Photo‐alignment material with azobenzene‐functionalized polymer linked in film

Application of a new azo‐polymer as a photo‐alignment material for liquid crystals (LCs) was demonstrated. 4‐(Vinyloxyethyloxy)azobenzene (VAZO), which has thermally reactive vinyl ether groups, reacted with the ? OH groups of poly(4‐hydroxystyrene) (PHS) during the baking process. The azo‐attached polymer (PHS‐VAZO) film showed anisotropic spectra after exposure to 365‐nm linear polarized light (LPL) unlike the VAZO‐doped poly(methylmethacrylate) (PMMA) film. The anisotropy of the film was small at high concentration of the azo‐chromophore because of thermal randomization of the polarized state. In the evaluation of photo‐alignment of the LC, the LC hybrid cell using the PHS‐VAZO film achieved high LC alignment. The azo‐attached polymer using the thermal reaction of vinyl ethers is useful for a photo‐alignment material. Copyright © 2002 John Wiley & Sons, Ltd.     

Permeation and separation of styrene/ethylbenzene mixtures through cross-linked poly(hexamethylene sebacate) membranes

Poly(hexamethylene sebacate) (PHS) which has strong affinity for styrene was selected as membrane material, and the characteristics of permeation and separation for the styrene/ethylbenzene mixtures through these PHS cross-linked with N,N,N′,N′-tetraglycidyl m-xylenediamine(TETRA-DX) membrane by pervaporation were investigated. The cross-linked PHS membranes exhibited a styrene permselectivity for the styrene/ethylbenzene mixtures and the permeation rate increased with increasing styrene in the feed solution. The permselectivity of their membranes was strongly governed by the sorption separation process depending on the difference of the solubility between styrene and ethylbenzene. The molecular weight of PHS had also influence to the separation factor and permeation rate in pervaporation.     

聚砜、聚二甲基硅氧烷、聚对羟基苯乙烯三元多嵌段共聚物的形态结构

利用动态力学分析（ＤＭＡ）．透射电子显微镜（ＴＥＭ）和小角Ｘ 光光散射（ＳＡＸＳ）对聚砜（ＰＳＦ）、聚二甲基硅氧烷（ＰＤＭＳ）和聚对羟基苯乙烯（ＰＨＳ）三元多嵌段共聚物ＰＳＦ—ＰＤＭＳ—ＰＨＳｎ的形态结构进行了研究．结果表明，ＰＳＦ—ＰＤＭＳ—ＰＨＳｎ的形态结构出现了许多新的现象，除具有微相分离的基本特征外，还出现双连续相双分散相的特征．在适当的嵌段长度和组成下，通过ＴＥＭ观察到一种新的特殊形态 蜂窝状形态结构，并在嵌段共聚物两相界面处直接观察到非常清晰的界面相．同时，对该形态的形成过程作了初步讨论．     

Electronic and photophysical properties of selected organic boron-containing molecules: Insight into effects of heteroatom substitution and aggregation

The density functional theory (DFT) and time-dependent DFT methods were used to investigate the electronic and optoelectronic properties of several main group atom-doped polycyclic aromatic hydrocarbons, such as oxygen-substituted PHO1 and PHO2, and sulfur-substituted PHS1 and PHS2. The ground-state structures of these molecules generally have an open-shell singlet configuration with a certain diradical character. In comparison with PHO1 and PHO2, PHS1 and PHS2 own larger diradical character indices due to their increased anti-aromaticity. Although the substitution of sulfur for the peripheral oxygen has a significant effect on the molecular geometry, the adiabatic excitation energy levels of the corresponding low-lying excited states of these molecules are less changed. Calculations reveal that here the intersystem crossing (ISC) and reverse intersystem crossing processes in CH₂Cl₂ mainly occur between the S₁ and T₂ states, and the cis molecules PHO2 and PHS2 have better charge transportation performance. Furthermore, the electronic and photophysical properties of these B-containing molecules are predicted to be tuned by the peripheral atom substitution and the structural and aggregation changes.     

