29Si N.M.R. investigations of polysiloxanes

A number of side chain liquid crystal polysiloxanes prepared from both homo-and co-polymeric backbones have been studied by ²⁹Si N.M.R. and the chemical shifts assigned. Partly mesogenated poly(hydrogenmethylsiloxanes) have been similarly studied and chemical shift assignments made for sequence distributions. The data should prove helpful in studies of compositional variation in preparations of side chain copolymeric polysiloxanes.     

Combined main chain/side chain polymers. A new class of liquid crystalline polymers with unusual structural, thermodynamic and dynamic properties

Combined main chain/side chain polymers carry rigid rod-like mesogenic units both in the side chain and along the chain backbone. The properties of such combined systems are expected to be controlled by the competition of the interactions between the mesogenic units in the side and main chains as well as the tendency of the chain backbones to maximize their entropy. The thermodynamic, structural and dynamic properties of such combined main chain/side chain liquid-crystalline polymers were investigated for various chain architectures. The combined systems were found to display properties corresponding in many cases to a favourable superposition of properties characteristic of both main and side chain systems. These include high transition temperatures (up to 530 K) and broad ranges of stability of liquid-crystalline phases (up to about ΔT = 170 K). The orientational order parameter was found to approach values of 0.9 and it was possible to orient some of the polymers in weak external fields such as 1 T for instance, for magnetic fields. Smectic antiphase formation corresponding to that observed in low molar mass systems carrying strong longitudinal dipoles and resulting from the presence of incommensurable lengths were observed in those cases in which the side groups were attached directly to the rigid part of the chain backbone whereas no such effects occurred if the side groups were fixed to the flexible part of the main chain. The reorientational motion of the mesogens about their short axis, which couples to dielectric and electro-optical properties was found to have a surprisingly low activation energy (as low as 115 kJ/mol) and a strong anisotropy of the dielectric constant (Δε = 7) despite a relatively small concentration of dipoles. It thus seems that the combined systems may be the material of choice for many future applications.     

Relaxation mechanism of epoxide resin cured with acid anhydrides. III. Effect of alkyl side chains on mechanical and dielectric β relaxations

Mechanical and dielectric β relaxations were investigated for bisphenol-A-type epoxide resin cured with succinic anhydrides with and without substituent linear or branched alkyl side chains. The dielectric β relaxation is due solely to the motion of the diester segment which is formed in the network from the reaction with the acid anhydride. The mechanical β relaxation is attributed to the motion of both the diester segment and another nonpolar segment, i.e., the linear alkyl side chain. Thus it is concluded that the long alkyl side chain in the diester segment not only restricts the motion of that segment, but also introduces additional motion of the side chain itself.     

Intramolecular hydrogen bonding and its influence on conformation. Circular dichroism of chiral bilirubin analogs

Enantiopure synthetic bilirubin analogs with variously modified (e.g. alkyl for natural propionic acid or ester) C(8) and C(12) side chains and with but a single chiral center in either or both, exhibited exciton coupled circular dichroism (CD) spectra. The CD intensity is greater when the stereogenic center is in a propionic acid side chain than in an alkyl side chain.     

Complex macromolecular dynamics:: I. Estimation technique for time-resolved emission anisotropy ratio of chromophores incorporated into polymer chains

Time-resolved fluorescence emission anisotropy ratios of carbazolyl groups incorporated into polystyrene chains in polyethyleneoxide(PEO)/1,2-dichloroethane mixtures have been measured by the single photon counting method. The fluorescence depolarization method is very excellent to clarify various dynamical modes of polymer chains, and many theoretical and experimental researches have so far been reported in the field of polymer chain dynamics. However there are few reports about the dynamics on the polymer side chain, because the dynamical mechanism of the polymer side chain is very complicated. In this report we tried to analyze the dynamical modes of the polymer side chains by the fluorescence depolarization method. Five dynamical modes of a polymer chain based on the Wöessner model were estimated by our original analytical technique `χ²-map method'. The value of each mode of a polymer side chain was discussed above the overlap concentration (C^*) of PEO and the micro-environments were clarified in the vicinity of the chromophore attached to the polymer side chain.     

