Search

The living cationic polymerizations of sulfide-containing vinyl ethers, namely, alkyl-sulfide-containing 2-(ethylthio)ethyl vinyl ether (ESEVE) and arylsulfide-containing 2-(phenylthio)ethyl and 2-[4-(methylthio)phenoxy]ethyl vinyl ethers (PSEVE and MSPEVE, respectively), were examined using HCl/ZnCl2, 1-(isobutoxy)ethyl acetate (IBEA)/Et1.5AlCl1.5, and IBEA /Et1.5AlCl1.5/SnCl4 as initiators. The polymerization of ESEVE terminated at a 35% monomer conversion, and a high-molecular-weight polymer was not obtained; instead, the nucleophilicity of the sulfur moiety in ESEVE led to cyclization, forming five-membered ring sulfonium species. In contrast, the side reactions were suppressed when PSEVE was used, which has a less-nucleophilic sulfur moiety on its benzene ring, and polymerization proceeded to an 88% conversion, affording a high-molecular-weight polymer with a narrow molecular weight distribution (Mw = 12,500, Mw/Mn = 1.18). Furthermore, cyclic sulfonium was not produced during the polymerization of MSPEVE, in which the sulfur atom was farther from the generated carbocation; the polymerization proceeded quantitatively producing a high-molecular-weight polymer with a narrow molecular weight distribution, despite the short lifetime of the growing species. In particular, a high-molecular-weight polymer with the narrowest distribution (Mw = 13,500, Mw/Mn = 1.08) was obtained when SnCl4 was used as the Lewis acid.

Fully aromatic polyimide particles were obtained in a single step via the polycondensation of diethyl (hexafluoroisopropylidene)diphthalate (6FE) and 4,4′-oxydianiline (ODA) using polyvinylpyrrolidone (PVP) as a steric stabilizer in ethylene glycol. Since the monomers are soluble in ethylene glycol, but the polyimide is insoluble, the polyimide particles grew gradually during the polycondensation process. The particle size and size distribution were controlled by varying the molecular weight and amounts of PVP. The particle size decreased with both increasing concentration and increasing molecular weight of the stabilizer. Furthermore, the solvent composition affected the particle size, i.e., the particle size decreased with increasing volume of glycerol as a cosolvent. Monodisperse particles (diameter: 8.5–1.8 μm) were obtained by varying the amounts of PVP and glycerol. Fully aromatic polyimide particles were obtained in a single step via the polycondensation of diethyl (hexafluoroisopropylidene)diphthalate and 4,4’-oxydianiline using polyvinylpyrrolidone (PVP) as a steric stabilizer in ethylene glycol. Since the monomers are soluble in ethylene glycol, but the polyimide is insoluble, the polyimide particles grew gradually during the polycondensation process. The particle size and size distribution were controlled by varying the molecular weight and amounts of PVP.

A ruthenium complex prepared in situ from [RuCl2( p-cymene)]2 and TpMe2K [TpMe2 = hydrotris(3,5-dimethylpyrazolyl)borate] is efficient for aromatic C–H borylation with pinacolborane (4,4,5,5-tetramethyl-1,3,2-dioxaborolane). Arenes were borylated at more electron-rich positions. DFT calculations and kinetic isotope effect experiments suggest that the catalytic cycle should involve an electrophilic aromatic substitution with a borenium cation.

The Ru-catalyzed dehydrogenative silylation of 2-alkyloxazolines with 1,1,1,3,5,5,5-heptamethyltrisiloxane took place site-selectively at methyl C(sp3)−H bonds located γ to the nitrogen atom of the oxazolyl groups. Pyridine and pyrazole rings could also be used as a directing group. A catalytic mechanism based upon successive σ-bond metathesis is proposed.

One of the authors discovered helix-sense-selective polymerization (HSSP) of an achiral substituted phenylacetylene which has two hydroxymethyl groups and a relatively hydrophobic substituent by using a chiral catalytic system in 2003. The one-handed helicity is stable and static in nonpolar solvents because it is maintained by intramolecular hydrogen bonds. Since the resulting polymer has extremely tight helicity in its main chain, it shows many interesting and unusual properties including highly selective photocyclic aromatization (SCAT). In this review, the discovery and development of the HSSP and SCAT reactions, and the properties and application of the resulting polymers prepared by HSSP and the resulting supramolecular polymers prepared by SCAT will be examined.