TSNet: predicting transition state structures with tensor field networks and transfer learning

Transition states are among the most important molecular structures in chemistry, critical to a variety of fields such as reaction kinetics, catalyst design, and the study of protein function. However, transition states are very unstable, typically only existing on the order of femtoseconds. The transient nature of these structures makes them incredibly difficult to study, thus chemists often turn to simulation. Unfortunately, computer simulation of transition states is also challenging, as they are first-order saddle points on highly dimensional mathematical surfaces. Locating these points is resource intensive and unreliable, resulting in methods which can take very long to converge. Machine learning, a relatively novel class of algorithm, has led to radical changes in several fields of computation, including computer vision and natural language processing due to its aptitude for highly accurate function approximation. While machine learning has been widely adopted throughout computational chemistry as a lightweight alternative to costly quantum mechanical calculations, little research has been pursued which utilizes machine learning for transition state structure optimization. In this paper TSNet is presented, a new end-to-end Siamese message-passing neural network based on tensor field networks shown to be capable of predicting transition state geometries. Also presented is a small dataset of S_N2 reactions which includes transition state structures – the first of its kind built specifically for machine learning. Finally, transfer learning, a low data remedial technique, is explored to understand the viability of pretraining TSNet on widely available chemical data may provide better starting points during training, faster convergence, and lower loss values. Aspects of the new dataset and model shall be discussed in detail, along with motivations and general outlook on the future of machine learning-based transition state prediction.

Transition states are among the most important molecular structures in chemistry, critical to a variety of fields such as reaction kinetics, catalyst design, and the study of protein function.     

Homopolymerization and copolymerization of a dilactone, 13,26‐dihexyl‐1,14‐dioxa‐cyclohexacosane‐2,15‐dione: Synthesis of bio‐based polyesters and copolyesters consisting of 12‐hydroxystearate sequences

A dilactone, 13,26‐dihexyl‐1,14‐dioxacyclohexacosane‐2,15‐dione (12‐HSAD), was synthesized by lipase‐catalyzed reaction of 12‐hydroxystearic acid (12‐HSA) in high yield. It was subjected to the ring‐opening polymerization with various catalysts to obtain poly(12‐hydroxystearate) (PHS). The polymerization system of 12‐HSAD showed an interesting polymerization behavior because of its large ring system. The polymers produced by this polymerization were directly reacted with L ‐lactide to obtain a diblock copolymer of poly(L ‐lactide)‐block‐poly‐(12‐hydroxystearate) (PLLA‐b‐PHS). Characterization of the resultant copolymers was also performed. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Aliphatic Polyester Blends Based upon Poly(Lactic Acid) and Oligomeric Poly(Hexamethylene Succinate)

Abstract

In an attempt to gain a degree of control over the mechanical and degradation properties of poly(lactic acid) [PLA], large-scale efforts are underway to alter the phase morphology of PLA through chemical and physical modification. Consistent with this theme, our work aims to adjust the molecular architecture of highly amorphous PLA with an increasing concentration of hydroxy-terminated oligomeric poly(hexamethylene succinate) [PHS]. Gel-permeation chromatography (GPC) verifies the enhanced presence of PHS in the blends with a concomitant reduction in number-average molecular weight as the weight fraction of PHS is raised from 0.10 to 0.40. Differential scanning calorimetry (DSC) indicates amorphous phase compatibility between PHS and PLA at weight compositions of 10/90 and 20/80. However, as the amount of PHS approaches 30 and 40 wt%, the PHS exhibits the ability to crystallize independently from the induced PLA crystalline phase. Dynamic mechanical thermal analysis (DMTA) illustrates variable behavior of the materials under tension as a consequence of structural alterations generated by the oligoester. Finally, preliminary results suggest that these alterations may suppress the hydrolytic degradation of PLA.     

