Mean-square Radius of Gyration of Poly[oxy(1-alkylethylenes)]

Taking account of the influences of both side groups and hetero-atoms in backbone, the mean-square radius of gyration of poly[oxy(1-alkylethylenes)] has been derived by the method of the rotational isomeric state approximation and matrix algebra. Numerical calculation with the parameters available in literature indicated that the dependence of 〈S²〉 on the molecular weight can be expressed as the general formula, 〈S²〉 = aM^b with b = 1 ± 0.02, for poly(oxypropylene), poly[oxy(1-ethylethylene)] and poly[oxy(1-tert-butylethylene)]. © 1997 John Wiley & Sons, Ltd.     

A NEW MODEL FOR CONCENTRATION DEPENDENCE OF POLYMER CHAIN DIMENSIONS

A new model for concentration dependence of polymer chain dimensions over the wholeconcentration range was proposed. The hydrodynamic volume of a solvated macromoleculewas found to be a universal function of the degree of coil overlapping (c/c~*). The radiusof gyration (R_g) and the expansion coefficient (α) of polymer in solution or in bulk. pre-dicted by this model are much better in agreement with the experimental data of small angleX-ray scattering and neutron scattering from literature, than with the values predicted byother models and theories.     

Chains in Critical Fluids and Nanopores

Summary: The conformational behavior of a polymer in a critical binary solvent confined in a porous medium is studied. The size of the polymer in bulk, which is mainly governed by the correlation length of the solvent density fluctuations, depends on the proximity to the critical point of the binary mixture. We find that in contrast to the bulk behavior, the conformational properties of the polymer in a porous medium depends strongly on the pore size. The latter controls the correlation length of the solvent density fluctuations and thus determines the polymer size.     

Molecular dimensions and chain conformation in glassy syndiotactic polystyrene

For the first time the small-angle neutron scattering (SANS) from mixtures of protonated and totally deuterated syndiotactic polystyrene (sPS) has been studied. Two amorphous samples with similar molecular weights have been measured at various concentrations of the protonated part. All measurements were performed at room temperature using the scattering equipment of two different laboratories. The molecular weight M_w evaluated from SANS data agreed with those obtained by gel permeation analysis (GPC). In the Kratky representation the scattering contribution due to the contrast scattering shows a plateau behavior up to q = 0.45 Å^?1, where q is magnitude of the scattering vector. This observation is in evident contrast to what is expected from the rotational isomeric state (RIS) model. In addition the characteristic ratios C_∞, derived either from the plateau height or from radii of gyration of the Zimm regime and being in reasonable agreement with each other, show strong deviations from the predictions of the RIS model. © 1994 John Wiley & Sons, Inc.     

Conformation of a chain polyelectrolyte in solution with low molecular weight salt: small angle neutron scattering measurements

Small angle neutron scattering measurements have been carried out on the tetramethylammonium salt of the polystyrenesulfonic acid withDP _w =310 and 1060 in water solution with tetramethylammonium chloride with ionic strength between 0.02 M and 1.0 M. The scattering curves in the scattering vector range 0.05 nm^–1Q1.8nm^–1 have been fitted using the form factor of a worm-like chain of finite thickness. The conformational parameters mean square radius of gyration, statistic chain element, mass per unit length and mean square radius of the cross-section have been determined experimentally and used for describing the conformation of the coils. By these molecular weights and ionic strengths, excluded volume is not necessary to explain the conformation changes depending on the salt content of the solutions; relatively short coil molecules can be described in their unperturbed dimensions even in a thermodynamically good solvent: a change in the stiffness of the chain according to Odijk's theory succeeds in describing the conformation of the polyions. Together with a slow decrease of the coil dimension by increasing salt content, a transition at ionic strength 0.1–0.5 M between two different conformations has been observed. The conformation at lower ionic strength is characterized by higher stiffness of the chain and lower mass per unit length than the form at higher salt concentration.     

高度支化共聚物的均方回转半径和支化度的关系

对于聚合物的均方回转半径和支化度的关系, 过去鲜有定量研究, 这是由于具有不同支化度的系列同种聚合物样品较难合成之故. 1982年, Kricheldorf等[1]报道了AB2和AB型单体的共缩聚反应, 这种反应可以方便地通过调节AB2和AB型单体的比例来控制产物的支化度.     

Molecular Architecture of Non-Linear Polymers: Kinetic Modeling and Experimental Characterization of the System Methyl Methacrylate + Ethylene Glycol Dimethacrylate

