Determination of the statistical segment of wormlike polymers using viscometric data

Using a new relation between the intrinsic viscosity and the molecular weight of wormlike polymers, we calculate the statistical segment of these polymers. Six wormlike polymers have been studied with this method and the results are in relatively good agreement with those already obtained by light scattering techniques or the Yamakawa-Fujii method. The best agreement with the results obtained by other methods is found in the case of DNA. We consider that the importance of the proposed method lies in its simplicity and on the possibility of its application for a very large range of molecular weights.     

Treating the polyelectrolytes as polymers with a draining effect. I. The statistical segment length

The statistical segment length of polyelectrolytes, A, in aqueous salt solutions is derived from the unperturbed dimensions parameter, K_θ, that is obtained from the graphical representations based on the Stockmayer–Fixman–Burchard and Dondos–Benoît equations. In order to obtain A from K_θ we use values of the Flory's parameter, Φ, which are given from an empirical equation established for the polymers presenting a draining effect, such as the wormlike polymers. With these values of Φ, the obtained values of A for different polyelectrolytes in aqueous salt solutions of different ionic strength are found very close to the values obtained from other more complicated methods. This result shows that the polyelectrolytes can be considered as polymers presenting a draining effect. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4225–4229, 2004     

A new approach to the determination of the statistical segment length of wormlike polymers

The Stockmayer-Fixman-Burchard (SFB) and the Dondos-Benoit (DB) equations have been applied to determine the unperturbed dimensions parameterK of wormlike polymers. An empirical relation between the Flory's constant and the Mark-Houwink-Sakurada (MHS) exponenta has been proposed. The values found by this equation are lower than the value 2.5×10²³ used in the case of flexible polymers and this deviation is attributed to the influence of the draining effect. From theK value and the so calculated value of , we calculate the Kuhn statistical segment length of wormlike polymers. The obtained — for a great number of wormlike polymers — statistical segment lengths are almost the same as these calculated by the Yamakawa-Fujii and the Bohdanecky methods. The molecular mass regions in which the SFB, the DB, and the MHS equations are valid are explored. A criterion for the distinction between flexible and wormlike polymers is proposed based on the way of approach to the power law.     

Universal behavior of flexible and wormlike polymers using relations derived from the blob theory and the statistical mechanical theory

The variation of the viscometric expansion factor of macromolecular chains, α_η, as a function of the number of blobs of which these chains consist, N/N_c, obeys a universal law, both for wormlike and for flexible polymers. Using also wormlike and flexible polymers, we show that the factor relating the excluded volume parameter, z, to the static expansion factor, α_G, varies with the number of statistical chain segments, in a universal manner. The universalities appear to be valid below chain lengths required for the appearance of a power law, and they do not seem to have an upper limit in molecular weight. For these two universalities concerning flexible and wormlike polymers we use relations derived from the blob theory [Polymer 20 (1979) 1083] and statistical mechanical theory [J. Chem. Phys. 57 (1972) 2843].     

Codendronized polymers pendent with alternating dendritic wedges

Codendronized polymers pendent with Fréchet‐type poly(benzyl ether) dendron and polyester dendron alternating structure have been produced by combining macromonomer and graft‐from approach. Alternating copolymerization of the styryl dendrons of three generations and N‐(2‐hydroxyethyl)maleimide was used to prepare the polymer backbone bearing the first kind of dendritic wedges, then polyester dendrons were grown up from the pendant hydroxy groups through iterative esterification and deprotection reactions. Then, a kind of codendronized polymer bearing different dendritic wedges with an alternating structure was thus obtained. Since the pendent dendrons were different and each of them was well‐defined, such codendronized polymer can be a multicompartment wormlike molecule. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3994–4001, 2007     

Characterization of supramolecular polymers

Supramolecular polymers are made of monomers that are held together by noncovalent interactions. This is the reason for the wide range of novel properties, such as reversibility and responses to stimuli, exhibited by supramolecular polymers. A range of supramolecular polymerization methods have been developed leading to a number of novel supramolecular materials. However, standard techniques for the characterization of supramolecular polymers have yet to be established. The dynamic nature of supramolecular polymers makes them difficult to be fully characterized using conventional polymer techniques. This tutorial review summarizes various methods for characterizing supramolecular polymers, including theoretical estimation, size exclusion chromatography, viscometry, light scattering, vapor pressure osmometry, mass spectrometry, NMR spectroscopy, scanning probe microscopy, electron microscopy, and atomic force microscopy-based single molecule force spectroscopy. Each of these methods has its own particular advantages and disadvantages. Most of the methods are used to characterize the supramolecular polymer chain itself. However, some of the methods can be used to study the self-assembled state formed by supramolecular polymers. The characterization of a supramolecular polymer cannot be realized with a single method; a convincing conclusion relies on the combination of several different techniques.     

