Effective Click Construction of Bridged- and Spiro-Multicyclic Polymer Topologies with Tailored Cyclic Prepolymers (kyklo-Telechelics)

Facile synthesis of monocyclic, dumbbell-shaped and jellyfish-like copolymers using a telechelic multisite hexablock copolymer

A heterofunctional hexablock copolymer comprising alternating reactive and non-reactive blocks is designed to generate cyclic, dumbbell-shaped and jellyfish-like copolymers.

Advancing macromolecular hoop construction: recent developments in synthetic cyclic polymer chemistry

Synthetic methodology to access cyclic macromolecules continues to develop via two distinct mechanistic classes: ring-expansion of macrocyclic initiators and ring-closure of functionalized linear polymers.

Synthesis of a multicyclic polymer with hyperbranched structure by click polymerization of an AB2 cyclic macromonomer

A multicyclic polymer with a hyperbranched structure was successfully synthesized.

Rhodanine-based Knoevenagel reaction and ring-opening polymerization for efficiently constructing multicyclic polymers

Cyclic polymers have a number of unique physical properties compared with those of their linear counterparts. However, the methods for the synthesis of cyclic polymers are very limited, and some multicyclic polymers are still not accessible now. Here, we found that the five-membered cyclic structure and electron withdrawing groups make methylene in rhodanine highly active to aldehyde via highly efficient Knoevenagel reaction. Also, rhodanine can act as an initiator for anionic ring-opening polymerization of thiirane to produce cyclic polythioethers. Therefore, rhodanine can serve as both an initiator for ring-opening polymerization and a monomer in Knoevenagel polymerization. Via rhodanine-based Knoevenagel reaction, we can easily incorporate rhodanine moieties in the backbone, side chain, branched chain, etc, and correspondingly could produce cyclic structures in the backbone, side chain, branched chain, etc, via rhodanine-based anionic ring-opening polymerization. This rhodanine chemistry would provide easy access to a wide variety of complex multicyclic polymers.

Pentaerythritol: A Versatile Substrate in Organic Transformations, Centralization on the Reaction Medium

BACKGROUND

Pentaerythritol (2,2-bis (hydroxymethyl) propane-1,3-diol) as white crystalline odorless solid has been synthesized in 1891. Pentaerythritol is multifaceted species in many compounds, which are wildly utilized in medicine and industry. Also, multicomponent reactions (MCRs) play a crucial role in organic and medicinal chemistry. Hence, in these reactions, pentaerythritol is a versatile substrate for the synthesis of many polyfunctionalized products, because of the presence of the neopentane core and one hydroxyl group in each of the four terminal carbons.

OBJECTIVE

The review describes pentaerythritol multicomponent reactions in the presence of different solvents in the reaction medium to produce various compounds including pentaerythritols. This review covers the literature relevant up to 2018.

CONCLUSION

It is obvious from the provided review that a great deal of research has been done in this field, utilizing various mediums (solvent-free conditions, aqueous media, and organic solvents) for the synthesis of the products of containing pentaerythritols. This classification is based on the importance of economic and environmental friendly reactions. Due to the whole aforesaid reports, some reactions required heat for their progress, and some others were accompanied by microwave or ultrasonic waves.

Ring-expansion cationic cyclopolymerization for the construction of cyclic cyclopolymers

A “cyclic cyclopolymer” was successfully synthesized via ring-expansion cationic cyclopolymerization with a cyclic initiator by using a divinyl ether carrying a gem-dimethyl group on the spacer as the monomer.

C3-C3' and C6-C6' Oxidative Couplings of Carbazoles

9-Substituted carbazoles are widely used units in materials science, and their oxidative reactions have been utilized for the synthesis and characterization of polymers. Though the oxidative mechanism of carbazoles has been known for a few decades, structural definition has remained difficult, because their polymers are generally insoluble with incomplete characterization and unknown dependence of the electrochemical potentials. The oxidative reactions of 9-substituted carbazoles should be carefully considered under specific oxidative conditions; otherwise, structure definitions could be wrong, because the IR and NMR spectra used previously cannot quantitatively analyze 3,3'-coupling and 6,6'-coupling of carbazoles. In this review, the best understanding of the C3-C3' and C6-C6' oxidative couplings of 9-substituted carbazoles is presented, and the benefit of these oxidative reactions from the viewpoints of electrochemical synthesis, film engineering, and the synthesis and processing of polymers is highlighted.

