Cyclic Polystyrene Research Articles

Comparison of Cyclic and Linear Poly(lactide)s Using Small-Angle Neutron Scattering.

Small-angle neutron scattering (SANS) experiments were conducted on cyclic and linear polymers of racemic and l-lactides (PLA) with the goal of comparing chain configurations, scaling, and effective polymer-solvent interactions of the two topologies in acetone-d 6 and THF-d 8. There are limited reports of SANS results on cyclic polymers due to the lack of substantial development in the field until recently. Now that pure, well-defined cyclic polymers are accessible, unanswered questions about their rheology and physical conformations can be better investigated. Previously reported SANS experiments have used cyclic and linear polystyrene samples; therefore, our work allowed for direct comparison using a contrasting (structurally and sterically) polymer. We compared SANS results of cyclic and linear PLA samples with various microstructures and molecular weights at two different temperatures, allowing for comparison with a wide range of variables. The results followed the trends of previous experiments, but much greater differences in the effective polymer-solvent interaction parameters between cyclic and linear forms of PLA were observed, implying that the small form factor and hydrogen bonding in PLA allowed for much more compact conformations in the cyclic form only. Also, the polymer microstructure was found to influence polymer-solvent interaction parameters substantially. These results illustrate how the difference in polymer-solvent interactions between cyclic and linear polymers can vary greatly depending on the polymer in question and the potential of neutron scattering as a tool for identification and characterization of the cyclic topology.

Synthesis and characterization of a polystyrene-type polymer bearing a cyclic perfluoroalkylene group

Perfluoroalkyl-containing aromatic compounds are predicted to have fascinating material properties. In this work, a styrene derivative bearing a cyclic perfluoroalkylene group, –(CF2)4–, was synthesized and polymerized to afford the corresponding polymer. The styrene derivative was obtained via the Ullmann coupling of I–(CF2)4–I with 3′-bromo-4′-iodoacetophenone, NaBH4 reduction of the ketone moiety, and dehydration using P4O10. Free-radical polymerization (FRP) of the styrene derivative afforded polymer with number-average molecular weight (Mn) and dispersity index (DI) of 1.1 × 104 and 3.1, respectively. The thermal stability of the synthesized polymer (Td10% 359 °C, Tg 149 °C) was greater than the previously reported n-C4F9-substituted polystyrene (Td10% 296 °C, Tg 19 °C). The increased thermal stability of the newly synthesized polymer is hypothesized to arise from the lack of terminal CF3 moieties. The cyclic perfluoroalkylene-substituted polystyrene exhibited hydro- and oleo-phobicities comparable to those of the n-C4F9-substituted polystyrene, suggesting that the introduction of cyclic perfluoroalkylene groups instead of the commonly used Rf groups may have the potential to develop thermo-resistant polymers with hydro- and lipo-phobicity. Thew newly synthesized polymer is suitable for a variety of applications requiring high-Tg optical polymeric materials.

Synthesis of cyclic polystyrene in supercritical carbon dioxide green solvent

This study presents the synthesis of cyclic polystyrene (cPS) in the supercritical carbon dioxide (SC-CO2) media for the first time. For this purpose, first of all α−ω difunctionalized polystyrene was prepared in the SC-CO2 solvent within the pressure range from 100 to 230 bar and at a temperature below the conventional methods 80℃. The end-to-end reaction method was then used to make cPS in SC-CO2 solvent with CH2Cl2 as a co-solvent. The effects of several factors such as pressure, time, and initiator concentration on polymer yield, morphology, and molecular weight were studied. FTIR,1H NMR, GPC, HPLC, DSC, TGA and SEM analyses were used to characterize the product and evaluate the effect of mentioned factors. The results indicated a prominent influence of SC-CO2 pressure on the product. Applying a green solvent, such as SC-CO2 allows us to produce a clean polymer with lower molecular weight and higher environmental compatibility.

Enhanced Dielectric Strength and Capacitive Energy Density of Cyclic Polystyrene Films.

