Polymer Chains In Solution Research Articles

Reentrant Stabilization of Grafted Nanoparticles in Polymer Solutions.

Polymer chains grafted onto nanoparticles may facilitate the dispersion of such particles in a polymer solution. We explore the optimal strategy for stabilizing polymer-grafted nanoparticles using self-consistent field theory and experiments. The best results are obtained for relatively low grafting densities and for chain lengths of the brush polymer NB larger than that of the freely floating polymers Nf. When Nf > NB, one finds a compatibilization gap and re-entrant stabilization: At both very low and very high polymer concentrations particles disperse in the polymer solution, while at intermediate concentrations the particles lose their colloidal stability. At low grafting densities the underlying surface is in contact with the solvent. Particles covered by a bidisperse brush can combine a low grafting outer region with full coverage of the surface by a densely grafted inner layer. Using classical colloid-chemical stabilization criteria the region in the phase diagram for which the particles are expected to mix with a concentrated polymer solution opens up. Now, also upon an increase in the length of the freely dispersed polymers, a re-entrant colloid-chemical stabilization is found for particles on the nanometer length scale: At both short and long polymer chains in solution the particles will not aggregate, whereas at intermediate lengths the colloidal stability is marginal. This multi re-entrant behavior is found from numerical self-consistent field calculations, and these predictions are consistent with corresponding experiments.

Intrachain exciton dynamics in conjugated polymer chains in solution.

We investigate exciton dynamics on a polymer chain in solution induced by the Brownian rotational motion of the monomers. Poly(para-phenylene) is chosen as the model system and excitons are modeled via the Frenkel exciton Hamiltonian. The Brownian fluctuations of the torsional modes were modeled via the Langevin equation. The rotation of monomers in polymer chains in solution has a number of important consequences for the excited state properties. First, the dihedral angles assume a thermal equilibrium which causes off-diagonal disorder in the Frenkel Hamiltonian. This disorder Anderson localizes the Frenkel exciton center-of-mass wavefunctions into super-localized local exciton ground states (LEGSs) and higher-energy more delocalized quasi-extended exciton states (QEESs). LEGSs correspond to chromophores on polymer chains. The second consequence of rotations-that are low-frequency-is that their coupling to the exciton wavefunction causes local planarization and the formation of an exciton-polaron. This torsional relaxation causes additional self-localization. Finally, and crucially, the torsional dynamics cause the Frenkel Hamiltonian to be time-dependent, leading to exciton dynamics. We identify two distinct types of dynamics. At low temperatures, the torsional fluctuations act as a perturbation on the polaronic nature of the exciton state. Thus, the exciton dynamics at low temperatures is a small-displacement diffusive adiabatic motion of the exciton-polaron as a whole. The temperature dependence of the diffusion constant has a linear dependence, indicating an activationless process. As the temperature increases, however, the diffusion constant increases at a faster than linear rate, indicating a second non-adiabatic dynamics mechanism begins to dominate. Excitons are thermally activated into higher energy more delocalized exciton states (i.e., LEGSs and QEESs). These states are not self-localized by local torsional planarization. During the exciton's temporary occupation of a LEGS-and particularly a quasi-band QEES-its motion is semi-ballistic with a large group velocity. After a short period of rapid transport, the exciton wavefunction collapses again into an exciton-polaron state. We present a simple model for the activated dynamics which is in agreement with the data.

Consistent model reduction of polymer chains in solution in dissipative particle dynamics: Model description

We introduce a framework for model reduction of polymer chain models for dissipative particle dynamics (DPD) simulations, where the properties governing the phase equilibria such as the characteristic size of the chain, compressibility, density, and temperature are preserved. The proposed methodology reduces the number of degrees of freedom required in traditional DPD representations to model equilibrium properties of systems with complex molecules (e.g., linear polymers). Based on geometrical considerations we explicitly account for the correlation between beads in fine-grained DPD models and consistently represent the effect of these correlations in a reduced model, in a practical and simple fashion via power laws and the consistent scaling of the simulation parameters. In order to satisfy the geometrical constraints in the reduced model we introduce bond–angle potentials that account for the changes in the chain free energy after the model reduction. Following this coarse-graining process we represent high molecular weight DPD chains (i.e., ≥200 beads per chain) with a significant reduction in the number of particles required (i.e., ≥20 times the original system). We show that our methodology has potential applications modeling systems of high molecular weight molecules at large scales, such as diblock copolymer and DNA.