A general kinetic approach allowing the prediction of the molecular architecture of non-linear polymers is applied to the study of the copolymerization of methyl methacrylate (MMA) with ethylene glycol dimethacrylate (EGDMA). Dynamic predictions of molecular weight distributions, sequence length distributions and mean square radius of gyration are possible before and after gelation. A set of experiments concerning the copolymerization of MMA and EGDMA was carried out in toluene solution at 60 °C for which classic radical kinetics is a good approximation. The time evolution of key polymer properties was followed using a SEC system with a refractive index detector coupled with MALLS allowing the determination of absolute weight average molecular weight and apparent molecular size distributions as well as z-average radius of gyration. Special focus was given to assess the influence of the initial amount of cross-linker on the dynamics of the non-linear structure build-up of these products. A kinetic scheme comprising 23 different chemical species and 76 chemical reactions was used in the modeling studies of this chemical system. Most of the kinetic parameters used in the simulations have been collected from previous studies. For experiments at low monomer conversion (up to about 0.5) a good agreement between predictions and experimental measurements is observed for molecular weights and z-average radius of gyration by fitting a small number of parameters describing gel effect (with a conversion dependent but chain length independent termination rate parameter) and the relative propagation on pendant double bonds. However, predicted values of weight-average molecular weights and z-average radius of gyration before gelation are too low at higher monomer conversions with non-linear systems. The likely cause is the presence of intramolecular reactions which should not be neglected in these circumstances.     

含引发机制的Ａf—Ａg型缩聚反应Z—均回转半径研究

讨论了含引发机制的Ａf-Ａg型缩聚反应体系Z－均回转半径,利用枝状高分子成键的统计分析,给出组合因子分解公式,并得到均方回转半径的表达式;进一步结合数量分布函数,定义k次高分子半径,并给出计算k次高分子回转半径的循环公式,最后得到凝胶点前Z－均回转半径的解析表达式。     

Static light scattering from poly(ethylene oxide) in methanol

Static light scattering measurements were performed on dilute solutions of monodisperse poly(ethylene oxide) (PEO) in methanol at 25°C. PEOs of five different molecular weights ranging from nominal M_w = 8.6 × 10⁴ to 9.13 × 10⁵ were used. Linear Zimm plots were obtained for all the PEO samples: no downturn was observed at small angles, indicating that no large aggregates of PEO molecules exist in the solution. From the plots, values of the weight-average molecular weight, M_w, the radius gyration, R_G, and the second virial coefficient, A₂, were successfully determined for respective PEOs. Observed relationship between R_G and M_w indicates that methanol is certainly a good solvent for the polymer. © 1996 John Wiley & Sons, Inc.     

原卟啉原IX的构象分析

在合理药物设计方法中 ,当靶标酶的三维结构未知时 ,对其底物进行构象分析 ,特别是确定其活性构象 ,对阐明靶标酶活性中心的空间形状和作用位点具有十分重要的意义。我们曾利用距离比较法确定了原卟啉原氧化酶的底物—原卟啉原IX的活性构象 ,本文从构象分析的角度对 4种不同构象的原卟啉原IX分子与二苯醚类分子的晶体学构象进行了几何参数的比较和分析 ,结果进一步证实了距离比较法所确定的活性构象更为可靠     

Molecular conformation search by distance matrix perturbations

Three-dimensional molecular structure is fundamental in chemical function identification and computer-aided drug design. The enumeration of a small number of feasible conformations provides a rigorous way to determine the optimal or a few acceptable conformations. Our contribution concerns a heuristic enhancement of a method based on distance geometry, typically in relation with experiments of the NMR type. Distance geometry has been approached by different viewpoints; ours is expected to help in several subtasks arising in the process that determines 3D structure from distance information. More precisely, the input to our algorithm consists of a set of approximate distances of varying precision; some are specified by the covalent structure and others by Nuclear Magnetic Resonance (NMR) experiments (or X-ray crystallography which, however, requires crystallization). The output is a valid tertiary structure in a specified neighborhood of the input. Our approach should help in detecting outliers of the NMR experiments, and handles inputs with partial information. Moreover, our technique is able to bound the number of degrees of freedom of the conformation manifold. We have used numerical linear algebra algorithms for reasons of speed, and because they are well-implemented, fully documented and widely available. Our main tools include, besides distance matrices, structure-preserving matrix perturbations for minimizing singular values. Our MATLAB (or SCILAB) implementation is described and illustrated.AMS subject Classification: 92E10 Molecular structure, 92C40 Biochemistry, molecular biology, 65F15 Eigenvalues, eigenvectors, 15A18 Eigenvalues, singular values, and eigenvectors     

The effect of nanoparticle nonuniformity on the ratio of gyration and hydrodynamic radiuses

The ratio of the radius of gyration, obtained by static light scattering, and the hydrodynamic radius, obtained by dynamic light scattering, are routine experimental techniques for the assessment of nanoparticle shape. The potential effect of particle nonuniformity is mostly not considered. In this communication, we demonstrate that, even with medium particle nonuniformities, it is advisable to apply appropriate corrections. The values of the correction factors are offered in a diagram for various particle shapes, and two types of particle-size distributions and their widths.     

Off-lattice Monte Carlo studies on size and shape of isolated polymer chains with isotactic and syndiotactic attached side groups

Chains containing side groups were generated with up to 102 bonds in the backbone for both iso- and syndiotactic arrangements. The mean-square end-to-end distance <h ²>, the mean-square radius of gyration <r ²> and the ratios <l _i ² >/<l ₁ ² > of the axes of inertia were investigated. It could be shown that the mean size and shape of such chains are not influenced by the kind of stereoregularity.Dedicated to Prof. Dr. K. Ueberreiter on the occasion of his 70th birthday.