The maximum capacitive energy stored in polymeric dielectric capacitors, which are ubiquitous in high-power-density devices, is dictated by the dielectric breakdown strength of the dielectric polymer. The fundamental mechanisms of the dielectric breakdown, however, remain unclear. Based on a simple free-volume model of the polymer fluid state, we hypothesized that the free ends of linear polymer chains might act as “defect” sites, at which the dielectric breakdown can initiate. Thus, the dielectric breakdown strength of cyclic polymers should exhibit enhanced stability in comparison to that of their linear counterparts having the same composition and similar molar mass. This hypothesis is supported by the ∼50% enhancement in the dielectric breakdown strength and ∼80% enhancement in capacitive energy density of cyclic polystyrene melt films in comparison to corresponding linear polystyrene control films. Furthermore, we observed that cyclic polymers exhibit a denser packing density than the linear chain melts, an effect that is consistent with and could account for the observed property changes. Our work demonstrates that polymer topology can significantly influence the capacitive properties of polymer films, and correspondingly, we can expect polymer topology to influence the gas permeability, shear modulus, and other properties of thin films dependent on film density.

Effects of chain ends and densities on the glass transition of polymer thin films probed by linear and cyclic polystyrene

There are substantial debates on the origin of glassy dynamic changes of nanoconfined polymers. We measure the glass transition temperature ( T g ) of linear and cyclic polystyrene thin films, and find that the T g of cyclic polystyrene nearly remains constant when the film thickness is decreased. The T g of analogous linear polystyrene, however, substantially decreases with decreasing film thickness. When the thin films are patterned into line gratings with a height of about 69 nm, T g -reduction is observed in both linear and cyclic polystyrene. The magnitude of T g -reduction of cyclic polystyrene is about 7 K regardless the molecular weight, whereas the T g -reduction of linear polystyrene ranges from about 20 K to 6 K depending on the molecular weight. These experimental results indicate that the effect of chain ends alone cannot explain the mechanism of confinement-induced T g depression, and the decreased chain density at interfaces may play an overwhelm role. • T g of linear polystyrene thin films decreases with decreasing thickness. • T g of cyclic polystyrene thin films remains constant when thickness is decreased. • T g reduction is observed in linear and cyclic polystyrene in nanostructures. • Decreased chain density at interfaces play an overwhelm role in T g reduction.

Study of Linear and Cyclic Graft Polystyrenes with Identical Backbone Contour in Dilute Solutions: Preparation, Characterization, and Conformational Properties

Study of Linear and Cyclic Graft Polystyrenes with Identical Backbone Contour in Dilute Solutions: Preparation, Characterization, and Conformational Properties

Optimization of injection molded polymer lab-on-a-chip for acoustic blood plasma separation using virtual design of experiment

This study presents the development towards the optimization and manufacturing of a novel cost-effective fully polymer-based ultrasound actuated chip as a Point-of-care (POC) diagnostic platform for blood plasma separation and analysis. The chip was designed following multi-physic functional simulation to obtain optimal dimensions with respect to blood separation enhanced capacity. Initial dimensional guidelines showed most favorable performance to be achieved with design dimensions of 150 µm height, 375 µm width and 34 mm length. The chip encompasses a micro-fluidic channel with a relatively long length compared to the height and the width. As such, main manufacturability challenge is represented by the capability to maintain the channel dimensional conformance throughout the entire length. In order to tackle the challenge and optimize the results, developing a feedback loop was initiated for the device process development where the data of the preliminary micro-injection molding (µIM) production was exploited to implement a simulation-based full-factorial virtual design of experiment (DOE) for all the four materials of interest: polymethyl methacrylate (PMMA), cyclic olefin copolymer (COC), polycarbonate (PC) and polystyrene (PS). The four essential µIM parameters namely, mold temperature, melt temperature, injection velocity and packing pressure were used as factors. Overall, simulations were performed based on the virtual DOE inputs for the four aforementioned materials. The input data for the utilized process parameters in the virtual DOE was provided by our first production batch. Ultimately, in the case of PMMA, parts were molded and characterized based on the process settings that had demonstrated the lowest linear shrinkage in our entire virtual DOE responses. For the linear shrinkage of these parts, a respective width and height difference of 1% and 3.3% between the simulations and production results were obtained. Moreover, as a secondary study sink marks were also inspected and minimized through simulations. Initially, sink marks as deep as 80 µm were spotted on the chip. After the use of optimization cycle the value decreased to as low as 10 µm. The results confirm the positive impact of the virtual experiments for future rapid assessment of potential new chip designs.

