Cyclic Polymer Chains Research Articles

Insight into the Alcohol-Free Ring-Opening Polymerization of TMC Catalyzed by TBD.

We report herein a study on the alcohol-free, ring-opening polymerization of trimethylene carbonate (TMC) in THF, catalyzed by 1,5,7-triazabicyclo [4.4.0] ec-5-ene (TBD) with ratios nTBD/nTMC ranging between 1/20 and 1/400. In all cases, the reaction proceeds very rapidly, even faster than in the presence of alcohol initiators, and provides PTMC with molecular weights up to Mn = 34,000 g mol−1. Characterization of the obtained PTMC samples by MALDI-TOF mass spectrometry, triple detection size exclusion chromatography and 1H NMR spectroscopy reveals the presence of both linear and cyclic polymer chains.

Glass-Transition Temperature of Cyclic Polystyrene: A Computational Study

Molecular-dynamics simulations are employed to study the glass transition of cyclic polystyrene melts. Gibbs and DiMarzio’s theory predict an increase in glass transition temperature, Tg upon lowering the length of cyclic polymer chains, which is opposite to the well-known trend for linear polymers. Their theory has been confirmed by some experiments; however, others observe a decrease in Tg upon lowering the chain length instead. When volumetric methods are employed to obtain the glass transition temperature in simulated cyclic polystyrene, a slight increase with decreasing cyclic polystyrene chain length is obtained. This increase is more pronounced when glass transition temperatures are obtained from dynamics. Both the glass transition temperature Tg obtained from diffusion data and the ideal glass transition temperature T0 obtained from the decay of the orientational autocorrelation function of the phenyl bond show a clear upturn.

Molecular Dynamics Simulation of Crystallization Cyclic Polymer Melts As Compared to Their Linear Counterparts

Large scale molecular dynamics simulations have been performed in the framework of a coarse-grained poly(vinyl alcohol) model to study the crystallization behavior of long unknotted and nonconcatenated cyclic polymer chains from the melt state. The results are compared with those for chemically identical linear chains. The crystallization and melting points, stem length, crystallinity, and latent heat of melting/crystallization of cyclic polymers are found to be substantially higher than their linear counterpart subjected to the same thermal history. The reduced amount of entanglements of cyclic polymers is suggested to explain the difference between cyclic polymers and their linear analogue. We applied primitive path analysis to quantify the entanglement state for all systems during crystallization and heating. While for linear chains the entanglement length is increasing during crystallization and annealing indicating a partial disentanglement process, the entanglement length is monotonously decreasing ...

Inside Cover: Precisely Assembled Cyclic Gold Nanoparticle Frames by 2D Polymer Single‐Crystal Templating (Angew. Chem. Int. Ed. 44/2017)

Free-standing frames can be prepared by a directed assembly method in which nanoparticles are precisely linked together by using polymer single crystals (PSCs) as a template. In their Communication on page 13645 ff., C. Y. Li and co-workers use preformed PSCs to direct the crystallization of block copolymers, which in turn direct gold NPs (AuNPs) to form precisely controlled AuNP frames. These AuNP frames topologically resemble nanoparticle rings and cyclic polymer chains, and show unique surface plasmon resonance behaviors.

Precisely Assembled Cyclic Gold Nanoparticle Frames by 2D Polymer Single‐Crystal Templating

AbstractIn recent decades, extensive studies have been devoted to assembling nanoparticles (NPs) into various ordered structures to achieve novel optical properties. However, it still remains a challenging task to assemble NPs into cyclic one‐dimensional (1D) shapes, such as rings and frames. Herein, we report a directed assembly method to precisely assemble NPs into well‐defined, free‐standing frames using polymer single crystals (PSCs) as the template. Preformed poly(ethylene oxide) (PEO) single crystals were used as the template to direct the crystallization of block copolymer (BCP) poly(ethylene oxide)‐b‐poly(4‐vinylpyridine) (PEO‐b‐P4VP), which directs the gold NPs (AuNPs) to form AuNP frames. By controlling the PSC growth, we were able to, for the first time, precisely tune both the size and width of the AuNP frame. These novel AuNP frames topologically resemble NP nanorings and cyclic polymer chains, and show unique surface plasmon resonance (SPR) behaviors.

Precisely Assembled Cyclic Gold Nanoparticle Frames by 2D Polymer Single-Crystal Templating.

In recent decades, extensive studies have been devoted to assembling nanoparticles (NPs) into various ordered structures to achieve novel optical properties. However, it still remains a challenging task to assemble NPs into cyclic one-dimensional (1D) shapes, such as rings and frames. Herein, we report a directed assembly method to precisely assemble NPs into well-defined, free-standing frames using polymer single crystals (PSCs) as the template. Preformed poly(ethylene oxide) (PEO) single crystals were used as the template to direct the crystallization of block copolymer (BCP) poly(ethylene oxide)-b-poly(4-vinylpyridine) (PEO-b-P4VP), which directs the gold NPs (AuNPs) to form AuNP frames. By controlling the PSC growth, we were able to, for the first time, precisely tune both the size and width of the AuNP frame. These novel AuNP frames topologically resemble NP nanorings and cyclic polymer chains, and show unique surface plasmon resonance (SPR) behaviors.