Self-assembly of brush-like amphiphilic statistical polymers: the effect of salt stimulus on the molecular associative mode

The solution properties of amphiphilic statistical polymers, originating from the nanostructures of macromolecular assemblies, strongly depend on the associative behaviours of the polymers. In this paper, we report the effect of salt stimulus on the associative mode of the 2-(acrylamido)-2-methylpropanesulphonic acid–2-(acrylamido)-dodecane sulphonic acid brush-like amphiphilic statistical polymers, employing steady-state fluorescence, dynamic light scattering and transmission electron micrograph methods. It was found that the stimulus effects work more intensely for the polymers with less hydrophobic side chains. As the salt concentration increases, the salt valence state increases or the salt structure adds an organic group, the polymer molecules associate at a lower critical concentration. Meanwhile the molecules undergo an intramolecular associative mode in preference to an intermolecular associative mode, forming hundreds of times smaller unimers rather than giant multipolymer aggregates.     

Exploring the domain validity of the equations relating the intrinsic viscosity to the molecular weight by using the characteristic numbers of polymers

Plotting log[η] versus logM (Mark-Houwink-Sakurada equation) we observe a crossover region in which a continuous variation of the exponent of this equation takes place. This crossover region is delimited by two characteristic numbers: Nc (or Mc), the number of statistical segments (or the molecular weight) in the onset of excluded volume behavior and Nc' (or Mc') the number of statistical segments (or the molecular weight) in the onset of the complete excluded volume behavior. Relations are given in order to obtain these numbers. The Stockmayer-Fixman-Burchard equation is valid for the flexible and wormlike polymers in the molecular weight region which lies above the crossover region while the Dondos-Benoit equation is valid in the medium and low-molecular-weight region including the crossover region.     

Recombinant protein-based polymers for advanced drug delivery

Advances in recombinant techniques have led to the development of genetically engineered polymers with exquisite control over monomer sequence and polymer length. The ability to study how precise structures correlate with function has provided opportunities for the utility of these polymers in drug delivery. Chemically derived and developed methods of synthesis have yielded many useful polymers for drug delivery to-date, including those currently used in patients. However they have drawbacks, including limitations involved in statistical characterization of conventional polymer synthetic techniques. Encoding at the genetic level and production of such recombinant polymers in organisms allow for precise order and accuracy of amino acid residues and production of monodisperse polymers with specific function and physicochemical properties. Research into elastin-like, silk-like, and silk-elastinlike protein polymers for example has led to the development of delivery systems based on natural motifs of structural proteins to take advantage of their physicochemical properties. Additionally, protein based polymers on other natural motifs and de novo designs are starting to produce promising constructs for drug and gene delivery applications where precise control over structure promises correlation with function and guides the development of new and improved constructs. Clinical applications based on recombinant polymers for delivery of bioactive agents have not been realized at this point. However lessons learned from fundamental research with these polymers can be used to guide design of safe and effective systems for use in the clinic. This tutorial review summarizes progress made in the design and utility of recombinant polymers in drug and gene delivery and discusses challenges and future directions of such polymers for this purpose.     

Surface structure of polymers for biomedical applications

Biological reactions with synthetic polymers are strongly influenced by the surfaces of those materials. The surfaces are often substantially different in composition and structure from the bulk. By using contemporary surface analysis methods, we can understand polymer surfaces. The surfaces of polymers can also be modified to generate desired biological responses. These points are illustrated with examples involving polyurethanes and RF plasma-deposited films.     

“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.     

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.     

Solution state coordination polymers featuring wormlike macroscopic structures and cage-polymer interconversions

In the absence of coordinating solvents and anions, silver salts and triphosphines form viscous, thixotropic coordination polymers in solution, which aggregate into unusual wormlike macroscopic structures and undergo cage-polymer interconversions depending on the stoichiometry and presence of templating anions.     

Quantitative treatment of the dye partition method of analysis of surfactants and of ionic groups in high polymers

A quantitative treatment of the extraction of ionic dyes from aqueous solutions into organic solvents of low dielectric constant by surfactants or polymers with ionic groups having a charge opposite to that of the dye ion, is presented. The assumption is made that the extracted species are ion-paired in the organic phase. Based on this, a graphical extrapolation method is suggested for the quantitative estimation of ionic groups in polymers. Theoretically, the method should yield quantitative results irrespective of polymer chain length and character. This method of analysis does not require any calibration data.     

