含偶氮基团的侧链液晶高分子的研究进展

综述了含偶氮基团的侧链液晶高分子的制备方法及其在可逆光信息存储与非线性光学领域的应用。     

Chain Dynamics in Solid Polymers and Polymerizing Systems as Revealed by Broadband Dielectric Spectroscopy

Broadband Dielectric Spectroscopy (BDS) provides a direct, powerful means of studying the chain dynamics of solid polymers. The present work discusses experimental data, phenomenological theories, molecular theories and recent molecular dynamics simulations of the relaxation functions and average relaxation times for the multiple dielectric relaxations observed for amorphous polymers. Examples of current applications of BDS are given, including studies of the dynamics of ultra-thin polymer films and real-time studies of (i) the crystallization behaviour of bulk polymers and (ii) thermo-polymerizing systems.     

柔性链高聚物的单分子链玻璃体和单晶*

本文综述了高分子单链颗粒的制备方法, 包括极稀溶液喷雾法、表面扩张膜法、冷冻干燥法、微乳液聚合法等。介绍和讨论了单链和寡链聚苯乙烯玻璃体微球的性质以及聚环氧乙烷、全同立构聚苯乙烯、顺-1, 4-聚丁二稀、反-1, 4-聚异戊二烯单链单晶电子显微镜和选区电子衍射观察的最新结果。     

刚性侧链型液晶高分子与含二维液晶基元的液晶高分子

提出了“刚性侧链型液晶高分子”与“含二维液晶基元的液晶高分子”两个新概念。     

侧链液晶聚合物相转变点的分子动力学模拟

液晶基本上可分为３类：向列型液晶、近晶型液晶和胆甾型液晶［１］．液晶材料的相转变温度的预测对选择和设计液晶材料具有非常重要的作用．本文用分子动力学模拟法对聚［ω－（４′－甲氧基联苯－４－氧基）己基］甲基丙烯酸酯（ＰＭ６ＭＰＰ）单链分子进行了研究,模拟...     

Influence of an Unnatural Amino Acid Side Chain on the Conformational Dynamics of Peptides

In this work, a non‐natural amino acid, H‐propargylglycine‐OH (Pra), is chosen to examine the side‐chain effect on the backbone conformation of small peptides. The conformations of two synthesized Pra‐containing tripeptides, Ac‐Pra‐Pra‐NH₂ (PPTP) and Ac‐Pra‐Ala‐NH₂ (PATP), are examined by infrared (IR) spectroscopy in combination with molecular dynamics (MD) simulations and quantum chemical computations. By analyzing the joint distributions of backbone torsional angles, several significant conformations can be identified for the two tripeptides solvated in D₂O. At room temperature, 44 % of PPTP exists in the α‐α conformation and 33 % of PATP exists in the α‐polyproline‐II conformation. Larger structural inhomogeneity is seen in both cases by MD simulations at elevated temperatures. Thus even a small side chain, such as the propargyl group can significantly alter the peptide backbone conformations. The results suggest that there is no overwhelming conformational propensity of the Pra residue in short peptides. IR spectra simulated in the amide‐I region using two different methods, reasonably reproduce the experimental IR spectra and their temperature dependence.     

Comprehensive Characterization of Chain End Groups of Vinylidene Fluoride Based Polymers

Summary: In this work an investigation of the chain end groups produced in the free radical copolymerization of vinilydene fluoride (VDF) and hexafluoropropylene (HFP) is performed. Type and amount of chain end groups are evaluated by a meticulous analytical characterization of VDF/HFP copolymer. At first pulsed gradient spin-echo nuclear magnetic resonance (spin-echo NMR) is used to identify all the chain end groups also at very low concentration (equal to 0.1 mmol · Kg⁻¹). The instrument sensitivity is increased of an order of magnitude in comparison with the traditional NMR. Moreover potentiometric titration and ion chromatography (IC) are also used to study the chain end groups and, as a consequence, the nature and the amount of the acidity showed by the polymer chains. In details two intensity of acidity are detected by potentiometric titration, namely strong and weak. The strong acidity is associated to the presence of residual surfactant and can be removed washing the polymer, while the weak acidity is due to free molecules of fluoride acid (HF). The standard ion chromatography facility is properly modified to quantify the fluoride in the polymer matrix without any pre extraction in water. Thanks to this the HF concentration in the polymer is evaluated with high accuracy. A detailed kinetic scheme for the VDF/HFP polymerization is also proposed taking into account all the findings obtained studying the chain end groups.     

