Search

Nanomechanical properties of natural and artificial nanomembranes can be strongly affected by anchored or tethered macromolecules. The intermolecular interactions in polymeric layers give rise to so-called induced bending rigidity which complements the bare rigidity of the membrane. Using analytical mean-field theory, we explore how macromolecular architecture of tethered polymers affects the bending rigidities of the polymer-decorated membranes. The developed theory enables us to consider explicitly various polymer architectures including regular dendrons, Ψ-shaped, star- and comblike macromolecules as well as macrocycles. Numerical self-consistent field computations for selected (regular dendritic) topology complement the analytical theory and support its predictions. We consider both cases of (i) quenched symmetric distribution of tethered molecules on both sides of the membrane and (ii) annealing distribution in which the tethered polymers can relocate from the concave to the convex side of the membrane upon bending. We demonstrate that at a given surface coverage an increase in the degree of branching or cyclization leads to the decrease in the induced bending rigidity. Relocation of the tethered molecules from concave to convex surfaces leads to the additional decrease in polymer contribution to the membrane bending rigidity. In the latter case, a decrease in configurational entropy due to this redistributions substantially contributes to the bending rigidity. [ABSTRACT FROM AUTHOR]

Next-generation liposome systems for anticancer and therapeutic delivery require the precise insertion of stabilizing polymers and targeting ligands. Many of these functional macromolecules may be lost to micellization as a competing self-assembly landscape. Here, hybrid stealth liposomes, which utilize novel cholesteryl-functionalized block copolymers as the molecular stabilizer, are explored as a scalable platform to address this limitation. The employed block copolymers offer resistance to micellization through multiple liposome insertion moieties per molecule. A combination of thermodynamic and structural investigations for a series of hybrid stealth liposome systems suggests that a critical number of cholesteryl moieties per molecule defines whether the copolymer will or will not insert into the liposome bilayer. Colloidal stability of formed hybrid stealth liposomes further corroborates the critical copolymer architecture value. [ABSTRACT FROM AUTHOR]

Heterografted macromolecular brushes are highly grafted macromolecules with two different side chains attached to a backbone. When endowed with an amphiphilic character, these can serve as unique stabilizers of biphasic systems and solute carriers and yield interesting self-assembled structures. Herein, we report on the solution structure of amphiphilic double-brush copolymers with short backbones--i.e., comparable to the length of the side-chains--in a selective solvent for one of the grafted blocks. As determined by small-angle neutron scattering measurements, poly(ethylene glycol)/poly(d,l-lactide) double brushes adopt a cylindrical structure with highly extended backbones in DMSO. In contrast, brushes undergo intermolecular self-assembly into spherical nanoparticles in water, with aggregation numbers that vary inversely with backbone degree of polymerization. While considerably less susceptible to intermolecular association than linear diblocks of similar hydrophobic and hydrophilic block lengths, the inability of the PEG component to maintain their unimolecular form results in well-defined spherical nanoparticles with very low aggregation numbers (3 < Nagg < 10) which could potentially lead to interesting compartmentalized nanomaterials. [ABSTRACT FROM AUTHOR]

The ordering of semiflexible polymers with persistence length lp and contour length L confined in a sphere of radius R is studied by molecular dynamics simulations of a coarse-grained model. Monomer densities are chosen where the corresponding bulk lyotropic solution or melt is a well-ordered nematic, and purely repulsive walls of the rigid confining sphere are considered. It is found that polymers close to the walls are bent according to the curvature of the confining spheres with all their monomers in a few layers parallel to the sphere surface, whereas the remaining macromolecules closer to the sphere center have one chain end and their center of mass far from the surface. The latter chains are responsible for the average nematic order of the system for sufficiently stiff chains. If L exceeds R, a single transition from isotropic to nematic states is found when lp increases. However, if R is close to an even multiple of L, a second transition occurs where chain ends are enriched near the equatorial plane (and two further planes parallel to it, if R ≈ 2L); i.e., the system develops a distorted smectic structure. The order in the surface shell then is characterized by topological defects. [ABSTRACT FROM AUTHOR]

A set of monodisperse macromolecular starbursts which are composed of triazine center substituted by heterogeneous carbazole and diphenylamine units with multibranched oligofluorenes (TF1 and TF2) have been designed, synthesized, and explored as gain media for organic lasers. The thermal, morphological, photophysical, and electrochemical properties and optical gain characteristics of the resulting starbursts have been investigated in comparison with those of their linear counterparts (2FCz and 4FCz) to shed light on better understanding the structure–property relationships. The results manifest that the resulting starburst architectures based on a triazine center with multibranched oligofluorenes are beneficial for depressing the crystallization tendency, leading to enhanced amorphous morphologies, excellent thermal stabilities, and favorable facile solution processability. The novel heterogeneous donor–acceptor core structure based on triazine center plays a key role to dominate the electronic properties of the resulting multibranched starbursts and endows the molecules with low-lying LUMO energy levels. Promising amplified spontaneous emission (ASE) characteristics are recorded for the multibranched starbursts, in which TF1 and TF2 exhibit rather low ASE threshold (EthASE) of 4.3 and 10.3 μJ/cm2, respectively. Remarkably, TF1 and TF2 manifest enhanced ASE stability with no obvious spectral variations (within 2 nm for TF1 and 1 nm for TF2) and almost unchanged EthASE upon increasing the annealing temperature even up to 200 °C in air. In contrast, their linear counterparts 2FCz and 4FCz showed distinct EthASE variations with increasing the annealing temperature above 100 °C. The results suggest that the novel molecular design is beneficial for enhancing the thermal and optical stabilities as well as fine modulating the electrical properties, rendering the resulting multibranched triazine-centered starbursts advantageous as efficient gain media for electrically pumped organic lasers. [ABSTRACT FROM AUTHOR]