Energy Transfer Between Squaraine Polymer Sections: From Helix to Zigzag and All the Way Back.

We provide a joint experimental and theoretical study of squaraine polymers in solution. The absorption spectra show evidence that two different conformations are present in the polymer: a helix and a zigzag structure. This unique situation allows investigating ultrafast energy-transfer processes between different structural segments within a single polymer chain in solution. The understanding of the underlying dynamics is of fundamental importance for the development of novel materials for light-harvesting and optoelectronic applications. Here, we combine femtosecond transient absorption spectroscopy with time-resolved 2D electronic spectroscopy in order to demonstrate that ultrafast energy transfer within the squaraine polymer chains proceeds from initially excited helix segments to zigzag segments or vice versa, depending on the solvent as well as on the excitation wavenumber. These observations contrast other conjugated polymers such as MEH-PPV where much slower intrachain energy transfer was reported. The reason for the very fast energy transfer in squaraine polymers is most likely a close matching of the density of states between donor and acceptor polymer segments because of the very small reorganization energy in these cyanine-like chromophores.

Solvatochromism and conformational changes in fully dissolved poly(3-alkylthiophene)s.

Absorption spectroscopy is commonly utilized to probe optical properties that can be related, among other things, to the conformation of single, isolated conjugated polymer chains in solution. It is frequently suggested that changes in peak positions of optical spectra result from variations in the stiffness of polymer chains in solution because this modifies the conjugation length. In this work we utilize ultraviolet-visible (UV-vis) spectroscopy, small angle neutron scattering (SANS), and all atom molecular dynamic (AA-MD) simulations to closely probe the relationship between the conformation of single-chains of poly(3-alkylthiophene)s (P3ATs) and their optical properties. SANS results show variations in the radius of gyration and Kuhn length as a function of alkyl chain length, and structure, as well as the solvent environment. Furthermore, both SANS and MD simulations show that dissolved P3HT chains are more rigid in solvents where self-assembly and crystallization are possible. Shifts in P3AT optical properties were also observed for different solvent environments. However, these changes were not correlated to the changes in polymer conformation. Furthermore, changes in optical properties could not be perfectly described by generalized solvent-solute interactions. AA-MD simulations provide new insights into specific polymer-solvent interactions not accounted for in generalized solvatochromic theory. This work highlights the need for experiments and molecular simulations that further inform the specific role of solvent molecules on local polymer conformation and on optical properties.

Colloidal stability of zwitterionic polymer-grafted gold nanoparticles in water

We investigate the colloidal stability of gold nanoparticles (AuNPs) coated with zwitterionic sulfobetaine polymers in aqueous solution. Zwitterionic polymers with different molar masses, synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization of N,N′-dimethyl(methacrylamido propyl)ammonium propanesulfonate (SPP) exhibit a well known Upper Critical Solution Temperature (UCST) in water, i.e., phase separate at low temperature. The colloidal stability of gold nanoparticles grafted with PSPP was studied as a function of the temperature. The effects of the molar mass of the grafted polymers, the salt concentration, and the presence of free polymer chains in solution were investigated. UV–vis spectroscopy and dynamic light scattering measurements show that whatever the molar mass of the grafted polymer, the nanoparticles never aggregate at low temperature in pure water. However, a reversible thermal-driven aggregation process of the gold nanoparticles is observed in presence of free polymer chains in solution and explained by a depletion process.

Joint aqueous solutions of dextran and bovine serum albumin: coexistence of three liquid phases.

