Synthesis and Solution Self-Assembly Properties of Cyclic Rod–Coil Diblock Copolymers

Abstract

Typical cyclic diblock polymers are synthesized from their linear precursors via the ring-closure strategy in dilute conditions. Here we demonstrate a pseudo-high-dilution condition strategy for the efficient synthesis of cyclic rod−coil diblock copolymer from its linear precursor in selective solvents. The critical association concentration (CAC) of linear precursor is used for the control of unimer concentration during cyclization, while high copolymer synthetic concentrations are achieved via the dynamic equilibrium between unimers and micelles. The effects of CAC and micelle concentration on cyclization yield are studied and pure cyclic rod−coil diblock copolymer was obtained after azide resin treatment. Property investigations show the cyclic rod−coil copolymer has a larger second virial coefficient than its linear counterpart and self-assembles in selective solvents to form larger but looser spherical micelles due to its constraint topological structure.

Study of Linear and Cyclic Graft Polystyrenes with Identical Backbone Contour in Dilute Solutions: Preparation, Characterization, and Conformational Properties

“…The above results clearly indicate that the cyclic graft topology can suppress the interchain association, which can be attributed to the advantages of more compact conformation and isotropic nature. Note that the ability to suppress interchain association for the cyclic graft topology is even much stronger than the reported cases of cyclic chains with “bare” backbones. − …”

Stimuli-Responsive Supramolecular Chirality Switching and Nanoassembly Constructed by n-Shaped Amphiphilic Molecules in Aqueous Solution

“…These molecular systems undergo structural isomerization, cyclization, or ring-opening reactions when exposed to light. − AZO derivatives, which are the most popular groups, endow self-assemblies with the functionalities of a reversible and quick dynamic response to stimuli and effective structural modulation because of their phototriggered isomerization. Rod–coil molecules consisting of a rigid conjugate sequence with AZO and flexible chain fragments have been used to construct functional nanoaggregates that span multiple nanosciences. − For example, Liu et al synthesized an aromatic foldamer containing an AZO group, which self-assembles into a novel pulsating vesicle with swelling and shrinking movements under different pH conditions . Meanwhile, vesicle structure can be damaged or repaired by ultraviolet and visible light, and such systems can be employed for drug delivery.…”

Efficient preparation of cyclic polymers via pre-stacking of photo-cycloaddition capable end groups and a continuous-flow technique

“…Tezuka and Oike et al 16,17 efficiently prepared various topologically unique polymers by an electrostatic self-assembly and covalent fixation strategy. Liu et al 18 and Tu et al 14 combined supramolecular selfassembly and a selective click reaction to prepare macrocyclic diblock copolymers under pseudo-high-dilution conditions by finely controlling the spatial accessibility between the terminal reactive groups. Zhu et al 19 designed a special evaporationcondensation-extraction-inflow circulation device to achieve efficient preparation of cyclic poly(methyl methacrylate) and polystyrene.…”

“…However, to avoid possible side reactions between chains, the ring-closure strategy to synthesize cyclic polymers must be carried out at a very low concentration, and a time-consuming dropwise addition process is indispensable, resulting in very low synthesis efficiency. 14 In addition, the reaction process often requires the use of metal catalysts to achieve high conversion, which results in a cumbersome post-treatment process and difficult removal of residual metal ions. 15 Therefore, it is necessary to develop a simple and efficient method for preparing well-defined cyclic polymers.…”