Optically Active Conjugated Polymer Nanoparticles from Chiral Solvent Annealing and Nanoprecipitation

Abstract

O ptically active polymers are very useful as chiral packing materials for optical resolution of various racemates. 1 Circular dichroism (CD) is of critical importance for evaluation of their chirality. Although these types of polymers have been evaluated in solution state, their practical applications are commonly with them in solid state, such as powders and membranes. Evaluation in solid state may directly provide chiral information about the packing materials and make it more reliable. Nanoporous materials or small-sized particles would be especially useful for optical resolution because the extremely high surface area-to-volume ratio could lead to an amplified interaction between the chiral packing material and racemic mixture, thus enhancing the optical resolution. 2 In this respect, optically active nanoporous nanoparticles should be one of the best candidates for highly advanced chiral packing materials. However, a facile preparation and evaluation of such elegant materials should be a great challenge.Among the many types of conjugated polymers, poly-(diphenylacetylene) (PDPA) derivatives are particularly unusual for the following reasons. First, PDPAs are amorphous and exist in a glassy state, depending on the alkyl side chain length. 3 Owing to their amorphous nature and low density, these polymers have relatively large fractional free volumes in the bulk solid state. 4 Second, PDPA derivatives provide highly porous and extremely thin nanofibers from electrospinning or freeze-drying of the polymer solution. 5 The nanoporous network structure is thought to be a result of abrupt phase separation or spinodal decomposition between the polymer and solvent. The porous structure is also very stable, both thermoand hydrodynamically, and is permanently maintained because of the stiff and rigid backbones of PDPAs. Third, the achiral PDPA derivative can be readily converted into optically active materials by heating it in a chiral solvent (chiral solvent annealing, CSA) such as limonene or pinene. 6 Nanoprecipitation (NP) is a very useful and facile method to prepare nanoparticles from conjugated polymers. 7 These polymer particles are referred to as conjugated polymer nanoparticles (CPNs). The principle mechanism for the formation of CPNs in the NP process is abrupt solvent quenching in water, which leads to phase separation between the polymer and solvent. 8 The theoretical product yields of CPNs in the NP process are quantitative, although the process should be conducted in a considerably dilute solution, thus requiring large amounts of solvent and water. Moreover, this method provides much smaller-sized nanoparticles relative to other methods such as emulsion.In this study, we prepared optically active CPNs from CSA and subsequent NP using a PDPA derivative. The solvent chirality was readily transferred to the PDPA simply by annealing it in chiral limonene solution. During the NP process, the chirality-transferred polymer chains came to a standstill with the side phenyl rings being fully relaxed, thus providi...

Properties, Functions, Chemical Transformation, Nano-, and Hybrid Materials of Poly(diphenylacetylene)s toward Sensor and Actuator Applications

“…Similarly, optically active p-C1-PDPA, obtained by chirality transfer as described in section 3.4, was also prepared as nanoparticles. 99 The water-dispersed nanoparticles showed the same CD as the usual solutions. It is very unusual that the polymer has exactly the same chiral information in the nanoparticle aggregate and solution.…”

Thin Films Bearing Conjugated Polymer Nanoparticles Fabricated by Microliter‐Scale Layer‐by‐Layer Deposition

“…The synthesis of PF‐Br was confirmed by 1 H (Figure S1, Supporting Information) and 13 C NMR (Figure S2, Supporting Information) spectra, and elemental analysis for carbon and hydrogen. Nanoparticles of PF‐Br were then successfully prepared via a nanoprecipitation process in which dilute chloroform solutions of PF‐Br were added dropwise to a nonsolvent, methanol, with ultrasonication. The mean diameter of the nanoparticles was 23.4 nm with a standard deviation of 6.8 nm, as determined by particle size analysis (Figure a and scanning electron microscopy (SEM) image (Figure b).…”

Graphene Oxide (GO) as Stabilizer for Preparing Chirally Helical Polyacetylene/GO Hybrid Microspheres via Suspension Polymerization

“…Optically active helical polymers have attracted great attention owing to their fascinating helical structures and significant potentials in chiral recognition, chiral separation, and asymmetric catalysis . Optically active spheres combining the advantages of helical polymers and the strength of particulate materials become increasingly interesting as a newly emerging type of advanced materials . More importantly, spheres with remarkable optical activity are expected to be prepared from chirally helical polymers holding “chiral amplification” effects .…”

“…[20] Optically active spheres combining the advantages of helical polymers and the strength of particulate materials become increasingly interesting as a newly emerging type of advanced materials. [21][22][23][24] More importantly, spheres with remarkable optical activity are expected to be prepared from chirally helical polymers holding "chiral amplification" effects. [25,26] In our earlier studies, we have prepared optically active polymeric spheres constructed by chirally helical substituted polyacetylenes by diverse polymerization methods.…”