高聚物的物理老化和链的凝聚缠结

本文基于高聚物在物理老化和拉伸变形过程中构象弛豫行为的实验结果,进一步阐明了高分子链局部凝聚缠结的观点。     

Synthesis and Properties of pH-Responsive Polymers with Cadaverine Side Groups

A water-soluble monomer N¹-(4-vinylbenzyl)-pentane-1,5-diamine dihydrochloride (VBPDA) with cadaverine (1,5-pentanediamine) group was synthesized. pH-responsive polymer with cadaverine group was obtained by free radical polymerization of VBPDA using 4,4-azobis(4-cyanovaleric acid) (ACVA) as the initiator. The structure and molecular weight of the polymer were characterized by FTIR, ¹H-NMR and GPC-MALLS. Aggregation behavior of the polymer in aqueous solution was investigated by dynamic light scattering (DLS), UV-Vis and fluorescence measurements. The experimental results show that the fluorescence intensity of the aggregates decreases and the size of the aggregates increases with increasing pH due to the continuous dehydration of the cadaverine side groups.     

Dynamics of Poly(vinylmethyl ether) Blends with a Strongly Interassociating Copolymer

We apply broadband dielectric relaxation spectroscopy to probe the dynamics of hydrogen bonded polymer blends. A copolymer consisting of 2,3-dimethylbutadiene (DMB) [86%] and p-(hexafluoro-2-hydroxyl-2-propyl)styrene (HFS) [14%] was synthesized and blended with poly(vinylmethyl ether) (PVME). The copolymer is capable of forming strong intermolecular hydrogen bonds, while minimizing the degree of intramolecular associations, and its blends with PVME are predicted to be miscible over the entire composition range. Two segmental processes, α and α₁, are present in blends containing 26, 50, and 76 weight percent copolymer. The slower process (α₁) is assigned to the segmental motion of the intermolecularly associated copolymer, and the faster process (α) to segmental motions of PVME modified by the HFS:DMB copolymer. A relaxation associated with residual water is present in the glassy state. A local process due to motions of the PVME ether groups (β) is also present in the glassy state, and does not change with blend composition.     

Synthesis of Liquid Crystalline Polymers with Side Chains

The present paper covers the synthesis and characterization of several intermediate products, monomer, and polymers. 3-{ 2-[ 4-( 4-Nitrophenylazo ) phenoxy] ethyloxycarbonyl} propanoyloxy (2-hydroxy) propyl acrylate (4) was prepared by the ring-opening reaction of glycidyl acrylate with the monoester of succinic acid (3). The polymers (5) with different molecular weights were prepared by the free-radical polymerization. The polymers (5) had liquid crystalline behavior without decomposition as revealed by DSC, optical microscope.     

表面上锚定聚乙烯链聚集的分子动力学模拟

利用分子动力学模拟方法研究了锚定于二维无限大表面上的聚乙烯分子链的聚集和有序化过程.聚乙烯链与表面的相互作用采用一个以平面法向距离为函数的势能表达式S(z).以均方回转半径垂直于表面的分量s²⊥作为指标,考察了模拟过程中表面势能函数的强度效应和模拟体系的温度效应.研究了锚定聚乙烯在表面上聚集的有序化过程,考察了锚定聚乙烯链的聚集成核的动力学过程,聚集体的形貌及分子量依赖性.发现锚定聚乙烯在300K时只在锚定点附近形成一个局部有序结构,然后以此为核进行生长.在模拟得到的有序程度不同的聚集体结构中,锚定点都位于聚集体链轴的端面.     

