Comparative theoretical studies of substituted bridged bipyridines and their N-oxides

In this work, the experimental synthesized bipyridines azo-bis(2-pyridine),4,4′-dimethyl-3,3′-dinitro-2,2′-azobipyridine, and N,N′-bis(3-nitro-2-pyridinyl)-methane-diamine and a set of designed bipyridines that have similar frameworks but different linkages and substituents were studied theoretically at the B3LYP/6-31G* level of density functional theory. The gas-phase heats of formation were predicted based on the isodesmic reactions, and the condensed-phase heats of formation and heats of sublimation were estimated in the framework of the Politzer approach. The crystal densities have been computed from molecular packing and results show that incorporation of –N=N–, –N=N(O)–, –CH=N–, and –NH–NH– into bipyridines is more favorable than –CH=CH– and –NH–CH₂–NH– for increasing the density. The predicted detonation velocities (D) and detonation pressures (P) indicate that –NH₂, –NO₂, and –NF₂ can enhance the detonation performance, and –NO₂ and –NF₂ are more favorable. Introducing –N=N–, –N=N(O)–, and –NH–NH– bridge groups into bipyridines is also favorable for improving their detonation performance. The oxidation of pyridine N always but that of –N=N– bridge does not always improve the detonation properties. E4–O, the derivative with –N=N– bridge and two –NF₂ substituent groups, has the largest D (9.90 km/s) and P (47.47 GPa). An analysis of the bond dissociation energies shows that all derivatives have good thermal stability.     

Chain center‐functionalized amphiphilic block polymers: Complementary hydrogen bond self‐assembly in aqueous solution

Hydrogen bonding self‐assemblies were formed in an aqueous medium from a pair of an amphiphilic ABA triblock copolymer and a hydrophobic homopolymer, both with a triple hydrogen bonding site that was complementary to each other and precisely placed at the main‐chain center: (PEGMA)_m–(MMA)_n– ADA –(MMA)_n–(PEGMA)_m and (MMA)_p– DAD –(MMA)_p ( A = hydrogen acceptor; D = hydrogen donor; PEGMA: PEG methacrylate; MMA: methyl methacrylate). The polymers were synthesized by the ruthenium‐catalyzed living radial polymerization with bifunctional initiators (Br– ADA –Br and Cl– DAD –Cl) aiming at pinpoint chain center functionalization to give a symmetric segmental sequence; ADA and DAD initiators were derived from 2,6‐diaminopyridine and thymine, respectively. On mixed equimolar in tetrahydrofuran (THF), both polymers spontaneously associated, and the apparently 1:1 assembly further grew into higher aggregate particles on subsequent addition of water. The aggregates in water/THF were relatively stable and uniform in size, which most likely stems from the intermolecular complementary hydrogen bond interaction at polymer chain centers. In sharp contrast, an equimolar mixture of ADA ‐block polymer and DAD ‐free poly(MMA) in water/THF resulted in larger and irregular particles, and thus short‐lived to eventually collapse. These results indicate that, however structurally marginal, precise pinpoint functionalization of macromolecular chains allows stable self‐assemblies via complementary hydrogen bond interaction even in aqueous media. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4498–4504     

Electrochemical properties of new n-type π-conjugated polybipyridines and polybiphenylenes with various bridging units

New electrochemically active π-conjugated polymers were prepared. They had polybipyridine or polybiphenylene type structure with an –NN–, –O–, or –NHCONH– bridging group between the two aromatic units, and underwent more facile electrochemical reduction (or n-type doping) than the mother π-conjugated polymers without the bridging group.     

Synthetic and biological polymers--merging the interface

The increasing control that synthetic chemists are able to exert over molecular architecture is allowing the design and preparation of macromolecular and polymeric systems of unprecedented sophistication. In form and function, synthetic polymers are able to mimic many biological polymers, in effect ‘blurring the boundaries’ between the worlds of artificial and natural materials. In this review, some key examples from the merging interface between synthetic and natural polymers are considered, and illustrations of both ‘bio-inspired’ synthetic macromolecular chemistry and new directions in polymer materials are given.     

Plant oils: The perfect renewable resource for polymer science?!

