Cyclization Of Polymers Research Articles

Proper adsorptive confinement for efficient production of cyclic polymers: a dissipative particle dynamics study.

Efficient production of cyclic polymers has been a hot topic in the past few decades. In this work, we found that an adsorptive porous template with an appropriate size has the capability to accelerate the ring closure of a linear polymer chain in a dilute solution with a higher yield. The restricted pore provides a confined space and the effect of its characteristics, such as pore size, shape and adsorption strength on cyclization time, is systematically studied by using dissipative particle dynamics simulations. As a prerequisite of cyclization in confinement, the entry process of linear precursors has been studied as well. Total production time is governed by a tradeoff between the size effect caused by decreasing the size of the pore and the adsorption of the pore. The strong size effect suppresses polymer entry but accelerates cyclization. The stronger adsorption promotes polymer entry but decelerates cyclization. According to our defined total production time, a small spherical confinement with strong adsorption results in a shorter total production time of cyclic polymers compared to that in free solution. If chain cyclization is permitted during its entering the confinement, the interplay between steric hindrance caused by pore size and adsorption provides an additional 'virtual' confinement at the boundary between confinement and free solution. In this case, an optimal cyclization time is observed with an appropriate adsorption strength under small confinement. Our results provide useful guidance for designing suitable porous templates for producing cyclic polymers with high efficiency.

A versatile synthetic strategy for macromolecular cages: intramolecular consecutive cyclization of star-shaped polymers.

Cage-shaped polymers, or "macromolecular cages", are of great interest as the macromolecular analogues of molecular cages because of their various potential applications in supramolecular chemistry and materials science. However, the systematic synthesis of macromolecular cages remains a great challenge. Herein, we describe a robust and versatile synthetic strategy for macromolecular cages with defined arm numbers and sizes based on the intramolecular consecutive cyclization of highly reactive norbornene groups attached to each end of the arms of a star-shaped polymer precursor. The cyclizations of three-, four-, six-, and eight-armed star-shaped poly(ε-caprolactone)s (PCLs) bearing a norbornenyl group at each arm terminus were effected with Grubbs' third generation catalyst at high dilution. 1H NMR, SEC, and MALDI-TOF MS analyses revealed that the reaction proceeded to produce the desired macromolecular cages with sufficient purity. The molecular sizes of the macromolecular cages were controlled by simply changing the molecular weight of the star-shaped polymer precursors. Systematic investigation of the structure-property relationships confirmed that the macromolecular cages adopt a much more compact conformation, in both the solution and bulk states, as compared to their linear and star-shaped counterparts. This synthetic approach marks a significant advance in the synthesis of complex macromolecular architectures and provides a platform for novel applications using cage-shaped molecules with polymer frameworks.

Tunable intramolecular cyclization and glass transition temperature of hyperbranched polymers by regulating monomer reactivity

In this work, the dialkynyl-functionalized A2 monomers with different alkyls and aromatic backbones were synthesized and employed as construction units to produce multi-component A2+B3 type hyperbranched polymers via copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC). The alkyl and aromatic backbones between two alkynyl groups were designed as hexyl (C6), dodecyl (C12), phenyl (Ar) and diphenyl (Ar2) to regulate monomer reactivity for investigating its effect on intramolecular cyclization and glass transition temperature (Tg). It was found that both the increase of backbone rigidity and the decrease of backbone length can enhance monomer reactivity. In addition, the differences of monomer reactivity can greatly influence the backbone compositions of hyperbranched polymers. High monomer reactivity can lead to high content of corresponding backbones, which can further control the degree of intramolecular cyclization and Tg of hyperbranched polymers. Thus, regulating monomer reactivity is an effective way to tune hyperbranched topology, backbone composition and physical properties.

Preparation of Distinct Ubiquitin Chain Reagents of High Purity and Yield

The complexity of protein ubiquitination signals derives largely from the variety of polyubiquitin linkage types that can modify a target protein, each imparting distinct functional consequences. Free ubiquitin chains of uniform linkages and length are important tools in understanding how ubiquitin-binding proteins specifically recognize these different polyubiquitin modifications. While some free ubiquitin chain species are commercially available, mutational analyses and labeling schemes are limited to select, marketed stocks. Furthermore, the multimilligram quantities of material required for detailed biophysical and/or structural studies often makes these reagents cost prohibitive. To address these limitations, we have optimized known methods for the synthesis and purification of linear, K11-, K48-, and K63-linked ubiquitin dimers, trimers, and tetramers on a preparative scale. The high purity and relatively high yield of these proteins readily enables material-intensive experiments and provides flexibility for engineering specialized ubiquitin chain reagents, such as fluorescently labeled chains of discrete lengths.