A versatile ring-closure method for efficient synthesis of cyclic polymer and tadpole-shaped copolymer

In this study, an efficient strategy was presented to prepare monocyclic polymers via combination of reversible addition-fragmentation chain transfer (RAFT) polymerization and light-induced cycloaddition reaction, and tadpole-shaped copolymer was further synthesized via ring-opening polymerization (ROP) using cyclic polystyrene (C-PS) as macroinitiator. A series of well-defined α, ω-hetero bifunctional homopolymers with furan-protected maleimide and o-methylbenzaldehyde terminals, including polystyrene (PS), poly (N, N-dimethylacrylamide) (PDMA) and poly (N-isopropylacrylamide) (PNIPAAm) were prepared via RAFT polymerization. After deprotection, highly active maleimide group at the end of linear polymer coupled intramolecularly with photoenol structure (photoisomer of o-methylbenzaldehyde) via Diels-Alder cycloaddition reaction under 365 nm UV irradiation in dilute solution, leading to the formation of cyclic polymer. The monocyclic polymers were characterized with 1H NMR, UV–Vis spectroscopy, gel permeation chromatography (GPC) and MALDI-TOF MS. Furthermore, the C-PS containing hydroxyl group was used as macroinitiator to prepare tadpole-shaped copolymer CPS-b-PCL via the ROP of ε-caprolactone.

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.

Liquid chromatography at critical conditions (LCCC): Capabilities and limitations for polymer analysis

This paper investigates liquid chromatography at critical condition (LCCC) for polymer analysis. Based on controversial claims on the separation of cyclic polymers from linear analogues in the literature, the efficiency of LCCC for separation and purity analysis is questioned. Polyisobutylene (PIB) and poly(3,6-dioxa-1,8-octanedithiols) (polyDODT) were used for the study. The structure of low molecular weight cyclic and linear polyDODT was demonstrated by MALDI-ToF. NMR did not show the presence of thiol end groups in higher molecular weight PIB-disulfide and polyDODT samples, so they were considered cyclic polymers. When a low molecular weight polyDODT oligomer with only traces of cycles, as demonstrated by MALDI-ToF, was mixed with an Mn = 27 K g/mol cyclic sample, LCCC did not detect the presence of linear oligomers at 6 wt%. Based on the data presented here, it can be concluded that the LCCC method is not capable of measuring <6 wt% linear contamination so earlier claims for cyclic polystyrene (PS) samples purified by LCCC having <3% linear contaminants are questioned.

The non-free draining effect for small cyclics in solution

It is commonly believed that cyclic polymers have smaller hydrodynamic radii (Rhs) than their linear counterparts due to the constraint topology. This consensus is based on the results from polymers with high molecular weights (MWs), where the chains are considered as coils. Herein, we investigate the Rhs of low MW cyclic polystyrenes (3000–11,000), cyclic alkanes and their linear counterparts by diffusion ordered NMR spectroscopy. For the first time, a non-free draining effect for small cyclics is revealed, due to the depletion of solvent molecules to pass through the rings, which leads to the increment of hydrodynamic size. With the decrement of polymer MW, this effect becomes more significant and Rhs of cyclic polystyrenes approach that of their linear counterparts. Below a crossover point at MW around 660, Rhs of cyclic polystyrenes are larger than their linear counterparts from the established scaling laws. This is supported by the observed phenomena that cycloalkanes have larger Rhs than their n-alkane counterparts. The results are helpful in understanding the thermodynamic behaviors of small cyclics in solution, especially those bioactive small ring molecules in life science.

A facile approach for preparing tadpole and barbell-shaped cyclic polymers through combining ATRP and atom transfer radical coupling (ATRC) reactions

A facile strategy was developed to prepare active tadpole-shaped cyclic polystyrene, which was then used to fabricate symmetrical barbell polystyrene.

