Cyclic Polymers Research Articles

Topological entrapment of macromolecules during the formation of metal-organic framework.

Here we present our preliminary results on a novel approach to encapsulate large guest molecules in nanoporous materials, metal-organic frameworks (MOFs), via a newly discovered in situ crystal formation. This method has exciting prospects not only in the design of new organic/inorganic hybrids but also in capturing and separating molecules that are significantly larger than the actual pore size of the host MOF.

Efficient preparation of cyclic polymers via pre-stacking of photo-cycloaddition capable end groups and a continuous-flow technique

A series of well-defined monocyclic polymers were efficiently synthesized by pre-stacking of photo-cycloaddition capable end groups and a continuous-flow technique.

Properties of polyrotaxane modified maleimide resin with a phase‐separated structure

AbstractPolyrotaxane (PR) is a supramolecular polymer in which an axial polymer extends through multiple cyclic molecules. Specifically, PR comprises polyethylene glycol, α‐cyclodextrin and adamantane as the axial polymer, cyclic molecule and terminal blocking group, respectively. PR is a useful stress relaxation material because the cyclic polymers can freely slide and rotate in cyclic motions on the axial polymer. In this study, 4,4′‐diphenylmethane bismaleimide (BMI)/2,2′‐diallylbisphenol A (DABPA) resin was blended with PR as a toughness modifier; the effect of PR on the cured properties of BMI/DABPA resin is reported and the properties are related to the phase structure of BMI/DABPA/PR alloy. The BMI/DABPA/PR alloy formed a microphase‐separated structure with PR particles dispersed in the BMI/DABPA resin matrix. Increasing PR concentration greatly improved the toughness, impact resistance and adhesiveness of the resin. The glass transition temperature also increased because the numerous hydroxyl groups of α‐cyclodextrins in PR formed intermolecular hydrogen bonds in the BMI/DABPA resin, forming a dense network structure. In contrast, owing to the small concentration ratio of PR to BMI/DABPA resin, the dielectric constant, dielectric loss tangent and water absorption were only slightly higher than those of the unmodified resin. © 2022 Society of Industrial Chemistry.

Effect of Water on the Mechanical Properties of Cyclic Peptide Polymers.

Biomaterials are an important source of inspiration for the development of strong and tough materials. Many improved and optimized synthetic materials have been recently developed utilizing this bioinspiration concept. Using side-chain-to-side-chain polymerization of cyclic β-peptide rings, a novel class of nanomaterials was recently introduced with outstanding mechanical properties such as toughness values greater than natural silks. In this work, molecular dynamics is used to understand the mechanics of side-chain-to-side-chain polymerization of cyclic β-peptide rings. Unbiased steered molecular dynamics simulations are used to show the difference in the strength of polymerized and unpolymerized processing of similar cyclic rings. The simulations are performed both in aqueous and vacuum environments to capture the role of water on the mechanical properties of the cyclic peptides. Our results show that unpolymerized peptides behave like brittle material, whereas polymerized ones can withstand some stress after initial failure with large values of strain-to-failure. Finally, we have shown that the strength of cyclic peptides in water is higher than in a vacuum.

Cycling a Tether into Multiple Rings: Pt-Bridged Macrocycles for Differentiated Guest Recognition, Pseudorotaxane Transformations, and Guest Capture and Release.

Macrocycle engineering is a key topic in supramolecular chemistry. When synthesizing a ring, one can obtain either complex mixtures of macrocycles of different sizes or a single ring if a template is utilized. Here, we unite these approaches along with post-synthetic modifications to transform a single tether into multiple rings-up to five per tether. The macrocycles contain two bridged phenylpyridine ligands that are connected through a Pt atom, which defines the rings' shape, size, and host activity. All rings undergo redox reactions (between PtII and PtIV ) that allow for large conformational changes. Their reactivity, together with their host performance, is a convenient way to control the capture and release of guests, to mediate ring transformations, and to control pseudorotaxane-to-pseudorotaxane conversions. This novel approach could serve to assemble other libraries of small ring molecules, create cyclic polymers bridged by responsive-at-metal nodes, and produce processable mechanically interlocked molecules.

