聚对苯二甲酸乙二酯(PET)/聚对乙酰氧基甲酸(PHB)共聚酯及同类共聚物序列分布表征的数学统计

由聚对苯二甲酸乙二酯(PET)和对-乙酰氧基苯甲酸制得的PET/PHB共聚酯代表了一类序列结构较一般二元共聚物复杂的共聚体系.在揭示了这类共聚物与序列分布有关的诸概率参数中只有一个是独立的之后,定义了参数B_q来描述此类共聚物的无规度.并指出,共聚物B_q=b时的序列分布,可以从一般二元共聚物无规度B=b时的序列结构加以推断.     

用1H-和13C-NMR方法研究聚对苯二甲酸乙二酯/聚一氧基苯甲酸酯共聚酯的序列分布

 测定了PET/30PHB和PET/60PHB共聚酯的高分辨¹H和¹³C谱,并采用INEPT方法和部分弛豫FT技术确定了季碳吸收峰,对NMR谱进行了归属.应用我们先前提出的方法对共聚酯的序列分布进行了表征.结果表明,两种共聚酯的无规度B_q值均小于1,序列分布不象Jackson等认为的那样为完全无规的.此外,文中还指出,某些研究者套用Flory公式判别PET/PHB共聚酯是否为无规的不妥之处.     

用1H NMR方法研究聚砜-聚脂类嵌段共聚物的组成和序列分布

本文测定了一系列聚矾-聚酯嵌段共聚物的高分辨核磁共振谱,研究了共聚物的组成和序列分布,山¹HNMR谱图的峰面积算出了共聚物的无规度(B)及数均序列长度(L),B值均在O相似文献   

用~1H-和~(13)C-NMR方法研究聚对苯二甲酸乙二酯/聚一氧基苯甲酸酯共聚酯的序列分布

测定了PET/30PHB和PET/60PHB共聚酯的高分辨~1H和~(13)C谱,并采用INEPT方法和部分弛豫FT技术确定了季碳吸收峰,对NMR谱进行了归属.应用我们先前提出的方法对共聚酯的序列分布进行了表征.结果表明,两种共聚酯的无规度B_q值均小于1,序列分布不象Jackson等认为的那样为完全无规的.此外,文中还指出,某些研究者套用Flory公式判别PET/PHB共聚酯是否为无规的不妥之处.     

~(13)C-NMR方法研究酚酞聚芳醚酮砜共聚物的序列结构

通过亲核共缩聚合成了一系列酚酞聚芳醚酮砜共聚物和嵌段共聚物 ,并利用1 3C NMR方法研究了共聚物的链结构 ,通过观察酚酞单元中三个位置的季碳原子的化学位移及其相应强度的变化 ,计算共聚物中不同链段的共聚物的组成、平均序列长度和无规度 .结果表明 ,除嵌段共聚物外 ,其它共聚物的无规度均接近 1 ,表明共聚物为无规共聚物 ,而且对三个位置的季碳原子分析均得出了相同的结果 .     

CnBδ(δ=0, ±1; n =1～6)团簇的结构、稳定性和光谱

采用密度泛函理论(DFT)的B3LYP方法,在6-31G*和6-311＋G(3df)水平上对C_nB(n=1～6)团簇及其阴离子和阳离子的几何构型和电子结构进行了优化和振动频率计算.得到了C_nB(n=1～6)团簇的电离能,绝热电子亲合势以及C_nB^δ(δ=0,±1)团簇的能隙.结果表明C_nB^－(n=1～6)团簇的基态构型均为线形,这与等电子的C_n簇合物的结构是一致的; C_nB(n=1～6)团簇的基态构型中,除C₂B为不对称的三角形,C₆B为具有C_2v对称性的环状结构外,其余均为线形结构.阳离子团簇中n=2、3、6的基态结构具有C_2v对称性外,其它几个均为线形结构.从几何参数和振动频率上发现,采用密度泛函B3LYP方法在6-311＋G(3df)和6-31G*两种基组上计算得到的键长参数和振动频率非常接近,说明B3LYP方法在计算C_nB簇合物结构参数上对于基组的选择是不太敏感的.通过对C_nB(n=1～6)的光电子能谱性质的研究发现,C₄B容易获得一个电子形成阴离子团簇,但失去一个电子是很困难的,这与实验上观测到的结果非常吻合.     

丙烯酰胺/2-丙烯酰胺基十六烷磺酸铵无规共聚物的形态结构研究

 本工作应用透射电子显微镜研究了丙烯酰胺/2-丙烯酰胺基十六烷磺酸铵无规共聚物(AM/AMC₁₆SNH₄)的形态结构.给出共聚物在水溶液中具有伸展网状结构,并存在一定程度的疏水基因间的缔合作用.是一种在耐盐性和储存稳定性方面有明显改善的新型改性聚丙烯酰胺.     