The phase diagram of the system water/dextran (DEX)/BSA was measured as well as modeled. On the experimental side, cloud points were determined and the coexisting phases were analyzed. The theoretical calculations use an approach capable of describing solutions of chain polymers and of globular proteins with the same formalism. The required thermodynamic input comes from experiments concerning the binary subsystems, except for the polymer blend for which one interaction parameter had to be adjusted. Both sources of information yield the same essential features: the existence of a large composition area of immiscibility, starting from the subsystem DEX/BSA and extending well into the region of dilute polymer solutions. This range is subdivided into three sections: one two-phase area at high polymer content, a two-phase area at low polymer content, and a three-phase region located in between. Measured and calculated phase diagrams match qualitatively; the reasons for the quantitative discrepancies are being discussed.

Imidazolium-substituted ionic (co)polythiophenes: Compositional influence on solution behavior and thermal properties

A series of ionic polythiophenes, in homopolymer and random copolymer configurations, is prepared via the Grignard metathesis (GRIM) polymerization protocol and subsequent substitution on the bromohexyl side chains with N-methylimidazole. The introduced structural variations – comonomer ratio, side chain composition, counter ions – allow tuning of the thermal properties and solution behavior of the resulting conjugated polymers. As expected, the solubility depends majorly on the number of ionic groups and the counter ions. The most peculiar behavior is observed for the P3HT-P3(MIM)HT-Br 50/50 random copolymer, which shows organization of the polymer chains in solution and thin film dependent on the preparation conditions. Dynamic light scattering studies confirm that the ordered solid-state structure is somewhat maintained when the copolymer is dissolved in a bad solvent mixture. The ionic (co)polythiophenes are generally more resistant to thermal degradation than their precursors. The precursor polymers all show a clear semi-crystalline behavior, with a decrease in crystallinity upon decreasing the number of regular 3-hexylthiophene units. On the other hand, the studied ionic (co)polythiophenes are fully amorphous. Changes in the counter ions have dramatic effects on the thermal properties. Bromine counter ions render the polymers strongly hygroscopic. The novel materials are of particular appeal in the field of organic photovoltaics, in which the imidazolium-substituted (co)polythiophenes can be beneficially applied as constituents of either active layers or electron transport layers. Their processability from green solvents is also of major importance for the field.

Stimuli‐responsive diblock copolymer brushes via combination of “click chemistry” and living radical polymerization

ABSTRACTpH‐ and temperature‐responsive poly(N‐isopropylacrylamide‐block−4‐vinylbenzoic acid) (poly(NIPAAm‐b‐VBA)) diblock copolymer brushes on silicon wafers have been successfully prepared by combining click reaction, single‐electron transfer‐living radical polymerization (SET‐LRP), and reversible addition‐fragmentation chain‐transfer (RAFT) polymerization. Azide‐terminated poly(NIPAAm) brushes were obtained by SET‐LRP followed by reaction with sodium azide. A click reaction was utilized to exchange the azide end group of a poly(NIPAAm) brushes to form a surface‐immobilized macro‐RAFT agent, which was successfully chain extended via RAFT polymerization to produce poly(NIPAAm‐b‐VBA) brushes. The addition of sacrificial initiator and/or chain‐transfer agent permitted the formation of well‐defined diblock copolymer brushes and free polymer chains in solution. The free polymer chains were isolated and used to estimate the molecular weights and polydispersity index of chains attached to the surface. Ellipsometry, contact angle measurements, grazing angle‐Fourier transform infrared spectroscopy, and X‐ray photoelectron spectroscopy were used to characterize the immobilization of initiator on the silicon wafer, poly(NIPAAm) brush formation via SET‐LRP, click reaction, and poly(NIPAAm‐b‐VBA) brush formation via RAFT polymerization. The poly(NIPAAm‐b‐VBA) brushes demonstrate stimuli‐responsive behavior with respect to pH and temperature. The swollen brush thickness of poly(NIPAAm‐b‐VBA) brush increases with increasing pH, and decreases with increasing temperature. These results can provide guidance for the design of smart materials based on copolymer brushes. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2677–2685

Well-defined cationic polyacrylamides with dot-charges: synthesis via an aqueous living RAFT polymerization, characterization, and intrinsic viscosity

