Non-centrosymmetric coordination polymer with a highly hindered octahedral copper center bridged by mandelate

A novel chiral coordination polymer, [Cu(C(6)H(5)CH(OH)COO)(μ-C(6)H(5)CH(OH)COO)] (1-L and 1-D), was synthesized through a reaction of copper acetate with L-mandelic acid at room temperature. Although previously reported copper mandelate prepared by hydrothermal reaction was a centrosymmetric coordination polymer because of the racemization of mandelic acid, the current coordination polymer shows noncentrosymmetry and a completely different structure from that previously reported. The X-ray crystallography for 1-L revealed that the copper center of the compound showed a highly distorted octahedral structure bridged by a chiral mandelate ligand in the unusual coordination mode to construct a one-dimensional (1D) zigzag chain structure. These 1D chains interdigitated each other to give a layered structure as a result of the formation of multiple aromatic interactions and hydrogen bonds between hydroxyl and carboxylate moieties at mandelate ligands. The coordination polymer 1-L belongs to the noncentrosymmetric space group of C2 to show piezoelectric properties and second harmonic generation (SHG) activity.     

Viscoelastic and structural properties of a phenyl-modified polysiloxane system with a three-dimensional structure

The relationships between the viscoelastic and structural properties of glass-forming materials with polysiloxane bonds, which serve as network formers, and phenyl groups, which act as network terminators, are examined based on shear viscoelasticity, (29)Si MAS NMR, and GPC measurements during the early stages of the network-forming process. The viscosities of the present samples do not depend on the frequency at temperatures up to 200 degrees C, suggesting that the origin of the viscous flow does not include intermolecular entanglement. According to the results of the strain dependence of the elastic modulus, the bridging-oxygen number, and molecular weight, the present polysiloxane system has a complex structure, or distribution of various-sized molecules composed of a polysiloxane network with various dimensionalities, and furthermore an elementary process of the viscosity is simple flow of these molecules. The structural factors that determine the viscosity and its temperature dependence are categorized into the molecular size and the intramolecular structure by using a theory based on the free-volume model. The relationship between the viscosity and the structure around the glass transition temperature is quantitatively examined and it is concluded that introducing larger numbers of Ph groups makes the viscosity less sensitive to structural factors.     

New crystalline polymers: poly(2,5‐dialkyl‐1,4‐phenylene oxide)s

New heat‐reversibly crystalline poly‐(alkylated phenylene oxide)s are described. the oxidative polymerization of 2,5‐dimethylphenol catalyzed by (1,4,7‐triisopropyl‐1,4,7‐triazacyclononane) copper dichloride produced poly(2,5‐dimethyl‐1,4‐phenylene oxide), which showed heat‐reversible crystallinity with a high melting point at ca. 300°C, although the isomeric polymer, poly(2,6‐dimethyl‐1,4‐phenylene oxide), never recrystallizes once melted. The polymerization of 2,5‐diethylphenol and 2,5‐dipropylphenol gave the polymers consisting of 1,4‐phenylene oxide units; the latter polymer possessed heat‐reversible crystallinity, however, the former one did not.     

Vinyl ethers with a functional group: Living cationic polymerization and synthesis of monodisperse polymers

The living cationic polymerization of vinyl ethers (VEs) having a (polar) functional pendant has been achieved by the hydrogen iodide/iodine (HI/I₂) initiating system to give polymers with a very narrow molecular weight distribution (MWD) (M_w/M_n ≤ 1.2). The functional pendants include benzyl, saturated or unsaturated ester, (poly) oxyethylene, and substituted phenoxyl groups. Although these polar groups often disturb cationic vinyl polymerization by inducing chain transfer and termination, the HI/I₂ initiator cleanly polymerized the “functionalized” VEs without side reactions, mostly in nonpolar media at low temperatures below −15 °C. The HI/I₂-initiated living polymerization also provided facile methods to synthesize new functional polymers, including water-soluble polymers, macromolecular amphiphiles, and macromers, all having a narrow MWD. The simplest example is the living polymerization of VEs carrying an oxyethylene chain [-(CH₂CH₂O)_n-R] as pendant, which directly yields water-soluble polymers. The debenzylation of poly(benzyl VE) prepared with HI/I₂ led to poly(vinyl alcohol). Polymers of the saturated ester-containing monomers (2-acetoxyethyl and 2-benzoyloxyethyl VEs) were readily hydrolyzed into poly (2-hydroxyethyl VE), soluble in water and swellable in methanol. This lead was extended to the synthesis of a new amphiphile, poly(cetyl VE-b-2-hydroxyethyl VE), from a block copolymer of cetyl and 2-acetoxyethyl VEs prepared by their sequential living polymerization initiated with HI/I₂. An adduct between HI and 2-vinyloxyethyl methacrylate [CH₃-CH(I)-OCH₂CH₂OCOC(CH₃) =CH₂] was found to initiate living polymerizations of VEs in the presence of iodine; the products were methacrylate-type macromers carrying a poly(VE) side chain with a narrow chain-length distribution.     

Design and initiators of living cationic polymerization of vinyl monomers

This paper discusses recent developments in living cationic polymerization of vinyl monomers, specifically focusing on (a) new initiating systems, (b) kinetics and mechanism, and (c) controlled polymer synthesis. The new initiating systems were based on nucleophilic stabilization of the growing carbocations, either by counteranions (as in phosphate/ZnI₂ and Me₃SiI/ZnI₂ systems) or by added Lewis bases (as 2,6-dimethylpyridine for EtAlCl₂). The kinetic study included the determination of the lifetime of living cationic polymers. The controlled polymer synthesis by living cationic processes led to not only end- and pendant-functionalized polymers of narrow molecular weight distributions but also star-shaped polymers and sequence-regulated vinyl ether oligomers with functional groups.     

Synthesis of star‐shaped poly(vinyl ethers) with many arms by living cationic polymerization

Star‐shaped polymers of isobutyl vinyl ether (IBVE) with many arms (“crew cut” type) have been synthesized by living cationic polymerization using the HCl‐IBVE adduct/ZnCl₂ initiating system. A short living polymer (DP_n ⪇ 30) of IBVE is allowed to react with a large amount of divinyl ether ([divinyl ether]₀/[P*] = 10–15) to give soluble star polymers whose number of arms ranged from 40 to 120. The diameter of such “crew cut” star polymers reached ca. 20 nm.