Stereospecific cyclopropane ring-opening of petrosterol. A possible biomimetic process.

Acid-catalyzed isomerization of the petrosterol side chain ($\text{1}$) proceeds stereospecifically to yield the naturally occurring 26-dehydro-25-epiaplysterol side chain ($\text{2}$); in addition, a 1.5-hydride shift leading to 22-dehydro-25-epiaplysteryl acetate ($\text{3}$) has also been observed.     

Bromothiophene reactions. II. A novel rearrangement in the zinc and acetic acid reduction

The elimination of the α-bromine atoms of the bromothienylethanolamine derivatives 2a,b,c,d with zinc and acetic acid unexpectedly involved a migration of the ethanolamine side chain from the 3 to the 2 position in the thiophene ring. Experiments carried out with simpler analogous compounds 3, 4 and 6 seem to indicate that this rearrangement takes place only in those cases in which the carbon atom of the side chain next to the ring supports an oxygen atom capable of being protonated in the reaction medium. A tentative mechanism is proposed to explain the experimental results.     

碳苷研究 XXVII. 黑豆素非环类似物的合成

本文报道天然黄酮碳苷黑豆素非环类似物的合成, 以2,4-二羟基苯乙酮为原料, 经酚羟基的单苄基化、Claisen重排、醇醛缩合、I2/DMSO/浓度H2SO4关环五步反应得到黄酮; 用Claisen重排, 分别在黄酮环生成之前和生成之后引入8-位取代基侧链, 收率国产高。修饰8-位烯丙基侧链, 得到了六个黑豆素类似物, 共中8的7-位为游离羟基。     

Statistical mechanical model for diffusion of simple penetrants in polymers. III. Applications—vinyl and related polymers

The theory developed in Part I of this series is modified to accommodate polymers that possess closely spaced, bulky side groups on the chains. The side groups give rise to free space between the chain “cores,” which reduces the chain separation required for penetrant motion transverse to the local chain axis. The theory is then identical to that of Part I, except that penetrant diameters minus a constant factor are employed in place of the normal diameters. In most of the cases studied the reduction factor for a given polymer may be estimated with reasonable precision from chain geometry data. This diameter-reduction effect is the likely explanation of the apparent proportionality between the activation energy of diffusion and the square of the penetrant diameter reported earlier for vinyl polymers. The data quoted here and in Part II are analyzed to give a semitheoretical correlation between the effective jump length L? and ΔE, the activation energy of diffusion. This correlation appears to be equally valid for glassy and rubbery noncrystalline polymers.     

The shape of leucine in the gas phase.

Two structures of neutral leucine are detected in the jet-cooled rotational spectrum of a laser-ablation molecular-beam Fourier transform microwave (LA-MB-FTMW) experiment. The comparison between the experimental rotational and (14)N nuclear quadrupole coupling constants and those calculated ab initio provides conclusive evidence for the identification of the conformers. The most stable species is stabilized by a N-H...O=C intramolecular hydrogen bond and a cis-COOH interaction, while a higher-energy conformer exhibits a N...H-O intramolecular hydrogen bond and trans-COOH, as in lower aliphatic amino acids. The isobutyl side chain adopts the same configuration in the two conformers of leucine, characterized by a trans arrangement of the C'-C(alpha)-C(beta)-C(gamma)-C(delta) chain. The differences with the preferred side chain configurations observed in valine and isoleucine are discussed.     

Controlled expansion of a molecular cavity in a steroid host compound.