Cycling a Tether into Multiple Rings: Pt‐Bridged Macrocycles for Differentiated Guest Recognition, Pseudorotaxane Transformations, and Guest Capture and Release

AbstractMacrocycle engineering is a key topic in supramolecular chemistry. When synthesizing a ring, one can obtain either complex mixtures of macrocycles of different sizes or a single ring if a template is utilized. Here, we unite these approaches along with post‐synthetic modifications to transform a single tether into multiple rings—up to five per tether. The macrocycles contain two bridged phenylpyridine ligands that are connected through a Pt atom, which defines the rings’ shape, size, and host activity. All rings undergo redox reactions (between PtII and PtIV) that allow for large conformational changes. Their reactivity, together with their host performance, is a convenient way to control the capture and release of guests, to mediate ring transformations, and to control pseudorotaxane‐to‐pseudorotaxane conversions. This novel approach could serve to assemble other libraries of small ring molecules, create cyclic polymers bridged by responsive‐at‐metal nodes, and produce processable mechanically interlocked molecules.

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.

Scalable Synthetic Route to PDMS Ring Polymers in High Yields from Commercially Available Materials Using the Piers-Rubinsztajn Reaction.

While cyclic polymers have intrigued researchers for their novel set of architecture-driven rheological interactions, the possibility of incorporating them in topological systems has been limited by the availability of large ring polymers. Thus, the need for scalable methods to produce ring polymers has become apparent. Here, a facile method to prepare polysiloxane ring polymers by means of Piers-Rubinsztajn chemistry is presented. The one-pot nature and commercial availability of reagents additionally confirm the applicability of the method for large-scale production. Furthermore, a highly efficient yet simple purification method was developed for the isolation of pure ring polymers without linear side products.

Ring-Opening Co- and Terpolymerization of Epoxides, Cyclic Anhydrides, and l-Lactide Using Constrained Aluminum Inden Complexes.

Seven constrained aluminum inden complexes having different substituents and diamine backbones were developed for the ring-opening copolymerization (ROCOP) of epoxides and bulky cyclic anhydrides giving alternating polyesters with Tg ranging from 49 to 226 °C. Among several catalyst/cocatalyst screenings, the aluminum inden complex having a rigid phenylene backbone coupled with 4-dimethylaminopyridine showed the best performance giving linear polyesters. In the case of cyclohexene oxide (CHO) and succinic anhydride (SA), the linear poly(CHO-alt-SA) could be transformed to cyclic polymer when the polymerization was left under prolonged reaction time to induce intramolecular transesterification. The kinetic studies of the ROCOP revealed a zeroth-order dependence on cyclic anhydride and a first-order dependence on epoxide and the catalyst. The catalysts can be extended efficiently to the one-pot CHO/PA/l-lactide terpolymerization giving uncommon tapered copolymers of poly(CHO-alt-PA) and PLA via switchable polymerization.

Injection Molding of Thermoplastics for Low-Cost Nanofluidic Devices

Thermoplastic micro- and nanofluidics are increasing in popularity due to their favorable chemical and physical properties as an alternative to poly(dimethyl siloxane) (PDMS)-based devices, which are more widely used in academia. Additionally, their fabrication is compatible with industrial processes, such as hot embossing and injection molding. Nevertheless, producing devices with sub-micrometer channel heights and low roughness while retaining high-throughput molding remains challenging. This article details the combination of grayscale e-beam lithography (g-EBL) and injection molding as a fabrication route for capillary 3D thermoplastic nanofluidic devices with unprecedented accuracy in the sub-micrometer range. We employed g-EBL to pattern the device profile in a poly(methyl methacrylate) (PMMA)-based resist, which served as a substrate for the subsequent fabrication of a negative nickel mold by using electroforming. These molds are used to fabricate devices in PMMA and cyclic olefin polymers (COP) using injection molding. We show that the 3D height profile of the nanofluidic devices is maintained throughout the entire replication cycle within very tight tolerances, retaining its nanoscale topography on a millimeter-length scale. Moreover, somewhat surprisingly, the roughness in the inflow section of the devices was significantly reduced, which we attribute to the nickel mold fabrication. Last, we show that the capillary-driven devices can be used to size-dependently trap nanoparticles of various sizes in a reliable and facile manner while only requiring a 4 μL sample volume. The presented device and fabrication procedure paves the way for applications in various scientific fields, ranging from immunology to neurology and material science, in a cost-effective manner.