Synthesis of Cyclic Polymers and Characterization of Their Diffusive Motion in the Melt State at the Single Molecule Level.

We demonstrate a method for the synthesis of cyclic polymers and a protocol for characterizing their diffusive motion in a melt state at the single molecule level. An electrostatic self-assembly and covalent fixation (ESA-CF) process is used for the synthesis of the cyclic poly(tetrahydrofuran) (poly(THF)). The diffusive motion of individual cyclic polymer chains in a melt state is visualized using single molecule fluorescence imaging by incorporating a fluorophore unit in the cyclic chains. The diffusive motion of the chains is quantitatively characterized by means of a combination of mean-squared displacement (MSD) analysis and a cumulative distribution function (CDF) analysis. The cyclic polymer exhibits multiple-mode diffusion which is distinct from its linear counterpart. The results demonstrate that the diffusional heterogeneity of polymers that is often hidden behind ensemble averaging can be revealed by the efficient synthesis of the cyclic polymers using the ESA-CF process and the quantitative analysis of the diffusive motion at the single molecule level using the MSD and CDF analyses.

Synthesis of Cyclic Polymers and Characterization of Their Diffusive Motion in the Melt State at the Single Molecule Level

We demonstrate a method for the synthesis of cyclic polymers and a protocol for characterizing their diffusive motion in a melt state at the single molecule level. An electrostatic self-assembly and covalent fixation (ESA-CF) process is used for the synthesis of the cyclic poly(tetrahydrofuran) (poly(THF)). The diffusive motion of individual cyclic polymer chains in a melt state is visualized using single molecule fluorescence imaging by incorporating a fluorophore unit in the cyclic chains. The diffusive motion of the chains is quantitatively characterized by means of a combination of mean-squared displacement (MSD) analysis and a cumulative distribution function (CDF) analysis. The cyclic polymer exhibits multiple-mode diffusion which is distinct from its linear counterpart. The results demonstrate that the diffusional heterogeneity of polymers that is often hidden behind ensemble averaging can be revealed by the efficient synthesis of the cyclic polymers using the ESA-CF process and the quantitative analysis of the diffusive motion at the single molecule level using the MSD and CDF analyses.

Surface enrichment driven by polymer topology

We report a molecular dynamics simulation study of free-standing films of a blend of linear and cyclic polymer chains. We find that the composition of linear chains at the interface is enhanced relative to their bulk value for short chains but is depleted for long chains. Our findings are in agreement with recent experimental evidence reported for blends of short linear and cyclic polystyrene chains and highlight the genuine surface behavior in the short chain-length regime where theoretical predictions are more difficult. We highlight surface enrichment at low-energy surfaces as the result of competition between different entropic and enthalpic contributions to the interfacial free energy of the system.

Single-Molecule Study on Polymer Diffusion in a Melt State: Effect of Chain Topology

We report a new methodology for studying diffusion of individual polymer chains in a melt state, with special emphasis on the effect of chain topology. A perylene diimide fluorophore was incorporated into the linear and cyclic poly(THF)s, and real-time diffusion behavior of individual chains in a melt of linear poly(THF) was measured by means of a single-molecule fluorescence imaging technique. The combination of mean squared displacement (MSD) and cumulative distribution function (CDF) analysis demonstrated the broad distribution of diffusion coefficient of both the linear and cyclic polymer chains in the melt state. This indicates the presence of spatiotemporal heterogeneity of the polymer diffusion which occurs at much larger time and length scales than those expected from the current polymer physics theory. We further demonstrated that the cyclic chains showed marginally slower diffusion in comparison with the linear counterparts, to suggest the effective suppression of the translocation through the threading-entanglement with the linear matrix chains. This coincides with the higher activation energy for the diffusion of the cyclic chains than of the linear chains. These results suggest that the single-molecule imaging technique provides a powerful tool to analyze complicated polymer dynamics and contributes to the molecular level understanding of the chain interaction.

Percolation in two-dimensional systems containing cyclic chains

The structure of the system consisting of adsorbed cyclic polymer chains and solvent molecules was studied. Our main aim was to check how the percolation threshold in such a system was related to the percolation threshold obtained for a system of “ordinary” flexible linear chains, i.e. how the geometry of objects influenced the percolation threshold of regarded objects and solvent molecules. The macromolecules were represented as sequences of statistical segments restricted to a two-dimensional triangular lattice. The system was athermal and the excluded volume was the only potential introduced. The properties of the system were determined by means of the Monte Carlo method using the cooperative motion algorithm (CMA). The percolation thresholds and critical exponents were determined. It was shown that the percolation threshold of cyclic chains was considerably higher than that of linear chains and depends on the chain length less significantly then for linear polymers.

