Yasuyuki Tezuka

Topological polymer chemistry: a cyclic approach toward novel polymer properties and functions

Recent progress observed in Topological Polymer Chemistry is outlined with particular emphasis on single-cyclic (ring) and multi-cyclic polymers having programmed chemical structures, now becoming obtainable with guaranteed purity by newly developed synthetic protocols. By making use of these topological polymers, unprecedented opportunities have now been realized to provide new insights on fundamental polymer properties either in solution or bulk, in static or dynamic states, or in self-assemblies. Moreover, unusual properties and functions for polymer materials have now been revealed based on their cyclic topologies, i.e., topology effects, unattainable either by linear or branched counterparts.

Topology-Directed Control on Thermal Stability: Micelles Formed from Linear and Cyclized Amphiphilic Block Copolymers

The thermal stability of a self-assembled micelle was remarkably enhanced by a topology effect. Linear poly(butyl acrylate)-block-poly(ethylene oxide)-block-poly(butyl acrylate) (1) and the cyclized product, poly(butyl acrylate)-block-poly(ethylene oxide) (2), were self-assembled to form flower-like micelles. By means of viscometry, the critical micelle concentrations were determined to be 0.13 and 0.14 mg/mL for 1 and 2, respectively. Dynamic light scattering, atomic force microscopy, and transmission electron microscopy studies revealed that both micelles are spherical and approximately 20 nm in diameter. Despite no distinctive change in the chemical composition or structure of the micelle, we found that the cloud point (T(c)) was elevated by more than 40 degrees C through the linear-to-cyclic topological conversion of the polymer amphiphile. Furthermore, the T(c) was tuned by coassembly of 1 and 2.

Topological polymer chemistry

Recent developments in designing non-linear polymer topologies comprising cyclic and branched segments are reviewed. Thus first, a systematic classification of non-linear polymer topologies is presented by reference to constitutional isomerism in a series of alkanes (CnH2n12), monocycloalkanes (CnH2n) and polycycloalkanes (CnH2n22 ,C nH2n24, etc.). A special emphasis is placed on constitutional isomerism as well as stereoisomerism occurring uniquely in such non-linear polymer molecules as cyclics, knots and catenanes. Secondly, a novel strategy based on an ‘electrostatic self-assembly and covalent fixation’ process is described to realize a variety of topologically unique polymer architectures. Those include monocyclic and polycyclic polymers, polymeric topological isomers, cyclic macromonomers and cyclic telechelics (kyklo-telechelics) and ‘a ring with a branch’ topology polymers, as well as such model branched polymers as star polymers and polymacromonomers. In this process, new telechelic polymer precursors having a moderately strained cyclic onium salt group as single or multiple end groups carrying multifunctional carboxylate counteranions has been prepared through an ionexchange reaction. The unique electrostatic self-assembly directed by these polymer precursors, particularly in a diluted organic solution, are transformed into the covalent product by the heat treatment of the polymer precursor, causing the ring-opening reaction to produce a variety of topologically unique, non-linear polymer architectures in high efficiency. q 2002 Elsevier Science Ltd. All rights reserved.

Effective Click Construction of Bridged- and Spiro-Multicyclic Polymer Topologies with Tailored Cyclic Prepolymers (kyklo-Telechelics)

An alkyne-azide addition, i.e., click, reaction in conjunction with an electrostatic self-assembly and covalent fixation (ESA-CF) process has been demonstrated to effectively construct a variety of unprecedented multicyclic polymer topologies. A series of single cyclic poly(tetrahydrofuran), poly(THF), precursors having an alkyne group (Ia), an azide group (Ib), two alkyne groups at the opposite positions (Ic), and an alkyne group and an azide group at the opposite positions (Id) have been prepared by the ESA-CF process. Moreover, a bicyclic 8-shaped precursor having two alkyne groups at the opposite positions (Ie) was synthesized. The subsequent click reaction of Ia with linear (IIa) and three-armed star (IIb) telechelic precursors having azide groups has been performed to construct bridged-type two-way (IIIa) and three-way (IIIb) paddle-shaped polymer topologies, respectively. Likewise, spiro-type tandem tricyclic (IVa) and tetracyclic (IVb) topologies resulted from Ib/Ic and Ib/Ie, respectively. Furthermore, three types of multicyclic topologies that are composed of repeating ring (Va), alternating ring/linear (Vb), and alternating ring/star (Vc) units have been synthesized from Id, Ic/IIa, and Ic/IIb, respectively.