Prior bubble inflation studies have shown strong evidence of rubbery-like stiffening behaviors for several organic and inorganic thin films. The possible origin is still unclear, but recently Ngai et al. [ J. Polym. Sci., Part B: Polym. Phys. 2013, 51 (3), 214-224] and Li and McKenna [ Macromolecules 2015, 48 (17), 6329-6336] proposed that the separation of molecular motions and dynamic fragility are closely related to the observed rubber-like stiffening behavior. In the present work, we report observations from bubble inflation measurements on nanometric thin polyisobutylene (PIB) films that test the correlations suggested by the Ngai coupling model (stiffening is related to the shape parameter describing the a-relaxation) and Li and McKenna (the rubbery stiffening correlates with the dynamic fragility). Mechanical properties and surface tension of nanometric thin PIB films were investigated through strain-stress measurements for film thicknesses ranging from 13 to 126 nm. The tests were performed at room temperature far above the glass transition temperature of PIB. In addition to stiffness and surface tension, rupture strengths were also measured. We find that the stiffness increases with decreasing film thickness and that the surface tension remains constant, independent of the film thickness. The rupture stress is found to increase with decreasing film thickness, whereas the rupture strain decreases with decreasing film thickness. Similar to the prior bubble inflation measurements in polymeric thin films, the thickness dependence of the stiffening followed a power law behavior with film thickness. The observed stiffening behavior agrees with the suggestion from Ngai et al. that the rubbery stiffening should correlate with the separation of the a- and Rouse-mode relaxations. However, unlike prior results for ultrathin polymer films, the stiffening behavior of PIB did not follow the linear relationship with dynamic fragility that was proposed by Li and McKenna. [ABSTRACT FROM AUTHOR]

From the beginning of life with the information-containing polymers until the present era of a plethora of water-based materials in health care industry and biotechnology, polyelectrolytes are ubiquitous with a broad range of structural and functional properties. The main attribute of polyelectrolyte solutions is that all molecules are strongly correlated both topologically and electrostatically in their neutralizing background of charged ions in highly polarizable solvent. These strong correlations and the necessary use of numerous variables in experiments on polyelectrolytes have presented immense challenges toward fundamental understanding of the various behaviors of charged polymeric systems. This Perspective presents the author's subjective summary of several conceptual advances and the remaining persistent challenges in the contexts of charge and size of polymers, structures in homogeneous solutions, thermodynamic instability and phase transitions, structural evolution with oppositely charged polymers, dynamics in polyelectrolyte solutions, kinetics of phase separation, mobility of charged macromolecules between compartments, and implications to biological systems. [ABSTRACT FROM AUTHOR]

The field of stimuli-responsive polymers has grown in the past three decades from a few obscure examples to one of the most vibrant domains of modern macromolecular science. Indeed, the research, development, and implementation of tailored materials that can respond in predefined ways to specific stimuli now cut across most areas in which "traditional" polymers play a role, and an ever-growing range of commercial products benefits from this class of materials. This Perspective is devoted to multistimuli, multiresponsive (MSMR) polymers, which are those materials that are able to respond to multiple, different stimuli with multiple, distinct responses. Somewhat akin to living systems, which have evolved to adapt and respond in complex ways to (combinations of) different environmental cues, MSMR polymers can offer a broad range of complex properties and functions. While much of the work on MSMR polymers has been devoted to the investigation of solutions or gels, this Perspective concentrates on solid materials, as this is the state of matter in which the vast majority of polymers are currently employed. In a tutorial fashion, an outline of some of the most common mechanisms used to implement stimuli-responsive behavior in polymer solids is provided. To convey a glimpse of the potential and the challenges of these general design principles, select examples of materials that display multistimuli, single-response as well as single-stimulus multiresponse behavior are presented, before polymeric materials that are truly multistimuli, multiresponsive are discussed, and an outlook on possible directions that future work in the field may take is presented. [ABSTRACT FROM AUTHOR]

Nature has long demonstrated the importance of chemical sequence to induce structure and tune physical interactions. Investigating macromolecular structure and dynamics is paramount to understand macromolecular binding and target recognition. To that end, we have synthesized and characterized flexible sulfonated oligothioetheramides (oligoTEAs) by variable temperature pulse field gradient (PFG) NMR, double electron-electron resonance (DEER), and molecular dynamics (MD) simulations to capture their room temperature structure and dynamics in water. We have examined the contributions of synthetic length (2-12mer), pendant group charge, and backbone hydrophobicity. We observe significant entropic collapse, driven in part by backbone hydrophobicity. Analysis of individual monomer contributions revealed larger changes due to the backbone compared to pendant groups. We also observe screening of intramolecular electrostatic repulsions. Finally, we comment on the combination of DEER and PFG NMR measurements via Stokes-Einstein-Sutherland diffusion theory. Overall, this sensitive characterization holds promise to enable de novo development of macromolecular structure and sequence-structure-function relationships with flexible, but biologically functional macromolecules. [ABSTRACT FROM AUTHOR]

This article describes central features of the mass transport during the coagulation in water of cellulose-1-ethyl-3-methylimidazoium acetate ([C2mim][OAc]) solutions, namely, that the diffusivities are mainly affected by the relative concentrations of water and [C2mim][OAc], that the concentration of cellulose does not affect diffusivities and coagulation rates, that the diffusivities of low-Mw compounds are similar to those in aqueous [C2mim][OAc] solutions without macromolecules, that the polymer concentration is diluted by the large influx of coagulant causing a positive net mass gain, NMG, from diffusive fluxes, and that such NMG, although observed only as a function in time, is also a function in space that has local peaks significantly higher than the mean NMG value. The conclusion from the first three findings was that the diffusion advances through a liquid phase which possesses a continuous pore network and most of the volume. The precipitated cellulose is concentrated into fibrils whose inhibitive effect on the diffusion of small molecules through the surrounding phase is marginal. This key understanding about mass transport during coagulation also simplifies numerical modeling significantly. [ABSTRACT FROM AUTHOR]

The application of polymer "brushes", with their unique physicochemical properties, has led to a radical change in the way we functionalize biomaterials or formulate hybrids; however, their attractive traits can be largely surpassed by applying different polymer topologies, beyond the simple linear chain. Cyclic and loop brushes provide enhanced steric stabilization, improved biopassivity, and lubrication compared to their linear analogues. Focusing on poly(2-ethyl-2-oxazoline) (PEOXA), an emerging polymer in nanobiotechnology, we systematically investigate how topology effects determine the structure of PEOXA brushes and to what extent technologically relevant properties such as protein resistance, nanomechanics, and nanotribology can be tuned by varying brush topology. The highly compact structure of cyclic PEOXA brushes confers an augmented entropic barrier to the surface, efficiently hindering unspecific interactions with biomolecules. Moreover, the intrinsic absence of chain ends at the cyclic-brush interface prevents interdigitation when two identical polymer layers are sheared against each other, dramatically reducing friction. Loop PEOXA brushes present structural and interfacial characteristics that are intermediate between those of linear and cyclic brushes, which can be precisely tuned by varying the relative concentration of loops and tails within the assembly. Such topological control allows biopassivity to be progressively increased and friction to be tuned. [ABSTRACT FROM AUTHOR]