Templates for Cyclic Polymers

Ring-expansion metathesis polymerization (REMP) can be used to prepare perfect cyclic polymer chains. Activated ester template A was prepared from 1 using Grubbs cyclic ruthenium-alkylidene catalyst. This template was transformed into a copper(I) click-ready template B. Both templates were post-functionalized to create cyclic gels (e.g., cyclic gel A and B) and cyclic polymer brushes (A, B, B′).

Size exclusion chromatography of plasmid DNA isoforms

There is considerable interest in using size exclusion chromatography (SEC) to analyze and purify specific plasmid isoforms, but there is currently no fundamental understanding of the effects of plasmid size and morphology on plasmid behavior in SEC. Experiments were performed for plasmids from 3.0 to 17.0 kbp in size. The linear and open-circular isoforms were generated from the supercoiled plasmid by appropriate enzymatic digestion. SEC retention data were obtained using a Sephacryl S-1000 SF resin packed column and an Agilent HPLC system over a range of flow rates using buffers of different ionic strength and composition. The plasmid partition coefficients, K P, were evaluated from the first statistical moment of the chromatographic peak. The partition coefficient decreased with increasing plasmid size as expected; K P varied from 0.299 to 0.045 for supercoiled plasmids of 3.0 to 17.0 kbp. The partition coefficient also increased with increasing ionic strength due to the compaction of the DNA associated with the shielding of the intramolecular electrostatic interactions. For any plasmid size, the supercoiled isoform had the highest K P followed by the open-circular and then the linear isoform, consistent with independent estimates of the plasmid radius of gyration as determined by static light scattering. The experimental data were analyzed using available theoretical models for the partitioning of linear and cyclic polymer chains in well-defined pore geometries. These results provide important insights into the behavior of different plasmid isoforms in size exclusion chromatography.

Steady-state behavior of ring polymers in dilute flowing solutions via Brownian dynamics

A bead and spring model is considered for the Brownian dynamics simulation of the behavior of cyclic polymer chains (rings) in a dilute solution under shear or elongational flow. Finite extensibility, excluded volume, and hydrodynamic interaction are taken into account to make the polymer model as realistic as possible. In shear flow, the deformation of the chain and the shear rate viscosity dependence (the flow curve), are studied and characterized. In elongational flow, the coil-stretch phenomenon is described and the relationship between the critical elongational rate and the molecular weight is given. The qualitative behavior obtained for ring polymers is analogous to that of linear polymers.

Matched ring diblock and linear triblock copolymers in dilute solution

AbstractA unique diblock copolymer ring and its linear triblock copolymer precursor composed of polystyrene and polydimethylsiloxane have been characterized by static and dynamic light scattering in dilute solution. The measurements were carried out with cyclohexane as the solvent over a temperature range of 12–35°C. Cyclohexane has the useful property that it is nearly isorefractive with the PDMS so that the PDMS block segments are invisible to the light‐scattering technique and it is a theta solvent for polystyrene at 34.5°C. The block polymers in this work contain 35.1 wt % of styrene as determined by proton NMR. In the linear triblock polymer, the polystyrene is the center block with PDMS blocks on each side. Static light scattering measurements give 4.31 × 104 for the average molecular weight of the whole polymer. Light scattering also shows that the apparent theta temperature for the linear triblock is shifted by 15°C to a value of 20°C at which point the second virial coefficient drops sharply and phase separation begins to induce aggregation. The diblock ring, however, shows a strongly positive second virial coefficient and no aggregation even at 12°C which is the limit of these experiments. The diffusion coefficients of cyclic diblock (Dc) and linear triblock copolymer (D1) are measured by dynamic light scattering. The ratio of diffusion coefficients of cyclic and linear copolymers at 14.9°C and 30°C are Dc/Dl = 1.13 and 1.107 respectively. These compare well with prediction of 1.18 for this ratio from consideration of the hydrodynamics of matched linear and cyclic polymer chains. Dynamic light scattering quantitatively confirms that the linear copolymer experiences a solvent quality change near 20°C but the cyclic polymer remains in good solvent over the entire experimental temperature range. © 1993 John Wiley & Sons, Inc.

The intrinsic viscosity of linear and cyclic polymer chains in the crossover region

The self-consistent Fourier configurational approach to the excluded volume has been used to investigate the intrinsic viscosity of linear and cyclic polymer chains in the crossover region following the Zimm-Hearst scheme with preaveraged hydrodynamic interaction. The results are compared to those obtained with other theoretical approaches and are shown to be in good agreement with extensive experimental results. We predict the ratio of the intrinsic viscosity of cyclic polymers to that of linear chains, g η , will change in a peculiar way with the strength of the excluded volume interaction. Owing to the non-affine expansion of the chains and to its interplay with hydrodynamic interaction g η increases slightly at very low strength and then it quickly decreases below the unperturbed value, in agreement both with perturbation theory results and with experimental data.