Tuneable enhancement of the salt and thermal stability of polymeric micelles by cyclized amphiphiles

Cyclic molecules provide better stability for their aggregates. Typically in nature, the unique cyclic cell membrane lipids allow thermophilic archaea to inhabit extreme conditions. By mimicking the biological design, the robustness of self-assembled synthetic nanostructures is expected to be improved. Here we report topology effects by cyclized polymeric amphiphiles against their linear counterparts, demonstrating a drastic enhancement in the thermal, as well as salt stability of self-assembled micelles. Furthermore, through coassembly of the linear and cyclic amphiphiles, the stability was successfully tuned for a wide range of temperatures and salt concentrations. The enhanced thermal/salt stability was exploited in a halogen exchange reaction to stimulate the catalytic activity. The mechanism for the enhancement was also investigated. These topology effects by the cyclic amphiphiles offer unprecedented opportunities in polymer materials design unattainable by traditional means.

Determination of substituent distribution in cellulose acetate by means of a 13C NMR study on its propanoated derivative

Cellulose acetate (1) is commercially important, and is produced with various degrees of substitution (DS) suitable for such applications as fibers, plastics, films, and coatings [1]. The final properties of these products may be optimized through control of the distribution pattern of acetyl groups on the glucose residue [2-5], as well as the total DS by acetyl groups. In consequence, a convenient and reliable analytical technique is important for both the elucidation of structure-properties relationships and for quality control in the production process. Although the total acetyl content in samples of 1 is readily determined by means of a standard titration technique [6,7], the individual DS at 0-2, -3, and -6 in the glucose residue is not readily obtainable through chromatographic techniques. A 1H NMR spectroscopic technique applied with derivatized samples of 1 [4,8] involves conversion of residual hydroxyl groups into the deuterated acetyl groups through reaction with acetyl chloride-d 3. The acetyl proton signals of the resulted cellulose triacetate appear as three lines corresponding to the 2-, 3-, and 6-OAc signals in the glucose residues. Perdeuterioacetylation avoids the spectral complication observed in the acetyl-proton signals of partially substituted 1.

Multimode Diffusion of Ring Polymer Molecules Revealed by a Single- Molecule Study**

Diffusion processes of synthetic polymer molecules are crucial in deciding their rheological properties, and subsequently in polymer processing and fabrication of plastics, films, and fibers. The topology of a polymer, whether linear, branched, or cyclic, can dramatically affect the motion in a dense entangled solution or in a melt. For linear and branched polymers, the reptation model has been accepted as a valid diffusion mechanism and verified experimentally by light scattering, NMR, and viscoelastic measurements. In the reptation model for linear and branched polymers, an entangled polymer diffuses in a dynamic tube confined by neighboring polymer chains. Single-molecule studies on naturally occurring macromolecules and also on synthetic polymers have demonstrated the reality of the tube and the diffusion scaling laws. The number and structure of end groups is a critical factor in the dynamics of the diffusion of linear or branched polymers. Ring polymers are, on the other hand, topologically unique by the absence of free chain ends. Therefore, their diffusion mechanism has attracted continuous attention, but is still an important challenge. Apart from cyclic DNA, a variety of synthetic ring polymers of sufficiently long chains and of guaranteed purity have recently become accessible. 21] As a result, unequivocal topology effects have now been disclosed by using custom-made ring polymers with specific segment structures and optional functional groups. Herein, we show, at the single-chain level, the direct and real-time observation of diffusion dynamics of synthetic ring and linear polymers incorporating a fluorophore. Singlemolecule spectroscopy is recognized as a powerful tool for monitoring of polymer dynamics, and is capable of revealing topology effects in their diffusion process. 32] We synthesized linear (1) and cyclic (2) poly(tetrahydrofuran)s (poly(THF)s) containing perylene diimide unit as a fluorophore by means of an electrostatic self-assembly and covalent fixation process 28] (Figure 1; see the Supporting