Polyacrylamides and their derivatives are widely used as polyelectrolytes or polyampholytes. The morphology of polymer chains in solution plays an important role in their application. To illustrate the relationship between microstructure and properties, intrinsic viscosity as an apparent indication of the polymer chain hydraulic volume was focused on. A series of well-defined cationic polyacrylamides (C-PAMs) with dot-charges have been prepared via an aqueous living reversible addition fragmentation chain transfer (RAFT) polymerization, in which “dot-charges” means that any two cationic monomer units in the copolymer are not immediately connected each other. Water-soluble 4,4′-azobis (4-cyanovaleric acid) (V-501) and 2-(2-carboxyethyl-sulfanylthiocarbonylsulfanyl) propionic acid (CTA) were employed as the initiator and the chain transfer agent respectively and acryloyloxyethyltrimethylammonium chloride (DAC) acted as the cationic unit. The number of dot-charges and segment size between dot-charges were varied by adjusting the feed ratio and the polymerization time. The polymerization followed first order kinetics as indicated by gel permeation chromatography (GPC) characterization and the quantitative 1H-NMR analysis showed that DAC was incorporated into PAM chains as single dot-charges. The intrinsic viscosity of the well-defined C-PAMs solution was determined in an electrolyte solution and the result showed that end-groups with opposite charges in C-PAMs had serious effects on the expansion of polymer coil in aqueous solution. According to modified Rushing–Hester theory, a semi-empirical model based on molecular weight, chain length, cationic degree and charge distribution was established to explain the dependence of a dimensionless viscosity upon a dimensionless length and a dimensionless mass by regression analysis. The model will give theoretical suggestions for designing polyelectrolytes with desired viscosity.

Dynamic behavior of crosslinked amphiphilic block copolymer nanofibers dispersed in liquid poly(ethylene oxide) below and above their glass transition temperature

Crosslinked polystyrene nanofibers were synthesized via RAFT-mediated aqueous emulsion polymerization and showed good shape stability in both the presence of solvent and at high temperature (typically above the Tg of polystyrene). The viscoelastic properties of their suspension in a low molar mass poly(ethylene glycol) matrix (PEG400) was studied as a function of the temperature, i.e., below the Tg of polystyrene at 25 °C, and above at 130 °C. Below Tg, the critical concentration ϕ* between the dilute and the semi-dilute regimes determined from the crossover of the scaling law on the zero shear viscosity for the dilute regime and the semi-dilute regime showed that a Brownian motion of the nanofibers was the dominant mechanism of relaxation according to the Doi–Edwards theory. Above Tg, the nanofibers are flexible and their Brownian dynamics did not obey the Doi–Edwards theory anymore. From the concentration dependence of the zero shear viscosity, it appeared that their dynamics obey the power laws for polymer chains in solution. Moreover, the flow activation energy at T > Tg was drastically dependent on the nanofiber concentrations whereas it was observed to be constant at T < Tg as expected from the Doi–Edwards theory. Finally, the flow activation energy became closer to the flow activation energy of polystyrene at concentrations above ϕ = 15%. Such qualitative agreement with the dynamics of flexible chains has never been observed before and might be fortuitous; it would therefore require further theoretical investigations.

RAFT-mediated synthesis of cationic poly[(ar-vinylbenzyl)trimethylammonium chloride] brushes for quantitative DNA immobilization

The synthesis of cationic poly[(ar-vinylbenzyl)trimethylammonium chloride)] [poly(VBTAC)] brushes was achieved via reversible addition-fragmentation chain transfer (RAFT) polymerization and used for quantitative DNA immobilization. Initially, silicon surfaces were modified with RAFT chain transfer agent by utilizing an amide reaction involving a silicon wafer modified with allylamine and 4-cyanopentanoic acid dithiobenzoate (CPAD). Poly(VBTAC) brushes were then prepared via RAFT-mediated polymerization from the surface immobilized CPAD. Various characterization techniques including ellipsometry, X-ray photoelectron spectroscopy, grazing angle-Fourier transform infrared spectroscopy, atomic force microscopy and contact-angle goniometer were used to characterize the immobilization of CPAD on the silicon wafer and the subsequent polymer formation. The addition of free CPAD was required for the formation of well-defined polymer brushes, which subsequently resulted in the presence of free polymer chains in solution. The free polymer chains were isolated and used to estimate the molecular weights and polydispersity index of chains attached to the surface. Moreover, from atomic force microscopy and ellipsometry measurements, it was also determined that the density of immobilized DNA on the cationic poly(VBTAC) brushes can be quantitatively controlled by adjusting the solution concentration.