Recyclable cyclic bio-based acrylic polymer via pairwise monomer enchainment by a trifunctional Lewis pair.

The existing catalyst/initiator systems and methodologies used for the synthesis of polymers can access only a few cyclic polymers composed entirely of a single monomer type, and the synthesis of such authentic cyclic polar vinyl polymers (acrylics) devoid of any foreign motifs remains a challenge. Here we report that a tethered B-P-B trifunctional, intramolecular frustrated Lewis pair catalyst enables the synthesis of an authentic cyclic acrylic polymer, cyclic poly(γ-methyl-α-methylene-γ-butyrolactone) (c-PMMBL), from the bio-based monomer MMBL. Detailed studies have revealed an initiation and propagation mechanism through pairwise monomer enchainment enabled by the cooperative and synergistic initiator/catalyst sites of the trifunctional catalyst. We propose that macrocyclic intermediates and transition states comprising two catalyst molecules are involved in the catalyst-regulated ring expansion and eventual cyclization, forming authentic c-PMMBL rings and concurrently regenerating the catalyst. The cyclic topology of the c-PMMBL polymers imparts an ~50 °C higher onset decomposition temperature and a much narrower degradation window compared with their linear counterparts of similar molecular weight and dispersity, while maintaining high chemical recyclability.

Efficient Cyclization of Linear Polymer with Pseudopolyrotaxane Assistance

The physical properties of cyclic polymers differ from those of linear polymers. To prepare cyclic polymers, the ends of a linear polymer must intramolecularly react. Cyclic polymers are typically synthesized at low concentration because intermolecular linkage is preferential to intramolecular linkage at high concentrations. Therefore, preparation of cyclic polymers at high concentrations is difficult. This study demonstrates a new approach to obtain cyclic polymers from highly concentrated polymer solutions using pseudo-polyrotaxanes (pPRxs). Cyclic polymers are prepared by penetrating a linear polymer into the cavity of a cyclic host to form pPRx and then the ends of the linear polymer are subsequently connected. Our approach allows the synthesis of cyclic polymers at concentration that do not allow conventional cyclic polymer synthesis. Specifically, although without pPRx, almost no cyclic polymers were obtained (<1%), with pPRx, the cyclic polymer was obtained as the main product (proportion of cyclic PEG 14%).

Scalable preparation and direct visualization of cyclic polymers via self-folding cyclization technique

Scalable preparation and direct visualization of cyclic polymers via self-folding cyclization technique

Eliminating the Tg-Confinement Effect in Polystyrene Films: Extraordinary Impact of a 2 mol % 2-Ethylhexyl Acrylate Comonomer

Nanoconfined polystyrene (PS) films exhibit substantial reductions in glass transition temperature (Tg) from bulk Tg. By incorporating 2–6 mol % 2-ethylhexyl acrylate (EHA) into styrene (S)-based random copolymers and characterization via ellipsometry, we show that the Tg-confinement effect for films supported on silicon wafers is eliminated within experimental uncertainty down to a 15 nm thickness. Previous studies have neutralized this confinement effect by the copolymerization of minority levels of styrene with majority levels of a comonomer that can undergo hydrogen bonding with hydroxyl groups on a substrate surface, thus counteracting the free-surface-based Tg reduction with a Tg increase near the substrate interface. In contrast, the Tg-confinement effect is eliminated in our 2–6 mol % EHA copolymers independent of the presence of substrate surface hydroxyl groups. Thus, polymer–substrate interfacial hydrogen bonds play no significant role in neutralizing the Tg-confinement effect in the S-based copolymers with 2–6 mol % EHA. Instead, the neutralization must come from suppressing free-surface effects via very low levels of an EHA monomer in the copolymer. Importantly, this simple approach to eliminate the Tg-confinement effects with as little as 2 mol % EHA is accompanied by only a minor change in bulk Tg and no change in thermal expansivity within the experimental error relative to PS. Furthermore, this approach cannot be generalized to other acrylate comonomers, such as n-butyl acrylate. It neither requires complex syntheses to achieve dense brush, bottlebrush, or cyclic or ring polymer topologies nor the addition of a plasticizer or a surfactant to the polymer, earlier approaches that suppressed the Tg-confinement effect in PS. For a 99:1 mol % S/EHA copolymer, the confinement effect is nearly identical to that of PS, indicating that a critical yet low EHA level is needed to eliminate the effect.

