线形、梳形和星形高分子静态和动态性质的模拟

以梳形高分子为纽带,基于粗粒化分子动力学模拟方法,研究了线形、梳形和星形拓扑结构高分子的静态和动态性质,以揭示稀溶液中高分子链行为与链拓扑结构依赖关系的一般性规律.研究结果表明,随着线形-梳形-星形的链拓扑结构转变,回转半径的标度关系由仅依赖分子聚合度转变为同时依赖链聚合度与臂数或侧链数.分析了星形高分子和梳形高分子的静态和动态性质的特征规律.星形高分子的臂数增加使其尺寸迅速减小,形状则由长椭球形转变为类球形,且扩散系数也随之增加;其均方回转半径(〈R_g〉)和扩散系数(D)与分子聚合度(N)及臂数(f)的标度规律为〈R_g〉~N~(0.581)f~(-0.402),D~N~(-0.763)f~(0.227).梳形高分子的静态与动态性质与分子聚合度及侧链数的依赖关系为〈R_g〉~N~(0.597)f~(-0.212)(每个支化点只有一条侧链)和〈R_g〉~N~(0.599)f~(-0.316)(每个支化点有多条侧链).     

A versatile approach for the preparation of end‐functional polymers and block copolymers by stable radical exchange reactions

A versatile strategy for the preparation of end‐functional polymers and block copolymers by radical exchange reactions is described. For this purpose, first polystyrene with 2,2,6,6‐tetramethylpiperidine‐1‐oxyl end group (PS‐TEMPO) is prepared by nitroxide‐mediated radical polymerization (NMRP). In the subsequent step, these polymers are heated to 130 °C in the presence of independently prepared TEMPO derivatives bearing hydroxyl, azide and carboxylic acid functionalities, and polymers such as poly(ethylene glycol) (TEMPO‐PEG) and poly(ε‐caprolactone) (TEMPO‐PCL). Due to the simultaneous radical generation and reversible termination of the polymer radical, TEMPO moiety on polystyrene is replaced to form the corresponding end‐functional polymers and block copolymers. The intermediates and final polymers are characterized by ¹H NMR, UV, IR, and GPC measurements. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 2387–2395     

Mechanical Properties of Interlocked-ring Polymers: A Molecular Dynamics Simulation Study

Interlocked-ring polymers, also known as polycatenanes, possess an interesting molecular architecture. These polymers are composed of many interlocked rings in a linear chain. The topological constrain between neighboring rings distinguishes the interlockedring polymer from its linear counterpart. Here we present extensive molecular dynamic simulations on the interlocked-ring polymers and analyze the static properties of the polymer. By applying external forces to the polymer, we also study the force-extension curves of the polymer, which provides rich information about the mechanical properties of the interlockedring polymers.     

Poly(propylene imine) dendrimers as hydrogen donor in Type II photoinitiated free radical polymerization

Three generations of poly(propylene imine) dendrimers, namely (PPI-16, PPI-32 and PPI-64; 16, 32 and 64 for generations 3, 4 and 5, respectively) were used as hydrogen donors in photoinitiated free radical polymerization of methyl methacrylate by using one of the following photosensitizers; benzophenone and thioxanthone. The effect of generation number of the dendrimer on photoinitiation efficiency and molecular weight of the resulting polymers was investigated. Glass transition temperatures and particle size measurements of the resulting polymers indicated the presence of nearly stretched polymer chains around the dendrimers. The location of hydrogen donating sites was evaluated by photolysis studies in the absence of monomer by using a stable radical namely, 2,2,6,6-tetramethylpiperidine-N-oxyl free radical (TEMPO) and showed that hydrogen abstraction occurs from the inner tertiary amino groups. The TEMPO attached dendrimers were further used in the nitroxide mediated radical polymerization (NMP) of styrene to yield star polymers.     

