Intramolecular consecutive cyclization was established as a versatile and robust strategy to synthesize macromolecular cages.

A novel synthesis of multicyclic polymers that feature ultradense arrays of cyclic polymer units has been developed by exploiting the cyclopolymerization of α,ω-norbornenyl end-functionalized macromonomers mediated by the Grubbs thirdgeneration catalyst (G3). Owing to the living polymerization nature, the number of cyclic repeating units in these multicyclic polymers was controlled to be between 1 and approximately 70 by varying the initial macromonomer-to-G3 ratio. The ring size was also tuned by choosing the molecular weight of the macromonomer; in this way we successfully prepared multicyclic polymers that possess cyclic repeating units composed of up to about 500 atoms, which by far exceeds those prepared to date by cyclopolymerization. Specifically, cyclopolymerizations of α,ω-norbornenyl end-functionalized poly(L-lactide)s (PLLAs) proceeded homogeneously under highly dilute conditions (∼0.1 mM in CH 2 Cl 2 ) to give multicyclic polymers that feature cyclic PLLA repeating units on the polynorbornene backbone. The cyclic product architectures were confirmed not only by structural characterization based on NMR, MALDI-TOF MS, and SEC analyses but also by comparing their glass transition temperatures, viscosities, and hydrodynamic radii with their acyclic counterparts. The cyclopolymerization strategy was applicable to a variety of α,ω-norbornenyl end-functionalized macromonomers, such as poly(ε-caprolactone), poly(ethylene glycol) (PEG), poly(tetrahydrofuran), and PLLA-b-PEG-b-PLLA. The successful statistical and block cyclocopolymerizations of the PLLA and PEG macromonomers gave amphiphilic multicyclic copolymers.

The development of precise folding techniques for synthetic polymer chains that replicate the unique structures and functions of biopolymers has long been a key challenge. In particular, spiro-type (i.e., 8-, trefoil-, and quatrefoil-shaped) polymer topologies remain challenging due to their inherent structural complexity. Herein, we establish a folding strategy to produce spiro-type multicyclic polymers via intramolecular ring-opening metathesis oligomerization of the norbornenyl groups attached at predetermined positions along a synthetic polymer precursor. This strategy provides easy access to the desired spiro-type topological polymers with a controllable number of ring units and molecular weight while retaining narrow dispersity (Ɖ < 1.1). This effective strategy marks an advancement in the development of functionalized materials composed of specific three-dimensional nanostructures.

Synthetic molecular crystals with one-dimensional nanoporous channels containing H 2 O molecules act as model systems for pores such as aquaporin-1 in cell membranes. The structural characteristics of water molecular clusters (WMCs) were investigated using X-ray crystal analysis of {[Ni II -(cyclam)] 3 (TMA) 2 ¢3534 H 2 O} n (2) (TMA: trimesate, cyclam: 1,4,8,11-tetraazacyclotetradecane) in a closed glass capillary to adjust the saturated humidity. The structural phase transition of WMCs with temperature depends only on the H 2 O structures around the centre, not on those in the primary hydrate layer nearest to the outer wall. The centre of a WMC was filled with H 2 O molecules under saturated humidity conditions; however, in air, the WMC had a nanotube-like structure with a vacant space. Thus, the centre portion of a WMC probably contains volatile and mobile H 2 O molecules. Therefore, we investigated the rapid proton conductivity using alternating current impedance and microwave spectroscopy and also carried out a transpiration experiment for transferring the mobile H 2 O molecules. The microwave spectroscopy results for 2 indicated no isotope effect, which would be observed by the rapid motion of H 2 O molecules without the breaking of hydrogen bonds between two site-disordering positions above the phase transition temperature. The results indicated reasonable water transpiration ability of the single crystal through its nanochannels; this property can be useful as a working principle to understand applications such as the desalination of seawater.