Search

The enthalpy and entropy of micellization in water, AHmic and ASmic, respectively, of three linear amphiphilic BAB block copolymers consisting of either poly(methyl acrylate) (Mn similar to 1200 and 700 Da) or poly(ethyl acrylate) (Mn similar to 800 Da) as hydrophobic (B) segments and poly(ethylene oxide) (PEO) as the hydrophilic (A, Mn similar to 3000 Da) segment were determined by isothermal titration calorimetry (ITC). The AHmic and ASmic of the cyclic AB block copolymers obtained by cyclization of the linear triblock copolymers were determined under the same conditions. The AHmic value of the cyclic copolymers was smaller than that of their linear precursors. The ASmic value showed the same trend, but the relative difference between the cyclized and linear copolymers was less pronounced. The hydrodynamic diameter (Dh), critical micelle concentration (CMC), molecular weight (Mw-mic), and second virial coefficient (A2) of the micelles were determined. The Dh value of the cyclic copolymer micelles was smaller than the linear counterpart. On the other hand, the CMC value became larger, whereas the A2 value was comparable or increased by cyclization. Overall, the results suggest that, in the unimer state, the hydrophobic segments of the cyclized copolymers form a tightly coiled structure to minimize contact with water, resulting in the smaller AHmic value. Contrary to the linear copolymer micelles, the cyclic copolymer micelles have no "dangling chains", which may explain the topology-driven slight difference in the ASmic value.

A set of four types of block copolymers consisting of topological amphiphilic segment pairs was effectively synthesized via

A series of zwitterionic polystyrene (PS) and poly(THF) telechelics having a pair of a cyclic ammonium and a carboxylate end groups have been prepared by making use of a living anionic and cationic...

A programmed polymer folding process has been demonstrated by employing a pair of periodically positioned tetrafunctional, linear telechelic poly(THF)s having 5-membered cyclic ammonium salt groups, i.e., N-ethyl or N-phenylpyrrolidinium groups at both chain ends, and N, N-dialkylpyrrolidinium groups at the two interior positions, accompanying two units of a dicarboxylate counteranion to balance the charges, Ia and Ib, respectively. The electrostatic self-assembly and covalent fixation process has subsequently been applied, to cause the ring-opening reaction of the pyrrolidinium units by carboxylate counteranions under dilution. The obtained doubly cyclized polymer products, IIa from Ia and IIb from Ib, were characterized by 1H NMR and by a MALDI-TOF mass technique, to indicate the formation of polymeric constitutional isomers of either manacle-, 8-, or θ-form. The SEC peak deconvolution analysis of IIa showed the preferential formation of the manacle-form isomer over the 8- and the θ-form counterparts, to accord with the polymer folding of Ia, having the equivalent chemical reactivity of the linking groups, directed by the spatial distance between the folding points. On the other hand, the relevant SEC analysis of IIb showed the predominant formation of the 8-form isomer, consistent with the polymer folding of Ib promoted by the enhanced chemical reactivity of the N-phenylpyrrolidinium end groups over the interior N, N-dialkylpyrrolidinium groups.

The self-assembly of molecules into a well-ordered structure is one of the most important processes in fabricating sophisticated materials. Here, we show that polymer chains can be self-assembled, distinguishing their direction (parallel or antiparallel), and could be a new useful scaffold for self-assembly in a controlled direction. The system that was used was a stereocomplex (SC) formation of linear and cyclic polylactide (PLA) stereoblock copolymers with a parallel and antiparallel chain arrangement in a Langmuir monolayer. The linear and cyclic stereoblock copolymers with a parallel arrangement formed a well-ordered lamellar SC in the first and second layers upon compression, but the linear and cyclic stereoblock copolymers with an antiparallel arrangement did not form a first-layer lamella and instead formed only the second-layer lamella. These results were only rationally explained by assuming that the enantiomeric PLA chains selectively assembled in a parallel direction, not in an antiparallel direction, in the SC. A simple polymer chain could be self-assembled, distinguishing the direction without a specific interaction group in it.