ICAR ATRP with ppm Cu Catalyst in Water

Initiators for continuous activator regeneration atom transfer radical polymerization (ICAR ATRP) with ppm amount of Cu catalyst was successfully developed in water. For the first time, Cu catalyst concentrations of 100 ppm and lower were used in aqueous media to prepare well-defined macromolecules. Polymers of oligo(ethylene oxide) methyl ether acrylate were synthesized with low dispersity (Mw/Mn = 1.15–1.28) using 20–100 ppm of an active CuBr/tris(pyridin-2-ylmethyl)amine-based catalyst in the presence of excess bromide anions. This technique was used to synthesize a thermoresponsive block copolymer of poly(oligo(ethylene oxide) methyl ether methacrylate)-b-poly(oligo(ethylene oxide) methyl ether acrylate). The methacrylic block had a lower critical solution temperature (LCST = 77 ± 2 °C) below that of the acrylic block. The hydrodynamic diameter of ca. 10 nm at temperatures below the LCST is consistent with free polymer chains in solution, and the diameter of ca. 30 nm above the LCST is consistent with a micellar structure. The aqueous ICAR ATRP technique was also used to successfully synthesize a well-defined bioconjugate by growing poly(oligo(ethylene oxide) acrylate) from a bovine serum albumin (BSA) protein functionalized with ca. 30 ATRP initiating sites.

High density cationic polymer brushes from combined “click chemistry” and RAFT‐mediated polymerization

AbstractA simple method for preparing cationic poly[(ar‐vinylbenzyl)trimethylammonium chloride)] [poly(VBTAC)] brushes was used by combined technology of “click chemistry” and reversible addition‐fragmentation chain transfer (RAFT) polymerization. Initially, silicon surfaces were modified with RAFT chain transfer agent by using a click reaction involving an azide‐modified silicon wafer and alkyne‐terminated 4‐cyanopentanoic acid dithiobenzoate (CPAD). A series of poly(VBTAC) brushes on silicon surface with different molecular weights, thicknesses, and grafting densities were then synthesized by RAFT‐mediated polymerization from the surface immobilized CPAD. The immobilization of CPAD on the silicon wafer and the subsequent polymer formation were characterized by X‐ray photoelectron spectroscopy, water contact angle measurements, grazing angle‐Fourier transform infrared spectroscopy, atomic force microscopy, and ellipsometry analysis. The addition of free CPAD was required for the formation of well‐defined polymer brushes, which subsequently resulted in the presence of free polymer chains in solution. The free polymer chains were isolated and used to estimate the molecular weights and polydispersity index of chains attached to the surface. In addition, by varying the polymerization time, we were able to obtain poly(VBTAC) brushes with grafting density up to 0.78 chains/nm2 with homogeneous distributions of apparent needle‐like structures. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Polymer dynamics with inertia

Some important recent advances in polymer science involve situations where molecular inertia plays an important role, for example, in the mass spectroscopy of large macromolecules. Only recently have we begun to understand how to analyze dynamics in such situations and what effects inertia has. In this review, we describe what is known about such effects and how nonlinearity plays a crucial role in generating damping, which is of a very different nature than is normally assumed. Not only is such analysis important in understanding polymers in low density environments but also in understanding the internal friction of a polymer chain in solution. The understanding of such situations is still in its infancy and we close by propounding a set of diverse questions for further study. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012

Quantification of uncertainties involved in the conformational study of polymers by light scattering