Strategy for Rapid and High-Purity Monocyclic Polymers by CuAAC “Click” Reactions

Cyclization of linear polymers by coupling end-groups together to form monocyclic polymers using the very fast Cu-catalyzed azide/alkyne cycloaddition (CuAAC) “click” reaction has been used for many polymer systems. However, the strategy based on the CuAAC methodology has not been guided by theory and relies on the very slow feed of polymer into a highly dilute reaction mixture of solvent and Cu catalyst. This leads to the production of monocyclic polymer in very low concentrations over long periods of time (>10 h) and at high temperatures (>100 °C). In this work we use the Jacobson−Stockmayer theory to predict the % monocyclic polystyrene (c-PSTY) in a one-pot reaction at 25 °C and find from an empirical relationship based on experimental diffusion-controlled rate coefficients for cyclization and condensation of α,ω-polymer chains that the Jacobson−Stockmayer theory is applicable for the CuAAC reaction. This means the % monocyclic can be predicted from theory and is independent of reaction rate parameters (such as catalytic concentration and temperature) and only dependent on polymer concentration. Given this quantitative knowledge, we investigated the effect of l-PSTY concentration, temperature, feed rate, Cu(I)Br concentration, and linear-PSTY molecular weight to find the optimum conditions for the synthesis of monocyclic polymers. It was found that for feed rates greater than or equal to the reaction rate high % monocyclic polymers could be formed. Our strategy allowed us to produce c-PSTY (with 51 monomer units) with high purity (>95%) at a concentration of 1.85 × 10−3 M in less than 9 min at 25 °C. This is the highest concentration, shortest time, and lowest temperature, to our knowledge, that anyone has used to obtain macrocycles in high purity by the CuAAC methodology. It also allowed us to develop strategies to produce high % monocyclic from parent l-PSTY with higher molecular weights.

Cooperative behavior of Escherichia coli cell-division protein FtsZ assembly involves the preferential cyclization of long single-stranded fibrils

A mechanism of noncooperative (isodesmic) assembly coupled with preferential cyclization of long polymers is proposed to explain the previously posed question of how a single-stranded filament of the bacterial cell-division protein FtsZ can assemble in an apparently cooperative manner. This proposal is based on results of GTP-mediated assembly of FtsZ from Escherichia coli that was studied under physiologically relevant steady-state solution conditions by a combination of methods including measurement of sedimentation velocity, atomic force and electron microscopy, and precipitation assays. Sedimentation-velocity experiments carried out at multiple protein concentrations reveal an essentially bimodal distribution of slowly sedimenting species and a relatively narrow distribution of rapidly sedimenting species that appears only above an apparent "critical concentration" of protein. In a precipitation assay, the amount of protein that pellets, which correlates with the fraction of rapidly sedimenting species observed in sedimentation-velocity experiments, increases linearly with the total concentration of protein in excess of the critical concentration. Sedimentation coefficients of the rapidly sedimenting fraction are qualitatively consistent with the presence of single-stranded cyclic oligomers with a size range of approximately 50-150 protomers, similar to polymeric single-stranded rings observed in atomic force and electron micrographs. The proposed model is in accord with the results obtained from our experimental observations.

Cyclic Polymers by Kinetically Controlled Step‐Growth Polymerization

AbstractThe theory of step‐growth polymerizations including the cascade theory is discussed in the light of new results focussing on the role of cyclization reactions. The identification of cyclic oligomers and polymers in reaction products of step‐growth polymerizations has been eased considerably by means of MALDI‐TOF mass spectrometry. Experimental examples concern syntheses of polyesters, polycarbonates, polyamides, polyimides, poly(ether sulfone)s, poly(ether ketone)s and polyurethanes. It was found in all cases that the percentage and molecular weight of the cycles increases when the reaction conditions favor high molecular weights. In the absence of side reactions all reaction products will be cycles when conversion approaches 100%. Cyclization may even take place in the nematic phase but even‐numbered cycles are favored over odd‐numbered ones due to electronic interactions between mesogens aligned in parallel. In contrast to Flory's cascade theory, cyclization also plays a decisive role in polycondensations of abn‐type monomers, and at 100% conversion all hyperbranched polymers have a cyclic core. Furthermore, it is demonstrated that in a2+b3 polycondensations intensive cyclization in the early stages of the process has the consequence that either no gelation occurs or the resulting networks consist of cyclic and bicyclic oligomers as building blocks. Finally, a comparison between cyclization of synthetic polymers and biopolymers is discussed. Schematic representation of a network structure mainly consisting of cyclic oligomers and multicyclic building blocks as derived from “a2” + “b3” polycondensation.magnified imageSchematic representation of a network structure mainly consisting of cyclic oligomers and multicyclic building blocks as derived from “a2” + “b3” polycondensation.