The ruthenium-catalyzed dehydrogenative borylation of 2-arylpyridines with pinacolborane took place at ortho-positions of the benzene ring. Density functional theory calculations and kinetic isotope effect experiments suggest that the catalytic cycle should involve oxidative addition of the CH bond, the rate-determining σ-bond metathesis of pinacolborane with the ruthenium hydride complex, and reductive elimination of the CB bond.

The intramolecular dehydrogenative cyclization of 2-(dialkylsilyl)biaryls proceeded in the presence of a catalytic amount of platinum(II) chloride and potassium tris(3,5-dimethyl-1-pyrazolyl)borohydride to give good yields of the corresponding dibenzosilole derivatives.

Highly selective photocyclic aromatization (SCAT) of poly(substituted acetylene)s, which can quantitatively yield the corresponding 1,3,5-trisubstituted benzene derivative, was applied to quantitative determination of the microstructures of copoly(substituted acetylene)s. By GPC analysis of the SCAT products of the copolymers of two substituted acetylenes having substituents whose molecular weights were greatly different, some clear information regarding the microstructures, such as sequence (triad) distribution and composition, which could not be obtained from NMR because of their broad peaks, could be obtained successfully under a mild condition.

Polycondensation of nylon salt-type monomer composed of diethyl hexafluoroisopropylidenediphthalate and diaminooctane was performed at 130°C in ethylene glycol to form confetti-shaped particles. Before the polycondensation, the salt monomer solution was homogeneous. As the polycondensation proceeded, the solution became turbid and polyimide particles grew to around 7 μm for 8 h. After the polycondensation, small particles precipitated and got deposited onto large particles to form confetti-shaped particles. Rod-shaped particles were also formed by the polycondensation at low monomer concentration in a long reaction time. They were found to be crystalline in form.

Cationic polymerization of 2-adamantyl vinyl ether (2-vinyloxytricyclo[3.3.1.13,7]decane; 2-AdVE) and copolymerization of 2-AdVE with n-butyl vinyl ether (NBVE), 2-methoxyethyl vinyl ether (MOVE), or 2-(2-vinyloxyethoxy)ethyl acrylate (VEEA), vinyl ethers containing a flexible chain or a polymerizable group, were performed to obtain poly(vinyl ether) plastics for optical use. With the living cationic initiating systems such as isobutyl vinyl ether–acetic acid adduct/ethylaluminum sesquichloride (IBEA/Et1.5AlCl1.5) or the hydrogen chloride/zinc chloride (HCl/ZnCl2), all the obtained copolymers had unimodal and relatively narrow molecular weight distributions (polydispersity ratio: M w/M n = ~1.5 at high conversion) throughout the copolymerizations. These results indicate that the copolymerizations of 2-AdVE with the three comonomers led to the statistical copolymers without contamination of homopolymers. With BF3OEt2 as an initiator, homopolymer of 2-AdVE and poly(2-AdVE)-based polymers, poly(2-AdVE-stat-NBVE), poly(2-AdVE-stat-MOVE), and poly(2-AdVE-stat-VEEA), were produced with high-molecular weights (M n = 31,800–116,000) in toluene at −30 °C in quantitative yield within 10 min. They have excellent thermal stability owing to their high glass transition and thermal decomposition temperatures. The transparency (86–91 %) and refractive index (1.52–1.53) of the molded polymers are similar to those of conventional optical plastics such as poly(methyl methacrylate) (PMMA) and polycarbonate (PC), whereas their specific gravity (1.09–1.12) and water absorption (0.06–0.17 %) are significantly lower than those of PMMA and PC. In addition, the Abbe number of poly(2-AdVE), poly(2-AdVE-stat-NBVE), and poly(2-AdVE-stat-MOVE) exceeded 60 and was higher than those of PMMA and PC, indicating that the poly(2-AdVE)-based plastics are very suitable for optical lens.