Junction-Controlled Topological Polymerization

Methodology that enables the controlled synthesis of linear and branched polymers from an identical monomer will be a novel pathway for polymer synthesis and processing. Herein we first describe the control of one or both of the C(3)-C(3') and C(6)-C(6') coupling reactions of carbazolyl. In a second approach, an identical monomer containing two carbazolyls is polymerized using chemical and electrochemical oxidizers, leading to topologically controllable growth of linear polymers in weak oxidizer or of cross-linked polymer chains in strong oxidizer, with satisfactory long chain propagation of step growth polymerization (M_n =6.0×10⁴  g mol^-1 , M_w /M_n =2.3). This very simple polymerization with cheap reagents and low levels of waste has provided a flexible pathway for synthesis and processing of polymers.

Scaling behavior of knotted random polygons and self-avoiding polygons: Topological swelling with enhanced exponent

We show that the average size of self-avoiding polygons (SAPs) with a fixed knot is much larger than that of no topological constraint if the excluded volume is small and the number of segments is large. We call it topological swelling. We argue an "enhancement" of the scaling exponent for random polygons with a fixed knot. We study them systematically through SAP consisting of hard cylindrical segments with various different values of the radius of segments. Here we mean by the average size the mean-square radius of gyration. Furthermore, we show numerically that the topological balance length of a composite knot is given by the sum of those of all constituent prime knots. Here we define the topological balance length of a knot by such a number of segments that topological entropic repulsions are balanced with the knot complexity in the average size. The additivity suggests the local knot picture.

Topological Polymer Chemistry Designing Complex Macromolecular Graph Constructions

The precision design of topologically intriguing macromolecular architectures has continuously been an attractive challenge in polymer science and polymer materials engineering. A class of multicyclic polymer topologies, including three subclasses of spiro, bridged, and fused forms, are particularly unique not only from a topological geometry viewpoint but also from their biochemical relevance to programmed folding structures. In this Account, we describe recent progress in constructing this class of macromolecules, in particular by means of an electrostatic self-assembly and covalent fixation (ESA-CF) protocol, in which ion-paired polymer self-assemblies are employed as key intermediates. All three dicyclic constructions having either 8 (spiro), manacle (bridged), or θ (fused) forms, as well as a tricyclic trefoil (spiro) graph, have been constructed by the ESA-CF process. Moreover, a triply fused-tetracyclic macromolecular K_3,3 graph has been constructed using a uniform-size dendritic polymer precursor having six cyclic ammonium salt end groups carrying two units of a trifunctional carboxylate counteranion. Remarkably, the K_3,3 graph is known in topological geometry as a prototypical nonplanar graph and has been identified as topologically equivalent to some multicyclic polypeptides (cyclotides) produced through the intramolecular S-S bridging with cysteine residues. A series of single cyclic (ring) polymers having one, two, and even three designated functional groups at the prescribed positions along their cyclic backbone segment (kyklo-telechelics) have also been obtained by the ESA-CF protocol. And in conjunction with a tandem alkyne-azide addition (i.e., click) and an olefin metathesis (i.e., clip) reaction, the precision design of complex multicyclic macromolecular architectures has been achieved. Thus, a series of tri-, tetra-, and even hexacyclic polymer topologies of spiro- and bridged-forms and three doubly fused-tricycle (β-, γ-, and δ-graph) forms, as well as a triply fused-tetracyclic and a quadruply fused-pentacyclic form (unfolded tetrahedron-graph, and "shippo"-form, respectively) were effectively constructed. Furthermore, the hybrid multicyclic polymer constructions comprised of three subclasses of spiro, bridged, and fused units have been produced using complementary pairs of single cyclic and dicyclic kyklo-telechelic precursors obtainable by the ESA-CF process. Upon these synthetic developments, we are now entering into an exciting new era of polymer science and polymer materials engineering based on the precision design of polymer topologies, which appears comparable to the "Cambrian explosion period" experienced in the evolution of life systems.