Already for a long time, plant oils and their derivatives have been used by polymer chemists due to their renewable nature, world wide availability, relatively low price, and their rich application possibilities. Although many different synthetic approaches have been used, more recent examples are pointing in the direction of catalytic transformations and other efficient reactions to achieve a more sustainable production of polymers from these renewable resources. In this context, olefin metathesis, thiol–ene additions, and other processes can contribute not only to a more efficient synthesis of plant oil based polymers, but also to broaden the application possibilities of plant oils. This feature article provides an overview of the present situation with special attention to the use of olefin metathesis and thiol–ene chemistry as synthetic methods and as polymerization techniques.     

Theoretic design of 1,2,3,4-tetrazine-1,3-dioxide-based high-energy density compounds with oxygen balance close to zero

Density functional theory method was used to study the heats of formation (HOFs), electronic structure, energetic properties, and thermal stability for a series of 1,2,3,4-tetrazine-1,3-dioxide derivatives with different substituents and bridge groups. It is found that the groups –NO₂, –C(NO₂)₃, and –N=N– play a very important role in increasing the HOFs of the derivatives. The effects of the substituents on the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels and HOMO–LUMO gaps are coupled to those of different substituents and bridges. The calculated detonation velocities and pressures indicate that the group –NO₂, –NF₂, –ONO₂, –C(NO₂)₃, or –NH– is an effective structural unit for enhancing the detonation performance for the derivatives. An analysis of the bond dissociation energies for several relatively weak bonds indicates that incorporating the groups –NO₂, –NF₂, –ONO₂, –C(NO₂)₃, and –N=N– into parent ring decreases their thermal stability. Considering the detonation performance and thermal stability, 18 compounds may be considered as the target compounds holding the greatest potential for synthesis and use as high-energy density compounds. Among them, the oxygen balances of four compounds are equal to zero. These results provide basic information for the molecular design of the novel high-energy compounds.     

Pesticide‐conjugated polyacrylate nanoparticles: novel opportunities for improving the photostability of emamectin benzoate

Emamectin benzoate, a macrocyclic lactone, can be used in low quantities to control arthropod pests, effectively. However, its poor photostability prevents its further use. To delay its photodegradation, novel acrylate‐type polymeric nanoparticles were synthesized and tested as materials for improving pesticide photostability. N‐acylated emamectin benzoate was synthesized via bonding emamectin benzoate to acrylamide. The resulting pesticide, containing the double bond linkage –C=C–N–, was copolymerized with butyl acrylate and methyl methacrylate by the emulsion polymerization method. The refined polymers were characterized by Fourier transform infrared spectroscopy spectroscopy, and result illustrated the pesticide was conjugated to the polymers. Atomic force microscope and dynamic light scattering analyses were also used for determining the average particle diameters of pesticide–polymer conjugates. Photostability tests showed that the nanoparticles obtained exhibited greatly improved photostability. Additionally, the laboratory toxicity tests demonstrated that the insecticidal effects of the novel emamectin benzoate formulation were better than those of the control pesticide formulation (emamectin benzoate EC). Copyright © 2012 John Wiley & Sons, Ltd.     

Grafting of Vinyl Monomers onto Nylon

Polymer chemists have been successful in applying polymerization techniques to develop copolymers of natural and synthetic macromolecules [l]. The literature abounds with examples of the successful formation of copolymers from natural and synthetic macromolecules [2–5]. Copolymerization is attractive to chemists as a means of modifying macromolecules since, in general, degradation can be minimized. Despite the heterogeneity and complexity of these copolymers, much has been achieved in their characterization. The desirable properties of the polymer are retained and additional properties are acquired through the added polymer. The desired material may be formed in situ by polymerization of a monomer or monomers, by condensation of reactants, or by the decomposition of a preformed polymer.     