A facile synthesis of novel five 2D (planar) surface modifiers having a triphenylbenzene derivatives as a 2D structure has been achieved by the highly selective photocyclic aromatization reaction. Efficient enhancement of oxygen permselectivities through the three polymer membranes has been achieved by adding a small amount ( P O 2 -α graph were over or close to the upper boundary line by Robeson in 1991. Since all the membranes containing the 2D surface modifiers showed better permselectivities than the corresponding substrate membranes, it is very promising for the future.

It is often difficult to observe nanoscale structures of polymeric materials using conventional transmission electron microscopy (TEM) because of their weak scattering contrast. To produce quantitative image contrast without any staining, low-angle annular dark-field scanning transmission electron microscopy (LAADF-STEM) was studied for its applicability for observing fine structures in block copolymers. The LAADF-STEM images displayed microphase-separated morphologies of block copolymers with high S/N contrast depending on the intrinsic density difference because of nonstaining. We found that the temperature dependence of the image contrast showed a kink around the glass-transition of the constituent phase, from which one can estimate glass transition temperatures and thermal expansion coefficients at nanoscale. This indicates that the LAADF-STEM imaging is an effective tool to quantitatively image nanoscale phases of polymers.

It has been achieved to obtain flexible self-supporting supramolecular polymeric membranes consisting of only 1,3,5-trisubstituted benzene derivatives prepared by highly selective photocyclic aromatization of the corresponding poly (substituted phenylacetylene)s having a columnar structure. The flexibilities of the self-supporting supramolecular polymeric membranes were enhanced by introducing hydroxyl groups or phenylene groups to the starting polymers (monomers). There were two reasons for the enhanced strength: 1) introduction of intercolumnar hydrogen bonds and 2) enhancement of the degree of intracolumnar stackings. This strength depended on the structure of the starting polymers which functioned as a template.

By using a new achiral phenylacetylene having bulky substituents as a monomer, living-like helix-sense-selective polymerization ( HSSP ) has been achieved. This is the first example of the HSSP of substituted acetylenes where the degree of polymerization was controlled. The resulting one-handed helical living polymer initiated polymerization of a second monomer to successfully yield a block copolymer.

Some heterocyclic substrates, substituted at the ortho-position of a heteroatom with alkyl substituents bearing a site-selective methyl group, are successfully silylated with reagent (II).

Polycondensations of nylon-salt-type monomers composed with diethyl pyromellitate and aliphatic diamines with various methylene lengths were performed at 130 °C in ethylene glycol to afford flower-like particles. Before the polycondensation, the salt monomer solution was homogenous. As the polycondensation proceeded, the solution became turbid and polyimide particles grew to around 15 µm in 8 h. Further polycondensation broke the particles into small pieces. The polyimide particles showed the distinctive odd-even effect of the methylene chain of diamine in both inherent viscosity and crystallinity. The polyimide particles using diamine with even-methylene length had higher crystallinity and lower inherent viscosity than those using diamine with odd-methylene length.

A soluble and stable one-handed helical conjugated polymer without the coexistence of any other chiral moieties was successfully synthesized by asymmetric-induced polymerization of a chiral monomer having two hydroxyl groups followed by desubstitution of the chiral groups in a solid membrane state . The reason for the success was the polymer reaction was carried out in the membrane state. This is an alternative method to obtain such a unique chiral polymer which was obtained only by the helix-sense-selective polymerization (HSSP) we reported before. In addition the efficiency of the chiral induction was higher than that of the HSSP. It is interesting that the “ Membrane state” acted like as if a protecting group.

Homochiral or enantioenriched helical polymers are essential for investigating the relationship between chirality of helical structures and their performance in the design of various optically active functional polymers. We have succeeded in obtaining the helical poly(phenylacetylene)s poly(1)–poly(6) possessing no chiral moieties, except for helicity; the enantioenriched helical sense of these polymers was induced by transformation in chiral solvents, followed by removal of the chiral solvents, even if the interaction between the chiral molecule and the polymer was weak such as solvent–solute interaction. In particular, the newly synthesized poly(6) retained the induced helical sense even in an achiral solvent. A series of racemic helical or achiral poly(phenylacetylene)s were prepared, and the preferential helical sense of the polymers was induced by transformation in chiral solvents, even if the interaction between the chiral molecule and the polymer was weak such as solvent–solute interaction. The enantioenriched helical poly(phenylacetylene)s possessing no chiral moieties except for helicity were obtained by removal of chiral solvents. In particular, one of them retained the induced helical sense even in an achiral solvent.

