Morphology Evolution of Polymeric Assemblies Regulated with Fluoro-Containing Mesogen in Polymerization-Induced Self-Assembly

Abstract

Mesogen-containing amphiphilic block copolymers have shown extremely abundant self-assembly behaviors because of the liquid crystalline (LC) alignment within the assemblies. However, development of an understanding of the self-assembly behaviors of these amphiphilic LC polymers is still constrained by the low assembly concentration and complex kinetic effects. Polymerization-induced self-assembly (PISA) is a powerful technique to prepare polymer assemblies at high solids content with good repeatability. Taking advantage of PISA, we systematically study the self-assembly behaviors of a series of mesogen-containing triblock copolymers poly­(2-dimethyl­aminoethyl methacrylate)-b-poly­(benzyl methacrylate)-b-poly­(2-perfluoro­octylethyl methacrylate) (PDMA-b-PBzMA-b-PFMA), which are prepared by seeded reversible addition–fragmentation chain transfer dispersion polymerization of FMA with PDMA-b-PBzMA micelles or vesicles as the seeds. When PDMA-b-PBzMA micelles are used, the morphology of the PDMA-b-PBzMA-b-PFMA assemblies evolves from spheroid to phase-segregated sphere, followed by phase-segregated spheroid, and eventually to cylinder, while the assemblies undergo a vesicle-to-micelle transition with a framboidal intermediate when PDMA-b-PBzMA vesicles are used as the seeds. These spherical micelles further fuse to cylinders or large spheres depending on the DPs of PBzMA and PFMA blocks. The LC ordering of the PFMA blocks is examined by differential scanning calorimetry and X-ray diffraction; the microphase segregation between PFMA and PBzMA blocks is studied with TEM and atomic force microscopy. These experiments evince that the formation of the ellipsoidal and cylindrical micelles is driven by the LC alignment of PFMA blocks, while the microphase segregation between PFMA and PBzMA blocks complicates the ultimate morphology through modulating the size of PFMA nanodomains. The interplay of the hydrophobic interaction among PBzMA blocks, lipophobic interaction, and LC ordering of PFMA blocks thus generates the above self-assembly behaviors.

Semi‐Fluorinated Methacrylates: A Class of Versatile Monomers for Polymerization‐Induced Self‐Assembly

“…The cylindrical morphology was further confirmed by scanning electron microscopy (SEM) characterization in Figure S13 (Supporting Information). Such peculiar self‐assembly behavior is originated from the liquid crystalline (LC) ordering of PFOEMA, which was reported to form smectic phase liquid crystals by our group and others . Different from the self‐assembly of coil–coil block copolymers, which tends to spherical nanoparticles, the smectic LC ordering of PDMA‐ b ‐PFOEMA assemblies entails the layered stacking of the polymer chains, favoring the formation of cylindrical micelles …”

“…Besides, M n of these block copolymers increases with the monomer conversion, and the dispersities are <1.30 for all the copolymers (Figure c). However, because of the strong associative interactions among the fluoro‐containing blocks, the solubility of PFBEMA decreases with the chain length of PFBEMA, leading to an increscent deviation between the theoretical and the actual M n . DLS studies indicate that after 3 h of polymerization, aggregates of 15 nm formed.…”

“…Compared with the traditional self‐assembly protocols, PISA allows preparing the desired polymer assemblies via readily adjusting the polymer‐related parameters, including hydrophilic/hydrophobic ratio and polymer concentration. Hence, PISA has been extensively studied to understand the self‐assembly mechanism of amphiphilic copolymers and to develop new drug carriers, dynamic gels, Pickering emulsifiers, etc …”

Photoinitiated Seeded RAFT Dispersion Polymerization: A Facile Method for the Preparation of Epoxy‐Functionalized Triblock Copolymer Nano‐Objects

“…Over the past decade, polymerization‐induced self‐assembly (PISA) of block copolymers via reversible addition–fragmentation chain transfer (RAFT)‐mediated dispersion polymerization has enabled block copolymer nano‐objects with a diverse set of complex morphologies to be synthesized at high solids content (up to 50%) . However, the RAFT‐mediated PISA is typically conducted at high temperatures (e.g., 70 C) by thermal initiation, which is not beneficial for the preparation of temperature sensitive polymer nano‐objects (e.g., protein–polymer conjugate).…”

Interfacial crosslinking of self‐assembled triblock copolymer nanoparticles via alkoxysilane hydrolysis and condensation

“…The advent of polymerization‐induced self‐assembly (PISA) has enabled the preparation of in situ self‐assembled block copolymer nanoparticles with various morphologies at high solids . Similar to the aforementioned methods, crosslinking approaches to stabilize a particular particle morphology have been adopted.…”