blocks'' (e.g., A or B blocks in an ABA triblock copolymer) to form a single macromolecule. 12 Block polymers will microphase separate into distinct domains as a result of the incompatibility between the polymer blocks.…”

“…Our strategy follows previously published work in which PS is grafted from the PBD backbone of a PS-PBD diblock copolymer via the generation of an allylic radical. 9,10 The in situ grafting during the polymerization of styrene resulted in both order-order and disorder-order nanostructural transitions, 9,10 but the impact of these changes on properties was not previously investigated. The polymer grafting chemistry has been shown to be generalizable to other unsaturated polymer motifs (hybrid inorganic nanoparticle/polymer materials) and grafting polymers (PS and poly(methyl methacrylate)).…”

Investigating Nanoparticle Organization in Polymer Matrices during Reaction-Induced Phase Transitions and Material Processing

“…The core–shell structure of the OAm-functionalized AuNPs is effectively similar to a polymer-functionalized nanoparticle with a surface brush of small graft length ( N OAm ) and high graft density (σ ≈ constant). ,, Approximation of these structural parameters ( N OAm = 4, σ ≈ 1.2 nm –2 ) gives a polymer-functionalized nanoparticle structure that would be predicted to adopt a phase-separated or connected nanosheet preferred state in a polymer matrix with large matrix length (α < 0.2) . As a result, the trending toward aggregation from well-dispersed particles reported here matches our understanding of preferred polymer-functionalized nanoparticle/polymer material phases. ,, …”

Polymerization-Induced Phase Separation in Rubber-Toughened Amine-Cured Epoxy Resins: Tuning Morphology from the Nano- to Macro-scale

“…Polymerization-induced phase separation (PIPS), the spontaneous segregation of otherwise miscible components upon an increase in the molecular weight of at least one of the components, has offered a distinct pathway for generating thermoset polymers with well-defined nanostructures and microstructures. Indeed, various morphologies have been produced with the PIPS strategy including co-continuous, − isolated or fused globular structures, − lamellae, − and cylinders , with applications for membranes, − sorbents, , functional coatings, , and UV-cured dental materials. , Owing to their versatile and pre-designed molecular nature, block copolymers are well suited for PIPS in thermosets where the molecular weight and volume fraction of polymer blocks regulate the domain size and morphology of the phase-separated systems. Early examples of block copolymer-driven PIPS employed amphiphilic copolymers blended with epoxy systems to yield highly ordered domains down to tens of nm. ,− However, the lack of a covalent bond connecting the secondary polymer and the thermoset matrix in these early works resulted in the expulsion of the copolymers from the matrix and set a lower bound for the domain size (e.g., above ∼10 nm) .…”