Gel permeation chromatography (GPC) combined with a multi-angle light scattering (MALS) is a very powerful characterization technique because it provides both absolute molecular weight ( M w) and the radius of gyration ( R g) throughout the separated slices obtained by GPC. This combination of M w and R g, can be used to obtain information about the conformation of polymer chains in solutions and the branching of molecules. Due to the interesting properties obtained for polymers, it is essential to quantify the effect of different error sources in light scattering measurements as well as in the data treatment that highly affect the accuracy of obtained molar mass and radius of gyration. Usually, the results obtained for M w and R g in this analysis are dispersed for determined ranges of retention time and to have both reliable R g and M w for calculation, only high confidence data points have to be chosen. This range is arbitrarily chosen by the user for the data observation. In this work a new method of calculation to obtain R g and M w by means of GPC–MALS technique has been developed. As a first point, a data analysis procedure was set in order to describe both R g and M w vs. retention time and to determine the range where experimental data are confident. Several aspects in the data analysis have been studied. The polynomial fit function, the influence of the concentration of the sample, the reproducibility of the experiments and the conformational scaling law have been investigated by statistic technique in order to quantify the uncertainties involved.

A facile route to end-functionalized poly( N-isopropylacrylamide) brushes synthesized by surface-initiated SET-LRP

In this study, the facile synthesis of well defined, end-functionalized poly( N-isopropylacrylamide) [poly(NIPAM)] brushes was achieved by surface-initiated single-electron transfer living radical polymerization (SET-LRP). Surface-initiated SET-LRP of N-isopropylacrylamide in the presence of cysteamine chain transfer agent was conducted via Cu(0) generated in situ by the disproportionation of Cu(I) to Cu(0) and Cu(II) in N,N-dimethylformamide at 90 °C. Initially, silicon surfaces were modified with 2-bromopropionyl bromide (2-BPB). [Poly(NIPAM)] brushes with amine end-group were then synthesized via surface-initiated SET-LRP from the immobilized 2-BPB. Various characterization techniques including ellipsometry, grazing angle-Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy and water contact-angle measurements were used to characterize the immobilization of 2-BPB on the silicon wafer and the subsequent polymer with amine end-group formation. The addition of free 2-BPB initiator was required for the formation of free polymer chains in solution. The free polymer chains were isolated and used to estimate the molecular weights and polydispersity index of chains attached to the surface. Although there are several chemicals methods for post-polymerization transformation of the halide chain end to amine groups, this study mainly provides a method for in situ functionalization of poly(NIPAM) brushes.

Ultrafast Relaxation of the Poly(3-hexylthiophene) Emission Spectrum

The femtosecond-resolved evolution of the emission spectrum of the important conjugated polymer poly(3-hexylthiophene) (P3HT) is presented. Detailed fluorescence up-conversion spectroscopy was performed on P3HT solid-state films and on P3HT in chlorobenzene solution. Two excitation wavelengths and several emission wavelengths, covering the entire fluorescence spectrum, were used. The data were complemented by polarization-sensitive measurements. Our global analysis allowed a reconstruction of the time-resolved emission spectra with 200 fs temporal resolution, so that spectral changes due to the early relaxation processes following π–π* interband absorption in the pristine polymer could be comprehensively characterized. Absorption occurs in isolated polymer chains in solution and in the solid state (including interchain interactions) for the film. In both cases, we find evidence of delocalization of the electrons and holes formed in the energy bands directly after photoexcitation with excess energy. This i...

Adsorption of linear polymers on polyethersulfone membranes: Contribution of divalent counterions on modifying of hydrophilic–lipophilic balance of polyelectrolyte chain

The effect of divalent metal ions on conformational changes, size and hydrophilicity of poly(acrylic acid), PAA, in solution as well as its relation with characteristics of adsorbed polymer layers on polyethersulfone membrane, PESm, were studied and analyzed by several techniques. PAA adsorption on PESm in the presence of divalent metal ions was established to be occurring by an adsorption mechanism promoted by interchain polymer–metal bonds between polymer molecules in solution and pre-adsorbed polymer layers on the surface. Results suggest that changes of hydrophilic–lipophilic balance of polymer chains can be related to adsorption mechanisms of PAA; these changes are consequence of decrease of negative charges on carboxylate groups by coordination of added metal ions and by increase of ionic strength. Besides, the surface and permeability characteristics of adsorbed polymer layers were related to the changes of size, aggregation and conformations of polymer chains in solution as metal ion concentration was increased.