The synthesis of defect-free cyclic poly(3-hexylthiophene) (P3HT) was achieved for the first time by the GRIM polymerization using an appropriate initiator, cyclization by a Pd-mediated end-to-end coupling reaction, and two isolation processes using functionalized resins by selective capture of the impurities by taking advantage of the discriminable end groups. Various properties were investigated for defect-free linear and cyclic P3HT with all head-to-tail couplings as well as those with inverted 3-hexylthiophene units formed through the conventional GRIM polymerization. Mn,SEC, Mw,SEC, Rh, and [η] were significantly smaller for cyclic P3HT, and the topologies were visualized by STM. Remarkably, fluorescence spectroscopy revealed the essentially forbidden 0–0 transition with an extended lifetime for the defect-free cyclic P3HT arising from the circular symmetry, while cyclic P3HT with inverted units showed a strong 0–0 transition, which was similar to linear P3HT, due to the defects causing the symmetry ...

A cyclic grafted polymer, as a novel and unique kind of polymer, possesses a cyclic backbone and linear grafted side chains. Their physical properties and conformations are controlled by steric hindrance from the grafted side chains. As a cyclic derivative, cyclic grafted polymers have been successfully prepared and characterized within the past decade. To the best of our knowledge, cyclic grafted polymers have not been systematically generalized and summarized. In this review, we illustrate the considerable advances in the architectural construction of cyclic grafted polymers with three different approaches, including “grafting through”, “grafting onto” and “grafting from”. Additionally, their potential applications are also briefly discussed.

ConspectusThe precision design of topologically intriguing macromolecular architectures has continuously been an attractive challenge in polymer science and polymer materials engineering. A class of multicyclic polymer topologies, including three subclasses of spiro, bridged, and fused forms, are particularly unique not only from a topological geometry viewpoint but also from their biochemical relevance to programmed folding structures.In this Account, we describe recent progress in constructing this class of macromolecules, in particular by means of an electrostatic self-assembly and covalent fixation (ESA-CF) protocol, in which ion-paired polymer self-assemblies are employed as key intermediates. All three dicyclic constructions having either 8 (spiro), manacle (bridged), or θ (fused) forms, as well as a tricyclic trefoil (spiro) graph, have been constructed by the ESA-CF process. Moreover, a triply fused-tetracyclic macromolecular K3,3 graph has been constructed using a uniform-size dendritic polymer p...

A series of cyclic poly(tetrahydrofuran)s, poly(THF)s, having a pair of stereoisomeric forms of axially chiral, 2,2′-disubstituted-1,1′-binaphthyl (BiNap) unit at the opposite positions, CR-R, CR-S, and CR-R/S, have been newly synthesized through an electrostatic self-assembly and covalent fixation (ESA-CF) process by using a center-functionalized (kentro-telechelic) poly(THF) having an axially chiral BiNap unit and N-phenylpyrrolidinium salt end groups, carrying a dicarboxylate counteranion having a BiNap unit. The relevant cyclic and linear analogues, having one axially chiral unit, CR (CR-1 and CR-2) and LR, respectively, have also been prepared according to the ESA-CF protocol. The subsequent CD measurements of these cyclic and linear polymers having axially chiral units by lowering the temperature toward −10 °C in hexane revealed the noticeable reduction of the dihedral angle of the binaphthyl units exclusively for the cyclic CR-R as well as for the CR-1 and CR-R/S. The observed thermally induced cyc...

Self-assembled monolayers (SAMs) have attracted considerable attention as a tool to confer desirable properties on material surfaces. So far, molecules used for the SAM formation are generally limited to linear ones and thus chain ends dominate the surface properties. In this study, we have successfully demonstrated unique frictional properties of a SAM composed of alkane loops from cyclic alkanedisulfide on a gold substrate, where both sulfurs are bound to gold. The frictional response was proportional to the load. However, once the load went beyond a threshold value, the frictional response became more dominant. Such a frictional transition was reversible and repeatable and was not discerned for a corresponding SAM composed of n-alkyl chains. The load-induced change in the frictional response from the alkane loops could be associated with the conformational change of the alkane loops. The present results differ from most studies, in which the surface properties are designed on the basis of functional chain end groups.

