Flexible Main Chain Research Articles

Characterization of photoresists for ArF‐excimer laser lithography using monoenergetic positron beams

AbstractThe volume and depth distributions of open spaces in photoresist films designed for ArF‐excimer laser light exposure were studied with monoenergetic positron beams. We measured the Doppler broadening spectra of the annihilation radiation and lifetime spectra of positrons for acrylate and cyclic olefin‐co‐maleic anhydride (COMA) polymers spin‐coated onto Si wafers with methyl amyl ketone, cyclohexanone, and propylene glycol methyl ether acetate solvents. The volume of open spaces in both prebaked acrylate and COMA films was estimated to be 0.12 nm3. The volume of open spaces in acrylate films decreased up to 20% by postexposure baking, but no large change was observed for COMA films. The decrease in the open volume was attributed to the removal of large molecules (adamantyl) from flexible main chains after the chemically amplified reaction of acrylate. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 341–346, 2004

系統的に分子構造を変化させたポリカーボネート類の粘弾性と複屈折

The complex Young's modulus and the complex strain-optical coefficient of two series of polycarbonate derivatives were measured around the glass transition zone to investigate the molecular structure-property relationships. The data were analyzed with the modified stress-optical rule: The complex Young's modulus was separated into two component function, R and G. Main chain flexibility and the intrinsic birefringence were estimated from the R component. It was found that the main flexibility was insensitive to the substitution on phenylene groups or propylene groups while the intrinsic birefringence could be significantly reduced.

Protein hydrogen exchange mechanism: local fluctuations.

Experiments were done to study the dynamic structural motions that determine protein hydrogen exchange (HX) behavior. The replacement of a solvent-exposed lysine residue with glycine (Lys8Gly) in a helix of recombinant cytochrome c does not perturb the native structure, but it entropically potentiates main-chain flexibility and thus can promote local distortional motions and large-scale unfolding. The mutation accelerates amide hydrogen exchange of the mutated residue by about 50-fold, neighboring residues in the same helix by less, and residues elsewhere in the protein not at all, except for Leu98, which registers the change in global stability. The pattern of HX changes shows that the coupled structural distortions that dominate exchange can be several residues in extent, but they expose to exchange only one amide NH at a time. This "local fluctuation" mode of hydrogen exchange may be generally recognized by disparate near-neighbor rates and a low dependence on destabilants (denaturant, temperature, pressure). In contrast, concerted unfolding reactions expose multiple neighboring amide NHs with very similar computed protection factors, and they show marked destabilant sensitivity. In both modes, ionic hydrogen exchange catalysts attack from the bulk solvent without diffusing through the protein matrix.

Para-Substituted Poly(styrene peroxide)s: Synthesis, Characterization, Thermal Reactivities, and Chain Dynamics Studies in Solution

The synthesis and spectroscopic characterization of three polymeric peroxides of styrene monomers with substituents in the para position are discussed. NMR spectroscopy revealed the alternating copolymer structure with labile peroxy bonds (-O-O-) in their main chain. The thermal reactivity of the polymers was studied by dif- ferential scanning calorimetry and thermogravimetry. The measured heat of degradation of these polymers is nearly the same as that of poly(styrene peroxide). The mechanism of the primary exothermic degradation has been substantiated by thermochemical calculations. The chain dynamics studies of these polyperoxides in terms of 13 C spin-lattice relaxation time (T 1 ) have been carried out to understand their main chain flexibility. The temperature dependence of correlation time has been utilized for the determination of the activation energy for the overall segmental motion and internal group rotation. Their flexibility in terms of glass transition temperature (T g ) have been examined. The flexibility trend observed in solution parallels that in the bulk.