Phase separation has been used for engineering microscale fluids and particles with designed structures. But it is challenging to use phase separation to create complicated microcapsules because phase separation in the shell correlates with applied osmotic pressure and affects capsule stability significantly. Here we employ two biodegradable polymers to study the phase separation in microcapsule shells and its effect on the mechanical stability. The dynamic process reveals that phase separation creates a patchy shell with distinct regions transiently, then transports the discrete domains across the shell, and coalesces them at the surface. The equilibrium structure with balanced osmotic pressure is a Janus shell, where one component forms the shell and the other component dewets on the surface. Under slight osmotic pressure to the shell, phase separation reaches a different Janus shape, which consists of two partial shells of each component. We can in further take advantage of phase separation and osmotic pressure to rupture microcapsules at specific locations. Phase separation in the shell provides a facile approach to create versatile capsule structures and affords a reliable strategy to harness the shell mechanics. [ABSTRACT FROM AUTHOR]

Structure and dynamics of melts of copolymers with an ABCBA topology, where C is an ionizable block, have been studied by fully atomistic molecular dynamics (MD) simulations. Introducing an ionizable block for functionality adds a significant element to the coupled set of interactions that determine the structure and dynamics of the macromolecule. The polymer consists of a randomly sulfonated polystyrene C block tethered to a flexible poly(ethylene-r-propylene) bridge B and end-capped with poly(tert-butylstyrene) A. The chemical structure and topology of these polymers constitute a model for incorporation of ionic blocks within a framework that provides tactility and mechanical stability. Here we resolve the structure and dynamics of a structured polymer on the nanoscale constrained by ionic clusters. We find that the melts form intertwined networks of the A and C blocks independent of the degree of sulfonation of the C block with no long-range order. The cluster cohesiveness and morphology affect both macroscopic translational motion and segmental dynamics of all the blocks. [ABSTRACT FROM AUTHOR]

Active use of wormlike micelle (WLM) solutions in a broad range of applications demands control of their viscoelastic properties under different external conditions that can be achieved by using hybrid materials, such as polymer-surfactant complexes. Understanding the properties of such hybrid materials remains a challenge. Using a combination of several experimental techniques with molecular dynamics simulations, we investigate the interaction of poly(4-vinylpyridine) with WLMs of the anionic surfactant potassium oleate. We find that this polymer is solubilized by the micelles at the interface between the tails and headgroups of surfactant, thus screening the hydrophobic polymer backbone from interactions with water while maintaining hydrogen bonding between the pyridine rings and water. By use of SANS with contrast variation, it was shown that the macromolecules associated with the micelles have an expanded coil-like conformation with persistence length 4-fold higher than that of a polymer chain in a good solvent. The rheological behavior of the micellar solutions shows that at low polymer concentrations (regime I) the system maintains high viscoelasticity with the plateau modulus remaining almost unchanged, while the zero-shear viscosity slightly decreases. At higher polymer concentrations (regime II), the viscosity drops by more than 4 orders of magnitude, approaching that of pure solvent. The transition from the I to II regime occurs when the number of added macromolecules is approximately equal to the number of elastically active strands in micellar network. The observed changes are attributed to polymer-induced shortening of WLMs accompanied by loop and branch formation. The saturated polymer-surfactant complex contains about one surfactant per repeat unit of the polymer and represents a best compromise when the WLM retains its general cylindrical geometry (but not the viscoelastic properties) and the polymer maintains an expanded coil-like conformation. [ABSTRACT FROM AUTHOR]

The ideal of living polymerization has defined research in polymer chemistry over the past 50 years. In this Perspective, we present the case that this concept has enabled the treatment of polymers as organic molecules, rather than impure mixtures of species, and allowed the translation of methods developed by synthetic organic chemists into ever more accessible living and/or controlled polymerization methods. The concurrent development of rapid analytical methods for screening new polymerization methods for living characteristics, chiefly size exclusion chromatography, has greatly aided in the expansion of living polymerization methods. [ABSTRACT FROM AUTHOR]

Recently, the ternary blend method has been successfully applied to nonfullerene organic solar cells (OSCs) and enhanced the device performance by utilizing complementary optical absorption. Here we demonstrate the two polymer donors and one small-molecule acceptor (i.e., 2D/1A) strategy to finely regulate the blend film morphology in fullerene-free OSCs. One crystalline polymer donor, PffBT4T-2OD, can act as an effective morphology regulator for a benchmark blend of PTB7-Th and ITIC, leading to appropriate phase-separated morphology, suppressed charge recombination, efficient charge transport and high carrier mobility. The resulting solvent additive- and annealing-free fabricated bulk-heterojunction OSCs show the best power conversion efficiency (PCE) of 8.22% with a significant increase of fill factor compared to their binary counterparts. Importantly, such ternary OSCs when processed under ambient condition retain excellent device performance with a PCE of 7.57%, indicative of good air-stability. [ABSTRACT FROM AUTHOR]

We studied structure development in block copolymer films with a regular surface roughness induced by the deposition on corrugated supports. Upon thermal annealing, the residual surface roughness in thin films of cylinder-forming polystyrene-b-polybutadiene (PS-b-PB) diblock copolymer was found to be independent both on the averaged starting film thickness h0 and on the initial thickness gradient induced by spin-coating. Surface patterns in PS-b-PB films on linear and squared wave gratings appear in a form of spatially registered cylinder and nonbulk lamella phases with the morphological sequences coupled to the topography of the substrate. The observed complex phase behavior is independent of the h0 in up to three layers thick films. At the same time, the initial surface roughness was shown to be essential for the flow-field-induced sequenced ordering of the microdomains. We identify a number of specific features of complex confinement on corrugated substrates as compared to flat space, such as extreme deviations from the bulk cylinder morphology to nonbulk lamella structures in thick films, as well as the violation of the surface-tension-driven segregation of the soft PB component to the free surface. Differences in the flow behavior of PS-b-PB films and of PS homopolymer films under strong confinement, reported earlier, confirm the decoupling of the dynamics of the chains at the free surface from the underlying layers and suggest novel insights into the distribution of the surface fields through the film. [ABSTRACT FROM AUTHOR]