In this monograph, we discussed and demonstrated ongoing developments in the unique collaboration of topological geometry and polymer chemistry. We described current topological polymer chemistry by highlighting the diverse nature of polymers with respect to both their chemistry and their line constructions. Topological analyses could provide fundamental insights on the principal materials and/or biological properties of polymers based on their segment geometries.

In this chapter, we discuss topological isomers of multicyclic polymers by using knots, links, and spatial graphs. Essential references on knot theory are [1, 2, 3, 4]. Chemistry applications of knot theory and low-dimensional topology are widely discussed in [5, 6].

In this chapter, we introduce polymers, long-chain molecules with diverse chemical compositions and structures. Topology can provide fundamental insights into the principle properties of polymers via their segment structures. We also present a brief description of the following chapters with respect to topological geometry and polymer chemistry.

In this chapter, we describe the chemistry-based, hierarchical classification procedure in which a series of nonlinear, cyclic, and branched polymer architectures are classified from the molecular graph presentation of alkanes and cycloalkanes. We also discuss a systematic notation protocol for nonlinear polymer topologies, modified from the previous version ([3]), that is based on classification via the terminus T and junction J values in graph constructions of topological polymers.

There are abundant examples in which the form of objects dictates their functions and properties at all dimensions and scales. In polymer chemistry and materials science, macromolecular structures have mostly been limited to linear or randomly branched forms. However, a variety of precisely controlled polymer topologies have been synthesized using intriguing techniques[1]. In particular, polymers with cyclic and multicyclic topologies have been made with unprecedented structural precision, and with qualities verified by new spectroscopic and chromatographic techniques[2].

The control of topological chain properties is essential in biopolymer processes, including DNA transcription and replication promoted by topoisomerase enzymes. Cleavage and re-bonding of DNA chains enables transformation of the chain topologies between a trivial knot (simple ring) and higher knotted constructions, as well as linked counterparts[1, 2]. Recently, topologically remarkable branching/folding structures have been identified in a class of proteins and polypeptides containing S-S bridging of selected cysteine pairs located along the cyclic polypeptide backbone[3, 4]. Their precise spatial 3D structures are crucial for specific biological functions, and enable chemical, thermal, and enzymatic stabilities [3, 4]. Ongoing breakthroughs in synthetic polymer chemistry now allow extensive choices in macromolecular structures beyond linear or randomly branched ones. Synthetic polymer systems with sufficiently long, flexible chains for random coil conformations are compatible with topological geometry conjectures. They are characterized by terminus (chain end) and junction (branching point) numbers as key invariant geometric parameters[5]. In this Chapter, we discuss the geometrical/topological operation of graph-structure polymers, with an emphasis on the relationships between chemical isomerism of topological polymers and geometrical graph transformations. A unique conception of topological isomerism is introduced that contrasts with constitutional and stereoisomerism in small molecules. From these considerations, rational and practical synthetic pathways are discussed for complex polymers having cyclic and multicyclic topologies.

In this chapter, we introduce graph theory for analyzing structures of multicyclic polymers. An essential graph theory reference is [1].

As seen in Chapter 2, topology variety increases with increasing multicyclic graphs: e.g., dicyclic, tricyclic, tetracyclic. Multicyclic graphs are classified into spiro, bridge, fused, and hybrid types [1]. In this chapter, we present graph theory definitions of the various multicyclic graphs and characterize each type via construction and decomposition. The characterizations may suggest polymer synthesis procedures. See Chapter 7 for the synthesis of multicyclic polymers.

A series of tri- and tetracyclic polymer topologies, composed of an elementary dicyclic unit of either theta-, eight- or manacle-forms, have been constructed by means of an ESA-CF (electrostatic self-assembly and covalent fixation) protocol in conjunction with an alkyne–azide click linking technique. Thus, a theta-shaped poly(THF) precursor having an alkyne group at the junction position (Ic) has newly been prepared by an ESA-CF process using an assembly (1b/2d), composed of a star poly(THF) having N-phenylpyrrolidinium salt groups carrying a counteranion of a trifunctional carboxylate having an alkyne group. In addition, monocyclic polymer precursors having an azide group (IIa) as well as linear-cyclic (tadpole) (IIb) and linear-dicyclic (twin-head tadpole) (IIc) polymer precursors, both having an azide group at the tail-end position, have been prepared through the tandem click reaction of the respective monocyclic and dicyclic (eight-form) precursors having an alkyne group (Ia and Ib, respectively) with...