Synthesis and Properties of Polyamides and Polyesters On the basis of 2,2‘-Bipyridine-5,5‘-Dicarboxylic Acid and the Corresponding Polymer−Ruthenium Complexes

Two series of polyamides and polyesters derived from 2,2‘-bipyridine-5,5‘-dicarboxylic acid have been synthesized. Different types of aliphatic and aromatic diamine and diol monomers with different structure were polymerized with the diacid or diacid chloride by using different polymerization methods. Most of these polymers exhibited modest thermal stabilities with decomposition temperatures in the range 320−500 °C, depending on the structure of the polymer main chain. It was found that some polyamides with a rigid main chain formed a lyotropic mesophase when dissolved in concentrated sulfuric acid or HMPA−4% LiCl solvent systems. For those polyamides and polyesters with a more flexible main chain, a thermotropic liquid crystal phase was observed. If a long and flexible pendant chain was attached to the polyesters, side chain melting was observed before the onset of the crystalline−nematic transition. The 2,2‘-bipyridyl moieties were able to form a complex with ruthenium. These polymer−ruthenium complexes...

Electro-rheological behavior of liquid crystal polymers (LCPs) dissolved in a nematic solvent: dependence on temperature and LCP structure

The viscosity increments δη on and δη off, upon dissolving a liquid crystal polymer (LCP) in a thermotropic nematic solvent, were determined by rheometry in the presence and absence, respectively, of a saturation electric field. Four species of molecular architectures were studied, a rigid main-chain LCP, two types of flexible main chain LCP, one with mesogens oriented perpendicular to the backbone, the other with mesogens parallel to the backbone, and a flexible side-chain LCP with mesogens attached side-on to the backbone. For all mixtures, δη on and δη off exhibit a similar Arrhenius dependence on temperature, determined by the viscous activation energy of the nematic solvent. However, the temperature dependence of the ratio δη on/ δη off and of the intrinsic viscosities, [ η on] and [ η off], is different for each LCP, and is strongly dependent on the flexibility of the LCP. By equating η on and η off to the Miesowicz viscosities, η c and η b, respectively, these results can be interpreted in terms of the ratio of the LCP chain dimensions parallel and perpendicular to the nematic director, R ∥ and R ⊥((since theory predicts δη c/ δη b= R ∥ 4/ R ⊥ 4). The results indicate that the conformation of each LCP is strongly prolate, i.e. R ∥≫ R ⊥((For the rigid main-chain LCP, R ∥/ R ⊥ changes very little with temperature; for the flexible LCPs, R ∥/ R ⊥ decreases strongly with increase of temperature, indicative that the conformation becomes more spherical. The behavior of R ∥/ R ⊥ is compared with recent theoretical models of LCP conformation(

Influence of electron donor-acceptor interaction on the liquid crystallinity of copolymers derived from malonates with a mesogenic group using oligo(ethylene glycol) as a main chain spacer

Copolymerization between two malonic acid esters with a mesogenic group (1) was carried out using oligo(ethylene glycol) as a flexible main chain spacer to see the effect of electron-donor acceptor interactions between the mesogens on the phase transition behavior of the copolymers. The following four mesogenic groups were employed: 4-(2-phenylethoxy)-4′-biphenoxy (1 a), p-nitrophenylazophenoxy (1 b), 4-(4′-nitrophenylvinylene)phenoxy (1 c), and p-methoxybiphenoxy group (1 d). Monomers 1 a and 1 d have a mesogen with an electron-donating group, while 1 b and 1 c have an electron-withdrawing group. The copolymers of 1 a with 1 b display a mesophase over a much wider temperature range than the respective homopolymers of the pair. The copolymers derived from the pairs, 1 a–1 c and 1 c–1 d, have a tendency to show a crystalline phase with convex curves for the dependence of the transition to the isotropic state on copolymer composition. These results were explained by taking into consideration the electron-donor acceptor interaction between their mesogens. The different thermal behavior was interpreted by assuming a stronger tendency for the formation of a molecular complex in the latter two. Only linear changes of transition temperatures between those of the respective homopolymer were observed for the copolymers derived from 1 a and 1 d.

High-resolution protein design with backbone freedom.