Universal Synthetic Strategy for the Construction of Topological Polystyrenesulfonates: The Importance of Linkage Stability during Sulfonation.

Polystyrenesulfonate (PSS), as one of the most important categories of polyelectrolytes, has received increasing attention due to its great potential in the applications of energy- and biomedical-related fields. However, most of the previous studies only focused on linear PSS and its derivatives, but little attention was paid to nonlinear topological PSSs. So far, the synthesis of nonlinear PSSs with well-defined structures is still a challenging task, and the main obstacle lies in the stability issue of functional chemical linkages during the sulfonation process of polystyrene (PS) precursors, such as the carbon-oxygen-containing linkages. Herein, by rationally designing the chemical structure of the functional linkage, we introduce a versatile and efficient strategy for the preparation of topological PSSs. Specifically, by embedding firm triazole linkages (without carbon-oxygen linkages) into the backbone structure of cyclic and hyperbranched PS precursors, the backbone and functional linkages are found to present excellent chemical stability under certain sulfonation conditions, which eventually lead to the successful preparation of cyclic and hyperbranched PSSs. By using two sets of PSS samples with varied molar masses, the scaling relations between the number of repeating units and the sedimentation coefficient are established for both linear and cyclic PSSs. We believe that our proposed synthetic strategy is universal and could be extended to the synthesis of other types of topological PSSs.

Glass transition temperature of cyclic polystyrene and the linear counterpart contamination effect

We present here a systematic investigation on the glass transition temperature (Tg) for a series of highly purified cyclic polystyrene (c-PS) samples with molecular weight (MW) varying from 3300 to 13,400. Compared with their linear counterparts, c-PS samples show much higher Tg and exhibit weak Tg-MW dependence. By blending linear polystyrenes with c-PS, the linear polymer contamination effect on the Tg of c-PS was systematically investigated. It was found that the measured Tg of the mixtures increases with the decrease of linear polymer content and the relationship is consistent with Fox equation. These results are helpful to understand the origin of previously reported different Tg-MW relationship for c-PS.

Anomalous Confinement Slows Surface Fluctuations of Star Polymer Melt Films.

The unusually large film thickness at which confinement effects manifest themselves in surface fluctuations of unentangled four-arm star polymers has been defined using film thicknesses from 10Rg to 107Rg. For 15k four-arm star polystyrene (SPS), confinement appears at a thickness between 112 nm (40Rg) and 72 nm (26Rg), which is remarkably larger than the thicknesses at which confinement appears for unentangled 6k linear (<15 nm, <7Rg) and 6k and 14k cyclic (24 and 22 nm, respectively) polystyrenes. Data for 15k star films can be rationalized using a two-layer model with a 17 nm (6Rg) thick highly viscous layer at the substrate, which is significantly thicker than the 1Rg thick "irreversibly adsorbed" layer. For a 29 nm (10Rg) thick film, more striking confinement occurs due to the combined influence of both interfaces. These results underscore the extraordinary role long-chain branching plays in dictating surface fluctuations of thin films.

Self-Assembly of Patterned Porous Films from Cyclic Polystyrenes via the Breath Figure Method

The architecture of polymers plays a crucial role in self-assembly processes. However, the effect of end groups is still not understood thoroughly in many processes including the breath figure method, which is effective for preparing patterned porous films. Herein, we synthesized a series of well-defined cyclic polystyrenes by the combination of atom transfer radical polymerization and azide–alkyne click cyclization and investigated the self-assembly behaviors. The corresponding linear polymers were also compared. Results indicate that polar end groups dramatically improve the regularity of the self-assembled films. For cyclic polystyrenes without any end group, the ability to form patterned porous films is between two groups of linear samples. On the one hand, the results confirm the effect of polar end groups in the breath figure method. On the other hand, the impact of cyclic topology is also verified. This work reveals the nature of stabilization of templating droplets via the polymers by the measurem...

Influence of Constraints within a Cyclic Polymer on Solution Properties.