The vibrational spectra of semicrystalline polyethylene and its distinct domains were investigated using molecular dynamics (MD) simulations. A method for the vibrational analysis of the domains within the lamellar stack model of semicrystalline polymers has been developed and demonstrated on semicrystalline polyethylene using force fields having either united atom (UA) or explicit atom (EA) detail. In the UA description, the calculated vibrational spectra were found to differ from the observed skeletal vibrations of polyethylene with the force field used in this work. Therefore, a modified UA force field with different stretching and bending force constants is proposed, which was found to reproduce the observed frequencies of the skeletal vibrations. In the EA description, the vibrational spectra of semicrystalline polyethylene were in satisfactory agreement with typical infrared and Raman signatures of polyethylene melts and crystals. Experimental interpretations regarding the assignment of peaks in the Raman spectra to components of semicrystalline polyethylene were examined. The spectrum of the interphase domain obtained using the EA model was found to be adequately reproduced by a superposition of the spectra of the crystalline and amorphous domains, at variance with experimental observation. The lack of a distinct interphase spectrum in the EA model was attributed to the absence of the CH2 bending peak associated with the orthorhombic phase, despite confirming an orthorhombic crystal structure in the crystalline domain. [ABSTRACT FROM AUTHOR]

We present a method for the direct measurement of the relative energy of interaction between a solvated polymer and a solid interface. By tethering linear chains covalently to the surface, we ensured the idealized and constant configuration of polymer molecules for measurement, modeling, and parameter estimation. For the case of amine-terminated polystyrene bound to a glycidoxypropylsilane film submerged in cyclohexane-d12, we estimated the χ parameter for the temperature range 10.7-52.0 °C and found a downward sloping trend that crosses the χ = 0.5 threshold at 37-40 °C, in agreement with solution estimates for the same system. We simultaneously estimated the surface interaction parameter χs at each temperature, finding a decreasing affinity of the chains for the surface with increasing temperature, consistent with empirical observations. The theoretical model shows some limitations in a stronger solvent (toluene-d8) that prevent rigorous parameter estimation, but we demonstrate a qualitative change in χ and χs toward stronger solvency and weaker surface interaction with increasing temperature. [ABSTRACT FROM AUTHOR]

The shape and diffusion of circular polyelectrolytes in salt-free dilute solutions are investigated over a large range of the Bjerrum length lB by mesoscale hydrodynamic simulations, where lB characterizes the strength of electrostatic interactions (EIs). A comprehensive comparison of linear and circular polyelectrolytes is also made to gain a deep understanding of the effects of topological constraints on the conformational and dynamical properties. As lB increases, counterions become increasingly important due to their condensations on the polyelectrolyte backbone. The shape of a circular polyelectrolyte changes from a prolate coil to an oblate ring at small lB, then to a prolate coil at intermediate lB, and finally to a dense coil at large lB; in contrast, the shape of a linear polyelectrolyte changes from a prolate coil to a rod, then to a prolate coil, and finally to a dense coil. By switching on/off hydrodynamic interactions (HIs), the simulations clarify the complex coupling effects of hydrodynamic and electrostatic interactions on the diffusion of polyelectrolytes. With increasing lB, the diffusion coefficient with HIs decreases rapidly and then increases gradually, but the diffusion coefficient without HIs displays an almost monotonically decreasing behavior and eventually approaches a plateau. The significant, quantitative but not qualitative difference in diffusion coefficient in the presence of HIs is found between linear and circular polyelectrolytes with an identical chain length, but there are only slight differences between their diffusion coefficients in the absence of HIs. By exploitation of the changes in chain size and the number of condensed counterions, we show that the diffusion of polyelectrolytes can be still qualitatively understood within the framework of Zimm and Rouse models. [ABSTRACT FROM AUTHOR]

By molecular dynamics simulations coupled with the stochastic polymerization model, we show a certain dependence of the polymer chain polydispersity on the heterogeneity of the initiator sites distribution during surface-initiated polymerization. The heterogeneity of the initiators will lead to change of the mass distribution and the uncontrollability of polydispersity index (PDI) as compared to the homogeneous counterpart. We find a linear master curve of the polymer chain PDI on the interplay of heterogeneity parameter and initiator density, which actually reveals a quantitative dependence of polymer PDI on the free space between neighboring chains. This study helps to better understand and predict the chain polydispersity in the grafted materials via the surface-initiated polymerization. [ABSTRACT FROM AUTHOR]

The mechanical properties of an amorphous polymer are a consequence of the inter- and intramolecular interactions which are typically similar. Yet, polymers can be made with covalent intramolecular cross-links, leading to stronger intramolecular interactions. Here, a study on the effect of this intramolecular cross-linking on the mechanical properties of a glassy polymer is shown. A linear poly(methyl methacrylate) with defined size was cross-linked at different ratios and assembled into solid samples by solvent casting. Mechanical testing indicates that intramolecular cross-linking does not affect the mechanical properties at the elastic region but does influence these properties at the plastic region. Interestingly, intramolecular cross-linking leads to different effects than "regular" interchain cross-linking. The results are consistent with a reduction in chain entanglement, reducing toughness and to a lesser extent strength. [ABSTRACT FROM AUTHOR]

The resolution of the crystal structure and the physical properties of isotactic 1,2-poly(E-3-methyl-1,3-pentadiene) (iPE3MPD) are presented. This new polymer is one of the very few examples of known crystalline isotactic 1,2-polydienes. It does not crystallize by cooling from the melt but crystallizes by aging the amorphous samples at room temperature for several days and successive annealing. The stretching of amorphous or low crystalline compression-molded samples gives oriented fibers of a highly disordered mesomorphic form. Well-oriented fibers of the ordered crystalline form of iPE3MPD have been prepared by stretching amorphous or low crystalline compression-molded samples and successive annealing at 60-70 °C under tension. The crystalline structure of iPE3MPD is characterized by macromolecules in 7/2 helical conformation packed in an orthorhombic unit cell with parameters a = 17.4 Å, b = 16.5 Å, c = 15.3 Å according to the space group P21 ab. iPE3MPD has shown interesting mechanical properties of high deformability with elastic behavior associated with the crystallization during deformation of the mesophase that melts upon relaxation. [ABSTRACT FROM AUTHOR]

The effect of the rate of PET deformation on the mechanism of penetration of flexible-chain macromolecules in the structure of crazes developing in PET has been considered. The penetration of the flexible-chain polymer in the porous structure is affected by the flow rate of the solute, the PEO solution characteristics (the concentration regime), and the porous structure parameters (porosity and pores radius of the crazed PET). PET films deformed via the crazing mechanism in solutions of PEO of different molecular mass have been examined. The influence of the concentration regime (dilute, semidilute unentangled, and semidilute entangled solutions) on the penetration of PEO in the forming porous PET structure has been demonstrated. In the case of PEO penetration from the dilute solution, a fraction of pores becomes accessible only under conditions of the flow-induced deformation at high rate of PET deformation. In the case of the semidilute entangled solution, at low deformation rate, PEO can penetrate in the forming porous PET structure via reptation motion. At the higher deformation rate, the fluctuation polymer network exhibits elastic behavior and cannot penetrate inside the porous PET structure via reptation. [ABSTRACT FROM AUTHOR]