Synthesis of novel polyxanthenes from poly (arylene ether)s containing benzoyl groups

Poly(arylene ether)s (3), (4) containing pendant benzoyl groups as precursors for novel polyxanthenes (7), (8) were prepared by nucleophilic substitution reaction of 2,5-difluoro-4-benzoylbenzophenone (1) or 2,5-difluoro-4-(4-dodecylbenzoyl)-4′-dodecylbenzophenone (2) with hydroquinone derivatives in the presence of potassium carbonate in N,N-dimethylacetamide. The polycondensation proceeded smoothly at 165°C and produced poly(arylene ether)s with inherent viscosities up to 0.80 dL/g. The novel polyxanthenes were synthesized via the reduction of poly(arylene ether)s followed by the Friedel-Crafts cyclization of diol polymers. The structure of the polyxanthenes was characterized by 1H-NMR and IR spectroscopies. Polyxanthene 8 was quite soluble in chloroform and THF. The 10% weight loss temperature of polyxanthene 7 was 510°C in nitrogen and it was 90°C higher than the corresponding poly(arylene ether) 3. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 2267–2272, 1997

Synthesis of novel polyxanthenes from poly (arylene ether)s containing benzoyl groups

Poly(arylene ether)s (3), (4) containing pendant benzoyl groups as precursors for novel polyxanthenes (7), (8) were prepared by nucleophilic substitution reaction of 2,5-difluoro-4-benzoylbenzophenone (1) or 2,5-difluoro-4-(4-dodecylbenzoyl)-4'-dodecylbenzophenone (2) with hydroquinone derivatives in the presence of potassium carbonate in N,N-dimethylacetamide. The polycondensation proceeded smoothly at 165°C and produced poly(arylene ether)s with inherent viscosities up to 0.80 dL/g. The novel polyxanthenes were synthesized via the reduction of poly(arylene ether)s followed by the Friedel-Crafts cyclization of diol polymers. The structure of the polyxanthenes was characterized by 1 H-NMR and IR spectroscopies. Polyxanthene 8 was quite soluble in chloroform and THF. The 10% weight loss temperature of polyxanthene 7 was 510°C in nitrogen and it was 90°C higher than the corresponding poly(arylene ether) 3.

The effect of SnCl 4 on the radical polymerization of N ‐allyl‐ N ‐phenylmethacrylamide and N ‐allyl‐ N ‐phenylacrylamide

The effects of SnCl 4 on the radical polymerization of N-allyl-N-phenylmethacrylamide (APM) and N-allyl-N-phenylacrylamide (APA) were investigated. The polymerizations of APM and APA with dimethyl 2,2-azobisisobutyrate (MAIB) were carried out at 50°C in benzene at various concentrations (0-1.0 mol/L) of SnCl 4 . The polymerization rates showed a maximum on varying the SnCl 4 concentration, while the molecular weights of the resulting poly(APM) and poly(APA) were decreased with increasing SnCl 4 concentration. In both systems, the degree of cyclization of polymers were decreased with the SnCl 4 concentration. From the IR results, the cyclic structure of the resulting poly(APM)s was confirmed to be five-membered, whereas poly(APA)s contained not only five-membered but also six-membered rings. The 1 H-NMR examination on the interactions of APM and APA with SnCl 4 revealed that these monomers form 1 :1 and 2 :1 complexes with SnCl 4 with fairly large stability constants. Copolymerizations of APM (M 1 ) with methyl methacrylate (MMA) and styrene (St) (M 2 ) were investigated at 60°C in benzene in the absence of SnCl 4 . APM units were found to be incorporated exclusively as five-membered rings in the resulting copolymer. Monomer reactivity ratios were estimated to be r 1 = 0.29, r 2 = 4.88 for APM/MMA and r 1 = 0.66, r 2 = 5.39 for APM/St. The presence of equimolar (to APM) SnCl 4 was found to enhance the reactivity of APM toward poly(MMA) radical ; r 1 = 0.24, r 2 = 2.56.