（PSF—PDMS—PHS）n／PSF共混物的相容性及表面组成

利用ＤＳＣ、ＤＭＡ、ＴＥＭ和ＸＰＳ对［ＰＳＦ－ＰＤＭＳ－ＰＨＳ］ｎ／ＰＳＦ共混物的相容性及表面组成进行了研究．结果表明，ＰＤＭＳ在共混物表面的富集与ＰＳＦ均聚物和［ＰＳＦ－ＰＤＭＳ－ＰＨＳ］ｎ中硬段的相容性有关；ＰＤＭＳ在相容的共混物体系表面的富集与对应的多嵌段共聚物组成基本相近；不相容共混物体系表面ＰＤＭＳ的富集程度相对较高，当共混物本体中有机硅含量从１％增至５％，表面层ＰＤＭＳ的含量迅速增加，可达到嵌段共聚物中ＰＤＭＳ的含量．     

Miscibility of poly(ε-caprolactone), a semicrystalline polymer,with amorphous poly(styrene-4-hydroxystyrene) copolymers

The miscibility of poly(ε caprolactone) (PCL) with poly(styrene-co-4-hydroxystyrene) (PHS) copolymers was investigated as a function of comonomer composition experimentally and with calculations by two models; the binary interaction model and the association model. PCL was found to be completely miscible with PHS copolymers containing 5 or more mole percent of 4-hydroxystyrene (HS) comonomer units for the entire range of blend compositions. Segmental interaction densities, B_ijs, were determined by the analysis of the equilibrium melting point depression and by the application of the binary interaction model. By correlating the segmental interaction energy densities with the binary interaction model, thermodynamic miscibility is for comonomer composition over five mole percent of 4-hydroxystyrene, which is in agreement with the experimental phase behavior. Application of the association model for specific interactions to blends also predicts the experimental miscibility boundary and phase behavior for all the PHS copolymers/PCL blends. © 1995 John Wiley & Sons, Inc.     

Synthesis of imidazole derivatives: Ester and hydrazide compounds with antioxidant activity using ionic liquid as an efficient catalyst

The pyrrolidinium hydrogen sulfate (PHS) was used as an excellent ionic liquid catalyst for the preparation of many imidazoles moiety, which have biologically application via one-pot multicomponent reaction. Imidazoles were afforded through the reaction of equimolar from 1,2-diphenylethane-1,2-dione, ammonium acetate, different aromatic aldehydes, and ethyl glycinate hydrochloride. This method has the advantages of giving excellent yield, shortened reaction times, and ease of establishment. Moreover, the yielded of imidazoles components can be purified and crystallized by a nonchromatographic technique, and the catalyst can be reused. These entire novel synthesized components have been identified by spectral data: IR, NMR and mass spectra. These compounds have an in vivo antioxidant activity on experimental animals (rats).     

Formation of intramolecular poly(4-hydroxystyrene) dimer radical cation

Poly(4-hydroxystyrene) (PHS) has been used in lithography as a backbone polymer and is also a promising material for extreme-ultraviolet or electron beam lithography. The dynamics of PHS radical cations generated upon exposure to electron beam were investigated. The transient absorption of PHS was observed in the near-infrared region in p-dioxane solutions by pulse radiolysis. Charge resonance (CR) bands that represent pi-pi interaction between the two chromophores of the intramolecular PHS dimer radical cation were observed, whereas p-cresol shows no distinct CR band. Although the radical cations of phenol derivatives are known to be easily deprotonated, it was found that the dimer radical cation formation leads to less deprotonation by its charge resonance stabilization.     

