Volume 44 Issue 1, January 2012

This paper reviews the synthetic strategies for HBPs with controlled DB by specially designing monomer architectures. Several research groups including our group have been overcoming the statistical determination of DB in a random polymerization by tuning the rate constant of the first substitution reactions (k₁) and that of the second reaction (k₂) of an AB₂ monomers. As a result, HBPs with 100% DB, linear polymers (0% DB) and HBPs with any percentage of DB have been successfully synthesized.

Poly[2]rotaxane and graft polyrotaxane were synthesized from a mixture of poly(crown ether) as a trunk polymer, boronic-acid-terminated secondary ammonium salt as an axle component and diol as an end-capping group by pseudorotaxane formation and subsequent catalyst-free dehydrative bondage between the boronic acid and the diol moieties. It turned out that the chemical stability of these supramolecular architectures primarily depends on the bulkiness of the diol group as the end-capping moiety and the inherence originating from the dynamic covalent bond of boronate.

Slide-ring gel with freely movable crosslinks shows extremely small Young's modulus and recovers the deformed shape to the original one instantaneously and completely. The small modulus arises from new entropic elasticity because of the heterogenous distribution of free cyclic molecules on polyrotaxane. The sliding elasticity appears in the sliding state, where axis polymer chains and cyclic molecules are sliding actively. In addition, the slide-ring gel should show the sliding transition between the rubber and sliding states. These aspects indicate that the slide-ring gel has its unique dynamics in mechanical properties.

We have observed a unique amplification of the helical-sense excess (majority rule effect) of dynamic helical, liquid-crystalline (LC) poly(phenylacetylene)s bearing non-racemic D- and L-alanine residues as the pendant groups in a dilute solution, in the cholesteric LC state and a two-dimensional crystal on substrate. The preferred-handed helical-sense and handedness excess of the copolymers in a dilute solution were sensitive to the solvent polarity and temperature, and amplification of the helical-sense excess was significantly affected by the solvents.

A pentamethylcyclopentadienyl (Cp*)-based ruthenium complex with phenolic phosphine ligands 4-(hydroxyphenyl)diphenylphosphine ([PPh₂(pPhOH)]) showed a high catalytic activity for aqueous living radical polymerizations of hydrophilic methacrylates (for example, poly(ethylene glycol) methacrylate (PEGMA), 2-hydroxyethyl methacrylate (HEMA) and so on). Importantly, the activity was high enough to control the aqueous polymerizations even with just catalytic amount. Such an advanced catalysis would be caused not only by a simple hydrophilicity of the ligand but also by a water-assisted dynamic transformation from the original saturated form [Cp*RuCl(PR₃)₂; 18e; PR₃=phosphine] into an unsaturated but active one [Cp*RuCl(PR₃); 16e] upon which water molecule(s) may additionally coordinate for further stabilization.

The colloidal polyion complex formed from sodium polyacrylate (NaPA) and poly(vinyl ammonium) chloride (PVACl) is almost stoichiometric but slightly charged by the adsorption of the excess polyelectrolyte component onto the neutral complex. The charge stabilizes the colloidal polyacrylate–poly(vinyl ammonium) complex in aqueous solution of a non-stoichiometric mixture of NaPA and PVACl, and the aggregation number of the colloidal complex increases with approaching the stoichiometric composition. On the basis of the experimental results obtained, we propose a simple model for the colloidal polyion complex formation.

Isotactic-poly(1-butene) shows superior mechanical property after crystal–crystal transitions. Very recently, Miyoshi. revealed molecular dynamics of the crystalline stems in metastable tetragonal form. In this study, molecular dynamics in stable trigonal crystal is investigated by ¹³C center bands only detection of exchange nuclear magnetic resonance. The experimental results indicate that overall motions and side-chain dynamics in slow dynamic range are frozen up to melting temperatures. On the basis of molecular dynamics, roles of (i) unique crystallization and (ii) solid–solid transitions for superior mechanical property are discussed.

The concept of controlling supramacromolecular self-assembly and disassembly of two building blocks (of polymers) with end-functional groups is displayed. By self-assembling two building blocks that carry non-covalent bonding moieties, a block copolymer-type supramacromolecule is formed via non-covalent bonding, resulting in a nanophase-separated structure with the length scale of the building blocks. By contrast, macrophase separation with a much larger length scale than the building blocks themselves can be observed if the two blocks are pulled apart under external stimuli such as heat or applied stress.

Structure studies were performed on PVA gels in mixtures of dimethyl sulfoxide (DMSO) and water using various scattering methods to see the hierarchic structure. It was found that the crosslinking points are crystallites, the nearest-neighboring distance is 180–200 Å and the bicontinuous structure due to phase separation is in μm scale for the gel in DMSO/water (60/40). Dynamics of three kinds of PVA gels were also studied in nm scale using neutron spin echo technique.

In situ observation of the formation process of mesophase of isotactic polypropylene (iPP) is reported in structural point of view. Combining a rapid temperature jump and a high-flux synchrotron radiation X-ray scattering techniques, very rapid transformation from the molten amorphous state to the mesophase has been observed. The transformation proceeded very quickly in a narrow temperature range accompanied by instantaneous fluctuations in micrometer scale, suggesting the mesophase formation proceeds similarly to spinodal decomposition.

Viscoelastic and dielectric properties were examined for miscible blends of moderately entangled cis-polyisoprene (PI) and poly(p-tert-butyl styrene) (PtBS). The dielectric response exclusively detected the global motion of PI chains having type-A dipoles. In most of the blends, PI and PtBS were the fast and much slower components, respectively. In those blends, the dielectric response of PI was thermo–rheologically complex because the slow PtBS chains quenched the dynamic frictional heterogeneity in the time scale of the PI relaxation. In contrast, the viscoelastic response of PtBS was thermo–rheologically simple because the fast PI chains smeared the heterogeneity. Nevertheless, PtBS exhibited no ordinary entanglement relaxation but retarded Rouse-like relaxation attributable to pseudo-constraint release activated by the PI motion. A simple model based on this molecular picture well described the viscoelastic data of the blends.

The ratio g_η between the values of the intrinsic viscosity of the Kratky–Porod wormlike regular four-arm star and linear touched-bead models, both having the same total contour length L and bead diameter d_b (in units of the stiffness parameter), is numerically evaluated in the Kirkwood–Riseman approximation. Its behavior as a function of L and d_b is examined (solid curves) and is compared with previous results for the three-arm star (dashed curves).

The chain dimension of surface-grafted poly[3-(N-2-methacryloyloxyethyl-N,N-dimethyl)ammonatopropanesulfonate)] brush on silica nanoparticles in aqueous NaCl solution was precisely estimated by dynamic light scattering and synchrotron radiation small-angle X-ray scattering measurements to reveal large dependency on salt concentration. On the other hand, we confirmed that the chain dimension of poly(2-methacryloyloxyethyl phosphorylcholine) brush in aqueous solution was hardly affected by salt concentration.