Intramolecular Cyclization in Tetrafunctional Monomer Free Radical Polymerization

Abstract Tetrafunctional monomer free radical polymerization was simulated by Monte-Carlo algorithm. Two mechanisms of cyclization were taken into account: interaction of two free radicals (chain termination) and that of a free radical with the double bond (“intramolecular propagation” of the chain). The considerable cyclization of polymers at the very beginning of the reaction was revealed. Intramolecular chain propagation provides the main factor contributed. The number of cycles by the termination mechanism makes up no more than 20% of total amount. The cycle size distribution dependencies on polymerization rate constants for two cyclization mechanisms were shown to be essentially different. The pregel stage of free radical polymerization of diallyl isophthalate and diallyl sebacate was investigated experimentally. The number of cycles was evaluated from the material balance of the double bonds. The significant cyclization of polymers was found out: a single cycle requires on average 6–8 monomer units....

Features of the intramolecular cyclization in the radical polymerization of tetrafunctional monomers. The computer experiment

Intramolecular cyclization in radical polymerization of tetrafunctional monomers has been investigated, using the Monte Carlo method. Two cyclization mechanisms are discussed, one involving the interaction of two radicals (chain termination) and the other, that of a radical with the double bond (intramolecular chain propagation). A significant amountof cyclization of polymers takes place in the early stages of the reaction, the major contribution being that of the intramolecular propagation reaction. The character of the dependence of length distribution of the rings on kinetic parameters of polymerization is essentially different in the case of the two cyclization mechanisms. It is shown that the intramolecular propagation reaction depends on the close range order and cannot be avoided under any (reaction) conditions. The cyclization in line with the termination mechanism depends on the long range order and may be controlled through appropriate selection of the polymerization conditions.

Synthesis and investigation of the properties of cardo‐copolyimides with different microstructure

AbstractCopolyimides, their microstructure being determined by the method of synthesis, were prepared by copolycondensation of 4,4′‐oxydiphthalic anhydride (1a), 4,4′‐carbonyldipthalic anhydride (1b), or 1,8:4,5‐naphthalenetetracarboxylic anhydride with a mixture of two diamines, hexa‐, octa‐, or dodecamethylene diamine (5a, 6a, 7a) and cardo‐diamines 9,9‐bis(4′‐aminophenyl)fluorene (3a) and 3,3‐bis(4′‐aminophenyl)phthalide (4) or two aromatic diamines, 4,4′‐oxydianiline (9) and 2,2‐bis(4‐aminophenyl)hexafluoropropane (8), at various mole ratios of the comonomers. Blockcopolyimides with five‐membered imide cycles were formed by catalytic imidization of the intermediate polymers prepared by addition of the solid dianhydride to a solution of the mixture of the two diamines, whereas the thermal cyclization of such polymers and the one‐step high‐temperature synthesis led to random copolyimides. The thermal and mechanical properties of the copolyimides with various microstructure and their solubility in organic solvents were compared.

13C-NMR studies of thermally isomerized polyphenylacetylenes prepared with MoCl5 and WCl6 catalysts

13C-NMR studies of thermally treated polyphenylacetylenes (PPA) prepared with MoCl5 and WCl6 catalysts provide evidence for intramolecular cyclization and chain scission of both cis and trans polymers. The microstructures of thermally treated cis and trans PPA are different from the microstructure of trans PPA obtained by thermal isomerization during propagation.

Investigation of the mechanism of polypentenamer degradation in the presence of metathesis catalysts

A MWD method has been used to investigate the mechanism of degradative cyclization of unsaturated polymers in the presence of the catalytic system taking polypentenamer as an example. It was found that the process takes place by a random chain mechanism, one fragment being stable, and the other depolymerizing down to monomer. The fact that the initial concentration of the catalytic system appears to have no influence on the degradation points to slow initiation in this system. The ratio of the constant for chain transfer to polymer to that of depolymerization was found by experiment to be k tr / k d = 5×10 −6 m 3 /mole.

Cyclization of dienne polymers—I. Cyclization of natural rubber in phenol solutions

Cyclization of dienne polymers—I. Cyclization of natural rubber in phenol solutions

Cyclization of dienic polymers — I. Cyclization of natural rubber in phenol solution : I. A. Tutorskii, V. V. Markov, L. P. Fomina, V. B. Belyanin and B. A. Dogadkin, Vysokomol. soyed. 5: No. 4, 593–597, 1963

Cyclization of dienic polymers — I. Cyclization of natural rubber in phenol solution : I. A. Tutorskii, V. V. Markov, L. P. Fomina, V. B. Belyanin and B. A. Dogadkin, Vysokomol. soyed. 5: No. 4, 593–597, 1963