A soluble and stable one-handed helical poly(substituted phenylacetylene) without the coexistence of any other chiral moieties was successfully synthesized by asymmetric-induced polymerization of a chiral monomer followed by two-step polymer reactions in membrane state: (1) removing the chiral groups (desubstitution), and (2) introduction of achiral long alkyl groups at the same position as the desubstitution to enhance the solubility of the resulting one-handed helical polymer (resubstitution). The starting chiral monomer should have four characteristic substituents: (i) a chiral group bonded to an easily hydrolyzed spacer group, (ii) two hydroxyl groups, (iii) a long rigid hydrophobic spacer between the chiral group and the polymerizing group, (iv) a long achiral group near the chiral group. As spacer group a carbonate ester was selected. The two hydroxyl groups formed intramolecular hydrogen bonds stabilizing a one-handed helical structure in solution before and after the two-step polymer reactions in membrane state. The rigid long hydrophobic spacer, a phenylethynylphenyl group, enhanced the solubility of the starting polymer, and realized effective chiral induction from the chiral side groups to the main chain in the asymmetric-induced polymerization. The long alkyl group near the chiral group avoided shrinkage of the membrane and kept the reactivity of resubstitution in membrane state after removing the chiral groups. The g value (g = ([θ]/3,300)/ε) for the CD signal assigned to the main chain in the obtained final polymer was almost the same as that of the starting polymer in spite of the absence of any other chiral moieties. Moreover, since the one-handed helical structure was maintained by the intramolecular hydrogen bonds in a solution, direct observation of the one-handed helicity of the final homopolymer has been realized in CD for the solution for the first time.

To develop new phenylacetylene monomers more suitable for helix-sense-selective polymerization (HSSP) we reported previously and to improve the efficiency of the HSSP and membrane performance of the resulting polymers, novel phenylacetylenes having a flexible oligosiloxanyl group (SnBDHPA) together with the other related three series of monomers were synthesized and polymerized by using a chiral catalytic system and enantioselectivity in permeation of the membranes from the resulting chiral polymers were examined. SnBDHPA was the most suitable for the HSSP and the CD absorptions (G values) of poly(SnBDHPA) were stronger and more stable than those of the corresponding polymers having rigid alkyl groups. The polymers could be fabricated to flexible self-supporting membranes by using solvent-casting method. In addition, enantioselectivity in permeation of one of poly(SnBDHPA) membranes was much higher than that of a poly(phenylacetylene) membrane having alkyl groups. This was because the polymers having olig...

Three novel chiral phenylacetylenes having an octyloxyethanolamine residue derived from a l-aminoalcohol and two hydroxymethyl groups were synthesized and polymerized by two achiral catalysts ((nbd)Rh+[η6-(C6H5)B−(C6H5)3] and [Rh(nbd)Cl]2/triethylamine (TEA)) and a chiral catalytic system ([Rh(nbd)Cl]2/(S)- or (R)-phenylethylamine ((S)- or (R)-PEA)). All of the resulting polymers showed Cotton effects at wavelengths around 430 nm. This observation indicated that they had an excess of one-handed helical backbones. Positive and negative Cotton effects were observed for the polymers having an l-valinol residue produced by using (S)- and (R)-PEA as a cocatalyst, respectively, although the monomers had the same chirality. The two polymers having an l-alaninol or l-phenylalaninol residues obtained by using (S)- and (R)-PEA as a cocatalyst showed CD absorptions with identical signs. Therefore, we found that the chiral monomer having an l-valinol residue was suitable for both modes of asymmetric polymerization, t...

To develop a new phenylacetylene monomer suitable for helix-sense-selective polymerization (HSSP) we reported previously and to improve the efficiency of the HSSP and membrane performance of the resulting polymer, a novel phenylacetylene having a trisiloxanyl group (S3BDHPA) was synthesized and polymerized by using a chiral catalytic system and enantioselectivity in permeation of its membrane was examined. S3BDHPA was suitable for the HSSP and the CD absorption of poly(S3BDHPA) was stronger and more stable than that of the corresponding polymer having no siloxanyl groups. In addition, enantioselectivity in permeation of poly(S3BDHPA) was much higher than that of a polymer membrane having no siloxanyl groups. They are thought to be caused by the flexibility and hydrophobicity of the trisiloxane groups.