Modulation of electroosmotic flow by neutral polymers

Polymer coating is widely used to modulate the fluid flow in micro- and nanometer pores and flows that are sensitive to surface properties such as electroosmotic flow. Here we report on the dissipative particle dynamics simulations of the modulation of electroosmotic flow by neutral polymers. In these coarse-grained simulations, fluid and polymers are resolved at a scale comparable to polymer size and the two-way coupling between polymer conformation and fluid flow are explicitly accounted for. The simulations indicate that, in the parameter space explored, the screening of electroosmotic flow by polymers decreases nonlinearly as the external electric field increases. Such an observation is understood by analyzing the surface coverage by polymers, height and orientation of the grafted polymers, and the two different modes of flow screening by polymer segments as a function of the external electric field. Understanding the effects and interplay of these physical processes is crucial for the rational design of polymer coating for flow control in microfluidic and nanofluidic systems.     

Ferrocene containing polymers

Polymers with pendent ferrocene units are synthesized by radical and anionic methods. It has been demonstrated that polymer-analogous reactions are an attractive alternative to prepare those polymers. Polymers with ferrocene units in the main chain are available from interfacial condensation reaction between ferrocene-1,1′-dicarbonic acid dichloride with α, ω-diamines. Addition of ferrocene-1,1′-dithiol onto norbornadiene yields a polymer with repeating units from ferrocene disulfide and norbornene and nortricyclane end-groups. End-capping reactions of α, ω-dimercapto-telechelics with vinylferrocene yield polymers with ferrocene end-groups.     

Effect of surface grafted polymers on the adsorption of different model proteins

Adsorption of a model protein to a surface with end-grafted polymers was studied by Monte Carlo simulations. In the model the effect on protein adsorption in the presence of end-grafted polymers was evaluated by calculating the change in free energy between an end-grafted surface and a surface without polymers. The change in free energy was calculated using statistical mechanical perturbation theory. Apart from ordinary athermal polymer-polymer and protein-polymer interactions we also study a broad selection of systems by varying the interaction between proteins and polymers and effective polymer-solvent interactions. The interactions between the molecules span an interval from -0.5 to +0.5 kT. Consequently, general features of protein adsorption to end-grafted surfaces is investigated by systematically changing properties like hydrophilicity/hydrophobicity of the polymer, protein and surface as well as grafting density, degree of polymerization and protein size. Increasing grafting density as well as degree of polymerization decreases the adsorption of protein except in systems with attractive polymer-protein interactions, where adsorption increases with increasing chain length and higher grafting density. At a critical polymer-protein interaction neither chain length nor grafting density affects the free energy of adsorption. Hydrophilic polymers were found to prevent adsorption better than hydrophobic polymers. Very small particles with radii comparable to the size of a polymer segment were, however, better excluded from the surface when using hydrophobic than hydrophilic polymers. For systems with attractive polymer-protein interaction not only the volume of the protein was shown to be of importance but also the size of the exposed surface.     

Stochastic model of photodynamics in multichromophoric conjugated polymers

A stochastic model of triplet exciton dynamics in multichromophoric conjugated polymers is presented and analyzed in detail, with a focus on the single molecule spectroscopy observables. The model deals with the evolution of a discrete statistical distribution of triplets in isolated polymer molecules. This approach should provide more accurate quantitative information on the dynamic processes involved, as compared to the previously used two-state model which assumes that a conjugated polymer cannot contain more than one triplet. In particular, it allows for determination of the triplet-triplet annihilation rate.     

Spontaneous birefringence in films of some phenyl-containing polymers

Spontaneous birefringence in films prepared by free evaporation of a solvent from solutions of sulfated phenyl-containing polymers has been investigated in relation to the thickness of films and the incidence angle of a polarized light beam. It has been demonstrated that not only the value but also the sign of the coefficient of surface birefringence depends on the mode of incorporation of benzene rings into a polymer chain. The structural and orientation factors determining the spontaneous birefringence in the films have been distinguished. The results are compared with the data available for the films of water-soluble polysaccharides. The degree of order in the near-surface layers of polymer films cast from solutions is determined by the statistical segment length of macromolecules and is independent of the chemical nature of chains in the number of water-soluble polymers under consideration.