Expansion of a molecular cavity is described by using elongation of the side chain of a bile acid host compound. Bishomocholic acid (2), which has a side chain that is longer by two methylene unit than cholic acid (1), includes many organic substances at 1:1 host:guest ratios. X-ray crystallographic studies revealed that 2 has two types of open host frameworks: a bilayer type and a crossing type. Both of them are isostructural to those of 1, indicating that they are robust against the elongation of the side chain. In the former type, the increment of the width of the host channel corresponds to that of the length of the molecular structures. Larger aromatic guest components such as 1-methylnaphthalene and 1-tetralone, are included in 2, but not in 1.     

Liquid-Crystalline Polyurethanes. 5. Polyurethanes Containing the Cholesterol Moiety in the Side Chain

In the preceding papers of this series, we reported the synthesis of liquid-crystalline polyurethanes containing mesomorphic moieties in the main chain and in side chains [1–4]. Liquid crystalline polymers with side groups containing the cholesterol moiety have also been studied [5, 6]. The main focus of attention has centered around the study of phase transitions of acrylic and methacrylic derivatives of cholesterol. This paper describes the synthesis of a new type of liquid-crystalline polyurethane containing the cholesterol moiety in side chains.     

Stereospecific synthesis of hydroxylated steroid side chains. Synthesis of 25,28-dihydroxy-7,8-dihydroergosterol and its c-24 epimer via [2,3] sigmatropic rearrangement.

An efficient, stereospecific synthesis of hydroxylated ergosterol and C-24 epi-ergosterol side chains has been developed using a C-20 keto-steroid as starting material. The side chain is elaborated via stereoselective hydroboration, asymmetric reduction and a stereospecific [2, 3] sigmatropic rearrangement.     

Biosynthesis of lipstatin. Incorporation of multiply deuterium-labeled (5Z,8Z)-tetradeca-5,8-dienoic acid and octanoic acid.

Fermentation experiments with Streptomyces toxytricini were performed using (5Z,8Z)-[10,11,12,12-(2)H]tetradeca-5,8-dienoic acid or a mixture of [2,2-(2)H(2)]- and [8,8,8-(2)H(3)]octanoic acid as supplements. (2)H NMR and mass spectroscopy confirmed the incorporation of (5Z,8Z)-[10,11,12,12-(2)H]tetradeca-5,8-dienoic acid into the C(13) side chain as well as into the C(6) side chain of lipstatin. Moreover, deuterium was incorporated into the C(6) side chain of lipstatin from the 8-position but not from the 2-position of octanoate. The data establish that the beta-lactone moiety of lipstatin is formed by condensation of a C(8) and a C(14) fatty acid with a concomitant exchange of the H-2 atoms of the C(8) fatty acid.     

Spiropyrans and spirooxazines 9. Photochromism of novel cationic spirooxazines

Novel photochromic spirooxazinoquinolines, their cationic derivatives, and cationic spirooxazine containing pyridinium cation in the aliphatic side chain of the oxazine moiety of the molecule were synthesized. Quaternization of the quinoline fragment leads to a substantial increase in the thermal stability of the merocyanine isomers of cationic spirooxazines and a decrease in the efficiency of photocoloration. Pyridinium cation in the aliphatic side chain of the spirooxazine does not exert a substantial effect on the kinetics of photocoloration and thermal bleaching.     

Crowned polyacetylene. 2. cis form determination of poly(4′-ethynylbenzo-15-crown-5) by solid-state NMR method

The chain structure of cis-poly(4′-ethynylbenzo-15-crown-5) (PEB15C5), prepared using the rhodium complex catalyst, was studied at ?175°C using the solid-state NMR technique. The second moment of PEB15C5 was 7.0 G² for the main chain and 19.0 G² for the side chain. These values agreed well with the respective theoretical ones for the cis form in the rigid state rather than the trans one. This agreement between experiment and theory suggested that the plane of the side chain (i.e., the benzo-15-crown-5 group) is orthogonal to the main chain plane of the cis-transoidal form. It was verified that the strong dipoledipole interaction between the side chains plays an important role as a clue to theoretically determine the cis-transoidal form. NMR results in solid state confirmed theoretically that multipeaks in the ¹H and ¹³C NMR spectra in CDCl₃ solution are attributed to cis-transoidal form in the chain. © 1995 John Wiley & Sons, Inc.     