We synthesized an optically active poly(binaphthyl-6,6′-diylethynylene-1,3-phenyleneethynylene) with pendant galvinoxyl residues. The hydrogalvinoxyl precursor polymer was given by polymerization of (1,3-diiodophenyl)hydrogalvinoxyl and 6,6′-diethynyl-2,2′-dihexyloxybinaphthyl using Pd(PPh3)4 catalyst (Mw = 4.6 × 104, Mw/Mn = 3.0). The polymer yielded the corresponding polyradical with high spin concentration by treatment of the polymer solution with PbO2. In the CD spectra of the polymer and polyradical taken in various solutions, clear Cotton effects were observed in the absorption region of the binaphthyl chromophore, while no Cotton effect was observed in that of the galvinoxyl chromophore. On the other hand, in the MCD, Faraday effects were observed in the absorption region of the backbone and galvinoxyl chromophore. The static magnetic susceptibility of the chiral polyradical was measured using a SQUID magnetometer, and showed weak antiferromagnetic interaction.

In this study, we synthesized four chiral helical poly(phenyleneethynylenes) having optically active menthoxycarbonyl groups and desubstituted the chiral groups in membrane state. Polycondensations of (+)-menthyl 3,5-diethynylbenzoate with (+)-menthyl 3,5-diiodobenzoate, 1,2-diiodobenzenen, 1,3-diiodobenzene, and 1,4-diiodobenzene using PdCl2(PPh3)2–PPh3–CuI were afforded helical polymers in good yields (named as PMtMt, o-PMtH, m-PMtH, and p-PMtH, respectively). Among them, PMtMt in a mixture of chloroform/benzene showed the largest Cotton effect in absorption region and gave self-supporting membrane by solvent-casting method. PMtMt membrane also showed a Cotton signal similar to that observed in solution. Desubstitution of PMtMt proceeded quantitatively by immersing the membrane into alkaline solution at room temperature for 3 days. The desubstituted PMtMt membrane showed circular dichroism (CD) signals similar shape to that of the original membrane in the UV region in despite of the polymer having no chiral moieties except for helical conformation. This is the first example of synthesis of chiral helical poly(phenyleneethynylenes) without the coexistence of any other chiral moieties.

4-Alkyloxy-3,5-bis(hydroxymethyl)phenylacetylenes with eight types of alkyl groups were synthesized and polymerized with a chiral catalytic system. We found that the length of the alkyl groups played a very important role in achieving helix-sense-selective polymerization. Five helix-sense-selective polymerizations were achieved resulting in polymers with alkyl groups whose chain length was longer than six. We think that the longer-chain alkyl groups prevented the polymers from becoming insoluble by forming intermolecular hydrogen bonds between the hydroxyl groups, and stabilized their one-handed helical structure by promoting the formation of intramolecular hydrogen bonds.

The living cationic polymerization of 5-ethyl-2-methyl-5-(vinyloxymethyl)-1,3-dioxane (1), a vinyl ether with a cyclic acetal unit, was investigated with various initiating systems in toluene or methylene chloride at 0 to -30 °C. With initiating systems such as hydrogen chloride (HCl)/zinc chloride (ZnCl 2 ), isobutyl vinyl ether-acetic acid adduct [CH 3 CH(OiBu)OCOCH 3 ]/tin tetrabromide (SnBr4)/di-tert-butylpyridine (DTBP), and CH 3 CH(OiBu)OCOCH 3 /ethylaluminum sesquichloride (Et 1.5 AlCl 1.5 )/ethyl acetate (CH 3 COOEt), the number-average molecular weights (M n 's) of the obtained poly(1)s increased in direct proportion to the monomer conversion and produced polymers with relatively narrow molecular weight distributions [MWDs; weight-average molecular weight/number-average molecular weight (M w /M n ) = 1.2-1.3]. To investigate the living nature of the polymerization with CH 3 CH(OiBu)OCOCH 3 /SnBr 4 /DTBP, a second monomer feed was added to the almost polymerized reaction mixture. The added monomer was completely consumed, and the M n values of the polymers showed a direct increase against the conversion of the added monomer, indicating the formation of a long-lived propagating species. The glass transition temperature and thermal decomposition temperature of poly(1) (e.g., M n = 13,600, M w /M n = 1.30) were 29 and 308 °C, respectively. The cyclic acetal group in the pendants of the polymer of 1 could be converted to the corresponding two hydroxy groups in a 65% yield by an acid-catalyzed hydrolysis reaction.