Surface modification of polystyrene by blending substituted styrene copolymers

The surface modification of polystyrene (PS) by the blending of 4‐acetoxystyrene polymers and their corresponding hydrolysis products, 4‐hydroxystyrene polymers, was investigated on the basis of X‐ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and contact‐angle measurements. According to XPS and AFM measurements, when polystyrene‐block‐poly(4‐acetoxystyrene) (PS‐b‐PAS) or polystyrene‐block‐poly(4‐hydroxystyrene) (PS‐b‐PHS) was incorporated into PS, the block copolymer was preferentially segregated at the highest surface region of the blend. This segregation increased to a plateau value when more than 5 wt % of either PS‐b‐PHS or PS‐b‐PAS was added. The contact angle of the modified PS by PS‐b‐PAS or PS‐b‐PHS was slightly lower than that of homopolystyrene, but no further decrease was observed with the blend ratio of the diblock copolymer increasing from 5 to 20 wt %. For a PS/PS‐b‐PHS blend, the surface atomic concentration ratio O/C increased linearly with the molecular weight of poly(4‐hydroxystyrene) blocks in diblock copolymer PS‐b‐PHS in the range of our study. The different structures of 4‐acetoxystyrene polymers and their hydrazinolyzed materials may affect the surface compositions of their blends with PS; among these polymers, PS‐b‐PHS and PS‐b‐PAS appeared to be most effective. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 1046–1054, 2001     

Synthesis of self‐assembled sphingolipid conjugates and their morphology effect on anticancer therapeutic potency

The shape of self‐assembling polymer–drug conjugates, influencing the cellular uptake, is one of the important factors to be considered for effective drug delivery. In this study, we described synthesis of polymeric drug conjugates of different morphologies with phytosphingosine (PHS) as a hydrophobic model drug and poly(amino acid) as a hydrophilic host polymer. By varying the amount of PHS grafted to poly(amino acid), PHS–poly(amino acid) conjugates exhibited morphological transition from spherical to worm‐like micellar aggregates in the aqueous media. We investigated the physicochemical properties of self‐assembled structures in terms of hydrodynamic size, surface charge, and critical aggregation concentration. The anticancer therapeutic potency of these self‐assembled structures was also discussed in terms of cellular uptake and cytotoxicity of prodrug micelles as a function of dose and time by in vitro cell study. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

A practical route for the preparation of poly(4‐hydroxystyrene), a useful photoresist material

The synthesis and characterization of poly(4‐hydroxystyrene) (PHS) and poly(4‐vinylphenol) (PVPh) by the polymer modification route are reported. Polystyrene prepared by free‐radical and anionic polymerization was acetylated quantitatively to poly(4‐acetylstyrene) (ACPS) with acetyl chloride and anhydrous aluminum trichloride in carbon disulfide. The acetylation worked equally well in a mixture of 1,2‐dichloroethane (DCE) and nitrobenzene containing largely DCE. The extent of the acetylation was estimated by ¹H NMR. The oxidation of ACPS was carried out with various oxidizing agents and reaction conditions. The peracetic acid oxidation in chloroform resulted in quantitative oxidation to poly(4‐acetoxystyrene) (APS) as estimated by ¹H NMR spectroscopy. The treatment of APS with hydrazine hydrate in dioxane resulted in the formation of PVPh. Deacetylation occurred with equal versatility in a mixture of aqueous sodium hydroxide and tetrahydrofuran. All the polymers were characterized via gel permeation chromatography, IR, UV, ¹H NMR, and ¹³C NMR spectroscopic techniques. This is the first report on the synthesis of ACPS, APS, and PHS of reasonably narrow molecular weight distributions or otherwise by the polymer modification route. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 453–461, 2000     

Recent Developments in Kramers’ Theory of Reaction Rates

In this short review, we provide an update of recent developments in Kramers’ theory of reaction rates. After a brief introduction stressing the importance of this theory initially developed for chemical reactions, we briefly present the main theoretical formalism starting from the generalized Langevin equation and continue by showing the main points of the modern Pollak, Grabert and Hänggi theory. Kramers’ theory is then sketched for quantum and classical surface diffusion. As an illustration the surface diffusion of Na atoms on a Cu(110) surface is discussed showing escape rates, jump distributions and diffusion coefficients as a function of reduced friction. Finally, some very recent applications of turnover theory to different fields such as nanoparticle levitation, microcavity polariton dynamics and simulation of reaction in liquids are presented. We end with several open problems and future challenges faced up by Kramers turnover theory.     