The theta-temperature depression caused by topological effect in ring polymers studied by Monte Carlo simulation

We studied equilibrium conformations of linear and ring polymers in dilute solutions over the wide range of segment number N of up to 2048 with Monte Carlo simulation, and evaluated N dependence of the radii of gyration, R(g), of chains. The polymer molecules treated in this study are assumed to be composed of beads and bonds, and they are put in a three-dimensional face-centered cubic (FCC) lattice. The values of Flory's critical exponent, ν, for linear and ring polymers were estimated from the N dependence of R(g), and the temperatures at which ν reach 1/2 were obtained. Here we define those as Θ-temperatures in this report. The simulation result shows that the Θ-temperature for ring polymers is evidently lower than that of the linear polymers, and the origin of the Θ-temperature depression is discussed. Since R(g) of a ring polymer is smaller than that for a linear polymer at the same N and temperature, the segment density for a ring polymer is increased by the topological effect and the repulsive force between segments of a ring polymer at the Θ-temperature for a linear polymer is stronger. Thus, the origin of the Θ-temperature depression for ring polymers is the repulsive force emphasized by the topological effect of rings.     

Cyclic polymers: past,present and future

Methods for characterising cyclic polymers are illustrated by reference first to dilute solution methods for cyclic poly(dimethylsiloxane) (PDMS) and then to the entrapment of cyclic polymers in networks. Preparative routes to cyclic polymers are then reviewed, including ring-chain equilibration reactions, coupling and condensation reactions and new methods using polymer-supported reagents. Some of the properties of cyclic PDMS are discussed, including differences between ring and chain polymer properties such as their melt viscosities and glass transition temperatures. Methods for preparing the first polymeric catenanes are described, using polymer-supported reagents. Future directions for cyclic polymer chemistry are indicated, including topological polymer chemistry.     

Progress in controlled polymerization and design of novel polymer architectures

Recent developments of new synthetic methods are stimulating the design of new polymers. Modern generations of highly active and selective transition metal catalysts give excellent control on molecular weight, regio- and stereoregularities, long- and short-chain-branching, polymer crystallization, and morphology of olefin, diene, cyclolefin, and styrene polymers. Ethene is copolymerized with polar comonomers such as carbon monoxide and acrylates in new low pressure processes. Catalytic coupling reactions of aromatic halogen compounds and bisphenols afford rigid polyarylenes. „Living” radical polymerization (“TEMPO” and “ATRP”) produce a wide range of telechelics, block copolymers and cascade macromolecules. In reactive processing oxazoline-mediated coupling reactions are the key to melt diversification of well-known polymers. Supramolecular concepts are being applied to tailor hybrid polymers and nanocomposites. Precision in polymer synthesis is the key to new materials with wide application range.     

“点击”反应在制备环状聚合物中的应用

环状聚合物具有不同于线性高分子的独特性质,是一类具有应用前景的新型聚合物材料,但复杂的结构导致其合成过程复杂繁琐.＂点击＂化学由于其高效、可靠、高选择性的特点已成为拓扑高分子合成的新方法,活性自由基聚合（ATRP、RAFT和NMP）具有聚合物结构可控等特点,二者联用为环状聚合物的合成拓宽了思路.本文就近几年＂点击＂反应、＂点击＂反应与活性自由基聚合联用以及其他方法联用在环状聚合物中的应用进行综述.＂点击＂反应与这些方法的结合将在功能性环状聚合物的设计与合成中发挥积极的作用.     

Phase transition of a single star polymer: a Wang-Landau sampling study

Star polymers, as an important class of nonlinear macromolecules, process special thermodynamic properties for the existence of a common connecting point. The thermodynamic transitions of a single star polymer are systematically studied with the bond fluctuation model using Wang-Landau sampling techniques. A new analysis method employing the shape factor is proposed to locate the coil-globule (CG) and liquid-crystal (LC) transitions, which shows a higher efficiency and accuracy than the canonical specific heat function. The LC transition temperature is found to obey the identical scaling law as the linear polymers. However, the CG transition temperature shifts towards the LC transition with the increasing of the arm number. The reason is that for the star polymer a lower temperature is needed for the attractive force to overcome the excluded volume effect of the polymer chain because of its high arm density. This work clearly proves the structural distinction of the linear and star polymers can only affect the CG transition while has no influence on the LC transition.     