Influence of UV Radiation on Mechanical Properties of Polymer Optical Fibers.

This paper presents an analysis of the mechanical properties of different polymer optical fibers (POFs) at ultraviolet (UV) radiation conditions. Cyclic transparent optical polymer (CYTOP) and polymethyl methacrylate (PMMA) optical fibers are used in these analyses. In this case, the fiber samples are irradiated at the same wavelength, pulse time and energy conditions for different times, namely, 10 s, 1 min, 2 min and 3 min. The samples are tested in tensile tests and dynamic mechanical thermal analysis (DMTA) to infer the variation in the static and dynamic properties of such fibers as a function of the UV radiation condition. Furthermore, reference samples of each fiber (without UV radiation) are tested for comparison purposes. The results show a lower UV resistance of PMMA fibers, i.e., higher variation in the material features in static conditions (Young's modulus variation of 0.65 GPa). In addition, CYTOP fiber (material known for its high UV resistance related to its optical properties) also presented Young's modulus variation of around 0.38 GPa. The reason for this reduction in the moduli is related to possible localized annealing due to thermal effects when the fibers are subjected to UV radiation. The dynamic results also indicated a higher variation in the PMMA fibers storage modulus, which is around 30% higher than the variations in the CYTOP fibers when different radiation conditions are analyzed. However, CYTOP fibers show a smaller operational temperature range and higher variation in the storage modulus as a function of the temperature when compared with PMMA fibers. In contrast, PMMA fibers show higher variations in their material properties when subjected to oscillatory loads at different frequency conditions. Thus, the results obtained in this work can be used as guidelines for the influence of UV radiation in POFs not only for the material choice, but also on the limitations of UV radiation in the fabrication of the grating as well as in sensor applications at UV radiation conditions.

Utilization of CO2 in supercritical conditions for the synthesis of cyclic poly (N-isopropylacrylamide) via emulsion and homogeneous reactions

In this study, cyclic poly (N-isopropylacrylamide) (cPNIPAAM) was synthesized in supercritical carbon dioxide (SC-CO2) using emulsion and homogeneous reactions for the first time. This was accomplished by applying free radical polymerization and nitroxide compounds to produce low molecular weight precursors in the SC-CO2 solvent. The cyclization reaction occurred in a homogeneous phase in the SC-CO2 solvent, with dimethylformamide (DMF) serving as a co-solvent for dissolving the linear precursor. This reaction was also conducted in emulsion of SC-CO2 in water. The effects of pressure and time on the morphology, molecular weight, and yield of a difunctionalized chain were investigated, where a higher pressure led to a higher yield. The maximum yield was 64% at 23 MPa, and the chain molecular weight (Mw) was 4368 (gr/mol). Additionally, a lower pressure reduced the solubility of materials (particularly terminator) in SC-CO2 and resulted in a chain with a higher molecular weight 9326 (gr/mol), leading to a lower conversion. Furthermore, the effect of cyclization reaction types on the properties of cyclic polymers was investigated. In cyclic reactions, the addition of DMF as a co-solvent resulted in the formation of a polymer with a high viscosity average molecular weight (Mv) and a high degree of cyclization (100%), whereas the CO2/water emulsion resulted in the formation of a polymer with a lower Mv and increased porosity. Polymers were characterized by 1HNMR, FTIR, DSC, TLC, GPC, and viscometry tests. The results were presented and thoroughly discussed.