An amphiphilic cyclic block copolymer consisting of poly(L- or D-lactide) and poly(ethylene oxide), that is, PLLA–PEO or PDLA–PEO, was synthesized from its corresponding linear triblock precursor, PLLA–PEO–PLLA or PDLA–PEO–PDLA, respectively, with alkenyl end groups. A mixture of the micellar dispersions of linear PLLA–PEO–PLLA and linear PDLA–PEO–PDLA formed a gel upon heating, whereas a mixture of the cyclic counterparts did not undergo this phase transition. These results suggest that the gelation behavior is directed by the topology of the polymer components. Furthermore, cyclic PLLA–PEO and cyclic PDLA–PEO block copolymers incorporating photocleavable o-nitrobenzyl units were synthesized. A mixture of the micellar dispersions of these block copolymers formed a gel upon ultraviolet irradiation via the ‘topological conversion’. A mixture of the micellar dispersions of linear PLLA–PEO–PLLA and linear PDLA–PEO–PDLA block copolymers formed a gel upon heating, whereas a mixture of the cyclic counterparts did not undergo this phase transition. These results suggest that the gelation behavior is directed by the topology of the polymer components. Furthermore, cyclic PLLA–PEO and cyclic PDLA–PEO block copolymers incorporating photocleavable o-nitrobenzyl units were synthesized. A mixture of the micellar dispersions of these block copolymers formed a gel upon ultraviolet (UV) irradiation via the ‘topological conversion’.

The “topological polymer chemistry” of amphiphilic linear and cyclic block copolymers at an air/water interface was investigated. A cyclic copolymer and two linear copolymers (AB-type diblock and ABA-type triblock copolymers) synthesized from the same monomers were used in this study. Relatively stable monolayers of these three copolymers were observed to form at an air/water interface. Similar condensed-phase temperature-dependent behaviors were observed in surface pressure–area isotherms for these three monolayers. Molecular orientations at the air/water interface for the two linear block copolymers were similar to that of the cyclic block copolymer. Atomic force microscopic observations of transferred films for the three polymer types revealed the formation of monolayers with very similar morphologies at the mesoscopic scale at room temperature and constant compression speed. ABA-type triblock linear copolymers adopted a fiber-like surface morphology via two-dimensional crystallization at low compression speeds. In contrast, the cyclic block copolymer formed a shapeless domain. Temperature-controlled out-of-plane X-ray diffraction (XRD) analysis of Langmuir–Blodgett (LB) films fabricated from both amphiphilic linear and cyclic block copolymers was performed to estimate the layer regularity at higher temperatures. Excellent heat-resistant properties of organized molecular films created from the cyclic copolymer were confirmed. Both copolymer types showed clear diffraction peaks at room temperature, indicating the formation of highly ordered layer structures. However, the layer structures of the linear copolymers gradually disordered when heated. Conversely, the regularity of cyclic copolymer LB multilayers did not change with heating up to 50 °C. Higher-order reflections (d002, d003) in the XRD patterns were also unchanged, indicative of a highly ordered structure. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015

The chain topology of polymer molecules arguably dictates their fundamental properties and functions. During the first two decades of this century a number of remarkable innovations have been observed in the field of polymer chemistry, to realize the precision designing of, in particular, a variety of cyclic and multicyclic polymer topologies. In this Perspective article, ongoing achievements and expectable breakthroughs in topological polymer chemistry are highlighted, by emphasizing the spectacular diversification of the choice of topologies in macromolecules beyond conventional linear or randomly branched forms.

Ring expansion metathesis polymerisation (REMP) has proven to be a viable approach to prepare high purity cyclic polymers. Macrocyclic polymers with a fully conjugated defect free backbone are of particular interest as these polymers have no end groups that can act as charge traps. In this work soluble macrocyclic poly(p-phenylenevinylene)s ( cPPVs) have been prepared directly via the REMP of substituted paracyclophanedienes. Single-molecule spectroscopy of the two topological forms of PPV i.e., linear ( lPPV) and cyclic ( cPPV) revealed that lPPV exists in an extended conformation whereas the cPPV adopts a restricted ring-like conformation. Despite such large differences in the chain conformation, the spectral properties of the two compounds are unexpectedly very similar, and are dominated by torsional deformations in relatively short conjugated segments.

