Direct Synthesis of Polymer Nanocapsules: Self-Assembly of Polymer Hollow Spheres through Irreversible Covalent Bond Formation

Abstract

A detailed study of the direct synthesis of polymer nanocapsules, which does not require any template, and core removal, is presented. Thiol-ene "click" reaction between a CB[6] derivative (1) with 12 allyloxy groups at the periphery and dithiols directly produced polymer nanocapsules with a highly stable structure and relatively narrow size distribution. Based on a number of observations including the intermediates detected by DLS, TEM, and SEM studies, a mechanism of the nanocapsule formation was proposed, which includes 2D oligomeric patches turning into a hollow sphere. A theoretical study supports that the formation of a hollow sphere from a disk-shaped intermediate can be thermodynamically favorable under certain conditions. In particular, the effects of various factors such as monomer concentration, reaction temperature, and medium on the formation of polymer nanocapsules have been investigated, which qualitatively agree with those predicted by our theoretical model. An interesting feature of the polymer nanocapsules was that the polymer shell made of a CB[6] derivative allows facile tailoring of its surface properties in a noncovalent and modular manner by virtue of the unique recognition properties of the accessible molecular cavities exposed on the surface. Furthermore, this approach appears to be applicable to any building unit with a flat core and multiple polymerizable groups at the periphery which can direct polymer growth in lateral directions. Other reactions, such as amide bond formation, can be used for the synthesis of polymer nanocapsules in this approach. This novel approach to polymer nanocapsules represents a rare example of self-assembly of molecular components into nanometer-scale objects with interesting structures, shapes, and morphology through irreversible covalent bond formation.

Direct Preparation of Hollow Nanospheres with Kraft Lignin: A Facile Strategy for Effective Utilization of Biomass Waste

“…Because they can encapsulate guest molecules in their interior, hollow spheres have great potential for applications such as drug storage and delivery (Kataoka et al 2012), separation (Wang et al 1998), adsorbents, microreactors (Vriezema et al 2005), catalysts (Lu et al 2015), supercapacitors (Liu et al 2014), and medical examination and diagnosis (Salata 2004). Methods for the fabrication of hollow spheres have been extensively reported, including template synthesis (Liu and Basu 2009), self-assembly (Breitenkamp and Emrick 2003), emulsion polymerization (Jang and Ha 2002), core removal of dendrimers (Zimmerman et al 2002), and direct polymerization reaction (Kim et al 2010); however, the most commonly used raw materials are synthetic polymers.…”

Self-templated chemically stable hollow spherical covalent organic framework

“…Furthermore, we also report the mechanism of the hollow sphere formation of crystalline COF in detail using different microscopic techniques. Self-templated synthetic methods [28][29][30][31][32][33][34][35] are considered to be the most costeffective synthetic methods for hollow sphere synthesis, since they do not require sacrificial templates. Template-free methods also avoid problems such as shell collapse and pore contamination during template removal [33][34][35] .…”

Fluorescent Dyes Used in Polymer Carriers as Imaging Agents in Anticancer Therapy

“…Such carriers improve the enhanced permeability retention effect (EPR) of the drugs [112]. The interesting example of self-assembly of molecular components into nanometer scale capsules with irreversible covalent bond formation using photoinitiated thiole-ene "click" reactions was reported by Kim et al [291]. The synthesis was carried out with (allyloxy)12cucurbit [6] uril as a disk shape monomer embedded with multiple polymerizable groups at the periphery and oligoethylene oxide or alkyl-based dithiols (Figure 29).…”