Cyclic polymers with internal constraints provide new insight into polymer properties in solution and bulk and can serve as a model system to explain the stability and mobility of cyclic biomacromolecules. The model system used in this work consisted of cyclic polystyrene structures, all with a nearly identical molecular weight, designed with 0-3 constraints located at strategic sites within the cyclic polymer, with either 4 or 6 branch points. The total number of branch points (or arms) within the cyclic ranged from 0 to 18. Molecular dynamic (MD) simulations showed that as the number of arms increased within the cyclic structure, the radius of gyration and the hydrodynamic radius generally decreased, suggesting the greater number of constraints resulted in a more compact polymer chain. The simulations further showed that the excluded volume was much greater for the cyclics compared to a linear polymer at the same molecular weight. The spirocyclic, a structure consisting of three rings joined in series, showed significant excluded volume effects in agreement with experimental data; the reason for which is unclear at this stage. Interestingly, under a size exclusion chromatography flow, the radius of hydration for all the cyclic structures increased compared with the DLS data, and could be explained from the greater swelling of the rings perpendicular to the flow found from previous simulations on rings. This data suggests that the greater compactness, greater excluded volume and structural rearrangements under flow of constrained cyclic polymers could be used to provide a physical basis for understanding greater stability and activity of cyclic biological macromolecules.

Preparation of low molecular weight cyclic polystyrenes with high purity via liquid chromatography at the critical condition

Cyclic polymers synthesized by ring-closure method from linear precursors contain some of linear contaminates. In this work, the origin of linear contaminates in cyclic polystyrenes (c-PS) is demonstrated by the coupling of liquid chromatography at the critical condition (LCCC) with matrix-assisted laser desorption/ionization time-of-flight mass spectra. The linear contaminates are revealed to be the “dead” chains during ATRP by chain termination, the unreacted linear polystyrene (l-PS) precursors, and the dimers by the imperfect ring-closure reaction. The c-PS are purified by LCCC fractionation, and the results show the LCCC fractionation at the critical adsorption point (CAP) of c-PS is more efficient than that at the CAP of linears for low molecular weight (<10,000) PS. A two-step LCCC method is presented for the preparation of c-PS with high purity (>99.6%) via the tandem-coupled LCCC fractionation at the CAP of l-PS and at the CAP of c-PS.

Intrinsic Viscosity of Cyclic Polystyrene

The intrinsic viscosity of cyclic polystyrenes (C-PS) and linear polystyrenes (L-PS) with molecular weight (MW) ranging from 16K to 370K was measured in THF using size exclusion chromatography coupled with a triple detection system. The C-PS samples were prepared by a ring-closure reaction of telechelic linear precursor synthesized by anionic polymerization. As-synthesized C-PS samples after the ring-closure reaction contain various byproducts, and they were fractionated by liquid chromatography at the critical condition to obtain highly pure C-PS. While the intrinsic viscosity of L-PS agrees well with the literature data, C-PS shows significantly lower value than the literature values. The Mark–Houwink exponent of C-PS is 0.67, somewhat lower than 0.70 for L-PS in the good solvent over the MW range examined. Therefore, the ratio of the intrinsic viscosity of C-PS to L-PS (g′ = [η]C/[η]L) in THF is not MW independent but decreases as MW increases (0.63 ≥ [η]C/[η]L ≥ 0.57). The trend of intrinsic viscosity...

Effects of polymer topology on biointeractions of polymer brushes: Comparison of cyclic and linear polymers

Cyclic polymers, having no chain ends, are in contrast to their linear counterparts with respect to topology and related properties. While the behavior of cyclic polymers in solution is well investigated, there is little information on the effects of cyclic chain topology on surfaces grafted with these polymers. In particular, the effects of topology on the interactions of such surfaces with biological systems are unknown. In this work, we prepared gold surfaces modified with either cyclic or linear polystyrene (CPS, LPS) using a grafting-to strategy, and used these surfaces to investigate the effects of chain topology on their biointerfacial interactions. It was shown that compared to LPS with similar molecular weight, the smaller hydrodynamic radius of CPS leads to brushes of higher chain density, and that the higher chain density facilitates the adsorption of larger proteins but suppresses the adsorption of smaller ones. However, no significant differences in bacterial attachment or mammalian cell proliferation between CPS and LPS brushes were found, indicating that topological effects are absent for the larger entities.