A pentacyclic quadruply fused polymer topology has been constructed for the first time through alkyne–azide addition (click) and olefin metathesis (clip) reactions in conjunction with an electrostatic self-assembly and covalent fixation (ESA-CF) process. Thus, a spiro-type, tandem tetracyclic poly(tetrahydrofuran), poly(THF), precursor having two allyloxy groups at the opposite positions of the four ring units was prepared by the click-linking of one unit of an eight-shaped precursor having alkyne groups at the opposite positions with two units of a single-cyclic counterpart having an azide and an alkene group at the opposite positions. Both are obtainable through ESA-CF. The subsequent metathesis clip-folding of the tetracyclic precursor could afford a pentacyclic quadruply fused polymer product, of “shippo” form, in 19 % yield.

Cyclized poly(L-lactide) and poly(D-lactide) (Mn ∼ 3 kDa) incorporating an o-nitrobenzyl group as a photocleavable linker were synthesized and photoirradiated for topological transformation to form photocleaved linear polylactides. By DSC, Tm of the cyclized stereocomplex (167 °C) decreased by more than 40 °C from that of the linear prepolymers (209 °C) despite their essentially identical molecular weights. Upon the photocleavage, the resulting linear stereocomplex showed almost the same Tm (211 °C) as that before the cyclization. The enthalpy of melting of crystals having an infinite thickness, i.e. ΔHm(100%), and the surface free energy (σe) were determined by the combination of WAXD, SAXS, and DSC. Both ΔHm(100%) and σe were considerably smaller for the cyclized polylactide homocrystals and stereocomplexes than those of the linear prepolymers and photocleaved products. These suggest that the absolute enthalpy of the melt state is lower, and the crystalline–amorphous interface is more stable for the cyclized polylactides arising from the topology.

The emulsion formation and the subsequent phase-separation process of water/toluene mixtures has been investigated by employing a pair of block copolymer surfactants having a linear A-B-A and its cyclized A-B topologies. The linear surfactant was found to be more effective to keep the emulsion layer in the water phase, attributable to the folding/extending motion of the hydrophobic A segments specifically in the linear surfactant.

A series of linear and cyclized amphiphilic block copolymers consisting of poly(acrylic acid) (AAm) and main-chain liquid crystalline (LC) poly(3-methylpentamethylene-4,4′-bibenzoate) (BBn) segments were newly synthesized. Solid state morphology was investigated by X-ray scattering. Linear AA21BB9AA21, cyclic AA33BB10, and cyclic AA51BB18 formed lamellar microdomains, where the BBn segment of cyclic AA51BB18 formed a smectic CA phase. On the other hand, cylinder-type microdomains were formed by linear AA44BB9AA44 and cyclic AA100BB9. These amphiphilic block copolymers were self-assembled in water to form vesicles or cylindrical micelles, depending on the polymer concentration of the initial THF solution. The response of these nanostructures against an electric field demonstrated that the vesicles formed from linear AA25BB14AA25 and cyclic AA51BB18 turned into substantially larger aggregates, likely due to the reorganization of the LC segment in the bilayer.

A concise two-step click/ESA-CF process has been developed to prepare a kyklo-telechelic poly(tetrahydrofuran), poly(THF), having three functional groups at the constant intervals. Thus, a key linear precursor (I), having N-phenylpyrrolidinium salt groups at the chain ends and having two hydroxyl groups at the prescribed inner positions, has been prepared through the alkyne–azide addition (click) reaction using one unit of a linear telechelic poly(THF) having a pair of an alkyne and a hydroxyl groups (1) and two units of a linear asymmetric telechelic poly(THF) having an azide and an N-phenylpyrrolidinium salt group (2). The subsequent polymer cyclization by means of an electrostatic self-assembly and covalent fixation (ESA-CF) process, by employing a dicarboxylate counteranion having an additional alkyne group (3) to I, could produce a trifunctional kyklo-telechelic poly(THF) (II), having two hydroxyl and one alkyne groups positioned at the constant intervals along the ring polymer backbone. The subseque...