Recent advances in computational techniques have allowed the design of precise side-chain packing in proteins with predetermined, naturally occurring backbone structures. Because these methods do not model protein main-chain flexibility, they lack the breadth to explore novel backbone conformations. Here the de novo design of a family of alpha-helical bundle proteins with a right-handed superhelical twist is described. In the design, the overall protein fold was specified by hydrophobic-polar residue patterning, whereas the bundle oligomerization state, detailed main-chain conformation, and interior side-chain rotamers were engineered by computational enumerations of packing in alternate backbone structures. Main-chain flexibility was incorporated through an algebraic parameterization of the backbone. The designed peptides form alpha-helical dimers, trimers, and tetramers in accord with the design goals. The crystal structure of the tetramer matches the designed structure in atomic detail.

Synthesis of side-chain liquid-crystalline polyesters using diethyl malonates with a mesogenic group and oligo(ethylene glycol)s and effect of specific interactions on their mesogenic behavior

Side-chain liquid-crystalline polymers were synthesized using malonic acid esters with a mesogenic group (1) linked through a hexamethylene spacer and oligo(ethylene glycol) (2n) as a flexible mainchain spacer. Polymers derived from 1 with a mesogen such as p-nitrophenylazophenoxy (1a) or 4-(4′-nitrophenylvinylene)phenoxy group (1b) form stable mesophases over a wide temperature range, through the increase of chain length of 2n decreases the thermal stability of the liquid-crystalline (LC) phases. LC polymers were obtained from 1 with a mesogen with p-substituted biphenoxy groups only when 2n with shorter chain length is employed. Copolymerizations were undertaken to see the effect of monomer pairs and copolymer compositions on the phase transition behavior of the copolymers formed, using three monomer pairs, 1a and 1 with the p-methoxybiphenoxy group as the mesogen, 1a and 1b, and 1a and 1 with the p-nitrobiphenoxy group as the mesogen. The copolymers formed from the first pair display a nematic phase over a much wider temperature range than the respective homopolymers. This was ascribed to the electron donor-acceptor interaction between the two mesogens in the monomer pair.

Synthesis of side-chain liquid-crystalline polyesters using diethyl malonates with a mesogenic group and oligo(ethylene glycol)s and effect of specific interactions on their mesogenic behavior

Side-chain liquid-crystalline polymers were synthesized using malonic acid esters with a mesogenic group (1) linked through a hexamethylene spacer and oligo(ethylene glycol) (2n) as a flexible mainchain spacer. Polymers derived from 1 with a mesogen such as p-nitrophenylazophenoxy (1a) or 4-(4′-nitrophenylvinylene)phenoxy group (1b) form stable mesophases over a wide temperature range, through the increase of chain length of 2n decreases the thermal stability of the liquid-crystalline (LC) phases. LC polymers were obtained from 1 with a mesogen with p-substituted biphenoxy groups only when 2n with shorter chain length is employed. Copolymerizations were undertaken to see the effect of monomer pairs and copolymer compositions on the phase transition behavior of the copolymers formed, using three monomer pairs, 1a and 1 with the p-methoxybiphenoxy group as the mesogen, 1a and 1b, and 1a and 1 with the p-nitrobiphenoxy group as the mesogen. The copolymers formed from the first pair display a nematic phase over a much wider temperature range than the respective homopolymers. This was ascribed to the electron donor-acceptor interaction between the two mesogens in the monomer pair.

Mutational analysis of a surface area that is critical for the thermal stability of thermolysin-like proteases.

Site-directed mutagenesis was used to assess the contribution of individual residues and a bound calcium in the 55-69 region of the thermolysin-like protease of Bacillus stearothermophilus (TLP-ste) to thermal stability. The importance of the 55-69 region was reflected by finding that almost all mutations had drastic effects on stability. These effects (both stabilizing and destabilizing) were obtained by mutations affecting main chain flexibility, as well as by mutations affecting the interaction between the 55-69 region and the rest of the protease molecule. The calcium-dependency of stability could be largely abolished by mutating one of its ligands (Asp57 or Asp59). In the case of the Asp57-->Ser mutation, the accompanying loss in stability was modest compared with the effects of other destabilizing mutations or the effects of (combinations of) stabilizing mutations. The detailed knowledge of the stability-determining region of TLP-ste permits effective rational design of stabilizing mutations, which, presumably, are also useful for related TLP such as thermolysin. This is demonstrated by the successful design of a stabilizing salt bridge involving residues 65 and 11.