Advancing Technology Through Measurement Science in the NIST Polymers Division

Established in 1962, the Polymers Division in the Material Measurement Laboratory of the National Institute of Standards and Technology (NIST) will soon celebrate its 50 th year as a world leader in polymers research. The mis-sion of the NIST Polymers Division is to serve as the Nation's reference laboratory responsible for producing the measurement methods, standards, and data needed to advance the manufacture and use of “soft” materials (poly-mers and complex fl uids), with the goal of improving industrial competitive-ness and addressing national needs. The NIST mission is unique because the work of the organization focuses on a facilitation role for technology development in the United States through a combination of strict objectivity and the highest levels of technical expertise. In order to maintain the broadest impact in facilitating technical competiveness, the Polymers Division advances the measurement science of polymers and complex fluids rather than engage in the development of new advanced materials for commercial use. NIST focuses on the underlying measurements needed for all companies competing in a particular sector, i.e., the important pre-competitive technical work that is needed to advance the fi eld rather than one company in particular. We develop measurement methods for physical/chemical properties and structure; processing, flow, and transport; and functional properties and performance (electrical, optical, biolog-ical, mechanical) of polymers and complex fluids. Measurement development has often accompanied fundamental break-throughs in polymer science within the Division. Novel measurements have lead to theoretical advances; precision measurements of semicrystalline polymers, polymer blends, and piezoelectric polymers resulted in leading theories of polymer morphology and crystallization kinetics, phase separation kinetics, and the current model for piezoelectric polymers, respectively. Alternatively, theoretical developments have often resulted in breakthroughs in polymer measurements and standards, such as the BKZ theory of non-linear viscoelasticity resulting in improved measurements of mechanical properties and theories for polymer chains in solution resulting in methods and standards for molecular mass distribution. Currently, the Polymers Division consists of nearly one hundred scientists with a broad portfolio of research that includes advanced imaging measurements of the interaction of biological systems with polymer materials, smallangle neutron and X-ray scattering measurements of nanostructured materials, the separation and purifi cation of single-wall carbon nanotubes, and the development of new tests for the reliability of soft body armor. The Division works closely with industry, government, and university partners to ensure that the critical measurement needs of the Nation are being met. For example, the Division has worked with International SEMATECH and Intel on identifying the potential limits of next-generation photoresist materials; the National Institutes of Health on standards development for dental materials; and with university groups around the world including Seoul National University, Stanford University, the University of Delaware, and the University of Colorado. Recent progress in some of these major areas is highlighted in this special issue. The unrelenting drive to shorter lengthscales in microelectronics presents new challenges in control of chemical and physical processes at molecular dimensions. Three papers highlight recent advances understanding and controlling these processes. One paper focuses on characterization of the complex interplay of chemistry and transport for photoresist development. Another paper focuses on high-performance mold materials for nanoimprint lithography. The fi nal paper highlights progress in identifying the potential limits and power of self-assembled nanoscale patterns with block copolymer thin films. Much of the work the Polymers Division does revolves around development of new and powerful characterization techniques. Several papers highlight advances following this theme. Surface wrinkling has been developed in the Polymers Division as a tool for making very sensitive rheological measurements of thin and ultrathin polymer membranes; we include a review of this topic. Also represented is pioneering work in the Division on interfacial rheological characterization of small volume liquid samples, characterization and separation of carbon nanotube dispersions, use of combinatorial methods to characterize interactions of mammalian cells with polymeric materials, and new conceptual approaches to understanding initial cell morphological response to polymeric surfaces. We hope you enjoy the issue. More information about the Division and its programs can be found at http://www.nist.gov/mml/polymers/.