A programmed polymer folding: click and clip construction of doubly fused tricyclic and triply fused tetracyclic polymer topologies.

A tandem alkyne-azide addition, i.e., click, and an olefin metathesis condensation, i.e., clip, reactions in conjunction with an electrostatic self-assembly and covalent fixation (ESA-CF) process, have been demonstrated as effective means to produce constructions of programmed folding of polymers having doubly fused tricyclic and triply fused tetracyclic topologies. Thus, a series of cyclic poly(tetrahydrofuran), poly(THF), precursors having an allyloxy group and an alkyne group (Ia), an allyloxy group and an azide group (Ib), and two alkyne groups (Ic) at the opposite positions was prepared by means of the ESA-CF method. The subsequent click reactions of Ia with a linear telechelic poly(THF) precursor having azide end groups (Id) and of Ib with Ic afforded a bridged dicyclic polymer (IIa) and a tandem spiro tricyclic precursor (IIb), respectively, both having two allyloxy groups at the opposite positions of the ring units. Finally, the intramolecular metathesis condensation reaction of IIa and of IIb in the presence of a Grubbs catalyst was performed to construct effectively a doubly fused tricyclic and a triply fused tetracyclic polymer topologies (III and IV), respectively.

Straightforward synthesis of functionalized cyclic polymers in high yield via RAFT and thiolactone–disulfide chemistry

An efficient synthetic pathway toward cyclic polymers based on the combination of thiolactone and disulfide chemistry has been developed. First, heterotelechelic linear polystyrene (PS) containing an α-thiolactone (TLa) and an ω-dithiobenzoate group was synthesized via reversible addition–fragmentation chain transfer (RAFT) polymerization, employing a newly designed TLa-bearing chain transfer agent (CTA). The subsequent reaction of this heterotelechelic polymer with an amine, which acts as a nucleophile for both the TLa and dithiobenzoate units, generated the α,ω-thiol-telechelic PS under ambient conditions without the need for any catalyst or other additives. The arrangement of thiols under a high dilution afforded single cyclic PS (c-PS) through an oxidative disulfide linkage. The cyclic PS (c-PS) disulfide ring formation was evidenced by SEC, MALDI-TOF MS and 1H-NMR characterization. Moreover, we demonstrated a controlled ring opening via either disulfide reduction or thiol–disulfide exchange to enable easy and clean topology transformation. Furthermore, to illustrate the broad utility of this synthetic methodology, different amines including functional ones were employed, allowing for the one-step preparation of functionalized cyclic polymers with high yields.

Environmentally induced macromolecular rearrangement on the surface of polyurethane−polysiloxane graft copolymers

Abstract The surface of polyurethane-polysiloxane graft copolymers possessing a controlled polysiloxane graft segment length and a defined siloxane content was studied in both dry and wet states. The top surface of casted graft copolymer film was covered completely with the polysioloxane component in dry state and the thickness of hte top polysiloxane layer range from more than about 100 A to less than about 20 A depending both on the graft segment length and on the total siloxane content. Along with the change of contacting medium from dry to aqueous phase, a dynamic surface rearrangement was observed during a 3-h period from a polysiloxane-like surface to a polyurethane-like surface only when the top polysiloxane layer of graft copolymers in dry state was less than around 100 A.