DSC and X-ray studies on side-chain crystallization of comb-like polymers

Thermal properties of acrylate and methacrylate monomers containing long-fluorocarbon chains (H(CF 2 ) n CH 2 OCOCH=CH 2 , (F n A) and H(CF 2 ) n CH 2 OCOC(CH 3 )=CH 2 , (F n MA), where n=6, 8, 10) and their comb-like polymers have been investigated by differential scanning calorimeter (DSC) and X-ray diffraction. The comb-like polymers (PF 10 A and PF 10 MA) with sufficiently long-fluorocarbon chains showed a simple melting and crystallizing behavior. For the fusion of PF 10 A in 1st heating, enthalpy change ΔH f was 18 kJ mol -1 and entropy change ΔS f was 45 J K -1 mol -1 , while for PF 10 MA the values ΔH f and ΔS f were 5.3 kJ mol -1 and 14 J K -1 mol -1 , respectively. Melted PF 8 A crystallized slowly, whereas PF 8 MA with same fluorocarbon chain and also both of PF 6 A and PF 6 MA with shorter fluorocarbon chains can hardly crystallize by the aggregation of side-chains. Effects of the length of side-chain and the flexibility of main chain on the side-chain crystallization of comb-like polymers are clear. Crystallization process of the methacrylate monomers was sensitively affected by the scanning rate of DSC measurement and the length of fluorocarbon chains.

Thermal and i.r.-dichroic properties of side-chain type liquid-crystalline elastomers

Several liquid-crystalline elastomers (LCEs) have been prepared by crosslinking side-chain type liquid-crystalline polymers (precursors) in which mesogens are dangling from flexible main chains through spacers. Thermal properties and phase behaviour of the precursors and LCEs have been investigated by means of differential scanning calorimetry (d.s.c.) and polarizing microscopy. The glass transition and meso-to-isotropic phase transition temperatures are slightly affected by an introduction of crosslinks to precursors. Orientation of the mesogens in the LCEs under uniaxial elongation has been evaluated in terms of order parameter for orientation ( f) obtained by i.r.-dichroism measurements. All the LCEs under deformation show negative values of f, meaning the orientation direction of mesogens perpendicular to the axis of elongation. The value of f changes greatly in the small deformation region, and reaches equilibrium at ca. 70% elongation, suggesting that a high degree of orientation for the mesogens in LCEs is achieved by a relatively small elongation. Dependence of f on elongation ratio is not influenced by spacer length nor by crosslinking density, implying that the interaction between mesogens is the most dominant factor for the orientational order of mesogens in the LCE system in this study.

A Series of Azo-type Side-chain Liquid Crystalline Polysiloxane - Palladium Complexes

A series of azo-type side-chain liquid crystalline polysiloxanes (AZLCPs) were synthesized, starting from organic polysiloxane and azo-type mesogenic compounds having an end allyl group. The AZLCPs were further used to coordinate with palladium dichloride and potassium chloride, by which a series of palladium complexes of AZLCPs (Pd–AZLCPs) were prepared. The mesogenic properties of all of the liquid crystalline polymers were characterized by using differential scanning calorimetry, polarized microscope and wide-angle X-ray diffraction. It was found that all of the polymer ligands and their palladium complexes showed thermotropic liquid crystallinity and that the incorporation of the palladium ions gave positive effects to the mesogenic properties of their polymer ligand counterpart. Compared with the corresponding AZLCPs, the Pd–AZLCPs have higher isotropization temperatures and a broader mesophase temperature range. The mesogenic properties of the liquid crystalline polymer ligands and their palladium complexes were also varied gradually by changing the length of the alkoxy groups on the side chain. The polymers that have a color emissive group and a highly flexible polysiloxane main chain may potentially be used as nonlinear optical materials.

