Synthesis and properties of a polyrotaxane network prepared from a Pd-templated bis-macrocycle as a topological cross-linker

Abstract

Polyrotaxane networks (PRNs) were synthesized by exploiting a Pd-templated bis-macrocycle as a topological cross-linker during radical polymerization of a vinyl monomer. The bis-macrocycle (9) was prepared by combining two macrocycles with a linear linker. Radical polymerization of 4-vinylpyridine in the presence of 9 and a catalytic amount of 2,2¢-azobisisobutyronitrile (AIBN) yielded a gelled polymer. The addition of 4-tert-butylstyrene as a vinyl co-monomer to the polymerization system afforded a sufficiently stable gel as the PRN, clearly indicating that 4-tert-butylstyrene was successfully introduced as end-capping moieties of the trunk polymer. The swelling properties of the PRN were evaluated using several solvents. The topological structure and swelling properties of the PRNs were confirmed by a control experiment using a bis-acyclic pincer-type Pd complex (13) Keywords: metal template; Pd-templated bis-macrocycle; polyrotaxane network; rotaxane; topological cross-linker INTRODUCTION Among networked polymers, polyrotaxane networks (PRNs) that have rotaxane structures on the cross-link points are the most interesting class of cross-linked polymers. The generation of unique properties in a network polymer having rotaxane-like cross-links was predicted by de Gennes; 1 one such property leads to easy polymer chain sliding. Ito and coworkers synthesized a hydrogel possessing rotaxane structures at the cross-link points 2 using Harada's cyclodextrin-based polyrotaxane, 3 and this hydrogel has recently been made practicable (Nissan, Kanagawa, Japan) and NTT docomo (Tokyo, Japan) used a PRN as a coating paint of automobile or mobile phone, which is termed as 'SCRATCH SHIELD' . The coating paint shows self-healing properties to scrapes depending on the high elasticity of PRN.). 4,5 However, we reported crown ether-based PRNs that exploit strategic rotaxanation as the cross-linking reaction. [6][7][8][9][10][11][12][13] Although the use of a crown ether as a wheel component allows more precise structures of PRNs than the use of cyclodextrin, the crown ether-based PRN requires the somewhat troublesome synthesis of sec-ammonium axle. To find a simple and widely applicable approach to PRNs, especially toward PRNs containing vinyl polymers, we planned the development of a topological cross-linker that includes a bis-macrocycle moiety to enable efficient penetration of the propagation end of radical polymerization into macrocyclic cavities. We became intrigued in exploiting a Pd(II)-templated bis-macrocycle based on the metal-templated method that is often used for rotaxane architectures (Scheme 1) 14-16 because of the following three merits: (1) the coordination bond of the Pd complex

Structural Analysis and Inclusion Mechanism of Native and Permethylated α‐Cyclodextrin‐Based Rotaxanes Containing Alkylene Axles

“…Rotaxanes are ac lass of mechanically interlocked molecules that have been considerably studied in terms of synthesis and applications. [1][2][3][4][5] Among the many types of rotaxanes, cyclodextrin (CD)-based polyrotaxanes have attracted particulari nterest due to their unique structural properties as scaffolds of supramolecular materials, such as polyrotaxane networks, molecular wires, and stimuli-responsive systems. [6][7][8][9] Indeed, future research should focus on regulating the structure of polyrotaxanes by manipulating the inclusion mechanism of CD by using low-molecular-weight rotaxanes to controlthe properties of the materials.…”

Synthesis of rotaxane cross-linked polymers derived from vinyl monomers using a metal-containing supramolecular cross-linker

“…The pseudorotaxane cross-linked polymer prepared without TBPMA (pseudoRCP VP ), as in the previous report, was completely dissolved under dilute conditions that prompted dissociation of the MSC AN from the trunk polymer chain (Scheme 1c). 18 This clearly shows that the formation of a stable interlocked structure was maintained without deslippage by introducing TBPMA.…”

“…18 However, the bulkiness of the tert-butyl phenyl component was not sufficient for the MSC VP . We therefore developed a novel end-capping reagent, TBPMA, to obtain more stable RCPs from various vinyl monomers.…”

“…[15][16][17] Previously, we reported a successful approach for RCP synthesis via vinyl polymerization using a 4-vinylpyridine (VP)-coordinated bis-macrocyclic metal-containing supramolecular cross-linker (MSC VP ). 18 However, the main chains of RCPs are limited to poly(4-vinylpyridine), and the utility of the MSC has not been sufficiently studied.…”

Topology-transformable polymers: linear–branched polymer structural transformation via the mechanical linking of polymer chains

“…[99][100][101][102][103][104][105] These pioneering works were followed by a variety of studies in which the movable junction point played a crucial role. [106][107][108][109][110][111][112][113][114][115][116][117][118][119][120][121][122] In these reports on RCPs, the number of wheel components utilized for the crosslink points and their movable length or range on the axle …”