Practical Synthesis of Dendritic Hyperbranched Polyacrylates and Their Topological Block Polymers by Organotellurium-Mediated Emulsion Polymerization in Water**

The practical synthesis of structurally controlled hyperbranched polymers (HBPs) by organotellurium-mediated radical polymerization (TERP) in water under emulsion conditions is reported. Copolymerization of vinyltelluride named evolmer, which induces controlled branch structure, and acrylates with TERP chain transfer agent (CTA) in water afforded HBPs having dendron structure. The molecular weight, dispersity, branch number, and branch length of the HBPs were controlled by changing the amount of CTA, evolmer, and acrylate monomers. HB-poly(butyl acrylate)s (HBPBAs) with up to the 8^th generation having an average of 255 branches were successfully synthesized. As the monomer conversion reached nearly quantitative and the obtained polymer particles were well dispersed in water, the method is highly suitable for synthesizing topological block polymers, block polymers consisting of different topologies. Thus, linear-block-HB, HB-block-linear, and HB-block-HB-PBAs with the controlled structure were successfully synthesized by adding the second monomer(s) to the macro-CTA. The intrinsic viscosity of the resulting homo- and topological block PBAs was systematically controlled by the degree of the branch, the branch length, and the topology. Therefore, the method opens the possibility of obtaining various HBPs with diverse branch structures and tuning the polymer properties by the polymer topology.     

金属-超分子聚合物的合成,结构与应用

金属-起分子聚合物(超分子配位聚合物)是重复单元经配价键相互作用连接在一起的阵列,可由有机高分子配体和金属离子自组装形成具有多样化的几何形状和拓扑结构：线性主链均聚物、嵌段共聚物、接枝共聚物、交联聚合物、金属树枝体、栅格阵列和拓扑结构,并可对无机和金属纳米粒子进行表面修饰。金属-超分子聚合物可在光电子信息、催化、生物医用、分子器件、纳米技术等领域广泛应用。综述了金属-超分子聚合物的合成与机理、结构、性能和应用。     

Topological effect in ring polymers investigated with Monte Carlo simulation

We studied equilibrium conformations of ring polymers in the melt over the wide range of segment number up to 1000 by the Monte Carlo simulations and the bond fluctuation model, and estimated Flory's scaling exponent nu. The radial distribution function of segments for the ring polymers in the melt is obtained. We have found that nu for ring polymers is decreased with increasing segment number N, and nu goes down to 0.365 when N reaches 1000, whose value is apparently smaller than the theoretically predicted one, i.e., 25. Those values are in contrast to the well established nu value of 0.5 for linear polymers in the melt. This is because ring polymer chains in the melt are squeezed both by their own topological effect and the compression effect by the neighboring ring polymer coils which are also squeezed at bulk state. The difference in our result and the theory may be due to the fact that the estimation of topological entropy loss was ignored in the theoretical prediction, while it has been taken into consideration in the present study. If polymer coils repel each other in melt at N --> infinity, we have the limiting nu value of 13, so we conclude that nu is in the range of 13 < or = nu < 0.365 when the molecular weight of a ring polymer is high enough.     

Aggregation of amphiphilic polymers in the presence of adhesive small colloidal particles

The interaction of amphiphilic polymers with small colloids, capable to reversibly stick onto the chains, is studied. Adhesive small colloids in solution are able to dynamically bind two polymer segments. This association leads to topological changes in the polymer network configurations, such as looping and cross-linking, although the reversible adhesion permits the colloid to slide along the chain backbone. Previous analyses only consider static topologies in the chain network. We show that the sliding degree of freedom ensures the dominance of small loops, over other structures, giving rise to a new perspective in the analysis of the problem. The results are applied to the analysis of the equilibrium between colloidal particles and star polymers, as well as to block copolymer micelles. The results are relevant for the reversible adsorption of silica particles onto hydrophilic polymers, used in the process of formation of mesoporous materials of the type SBA or MCM, cross-linked cyclodextrin molecules threading on the polymers and forming the structures known as polyrotaxanes. Adhesion of colloids on the corona of the latter induce micellization and growth of larger micelles as the number of colloids increase, in agreement with experimental data.     