Side-chain liquid crystalline polyesters derived from diethylmalonate and/or 1,3-propanediol

A series of azo monomers for polycondensation have been synthesized and characterized. These monomers, which contain electron-donor or acceptor substituents, have been condensed with aliphatic monomers to obtain two different series of aliphatic main-chain polyesters with pendant mesogenic groups. The polymers display nematic or smectic phases depending on the structural modifications of pendant mesogenic groups and the length of the flexible main-chain. In addition to these series, two polyesters with a high concentration of side pro-mesogenic groups have been synthesized. © 1996 John Wiley & Sons, Inc.

Comb-Branched Polymers: Monte Carlo Simulation and Scaling

The Monte Carlo simulation technique (the bond fluctuation model) has been used for the study of the equilibrium conformations of comb-branched polymers consisting of a long flexible main chain and side chains grafted at a regular separation onto the main chain. The solvent has been supposed to be good (athermal) for the main and side chains. The global conformation and the gyration radius of the polymer, as well as the local conformational structure of the comb, have been analyzed as functions of the length of the side chains and spacers. The effect of induced rigidity of the comb due to the interaction between side chains has been observed. We have found the results of the simulation to be in reasonable agreement with the predictions of the scaling theory of comb-branched polymers.

Statistical Theory on Polymer Liquid Crystals

AbstractBased on common molecular model, polymer liquid crystals of hard-rod and flexible main-chain are studied statistical mechanically. The hard-core repulsion and also the attractive potentials are assumed between molecules. The nematic-isotropic phase transitions, and molecular orientations at interfaces in polymers and polymer-liquid crystal composite systems are discussed.

Repacking protein cores with backbone freedom: structure prediction for coiled coils.

Progress in homology modeling and protein design has generated considerable interest in methods for predicting side-chain packing in the hydrophobic cores of proteins. Present techniques are not practically useful, however, because they are unable to model protein main-chain flexibility. Parameterization of backbone motions may represent a general and efficient method to incorporate backbone relaxation into such fixed main-chain models. To test this notion, we introduce a method for treating explicitly the backbone motions of alpha-helical bundles based on an algebraic parameterization proposed by Francis Crick in 1953 [Crick, F. H. C. (1953) Acta Crystallogr. 6, 685-689]. Given only the core amino acid sequence, a simple calculation can rapidly reproduce the crystallographic main-chain and core side-chain structures of three coiled coils (one dimer, one trimer, and one tetramer) to within 0.6-A root-mean-square deviations. The speed of the predictive method [approximately 3 min per rotamer choice on a Silicon Graphics (Mountain View, CA) 4D/35 computer] permits it to be used as a design tool.

Side Chain Liquid Crystalline Ionic Polysiloxanes

Abstract A variety of side chain liquid crystalline ionic polysiloxanes with quaternized ammonium groups incorporated into the mesogenic moiety or into the spacer have been synthesized and studied by a combination of DSC, TGA, polarizing microscopy and X-ray diffraction. The polysiloxanes exhibit a nematic mesophase. Due to their flexible main chain, the transition temperatures are low. Thermal stability and liquid crystallinity of quaternized and unquaternized polysiloxanes are compared. It appears that in these ionic polymers the geometry of the mesogenic group plays an important part in the development of the mesophase.

Induced Network Structure in Liquid Crystalline Polymer Evidenced from Electrorheological Normal Stress Measurements

It is clarified that the electrorheological (ER) effect of a random copolymer composed of flexible main chain of silicone and flexible side chains connecting mesogens of p-cyanobiphenyl benzoate residue is based on the network structure induced by the electric field. It is also shown that the electrorheological normal stress measurement is useful as a new method for evaluating the ER effects