Densely Packed Multicyclic Polymers

Highly dense polymer chains were formed through coupling cyclic polymeric units in a sequence controlled manner. It was found that as the number of cyclic units increased the compactness substantially increased in a good solvent to a limiting value after only 12 units. This limiting value was close to that of a linear polymer chain in a θ solvent, in which polymer segment interactions with solvent are minimized. This remarkable result suggests that the unique architecture of the cyclic structure plays an important role to significantly change the polymer conformation and remain soluble in solution, which circumvents the need for cross-linking. The insight found in this work provides a physical mechanism as to why Nature uses cyclic structures in proteins to confer stability and the compacting of DNA strands to induce chromosome territories.

Knotting probability of self-avoiding polygons under a topological constraint

We define the knotting probability of a knot K by the probability for a random polygon or self-avoiding polygon (SAP) of N segments having the knot type K. We show fundamental and generic properties of the knotting probability particularly its dependence on the excluded volume. We investigate them for the SAP consisting of hard cylindrical segments of unit length and radius r_ex. For various prime and composite knots, we numerically show that a compact formula describes the knotting probabilities for the cylindrical SAP as a function of segment number N and radius r_ex. It connects the small-N to the large-N behavior and even to lattice knots in the case of large values of radius. As the excluded volume increases, the maximum of the knotting probability decreases for prime knots except for the trefoil knot. If it is large, the trefoil knot and its descendants are dominant among the nontrivial knots in the SAP. From the factorization property of the knotting probability, we derive a sum rule among the estimates of a fitting parameter for all prime knots, which suggests the local knot picture and the dominance of the trefoil knot in the case of large excluded volumes. Here we remark that the cylindrical SAP gives a model of circular DNA which is negatively charged and semiflexible, where radius r_ex corresponds to the screening length.

Statistical and Dynamical Properties of Topological Polymers with Graphs and Ring Polymers with Knots

We review recent theoretical studies on the statistical and dynamical properties of polymers with nontrivial structures in chemical connectivity and those of polymers with a nontrivial topology, such as knotted ring polymers in solution. We call polymers with nontrivial structures in chemical connectivity expressed by graphs "topological polymers". Graphs with no loop have only trivial topology, while graphs with loops such as multiple-rings may have nontrivial topology of spatial graphs as embeddings in three dimensions, e.g., knots or links in some loops. We thus call also such polymers with nontrivial topology "topological polymers", for simplicity. For various polymers with different structures in chemical connectivity, we numerically evaluate the mean-square radius of gyration and the hydrodynamic radius systematically through simulation. We evaluate the ratio of the gyration radius to the hydrodynamic radius, which we expect to be universal from the viewpoint of the renormalization group. Furthermore, we show that the short-distance intrachain correlation is much enhanced for real topological polymers (the Kremer⁻Grest model) expressed with complex graphs. We then address topological properties of ring polymers in solution. We define the knotting probability of a knot K by the probability that a given random polygon or self-avoiding polygon of N vertices has the knot K. We show a formula for expressing it as a function of the number of segments N, which gives good fitted curves to the data of the knotting probability versus N. We show numerically that the average size of self-avoiding polygons with a fixed knot can be much larger than that of no topological constraint if the excluded volume is small. We call it "topological swelling".

Polymerizing Insulin with Photocleavable Linkers to Make Light-Sensitive Macropolymer Depot Materials

The use of light-sensitive polymers for the release of therapeutics is an important approach allowing the timing and amount of the release to be controlled precisely. The use of light has been pioneered to control insulin release from a dermal photoactivated depot, or PAD. One of the main impediments to the use of light-sensitive polymers in this context is the density of the materials: The large majority of the material is the carrier polymer, with the minority being the therapeutic. In this work, the feasibility of using insulin itself as a monomer in the polymerization process is demonstrated. Insulin modified with either one or two light cleavable azide groups is polymerized with a tridentate alkyne-bridging monomer using a click reaction. The resulting material called a "macropolymer" is ≈85% insulin, is insoluble in aqueous solvent, and releases native, soluble insulin upon irradiation.