Diffusion dynamics of topological isomers of polymer molecules was investigated at the single-molecular level in the melt state by employing the fluorophore-incorporated 4-armed star and the corresponding doubly-cyclized, 8-shaped poly(THF) chains. While the single-molecule fluorescence imaging experiment revealed that the diffusion of the 4-armed star polymer was described by a single Gaussian distribution, the diffusion of the 8-shaped polymer exhibited a double Gaussian distribution behaviour. We reasoned that the two 8-shaped polymeric isomers have distinct diffusion modes in the melt state, although ensemble-averaged experimental methods cannot detect differences in the overall conformational state of the isomers. The single-molecule experiments suggested that one of the 8-shaped polymeric isomers, having the horizontally oriented form, causes an efficient threading with the linear matrix chains which leads to slower diffusion compared with the corresponding 4-armed star polymer, while the other 8-shaped polymeric isomer, having the vertically oriented form, displayed faster diffusion by the suppression of effective threading with the linear matrix chains due to its contracted chain conformation.

A dicyclic, eight-shaped and a tricyclic, trefoil-shaped poly(THF) both having an alkyne group at the core position (II and III, respectively) have been introduced as versatile core-clickable kyklo-telechelic precursors. The prepolymer II has been prepared by an ESA-CF (electrostatic self-assembly and covalent fixation) process using an assembly (1a/2b), composed of two units of linear poly(THF) having N-phenylpyrrolidinium salt groups carrying one unit of a tetrafunctional carboxylate having an alkyne group as a counteranion. Alternatively, the prepolymer III has been produced through a click process using a cyclic poly(THF) precursor having an azide group (Ia), obtainable also by the ESA-CF technique, with a tripropargylated pentaerythritol derivative (2c) followed by the esterification with 4-pentynoic acid to introduce again an alkyne group. The subsequent click coupling reaction of II and III with a linear telechelic poly(THF) having azide groups (1b) afforded successfully novel tetra- and hexacyclic...

Ring expansion metathesis polymerisation (REMP) has proven to be a viable approach to prepare high purity macrocyclic phenylenevinylene polymers., Ring expansion metathesis polymerisation (REMP) has proven to be a viable approach to prepare high purity cyclic polymers. Macrocyclic polymers with a fully conjugated defect free backbone are of particular interest as these polymers have no end groups that can act as charge traps. In this work soluble macrocyclic poly(p-phenylenevinylene)s (cPPVs) have been prepared directly via the REMP of substituted paracyclophanedienes. Single-molecule spectroscopy of the two topological forms of PPV i.e., linear (lPPV) and cyclic (cPPV) revealed that lPPV exists in an extended conformation whereas the cPPV adopts a restricted ring-like conformation. Despite such large differences in the chain conformation, the spectral properties of the two compounds are unexpectedly very similar, and are dominated by torsional deformations in relatively short conjugated segments.

A pair of four-armed star and dicyclic 8-shaped poly(tetrahydrofuran)s, poly(THF)s, possessing a perylene diimide group at the core position (Ia and Ib, respectively) were synthesized by means of an electrostatic self-assembly and covalent fixation (ESA–CF) protocol. Mono- and bifunctional poly(THF)s having N-phenylpiperidinium salt end groups accompanying a perylene diimide tetracarboxylate as a counteranion were prepared by the ion-exchange reaction, and the subsequent covalent conversion by reflux in toluene afforded the corresponding core-fluorescent four-armed star and dicyclic 8-shaped poly(THF)s, (Ia and Ib, respectively) for the use of single-molecule fluorescence microscopy measurements.

A "topological polymer chemistry" at air/water interface is investigated by using an amphiphilic linear and cyclic block copolymers. A cyclic copolymer and two kind of linear polymers (AB-type diblock and ABA-type triblock copolymers) with same components were used in the study. The relatively stable monolayers of these three kinds of copolymers were formed at the air/water interface. The analogous condensed tendency and temperature dependency were observed in surface pressure-area isotherms of three kinds of monolayers. It is considered that molecular orientation at air/water interface of two kinds of liner block copolymers is similar to that of cyclic block copolymer. From the result of atomic force microscopic observation of transfered films, monolayers of the three kinds of polymers have formed a very similar morphology at mesoscopic scale under the conditions at room temperature and the constant compression speed. It finds that ABA type triblock liner copolymer formed fiber-like surface morphology by the two-dimensional crystallization based on the low compression speed. On the other hand, cyclic block copolymer formed shapeless domain.