B12Sc4和B12Ti4团簇的储氢性质

提出了两个稳定的团簇B₁₂Sc₄和B₁₂Ti₄, 基于理论计算, 研究了它们的结构与储氢性质. 结果发现, 在这两个稳定的团簇中, 过渡金属原子不会聚合在一起而影响它们对氢气的吸附. B₁₂Sc₄最多可以吸附12个氢分子, 达到7.25% (质量分数)的储氢量. 它的平均每氢分子吸附能量为10.5 kJ·mol^-1. B₁₂Ti₄最多只能吸附8个氢分子, 储氢量为4.78%. 但平均每氢分子吸附能量可达50.2 kJ·mol^-1. 进一步计算表明, 即使在77 K,也需要很高的氢气压力才能使12个氢分子都吸附到B₁₂Sc₄上. 电子结构分析表明, B₁₂Ti₄-nH₂吸附结构中的Kubas作用要大于相应B₁₂Sc₄-nH₂结构中的Kubas作用.     

应用分子全息QSAR预测多溴二苯醚(PBDEs)的毒性

多溴二苯醚(PBDEs)可能会激活芳香烃受体的信号传导通路, 从而对人类和野生动物的健康产生负面影响. 鉴于多溴二苯醚实验毒性数据有限, 发展基于结构的化合物毒性预测模型具有重要的实际意义. 本文基于一种新的分子结构表征方法—— 分子全息, 研究了18种多溴二苯醚结构与毒性之间的关系, 建立了相关性显著、稳健性强的QSAR模型(r²= 0.991, q²_LOO= 0.917). 随机选出14种多溴二苯醚为训练集, 其他4种化合物为测试集以验证分子全息QSAR模型的稳健性和预测能力. 结果在最佳建模条件下得到模型的统计参数如下：r² = 0.988, q²_LOO = 0.598, r²_pred = 0.955, 预测值与实验值之间的均方根误差(RMSE)为0.155. 这表明基于分子全息的QSAR模型可以对多溴二苯醚毒性进行比较准确的预测. 本文同时利用分子全息QSAR模型色码图, 探讨了影响多溴二苯醚毒性的分子结构特征及分子机理.     

273.15 K下Li2B4O7-LiCl-H2O体系热力学性质的等压研究及离子作用模型

用等压法研究了273.15 K下Li₂B₄O₇-LiCl-H₂O体系不同质量摩尔浓度分数的等压平衡浓度和水活度; 计算了LiCl和Li₂B₄O₇混合盐溶液的渗透系数等热力学性质. 用273.15 K下的实验数据对Pitzer离子相互作用模型进行了参数化研究, 拟合求取了273.15 K下Pitzer离子相互作用参数, 用获得的参数计算了LiCl和Li₂B₄O₇在Li₂B₄O₇-LiCl-H₂O体系中的活度系数. 273.15 K下由相应的Pitzer模型计算的渗透系数值与实验结果一致. 这对完善含锂、硼盐湖卤水体系的热力学模型具有重要意义.     

Transesterification and crystallization behavior of poly(butylene succinate)/poly(butylene terephthalate) block copolymers

The block copolymers of poly(butylene succinate) (PBS) and poly(butylene terephthalate) (PBT) were synthesized by melt processing for different times. The sequence distribution, thermal properties, and crystallization behavior were investigated over a wide range of compositions. For PBS/PBT block copolymers it was confirmed by statistical analysis from ¹H-NMR data that the degree of randomness (B) was below 1. The melting peak (T_m) gradually moved to lower temperature with increasing melt processing time. It can be seen that the transesterification between PBS and PBT leads to a random copolymer. From the X-ray diffraction diagrams, only the crystal structure of PBS appeared in the M1 copolymer (PBS 80 wt %) and that of PBT appeared in the M3 (PBS 50 wt %) to M5 (PBS 20 wt %) copolymers. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 147–156, 1998     

Modification of PET with sterically hindered diols

Poly(ethylene terephthalate) was modified by incorporating bis(hydroxyethyl) tetrasubstituted terephthalates (methyl, chlorine, and bromine) as a third component in the mole ratios of 2–50% (based on dimethyl terephthalate) which resulted in random copolyesters. The presence of steric hindrance imparted additional chain rigidity to the copolymer structure, as shown by increased glass transition temperature (T_g). The effectiveness of the steric groups for conferring rigidity to the copolymer structure was CH₃ > Cl?Br. The copolyesters which contained halogen substituents showed substantial enhancement in flame retardency compared with PET.     