Peptide-π-peptide triblock molecules can self-assemble into 1-D nanostructures with extensive hydrogen-bonding networks under appropriate pH conditions. These materials are of interest due to the embedded π-electron units that can facilitate energy and charge transport within biocompatible peptide matrices. Interactions among amino acid residues presented along these hydrogen-bonded structures lead to hierarchical bundling into larger fibrillar assemblies. This complicates the analysis of individual fibrils, an understanding of which is important for tailoring the functionality of the resulting nanomaterials. Appending large bulky groups onto the peptides should frustrate these bundling interactions and significantly alter the self-assembly behavior by restricting the formation of higher order assemblies. Here we evaluate the self-assembly behavior of peptide-π-peptide molecules appended with poly(alkyl ether) dendrons containing tetraethylene glycol functionalities. These dendrons render the peptide-dendron hybrid (PDH) molecules incapable of assembly under conditions that typically promote assembly of the parent peptides. However, 1,1,1,3,3,3-hexafluoro-2-propanol, a fluorinated alcohol known to denature proteins, triggers the aqueous assembly of the PDH molecules, thus yielding platelike nanostructures with narrow size distributions. This presents a new methodology for generating self-assembled nanostructures from peptide-π-peptide materials and provides an opportunity for orthogonal functionalization using motifs with varying degrees of hydrophilicity and functions. The effects of peptide sequence and dendron position along the peptide backbone on the assembly behavior were investigated using UV-vis, photoluminescence, and circular dichroism spectroscopies, and the morphologies of the resulting self-assembled nanostructures were investigated using transmission electron microscopy. [ABSTRACT FROM AUTHOR]

Two triarmed organic-inorganic hybrid materials based on carboxylic acid-functionalized polyhedral oligomeric silsesquioxane (APOSS) with/without PS linkers are designed and synthesized (tri-PS-APOSS and tri-APOSS). They can both self-assemble into hollow spherical nanostructures in water/organic mixed solvents, as confirmed by light scattering and TEM techniques, yet they possess completely different mechanisms and driving forces. With the PS linkers, the hybrid forms bilayer vesicles similar to surfactants; while without the PS linkers, the hybrid behaves like hydrophilic macroions and assembles into single-layered, vesicle-like "blackberry"-type structure. Consequently, the trend of the assembly size in response to the change of the solvent polarity is different for the two scenarios. This work shows a simple, universal approach of controlling the mechanism and product of the self-assembly process via minor adjustment of the organic-inorganic hybrid structures. [ABSTRACT FROM AUTHOR]

We use a combination of the coarse-grained molecular dynamics simulations and scaling analysis to study conformations of bottlebrush and comb-like polymers in a melt. Our analysis shows that a crossover between comb and bottlebrush regimes is controlled by the crowding parameter, Φ, describing overlap between neighboring macromolecules. In comb-like systems characterized by a sparse grafting of side chains (Φ < 1), the side chains and backbones belonging to neighboring macromolecules interpenetrate. However, in bottlebrushes with densely grafted side chains (Φ ≥ 1), the interpenetration between macromolecules is suppressed by steric repulsion between side chains. In this regime, bottlebrush macromolecules can be viewed as filaments with diameter proportional to size of the side chains. For flexible side chains, the crowding parameter is given by Φ ≈ [v/(lb)3/2][(nsc/ng + 1)/nsc1/2], which depends on both the architectural parameters (degree of polymerization of the side chains, nsc, and number of backbone bonds between side chains, ng) and chemical structure of monomers (bond length l, monomer excluded volume v, and Kuhn length, b). Molecular dynamics simulations corroborate this classification of graft polymers and show that the effective macromolecule Kuhn length, bK, and the mean-square end-to-end distance of the backbone, Re,bb², are universal functions of the crowding parameter Φ for all studied systems. [ABSTRACT FROM AUTHOR]

We introduce the formation of a dual responsive supramolecular star polymer system, displaying gated self-assembly behavior. The redox- and thermoresponsive star polymers are based on a 6-fold β-CD functionalized core molecule and RAFT-derived ferrocene end functionalized poly(N,N-dimethylacrylamide) (PDMA) and poly(N,N-diethylacrylamide) (PDEA) linear polymers. Complex formation is analyzed via various methods including dynamic light scattering (DLS). Chemical redox triggers, namely NaOCl and ascorbic acid, as well as electrochemical triggers can be utilized to shift the star polymers to the unbound state via CD/ferrocene complex dissociation. Moreover, heating above the lower critical solution temperature (approximately 34 °C) allows for a change from the coil to the globular state of the star polymers in the case of PDEA arms. For PDMA arms, heating to 70 °C allows shifting of the system to the unbound state. The response of the supramolecular star polymers is carefully studied via various methods including cyclic voltammetry (CV), DLS, and turbidimetry. Overall, the supramolecular star polymers can be transformed into predefined states via individually addressable temperature and/or redox stimuli, presenting a novel dual gated self-assembling supramolecular star polymer system in aqueous solution. [ABSTRACT FROM AUTHOR]