Reproducible and controlled peptide functionalization of polymeric nanoparticles

Polymeric nanoparticles containing multiple amines and carboxylates have been frequently used in drug delivery research. Reproducible and controlled conjugation among these multifunctional biomaterials is necessary to achieve efficient drug delivery platforms. However, multiple functional groups increase the risk of unintended intramolecular/intermolecular reactions during conjugation. Herein, conjugation approaches and possible undesired reactions between multi-amine functionalized peptides, multi-carboxylate functionalized polymers, and anhydride-containing polymers [Poly(styrene-alt-maleic anhydride)-b-poly(styrene)] were investigated under different conjugation strategies (carbodiimide chemistry, anhydride ring-opening via nucleophilic addition elimination). Muti-amine peptides led to extensive crosslinking between polymers regardless of the conjugation chemistry. Results also indicate that conventional peptide quantification methods (i.e., o-phthalaldehyde assay, bicinchoninic acid assay) are unreliable. Gel permeation chromatography (GPC) provided more accurate qualitative and quantitative evidence for intermolecular crosslinking. Crosslinking densities were correlated with higher feed ratios of multifunctional peptides and carbodiimide coupling reagents. Selectively protected peptides (Lys-Alloc) exhibited no crosslinking and yielded peptide-polymer conjugates with controlled dispersity and molecular weight. Furthermore, anhydride ring-opening (ARO) nucleophilic addition elimination was successfully introduced as a facile yet robust peptide conjugation approach for cyclic anhydride-containing polymers.

A dispenser for cyclic polymers

A dispenser for cyclic polymers

Assembly of transmembrane pores from mirror-image peptides

Tailored transmembrane alpha-helical pores with desired structural and functional versatility have promising applications in nanobiotechnology. Herein, we present a transmembrane pore DpPorA, based on the natural pore PorACj, built from D-amino acid α-helical peptides. Using single-channel current recordings, we show that DpPorA peptides self-assemble into uniform cation-selective pores in lipid membranes and exhibit properties distinct from their L-amino acid counterparts. DpPorA shows resistance to protease and acts as a functional nanopore sensor to detect cyclic sugars, polypeptides, and polymers. Fluorescence imaging reveals that DpPorA forms well-defined pores in giant unilamellar vesicles facilitating the transport of hydrophilic molecules. A second D-amino acid peptide based on the polysaccharide transporter Wza forms transient pores confirming sequence specificity in stable, functional pore formation. Finally, molecular dynamics simulations reveal the specific alpha-helical packing and surface charge conformation of the D-pores consistent with experimental observations. Our findings will aid the design of sophisticated pores for single-molecule sensing related technologies.

Microcontact Printing of Biomolecules on Various Polymeric Substrates: Limitations and Applicability for Fluorescence Microscopy and Subcellular Micropatterning Assays.

Polymeric materials play an emerging role in biosensing interfaces. Within this regard, polymers can serve as a superior surface for binding and printing of biomolecules. In this study, we characterized 11 different polymer foils [cyclic olefin polymer (COP), cyclic olefin copolymer (COC), polymethylmethacrylate (PMMA), DI-Acetate, Lumirror 4001, Melinex 506, Melinex ST 504, polyamide 6, polyethersulfone, polyether ether ketone, and polyimide] to test for the applicability for surface functionalization, biomolecule micropatterning, and fluorescence microscopy approaches. Pristine polymer foils were characterized via UV–vis spectroscopy. Functional groups were introduced by plasma activation and epoxysilane-coating. Polymer modification was evaluated by water contact angle measurement and X-ray photoelectron spectroscopy. Protein micropatterns were fabricated using microcontact printing. Functionalized substrates were characterized via fluorescence contrast measurements using epifluorescence and total internal reflection fluorescence microscopy. Results showed that all polymer substrates could be chemically modified with epoxide functional groups, as indicated by reduced water contact angles compared to untreated surfaces. However, transmission and refractive index measurements revealed differences in important optical parameters, which was further proved by fluorescence contrast measurements of printed biomolecules. COC, COP, and PMMA were identified as the most promising alternatives to commonly used glass coverslips, which also showed superior applicability in subcellular micropatterning experiments.