Quantifying and Controlling the Composition and ‘Randomness’ Distributions of Random Copolymers

The effect of disparity in the reactivity ratios of monomer pairs on the composition distribution and microstructure of the resultant copolymer formed through free‐radical polymerization is quantified computationally. This correlation has been determined for the monomer pairs of styrene/methyl methacrylate and styrene/2‐vinyl pyridine for a variety of monomer feed ratios. These monomer pairs were chosen as they represent systems that have been utilized to experimentally examine the importance of copolymer architecture on its ability to compatibilize an immiscible polymer blend. Moreover, their respective random copolymers show conflicting results for this examination. The results of this work show that the difference in the reactivity ratios of styrene and 2‐vinyl pyridine copolymer (r₁ = 0.5, r₂ = 1.3) significantly broadens the composition and randomness distribution of the resultant copolymer. This breadth is not easily avoided as it evolves even in the early stages of the copolymerization. Conversely, for the styrene/methyl methacrylate pair, the reactivity ratios are similar (r₁ = 0.46, r₂ = 0.52) and this results in a copolymer with a narrow composition distribution and sequence distribution dispersion. Stopping the polymerization at early conversion further narrows both distributions. The presented results, therefore, provide fundamental information that must be considered when planning an experimental procedure to evaluate the relative importance of sequence distribution and composition distribution of a random on its application.     

Morphology and degradation behavior of aliphatic/aromatic copolyesters

Random and segmented block copolymers of Poly(tetramethylene succinate) (PTMS) and Poly(tetramethylene terephthalate) (PTMT) were synthesized and characterized regarding sequence distribution and crystalline parameters. Biodegradation behaviors of the copolyesters were examined in activated sludge and enzyme solution in terms of CO₂ evolution. It was found that the initial degradation was strongly dependent on the crystallinity in the random copolymer. However, the chemical compositions become a dominant factor at the later stage of degradation. In the case of block copolymers, the biodegradation rate was most significantly affected by size and degree of perfectness of PTMS crystallites.     

Characterization of ethylene/propylene copolymers by means of a GPC-4D technique

Copolymer composition and comonomer distribution are important magnitudes in polymer material that have a big effect on different kind of properties and consequently there are several ways to study.In this work several ethylene/propylene copolymers synthesized with two different metallocene catalysts and a Ziegler–Natta catalyst and covering a wide composition range were studied. Characterization was carried out by nuclear magnetic resonance (¹³C NMR) and by gel permeation chromatography with 4 detectors (GPC-4D): refractive index, viscosity, multi-angle light scattering and infrared detectors.Different behaviour in the comonomer distribution along the molecular weight was obtained for metallocene and for ZN copolymers as expected due to the differences between these catalytic systems. Nevertheless, Ziegler–Natta copolymers present more homogeneous comonomer distribution due to the synthesis method. Study of conformation of chains in solution was improved by defining the scaling law of R_g against the number of repeat units because it avoids the effect of the repetitive unit size. Both metallocene copolymer sets show similar dependence of q value with the copolymer composition, however Ziegler–Natta copolymers show different behaviour with q values independent on copolymer composition. This different behaviour has been related with the effects of the heterogeneity of the ethylene distribution and of the molecular weight of the samples.     

Protein-like copolymers: Computer simulation

The model ofAB copolymers with a “protein-like” primary sequence was developed. This type of copolymers was obtained in a computer experiment. First, the conformation of a collapsed dense homopolymer globule was generated and then, based on this conformation, the primaryAB sequence was determied by denoting the monomeric units located near the surface of the globule as unitsA and those constituting the core of the globule as unitsB. After that, the primary structure of the chain was fixed, and different interaction potentials for theA andB units were introduced. Drawing an analogy of this model to aqueous solutions of globular proteins,A units were interpreted as hydrophilic, andB units were regarded as hydrophobic. By means of Monte Carlo simulation using the bond fluctuation model, the coli—globule transition in “protein-like”AB copolymer, induced by an increase in the attraction between the hydrophobicB units, was studied. The coil—globule transition in a copolymer with the “protein-like” primary sequence occurs at a higher temperature and has higher rate and is sharper than that in a random copolymer with the sameA/B composition and in a random block copolymer with the sameA/B composition and the same “degree of blockiness”. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 884–889, May, 1998.     

Syndiospecific copolymerization of styrene with styrene terminated isoprene macromonomer by CpTiCl3-methylaluminoxane catalyst

Copolymerization of styrene with styrene terminated polyisoprene macromonomer (SIPM) by CpTiCl₃-methylaluminoxane (MAO) catalyst has been investigated (Cp: cyclopentadienyl). SIPM was prepared by reaction of living polyisoprene initiated with sec-butyllithium (s-BuLi) and p-chloromethylstyrene. The synthesized macromonomer has a high terminal degree of functionalization and a narrow molecular weight distribution. Graft copolymers of polystyrene-graft-polyisoprene have been synthesized with the CpTiCl₃-MAO catalyst. The synthesized graft copolymer was confirmed to have a highly syndiotactic sequence on the main chain.