The nucleophilic esterification of 5- and 7-membered N-phenylcyclic ammonium salts resulted in distinctive regioselectivity, despite their comparable ring strain in the ground states relative to the corresponding cyclopentane and cycloheptane (both 25.9 kJ mol(-1)). The former underwent a selective ring-opening reaction, while the latter predominantly underwent ring-emitting with concurrent ring-opening reactions. A DFT study of the model compounds revealed that the regioselection in the 5- and 7-membered azacycloalkane quaternary salts is plausibly directed by the transition state ring conformation, and not by the ground state ring strain. Remarkably, at the ring-opening transition state, the 5-membered cyclic skeletal structure expands toward the unstrained and thus less frustrated 6-membered cyclohexane conformation. On the other hand, the 7-membered counterpart expands at the ring-opening transition state toward the more frustrated 8-membered cyclooctane conformation to promote the alternative ring-emitting process.

Nanosilica (NS) was recently used as a filler to improve mechanical properties, morphology behaviors of natural rubber (NR) composites and also for light colored product. NS is hard to disperse in NR composite compare to carbon black due to large number of Silanol (Si-OH) group leads to strong filler-filler interaction. Silane coupling agent was extensively used to improve reinforce efficiency of NS and also for good filler-matrix interaction by reducing Si-OH group. In this study, Bis[3-(triethoxysilyl)propyl] tetrasulfide (Si-69) and (3-aminopropy)triethoxysilane (APTES) were used as a coupling agents with various loading 1.5, 3, 4.5 phr in conventional sulphur vulcanization system. Both Si69 and APTES gave a significance of the NR compound processing. However, hardness was gradually decreased up to 4.5 phr due to plasticizing effect. Si-69 can increase crosslink density because of 4 molecular of sulphur (S) and its structure retarded the curing where APTES accelerated the cured because APTES has lower molecular weight and viscosity than Si-69.

An alkyne–azide addition (click) reaction of a linear poly(tetrahydrofuran), poly(THF), precursor having an alkyne group at the center position and cyclic ammonium salt end groups has been applied with the complementary linear poly(THF) precursors having an azide group at single or both chain ends to produce asymmetric star- and H-shaped poly(THF) precursors having cyclic ammonium salt end groups. The subsequent electrostatic self-assembly and covalent fixation (ESA-CF) process after introducing dicarboxylate counteranions having an additional alkene or alkyne group could afford the designated kyklo-telechelic precursors, having either a tadpole form containing an alkyne group at the top-head and an alkene group at the tail-end positions or an isomeric manacle/theta form containing two alkene groups at the orthogonal positions. The further click coupling of the former with a linear telechelic precursor having azide groups followed by the metathesis folding (clip) process could produce effectively a doubly...

A set of four types of block copolymers consisting of topological amphiphilic segment pairs was effectively synthesized via kyklo- (functionalized cyclic) and kentro- (center-functionalized linear) telechelic poly(ethylene oxide) (PEO) and poly(tetrahydrofuran) (poly(THF)). Accordingly, kyklo- and kentro-telechelic PEO with an ethynyl group was newly prepared from relevant linear PEO precursors with quinuclidinium end groups and an ethynyl-functionalized dicarboxylate counteranion by the electrostatic self-assembly and covalent fixation (ESA-CF) process. Similarly, kyklo- and kentro-telechelic poly(THF) with an azido group was obtained. The PEO and poly(THF) telechelics were subjected to click chemistry to systematically produce amphiphilic block copolymers with two symmetric topological forms, that is, an “8” shape (IC·IIC) and a four-armed star shape (IL·IIL), and two asymmetric topological forms, that is, twin-tailed tadpole shapes (IL·IIC and IC·IIL) with respect to the hydrophilic–hydrophobic plane.