Dynamics in ferro- and antiferroelectric phases of a liquid crystal with fluorinated molecules as studied by dielectric spectroscopy

For 1-[3-fluoro-4-(1-methylheptyloxycarbonyl)phenyl]-2-[4-2,2,3,3,4,4,4-heptafluorobutoxybutoxy)biphenyl-4-yl]ethane (1F7), built of chiral molecules, results of dielectric measurements of liquid-crystalline and solid phases are presented. Rich polymorphism of liquid-crystalline (SmC*, SmC*_A and SmI*_A) phases as well as of solid (Cr1 and Cr2) phases were observed down to –130°C. At a frequency range from 0.1 Hz to 3 MHz, the relaxation processes were detected in ferroelectric SmC*, antiferroelectric SmC*_A and highly ordered SmI*_A smectic phases. The mechanism of complex dynamics (moleculear and collective) was identified with the help of the bias field. Vitrification of conformationally disordered crystal phase Cr2 was found in accordance with calorimetric observations.     

Conformational Space of a Polyphilic Molecule with a Fluorophilic Side Chain Integrated in a DPPC Bilayer

We investigate the conformational space of a polyphilic molecule with hydrophilic, lipophilic and fluorophilic parts inserted as a transmembrane agent into a dipalmitoylphosphatidylcholine bilayer by means of all‐atom molecular dynamics simulations. Special focus is put on the competing structural driving forces arising from the hydrophilic, lipophilic and fluorophilic side chains and the aromatic backbone of the polyphile. We observe a significant difference between the lipophilic and the fluorophilic side chains regarding their intramembrane distribution. While the lipophilic groups remain membrane‐centered, the fluorophilic parts tend to orient toward the phosphate headgroups. This trend is important for understanding the influence of polyphile agents on the properties of phospholipid membranes. From a fundamental point of view, our computed distribution functions of the side chains are related to the interplay of sterical, enthalpic and entropic driving forces. Our findings illustrate the potential of rationally designed membrane additives which can be exploited to tune the properties of phospholipid membranes. © 2017 Wiley Periodicals, Inc.     

Molecular Dynamics of PGA Bioabsorbable Polymer During Isothermal Cold Crystallization

An investigation was carried out on the molecular dynamics of poly(glycolide) (PGA) in its completely amorphous state and during isothermal cold crystallization. Experimental results were generated over a wide range of frequency and temperature by broad-band dielectric spectroscopy (DRS). The variation of the average relaxation time (defined as τ= ½πf_max where f_max is the frequency at maximum loss for the main α relaxation) has been studied during cold crystallization and the temperature dependence of this average relaxation time for completely amorphous and crystallized samples has been analyzed. This behaviour has been modelled by Havriliak-Negami and Vogel-Fulcher equations. The sensitiveness of the segmental dynamics to the degree of crystallinity has been analyzed, taking into account the relaxing segments and the amorphous layers between lamellae. Supporting evidence about the thermal behaviour of the polymers has been obtained with DSC. Complementarily, the evolution of the morphologies obtained during crystallization processes has been followed by optical microscopy.     

Hydrogen-Bond Structure and Low-Frequency Dynamics of Electrolyte Solutions: Hydration Numbers from ab Initio Water Reorientation Dynamics and Dielectric Relaxation Spectroscopy