Solvent dynamics in a model system

We report herein a study of the solvent reorganization process in an electron transfer reaction. The calculations are based on a model consisting of 26 or 62 solvent particles. Molecular dynamics simulations are performed to calculate the electric field fluctuations during the orientational and translational motion of the solvent molecules. The changes in the electric fields at various points near the reacting sites in the system are evaluated as a function of time. From these electric fields, electric field time correlation functions are calculated. The main conclusion in this work is that it requires nearly 3 ps for the model solvent to reorient during the charge transfer. These results suggest ways of incorporating solvent dynamics based on molecular models into theoretical studies of electron transfer rates in condensed media.     

Catalytic Effect of Electric Fields on the Kemp Elimination Reactions with Neutral Bases

The effect of solvent reaction fields and oriented electric fields on the Kemp elimination reaction between methylamine or imidazole and 5-nitrobenzisoxazole has been theoretically studied. The Kemp reaction is the most widely used for the design of new enzymes. Our results, using the SMD continuous model for solvents, are in quite good agreement with the experimental fact that the rate of the analogous reaction with butylamine is one order of magnitude smaller in water than in acetonitrile. In the case of external electric fields, our results show that they can increase or decrease the energy barrier depending on the magnitude and orientation of the field. A duly oriented electric field may have a notable catalytic effect on the reaction. So, external electric fields and reaction fields due to the medium can contribute to the design of new enzymes. Several factors that must be taken into account to increase the catalytic effect are discussed.     

Refinement of the primary hydration shell model for molecular dynamics simulations of large proteins

A realistic representation of water molecules is important in molecular dynamics simulation of proteins. However, the standard method of solvating biomolecules, that is, immersing them in a box of water with periodic boundary conditions, is computationally expensive. The primary hydration shell (PHS) method, developed more than a decade ago and implemented in CHARMM, uses only a thin shell of water around the system of interest, and so greatly reduces the computational cost of simulations. Applying the PHS method, especially to larger proteins, revealed that further optimization and a partial reworking was required and here we present several improvements to its performance. The model is applied to systems with different sizes, and both water and protein behaviors are compared with those observed in standard simulations with periodic boundary conditions and, in some cases, with experimental data. The advantages of the modified PHS method over its original implementation are clearly apparent when it is applied to simulating the 82 kDa protein Malate Synthase G. © 2009 Wiley Periodicals, Inc. J Comput Chem 2009     

聚羟基苯乙烯在光致抗蚀剂中的应用及其合成

主要综述了聚羟基苯乙烯用作深紫外光致抗蚀剂主体成膜树脂的发展历程、应用现状以及一些最新的研究进展,并简要介绍了聚羟基苯乙烯的单体衍生物及其聚合物的制备方法.     

Oxygen permeability of novel organic-inorganic coatings: II. Modification of the organic component with a hydrogen-bond forming polymer

The oxygen permeability of composite materials, consisting of a LDPE substrate coated with a thin layer (0.7-1 μm) of new hybrid organic/inorganic materials based on SiO₂ and PE-PEG block copolymers, has been characterized at 35 and 50 °C. The effect of adding a second organic component capable to form hydrogen bonds, namely either poly(4-hydroxystyrene) (PHS) or malic acid, has been studied. While the addition of PHS leads to a further significant decrease (50-70%) of the oxygen permeability both at 35 and 50 °C, on the contrary, the addition of malic acid leads to poorer barrier properties. A slight decrease of the permeability was obtained after plasma treatment of the LDPE surface.