Two indacenodithiophene derivative bridged diketopyrrolopyrroles (DPP), i.e., 2,7-bis(2,5-bis(2-decyltetradecyl)-3,6-dioxo-4-(thiophen-2-yl)-2,3,5,6-tetrahydropyrrolo[3,4-c]pyrrol-1-yl)-s-indaceno[1,2-b:5,6-b']dithiophene-4,9-dione (DDPP-PhCO) and 2,2'-(2,7-bis(2,5-bis(2-decyltetradecyl)-3,6-dioxo-4-(thiophen-2-yl)-2,3,5,6-tetrahydropyrrolo[3,4-c]pyrrol-1-yl)-s-indaceno[1,2-b:5,6-b']dithiophene-4,9-diylidene)dimalononitrile (DDPP-PhCN), were developed via intramolecular Friedel-Crafts acylation and Knoevenagel condensation. A series of donor-acceptor (D-A) conjugated polymers were synthesized by Stille or direct arylation polycondensation with these two novel units as acceptors and vinyl or thiophene derivatives as donors. The polymers with DDPP-PhCO as acceptor unit exhibited optical bandgaps (Egopt) of ca. 1.2 eV and the highest occupied molecular orbital (HOMO) energy levels of ~-5.3 eV with the difference less than 0.1 eV, and their lowest unoccupied molecular orbital (LUMO) levels were in the range of -3.73 to -3.91 eV. The polymer based on DDPP-PhCN showed similar HOMO level (-5.29 eV) but remarkably lower LUMO level (-4.21 eV). Top-gate/bottom-contact (TGBC) organic field-effect transistors (OFETs) of all the polymers exhibited ambipolar transport behavior with the highest hole mobility (μh) and electron mobility (μe) up to 1.09 and 0.44 cm2 V-1 s-1, respectively, in air. Owing to their favorable molecular orientation and frontier molecular orbital distribution, the polymers based on DDPP-PhCO displayed much higher hole and electron mobilities than that based on DDPP-PhCN. [ABSTRACT FROM AUTHOR]

We synthesize heterofluorene monomers with Si, Ge, N, As, Se, and Te occupying the 9-position of the fluorene motif, which are then polymerized by Suzuki coupling. The optical properties of the obtained polymers are investigated in their solid state. We compare and elucidate effects in the materials absorption, emission, quantum yield (ϕ), and fluorescence lifetime. Moreover, we determine the refractive indices n and absorption coefficient k by variable angle spectroscopic ellipsometry (VASE). We show that in addition to already known C, Si, and N containing polyfluorenes also Ge and As containing polymers exhibit amplified spontaneous emission. [ABSTRACT FROM AUTHOR]

The scope of this Perspective is to highlight innovative contributions in the synthesis of well-defined complex macromolecular architectures and to emphasize the importance of these materials to polymer physical chemistry, physics, theory, and applications. In addition, this Perspective tries to enlighten the past and show possible pathways for the future. Among the plethora of polymerization methods, we briefly report the impact of the truly living and controlled/living polymerization techniques focusing mainly on anionic polymerization, the mother of all living and controlled/living polymerizations. Through anionic polymerization well-defined model polymers with complex macromolecular architectures having the highest molecular weight, structural and compositional homogeneity can be achieved. The synthesized structures include star, comb/graft, cyclic, branched and hyberbranched, dendritic, and multiblock multicomponent polymers. In our opinion, in addition to the work needed on the synthesis, properties, and application of copolymers with more than three chemically different blocks and complex architecture, the polymer chemists in the future should follow closer the approaches Nature, the perfect chemist, uses to make functional complex macromolecular structures by noncovalent chemistry. Moreover, development of new analytical methods for the characterization/purification of polymers with complex macromolecular architectures is essential for the synthesis and properties study of this family of polymeric materials. [ABSTRACT FROM AUTHOR]

The field of polymer nanocomposites has been at the forefront of research in the polymer community for the past few decades. Foundational work published in Macromolecules during this time has emphasized the physics and chemistry of the inclusion of nanofillers; remarkable early developments suggested that these materials would create a revolution in the plastics industry. After 25 years of innovative and groundbreaking research, PNCs have enabled many niche solutions. To complement the extensive literature currently available, we focus this Perspective on four case studies of PNCs applications: (i) filled rubbers, (ii) continuous fiber reinforced thermoset composites, (iii) membranes for gas separations, and (iv) dielectrics for capacitors and insulation. After presenting synthetic developments we discuss the application of polymer nanocomposites to each of these topic areas; successes will be noted, and we will finish each section by highlighting the various technological bottlenecks that need to be overcome to take these materials to full-scale practical application. By considering past successes and failures, we will emphasize the critical fundamental science needed to further expand the practical relevance of these materials. [ABSTRACT FROM AUTHOR]

Block polymers have undergone extraordinary evolution since their inception more than 60 years ago, maturing from simple surfactants to an expansive class of macromolecules encoded with exquisite attributes. Contemporary synthetic accessibility coupled with facile characterization and rigorous theoretical advances have conspired to continuously generate fundamental insights and enabling concepts that target applications spanning chemistry, biology, physics, and engineering. Here, we parse the vast literature to examine the forefront of the field and identify exciting themes and challenging opportunities that portend a bracing future trajectory. This Perspective celebrates the visionary role played by Macromolecules in advancing our understanding of this remarkable class of materials. [ABSTRACT FROM AUTHOR]

The long-range internal dynamics (LRID) of 74 pyrene-labeled macromolecules (PyLMs) were characterized in four solvents representing a broad range of dielectric constants equal to 2.4 (toluene), 7.6 (tetrahydrofuran, THF), 37.8 (N,N-dimethylformamide, DMF), and 46.7 (dimethyl sulfoxide, DMSO). The LRID of the PyLMs were quantified based on the parameters retrieved from the global model free analysis (MFA) of the time-resolved fluorescence (TRF) decays of the pyrene monomer and excimer. These parameters were combined to yield 'k', the average rate constant of pyrene excimer formation in the PyLMs, and (IE/IM)TRF(ffree = 0), the ratio of excimer to monomer fluorescence intensity obtained in the absence of pyrene labels that do not form excimer. (IE/IM)TRF(ffree = 0) was found to increase linearly with increasing 'k' values over 3 orders of magnitude in the four solvents studied with a slope that equaled the average lifetime of the pyrene excimer (τE). The 'k' values obtained to build these master lines could be correlated back to the expected LRID of the macromolecules. The lowest 'k' values were obtained for the end-labeled linear chains holding the pyrene groups far apart, whereas the branched macromolecules bringing the pyrene labels close to each other yielded the larger 'k' values. Furthermore, the fact that these master curves were observed for so many different PyLMs in the four solvents covering such a broad range of solvent polarity suggests that this relationship represents a general physical phenomenon that applies to all PyLMs. Considering the importance of characterizing the LRID of macromolecules in solution, the (IE/IM)TRF(ffree = 0) vs 'k' plots presented in this report can be viewed as calibration curves against which the LRID of any PyLM can now be compared. Thus, the 3 orders of magnitude range found for these master curves offers the scientific community an impressive analytical opportunity to gauge the LRID of macromolecules in solution. [ABSTRACT FROM AUTHOR]