端基功能化聚合物的表面性能

综述了端基功能化聚合物表面结构与性能的最新研究进展.聚合物端基功能化是实现聚合物表面改性的一种有效技术.通过端基功能化可以精确控制聚合物表面功能基团的种类和数量,从而影响聚合物表面的化学结构与性能.重点论述了功能化端基在聚合物表面的离析现象和产生这一现象的原因,以及功能化端基对聚合物表面分子运动能力的影响.本文还介绍了近年来用于研究端基功能化聚合物表面的表征新技术,如SFG、NR、SSIMS等.对端基功能化聚合物表面的环境响应性也进行了阐述.指出了利用不同功能化端基可以有效地控制聚合物表面的亲疏水性.并对端基功能化聚合物的应用进行了展望.     

Production of biological polymers from organic wastes

Biologically-produced polymers, from microbial fermentation are naturally biodegradable and are potential environment-friendly substitutes for some synthetic plastics. However, broader applications are restricted by the high production costs and limitations in physical and mechanical properties. In this study, activated sludge bacteria in a conventional wastewater treatment system treating a wastewater that contained organic pollutants, were induced by nitrogen deficiency to accumulate intracellular storage polymers, which can be extracted as a low-cost source of biodegradable plastics. Chromatographic analysis of the extracted polymers revealed a composition of poly-hydroxyalkanoate and a number of related co-polymers. Alcaligene spp. in the activated sludge microbial consortium was identified as the main genus accumulated these polymers. When the C:N ratio was increased from 20 to 140, the specific polymer yield increased to a maximum of 0.39 g polymer/g dry cell while specific growth yield decreased to 0.26 g dry cell/g carbonaceous matter consumed. The highest overall polymer production yield of 0.11 g polymer/g carbonaceous matter consumed was achieved when the C:N ratio was maintained at a nitrogen-deficient level of 100. The specific polymer yield in the isolated Alcaligene spp. cells were as high as 0.7 g polymer/g dry cell mass. The composition of the co-polymers, and hence the physical and mechanical properties, could be controlled by manipulating the influent organic compositions.     

A topology preserving method for generating equilibrated polymer melts in computer simulations

A new method for generating equilibrated configurations of polymer melts is presented. In this method, the molecular weight of an equilibrated melt of polymers is successively doubled by affinely scaling the simulation box and adding beads along the contour of the chains. At each stage of molecular weight doubling, compressive deformations are produced on all length scales, while the random walk nature of the polymers is preserved, thereby requiring relaxation times significantly smaller than the reptation time to fully equilibrate the melt. This method preserves the topological state of individual polymers in the melt and its effectiveness is demonstrated for linear polymers with molecular weight N up to 1024, and cyclic polymers with N up to 8192. For the range of N studied, the method requires simulation time that scales as N(2) and is thought to be applicable to a variety of polymer architectures.     

Carbon-13 nuclear magnetic resonance quantitative measurements of average sequence lengths of like stereochemical additions in polypropylene and polystyrene

Sequence lengths of stereochemical additions in vinyl polymers are described in terms of the number average lengths of like configurational placements. Under these circumstances, a pure syndiotactic polymer has a number average sequence length of 1.0; a polymer with 50:50 meso, racemic additions has a number average sequence length of 2.0 and polymers with more meso than racemic additions have number average sequence lengths greater than 2. Amorphous and crystalline polypropylenes and an amorphous polystyrene are examined using ¹³C NMR as examples of the applicability of the average sequence length method. The results appear to be accurate for amorphous and semicrystalline polymers but limitations are present when this method is applied to highly stereoregular vinyl polymers containing predominantly isotactic sequences.     

An investigation of the interconnection between topological characteristics of physical and chemical networks of anhydride adamantane-containing epoxy polymers

The interconnection between topological characteristics of chemical and physical networks of adamantane-containing epoxy polymers of anhydride curing is studied. It is shown that the introduction of adamantane fragments into the network of an epoxy polymer by different methods affects the glass-transition point and stress-strain properties. The changes in polymer properties depending on the concentration of modifying agents are analyzed during comparison of the frequency parameters of the networks of chemical bonds and engagements within a cluster model of the structure of the polymer amorphous state.