We present an atomistic simulation scheme for the determination of the hydration number (h) of aqueous electrolyte solutions based on the calculation of the water dipole reorientation dynamics. In this methodology, the time evolution of an aqueous electrolyte solution generated from ab initio molecular dynamics simulations is used to compute the reorientation time of different water subpopulations. The value of h is determined by considering whether the reorientation time of the water subpopulations is retarded with respect to bulk-like behavior. The application of this computational protocol to magnesium chloride (MgCl₂) solutions at different concentrations (0.6–2.8 mol kg⁻¹) gives h values in excellent agreement with experimental hydration numbers obtained using GHz-to-THz dielectric relaxation spectroscopy. This methodology is attractive because it is based on a well-defined criterion for the definition of hydration number and provides a link with the molecular-level processes responsible for affecting bulk solution behavior. Analysis of the ab initio molecular dynamics trajectories using radial distribution functions, hydrogen bonding statistics, vibrational density of states, water-water hydrogen bonding lifetimes, and water dipole reorientation reveals that MgCl₂ has a considerable influence on the hydrogen bond network compared with bulk water. These effects have been assigned to the specific strong Mg-water interaction rather than the Cl-water interaction.     

侧链中含二苯甲酮基的聚硅氧烷的合成与结构表征

在相转移催化剂四乙基溴化铵作用下,利用2,4-二羟基二苯甲酮与烯丙基缩水甘油醚在碱性水溶液中的开环加成反应,合成了中间体4-(β-羟基-γ-烯丙氧)丙氧基-2-羟基二苯甲酮(MUV-0),将其进-步与聚甲基氢硅氧烷进行硅氢化加成反应。合成了侧链中含二苯甲酮基的聚有机硅氧烷。用元素分析、红外光谱、紫外光谱和核磁共振等仪器对中间体以及目标聚硅氧烷的结构进行了表征和测定。结果表明：中间体和聚硅氧烷在紫外光区均具有二苯甲酮衍生物特有的三条吸收谱带,对波长240～400nm的紫外光有良好的吸收作用。     

单分子链穿插进入双链凝聚线团的分子动力学方法模拟

用分子动力学(MD)方法模拟了聚乙烯(含300个CH₂单元)单链凝聚线团与一个双链处于平衡态的凝聚线团相互穿插的融合过程,考察分析了体系结构演变的能量信息及第三个链的引入对原来两链穿插状态的影响.研究发现,在两部分线团凝聚成一体后,各分子链一方面在表面势能各向异性的作用下试图挤入体系内部,另一方面在构象熵的驱动下又尽可能地占据体系的空间,线团的穿插是在两者共同作用下逐步完成的.第三个链的融入使得原来两个链的质心距离有所增加,链段的邻接程度减弱.     

Dielectric Properties of Hyperbranched Polyesteramide with Long Alkyl Chain End Groups

Summary: Hyperbranched polyesteramides were prepared using phethalic anhydride (Ph An) or maleic anhydride (M An) as an A₂ monomer and diethanol amine (DEA) as B′B₂ monomer. Bulk condensation technique was used to synthesize polymers with both OH and modified polymers with long alkyl chain end groups. The prepared polymers were characterized using ¹H-NMR, FTIR and TGA. Solution viscosity for hyperbranched polyester amide with hydroxyl end groups was measured as well. Dielectric and electric properties of the modified samples were investigated over a range of frequency and temperatures. No relaxation peak is noticed in the dielectric spectrum ε(ν) at various temperatures. The illustration of the imaginary part of the electric modulus M″ versus frequency shows a peak which is shifted towards higher frequency in increasing temperature.     

Correlating Charge-Carrier Dynamics with Efficiency in Quantum-Dot Solar Cells: Can Excitonics Lead to Highly Efficient Devices?

The photovoltaic performance of quantum-dot solar cells strongly depends on the charge-carrier relaxation and recombination processes, which need to be modulated in a favorable way to obtain maximum efficiency. Recently, significant efforts have been devoted to investigate the carrier dynamics of nanocrystal sensitizers, both in solution and deposited on TiO₂ photoanodes, with the aim to correlate the excitonics with solar-energy conversion efficiency. This Minireview summarizes some proof of the concepts that efficiency can be directly correlated to the exciton dynamics of quantum-dot solar cells. The presented findings are based on CdSeS alloy, CdSe/CdS core/shell, Au/CdSe nanohybrids, and Mn-doped CdZnSSe nanocrystals, where the favourable excitonic processes are optimized to enhance the efficiency. Future prospects and limitations are addressed as well.