Rigid-rod polymers with polysiloxane side chains. I. Synthesis and characterization of rigid-rod polyimides with polysiloxane side chains and their compatibility with linear polysiloxanes

Rigid-rod aromatic polyimdies having polydimethylsiloxane side chains were prepared for the purpose of dispersing rigid-rod molecules in silicone matrices for molecular reinforcement. The polyimides were obtained by imidizing the polyamide-acids bearing the side chains either thermally or chemically, which were synthesized by reacting 4,4′-diaminobiphenyl-terminated polysiloxane macromonomers with pyromellitic dianhydride in THF. The polyamide-acid films obtained by removing the solvent were soluble in THF, but the polyimides were insoluble in any common solvent. The polyimides showed no melting transition below 350°C on DSC analysis, at which temperature the side chain started decomposing. Although all the polyimides were anisotropic as observed by a polarizing microscope, x-ray diffraction analysis suggested the presence of only limited chain organization. Blends with linear polydimethylsiloxanes were prepared by casting the THF solution containing the polyamide-acid and the polydimethylsiloxane, followed by solvent evaporation and thermal imidization. With relatively longer side chains, the polyimides were proved to be compatibilized with polydimethylsiloxanes. © 1994 John Wiley & Sons, Inc.     

Metal Complexes with Macrocyclic Ligands. Part XXVI. Synthesis and spectral properties of Cu2+ complexes with mono-N-functionalized 1,4,8-trimethyl-1,4,8,11-tetraazacyclotetradecanes

A series of mono-N-functionalized 1,4,8-trimethyl-1,4,8,11-tetraazacyclotetradecanes 3 – 14 were synthesized by alkylating the secondary N-atom of the macrocycle 1 . The spectral properties of the Cu²⁺ complexes, studied under different pH conditions, are discussed in relation to the possibility of coordination of the donor group of the side chain to the axial position of the metal ion and to the effect of the length of the side chain.     

Extended-chain crystals. V. Thermal analysis and electron microscopy of the melting process in polyethylene

Differential thermal analysis and electron microscopy of partially molten, extended-chain polyethylene crystals, grown under elevated pressure, was performed. It could be shown that melting peaks on the low temperature side of the main melting peak are due to narrowly distributed, low molecular weight polymer segregated in extended-chain crystals. Superheating of crystals before melting increased with molecular weight and chain extension. The melting mechanism of extended chain crystals was shown to be a successive peeling off of chains which leaves the chain extension constant up to melting of the last crystal trace.     

N-烷基化聚对苯二甲酰对苯二胺梳状高分子中烷基侧链对刚性主链堆积行为的影响

基于聚对苯二甲酰对苯二胺(PPTA), 采用N-烷基化方法制备了系列PPTACns(烷基侧链碳原子数n=8, 10, 12, 14, 16, 18)刚性主链梳状高分子, 利用DSC, XRD和FTIR等方法研究了其主链堆积行为、 分子链构象及热性能等与烷基侧链长度及结晶特性之间的关系. XRD和DSC结果表明, 当烷基侧链碳原子数达到14时, 烷基侧链发生结晶. XRD结果显示, PPTACns具有层状结构, 烷基侧链长度对主链层间距影响显著. FTIR研究发现, 烷基侧链的聚集状态对PPTACns分子链的构象产生较大影响, 伴随着烷基侧链结晶的熔融, PPTACns的分子链构象发生显著改变. 烷基侧链处于熔融状态的PPTACns的ν_C=O和γ_C-H谱带峰位与烷基侧链不结晶的PPTACn接近.