We have simulated the melt of poly(carbosilane) dendrimers using atomistic models and have reproduced the effect predicted by the analytical theory; i.e., orientational autocorrelation functions of a segment from the same layer (numbered from periphery) are practically identical and do not depend on dendrimer size. The frequency dependences of the dielectric and NMR relaxation were obtained and studied in detail. The main contribution to the maxima of these dependences is given by the pulsation process. It leads to a shift of the maxima to low frequencies for the core segment in comparison with the maxima for peripheral segments. The contribution of local reorientation can also be significant, and in some cases this contribution manifests as an additional maximum. The nontrivial scaling laws in the frequency dependences of dielectric permittivity and NMR relaxation rate averaged over all layers of a dendrimer macromolecule are found. A similar scaling law is observed in the experiments on NMR relaxation but is not described by the analytical theory. [ABSTRACT FROM AUTHOR]

The electrostatic origins behind the speed of translocation of a uniformly charged flexible macromolecule through α-hemolysin (αHL) protein pores under a voltage are investigated using variations in pH and electrolyte concentration. We have measured durations of successful threading of poly(styrenesulfonate) through αHL at two different pH conditions, pH 4.5 and pH 7.5, under various salt concentration conditions. Salt concentrations in the donor (cis) and the recipient (trans) compartments influence the polymer translocation dynamics differently, depending on pH. At both pH 4.5 and pH 7.5, decreasing the cis salt concentration, cs,cis, results in faster polymer translocations. On the other hand, a decrease in trans salt concentration, cs,trans, retards the polymer transport process at pH 4.5, while at pH 7.5 the translocation time is observed to be independent of cs,trans. We present a theoretical model to calculate the translocation times from the free energy of the polymer along the translocation process to describe our experimental results. We show that the charge density of the polymer inside the nanopore is significantly affected by cs,cis, explaining the cis salt effect on the speed of polymer translocation. The trans salt effects are attributed to the electrostatic interaction between the polymer and the exit portion of the αHL pore, which is determined by the pH of the trans compartment. At low pH where the net charge of the end of the αHL is positive, the attractive electrostatic interaction in trans becomes stronger, as cs,trans decreases, resulting in delays in translocation process. [ABSTRACT FROM AUTHOR]

The specific activity of proteins can be traced back to their highly defined tertiary structure, which is a result of a perfectly controlled intrachain folding process. In the herein presented work the folding of different distinct domains within a single macromolecule is demonstrated. RAFT polymerization was used to produce multiblock copolymers, which are decorated with pendant hydroxyl groups in foldable sections, separated by nonfunctional spacer blocks in between. OH-bearing blocks were folded using an isocyanate cross-linker prior to chain extension to form single chain nanoparticles (SCNP). After addition of a spacer block and a further OH decorated block, folding was repeated to generate individual SCNP within a polymer chain. Control experiments were performed indicating the absence of interblock cross-linking. SCNP were found to be condensed by a combination of covalent and supramolecular (hydrogen bonds) linkage. The approach was used to create a highly complex pentablock copolymer having three individually folded subdomains with an overall dispersity of 1.21. The successful formation of SCNP was confirmed by size exclusion chromatography (SEC), nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), and atomic force microscopy (AFM). [ABSTRACT FROM AUTHOR]

We examine the role of molecular connectivity and architecture on the complexation of ionic macromolecules (polyelectrolytes) of finite size. A unified framework is developed and applied to evaluate the electrostatic correlation free energy for point-like, rod-like, and coil-like molecules. That framework is generalized to molecules of variable fractal dimensions, including dendrimers. Analytical expressions for the free energy, correlation length, and osmotic pressure are derived, thereby enabling consideration of the effects of charge connectivity, fractal dimension, and backbone stiffness on the complexation behavior of a wide range of polyelectrolytes. Results are presented for regions in the immediate vicinity of the critical region and far from it. A transparent and explicit expression for the coexistence curve is derived in order to facilitate analysis of experimentally observed phase diagrams. [ABSTRACT FROM AUTHOR]

The dynamics of spin-labeled poly(acrylic acid) (PAA) in polyelectrolyte complexes (PECs) has been studied by EPR. It has been found that the segmental mobility of the PAA in the PECs is nearly constant in the pH range 10 to 5 but decreases dramatically for pH < 5. Recently, we have studied the dynamics of spin-labeled poly(ethylene-alt-maleic acid) (P(E-alt-MA)) in PECs. The rotational mobility of the P(E-alt-MA) has been observed to depend on pH, which has been related to the formation of hydrogen bonds of the maleic acid units at low pH [ Macromolecules 2015, 48, 3577]. To test this hypothesis, in the present study, P(E-alt-MA) has been replaced with PAA, which is a structural isomer of P(E-alt-MA). Now with the results for PAA at hand, we can conclude that the low mobility of the P(E-alt-MA) at low pH cannot be exclusively attributed to the presence of maleic acid units. Nevertheless, it has been confirmed that the dynamics in the PECs is strongly influenced by the degree of dissociation of the weak polyacid. [ABSTRACT FROM AUTHOR]

We present a theory describing structural properties of brushes formed by cycled macromolecules tethered to planar surface. Diverse architectures of macromolecules that differ with respect to position and number of subchains in macrocycle are considered. We use the self-consistent field analytical approach based on strong stretching approximation and assumption of Gaussian elasticity of brush-forming molecules. Predictions of the analytical theory are systematically compared to the results of numerical SF-SCF modeling. Similarity of the effects of cyclization and branching on large-scale properties of polymer brush is demonstrated. It is also predicted that weaker interpenetration of sliding brushes formed by cyclic macromolecules might enhance their performance as lubricants. [ABSTRACT FROM AUTHOR]

Melt rheology and thermal phase transition of a series of hyperbranched polyglycerol samples (hbPG) (DB ≈ 60%) in a broad molecular weight range (Mn = 600-440 000 g/mol) were investigated and correlated to both molecular weight and nature of the end group (hydroxyl vs permethylated and trimethylsilylated). The well-characterized and defined flexible polyethers are particularly suitable to shed light on the linear viscoelastic behavior with respect to (i) hyperbranched topology and (ii) hydrogen bond interactions, particularly in comparison to the perfectly linear polyglycerol counterparts studied recently [Osterwinter, C.; Macromolecules 2015, 48, 119-130]. We present a detailed examination of differences found in the characteristic moduli as a consequence of functionality and topology leading to an estimation of both a stickiness parameter and a connectivity parameter of hyperbranched molecules. The appearance of a plateau region of the dynamic moduli indicates entanglement behavior, although the determined apparent entanglement molecular weight Me ≈ 6000 g/mol is significantly higher than the molecular weight between two branching points (Mx ⪡ Me). Zero shear viscosities and terminal relaxation times show a unique scaling behavior with respect to the nature of the multiple end groups of the hyperbranched topology, suggesting entanglement transitions with a critical molecular weight around 55 000 g/mol. Most striking and in pronounced contrast to linear PG as the perfect linear analogue, the derived structure-property relationships depend on the functionality of the repeating unit of the polymer. [ABSTRACT FROM AUTHOR]