Benzamides containing both electron-donating and electron-withdrawing groups are utilized in silylation reaction which takes place in ortho-position to the amide-moiety of the benzene ring.

The ruthenium-catalyzed dehydrogenative borylation of 2-arylpyridines with pinacolborane took place at ortho-positions of the benzene ring. Density functional theory calculations and kinetic isotope effect experiments suggest that the catalytic cycle should involve oxidative addition of the CH bond, the rate-determining σ-bond metathesis of pinacolborane with the ruthenium hydride complex, and reductive elimination of the CB bond.

An amphiphilic 1,3,5-trisubstituted benzene as a new 2D surface modifier (T-EO) which has six hydroxy groups and three oligoethylene groups was successfully and easily synthesized by selective phot...

To study the possibility of living cationic polymerization of vinyl ethers with a urethane group, 4-vinyloxybutyl n-butylcarbamate (1) and 4-vinyloxybutyl phenylcarbamate (2) were polymerized with the hydrogen chloride/zinc chloride initiating system in methylene chloride solvent at -30 °C ([monomer] o = 0.30 M, [HCl] 0 /[ZnCl 2 ] 0 = 5.0/2.0 mM). The polymerization of 1 was very slow and gave only low-molecular-weight polymers with a number-average molecular weight (M n ) of about 2000 even at 100% monomer conversion. The structural analysis of the products showed occurrence of chain-transfer reactions because of the urethane group of monomer 1. In contrast, the polymerization of vinyl ether 2 proceeded much faster than 1 and led to high-molecular-weight polymers with narrow molecular weight distributions (MWDs ≤ ∼1.2) in quantitative yield. The M n 's of the product polymers increased in direct proportion to monomer conversion and continued to increase linearly after sequential addition of a fresh monomer feed to the almost completely polymerized reaction mixture, whereas the MWDs of the polymers remained narrow. These results indicated the formation of living polymer from vinyl ether 2. The difference of living nature between monomers 1 and 2 was attributable to the difference of the electron-withdrawing power of the carbamate substituents, namely, n-butyl for 1 versus phenyl for 2, of the monomers.

The intermolecular dehydrogenative coupling of 1,1,1,3,5,5,5-heptamethyltrisiloxane with aromatic compounds such as aryloxazolines and arylimines in the presence of a catalytic amount of [RuCl2(p-c...

A new polymer prepared by polymerization of 3,5-bis(hydroxymethyl)phenylacetylene having a chiral menthyl group via a very long and rigid spacer by an achiral rhodium complex with triethylamine as ...

The borylated products (III) and (V) can be readily converted to the corresponding boronic acids under acidic conditions.

We synthesized optically active polyradicals possessing an excess of one-handed helical backbone by helix-sense-selective polymerization (HSSP) of achiral monomers which was promoted by rhodium complex catalyst in the presence of (R)- or (S)-1-phenylethylamine. The monomer, which had two hydroxy groups and a hydrogalvinoxyl unit, gave the corresponding polymer with an optically active helical conformation stabilized by intramolecular hydrogen bonding. The chemical oxidation of the polymer yielded the corresponding optically active helical polyradical with high spin concentration. The static magnetic susceptibility of the chiral polyradical was measured using a SQUID magnetometer. We have found that the stronger antiferromagnetic interaction was observed for the polyradical synthesized by HSSP in comparison with the polyradical via polymerization in the presence of racemic phenylethylamine.

Electron-donating or ortho substituted aromatic bromides give low yields compared to the corresponding iodides (IIa) and (IId).