We employ molecular simulations to show that a generic isolated macromolecule behaves as a glass-forming liquid in an extreme state of nanoconfinement. Specifically, its glass transition temperature Tg is strongly suppressed with respect to a corresponding bulk-state polymer, but adsorption onto an attractive substrate can reverse this effect. Results indicate that observations of bulklike Tg in individual nanoconfined systems can result from a "compensation point" between Tg enhancement and Tg suppression. In addition to their implications for the understanding of nanostructured synthetic materials, these results are also likely relevant to the dynamics of globular and adsorbed biological macromolecules. [ABSTRACT FROM AUTHOR]

A base-to-base organocatalytic approach has been developed for one-pot synthesis of poly(ethylene oxide)-block-polyesters and poly(ethylene oxide)-based polyurethanes. Ethylene oxide is first polymerized from a diol in the presence of a phosphazene superbase; then a thiourea is added to be deprotonated by the strongly basic alkoxide, which attenuates the basicity of the catalytic system and thus allows for controlled polymerization of the subsequently added cyclic ester from the polyether chain end or for step-growth polymerization of an added diisocyanate with the macrodiol which is free from anionic homopolymerization of the diisocyanate. The approach shows several advantages in addition to the one-pot facile character, e.g., a wide applicability toward different "second monmers" including (but not limited to) ε-caprolactone, l-lactide, and diisocyanate, and a low amount of "second catalyst" required as the deprotonated thiourea itself serves as the mildly or weakly basic organocatalyst. Impact of the N-substituent, i.e., pKa of the thiourea, on the catalytic efficacy of the deprotonated thiourea has also been preliminarily revealed. [ABSTRACT FROM AUTHOR]

Brush macromolecules (BMs) are unique because of their distinct properties from linear or other nonlinear polymers, relying on side chain steric repulsions and backbone stiffness. BMs with densely grafted side chains have been synthesized either by cationic, anionic, or controlled radical polymerization, yet CO2-epoxide immortal alternating copolymerization has rarely been applied for the synthesis of BMs via the "grafting-from" approach. Here we report synthesis of BMs by alternating copolymerization of CO2 and propylene oxide (PO) initiated from poly(acrylic acid) as a multifunctional macroinitiator. The copolymerization afforded ultrahigh-molecular-weight BMs with poly(propylene carbonate) (PPC) side chains (molecular weight >106), and the side chain length was tunable via further CO2-PO alternating copolymerization initiated from hydroxy end groups of the resulting side chain PPCs. These BMs were directly observed by atomic force microscopy, demonstrating that the BMs have ellipsoidal morphologies with 20-50 nm. Furthermore, the BMs were thermally decomposable at around 240 °C. [ABSTRACT FROM AUTHOR]

Chain shuttling polymerization (CSP) has exhibited unique privilege to combine monomer sequences of different properties into one macromolecular chain, which, however, is difficult to achieve because of low chain transfer efficiency and thus lead to poor architecture control over the resulting polymers. Herein, we reported that the pyridyl-methylene fluorenyl scandium complex 1 in combination with [Ph3C][B(C6F5)4] and AliBu3 showed a high transfer efficiency (93.8%) in the presence of 10 equiv of AliBu3 toward the chain-transfer polymerization (CTP) of isoprene (IP) in high 1,4-selectivity (83%). Meanwhile, under the same conditions, the analogous lutetium precursor 3 based system was 3,4-regioselective and exhibited almost perfect chain transfer efficiency (96.5-100%) in a wide range of AliBu3-to-Lu ratios from 10:1 to 100:1, indicating that each Lu generated apparently 100 polyisoprene (PIP) macromolecules. Both CTPs performed fluently without compromising the selectivity and the activity and had comparable chain transfer rate constants. Based on this, 1,4- and 3,4-regioselective CSPs were realized by mixing 1 and 3 in various ratios to give a series of PIPs bearing different distribution of 1,4- and 3,4-PIP sequences and Tg values. This work provides a new strategy to access stereoregular and architecture controlled polymers from a single monomer. [ABSTRACT FROM AUTHOR]

Over the years, fluorescence quenching experiments have provided a robust analytical means to retrieve information about the internal dynamics of macromolecules in general and the long range polymer chain dynamics (LRPCD) of linear chains in particular. This report reviews the results obtained to date with the two main fluorescence experiments based on collisional quenching that have been used over the years to describe LRPCD. These experiments involve the labeling of a chain with dyes and quenchers either at the ends of a monodisperse chain for fluorescence quenching end-to-end cyclization (fqEEC) experiments or randomly along a polydisperse chain for fluorescence decay analysis with the fluorescence blob model (FBM). The advantages and disadvantages of these two types of experiments are discussed as well as their range of applications and applicability to the field of protein folding. In particular, this Perspective illustrates how fqEEc experiments are being applied to probe loop formation in polypeptides and how FBM analysis of randomly labeled polypeptides could help determine the size of foldons which are expected to solve Levinthal's long-standing paradox. [ABSTRACT FROM AUTHOR]

Dynamic properties play an important role in designing functional polymer nanocomposites, impacting molecular transport and phase separation kinetics. When nanoparticle (NP) size is comparable to polymer chain size, segmental relaxations may be influenced by changes in chain conformations and packing at the polymer/NP interface. Following the reptation model, these changes can perturb the longest relaxation time, in particular, the center-of-mass (COM) dynamics of polymer chains in entangled melts. This Perspective focuses on unsolved issues in polymer COM diffusion and local dynamics and segmental motions in the presence of NPs. The article introduces the effect of NP size, shape, surface modification, and enthalpic interactions on polymer diffusion and further relates dynamic studies in PNCs to macromolecular transport in bio-related systems and nanopores. Studies of local dynamics also provide insights into how entanglement density, monomeric friction, and chain conformation are influenced by NPs and how the interplay between these key parameters relates to COM dynamics to provide a unified picture across length scales. Moving forward, new studies investigating dynamics in PNCs are needed to address these unresolved problems and motivate potential applications from membranes for separations to NP carriers for drug delivery. [ABSTRACT FROM AUTHOR]