Evaluation of poly([2‐(acryloyloxy)ethyl]trimethylammonium chloride) cationic polymer capillary coating for capillary electrophoresis and electrokinetic chromatography separations

Capillary electrophoresis and electrokinetic chromatography are typically carried out in unmodified fused‐silica capillaries under conditions that result in a strong negative zeta potential at the capillary wall and a robust cathodic electroosmotic flow. Modification of the capillary wall to reverse the zeta potential and mask silanol sites can improve separation performance by reducing or eliminating analyte adsorption, and is essential when conducting electrokinetic chromatography separations with cationic latex nanoparticle pseudo‐stationary phases. Semipermanent modification of the capillary walls by coating with cationic polymers has proven to be facile and effective. In this study, poly([2‐(acryloyloxy)ethyl]trimethylammonium chloride) polymers were synthesized by reversible addition‐fragmentation chain transfer polymerization and used as physically adsorbed semipermanent coatings for capillary electrophoresis and electrokinetic chromatography separations. An initial synthesis of poly([2‐(acryloyloxy)ethyl]trimethylammonium chloride) polymer coating produced strong and stable anodic electroosmotic flow of –5.7 to –5.4 × 10⁻⁴ cm²/V⋅s over the pH range of 4–7. Significant differences in the magnitude of the electroosmotic flow and effectiveness were observed between synthetic batches, however. For electrokinetic chromatography separations, the best performing batches of poly([2‐(acryloyloxy)ethyl]trimethylammonium chloride) polymer performed as well as the commercially available cationic polymer polyethyleneimine, whereas polydiallylammonium chloride and hexadimethrine bromide did not perform well.     

Microreaction Technology for Synthetic Chemistry

Microreaction technology as an emerging tool for synthetic chemistry has been extensively applied in academic and industrial researches. Normally, synthetic chemists used to running reactions in the classical glassware for centuries are unfamiliar and unaccustomed to use microreaction technology for routine synthetic work. This review tries to give a general introduction of the capabilities of microreaction technology. After introducing the origin and history of microreaction technology, we review and discuss mainly several synthetic examples of high T‐P reactions, hazardous reactions, flash chemistry, polymerization, photochemistry, electrochemistry and multistep API's syntheses to demonstrate the capabilities of microreactors. A summary and perspectives on microreactor technology are also given in this paper. It is anticipated that more and more chemists will understand the capabilities and limitations of microreaction technology, and could work together with chemical engineers for the synergic development of chemistry and chemical engineering.     

Stereospecificity of 1H, 13C and 15N shielding constants in the isomers of methylglyoxal bisdimethylhydrazone: problem with configurational assignment based on 1H chemical shifts

In the ¹³C NMR spectra of methylglyoxal bisdimethylhydrazone, the ¹³C‐5 signal is shifted to higher frequencies, while the ¹³C‐6 signal is shifted to lower frequencies on going from the EE to ZE isomer following the trend found previously. Surprisingly, the ¹H‐6 chemical shift and ¹J(C‐6,H‐6) coupling constant are noticeably larger in the ZE isomer than in the EE isomer, although the configuration around the –CH═N– bond does not change. This paradox can be rationalized by the C–H?N intramolecular hydrogen bond in the ZE isomer, which is found from the quantum‐chemical calculations including Bader's quantum theory of atoms in molecules analysis. This hydrogen bond results in the increase of δ(¹H‐6) and ¹J(C‐6,H‐6) parameters. The effect of the C–H?N hydrogen bond on the ¹H shielding and one‐bond ¹³C–¹H coupling complicates the configurational assignment of the considered compound because of these spectral parameters. The ¹H, ¹³C and ¹⁵N chemical shifts of the 2‐ and 8‐(CH₃)₂N groups attached to the –C(CH₃)═N– and –CH═N– moieties, respectively, reveal pronounced difference. The ab initio calculations show that the 8‐(CH₃)₂N group conjugate effectively with the π‐framework, and the 2‐(CH₃)₂N group twisted out from the plane of the backbone and loses conjugation. As a result, the degree of charge transfer from the N‐2– and N‐8– nitrogen lone pairs to the π‐framework varies, which affects the ¹H, ¹³C and ¹⁵N shieldings. Copyright © 2012 John Wiley & Sons, Ltd.     

Controlling supramolecular polymerization through multicomponent self‐assembly

The self‐assembly into supramolecular polymers is a process driven by reversible non‐covalent interactions between monomers, and gives access to materials applications incorporating mechanical, biological, optical or electronic functionalities. Compared to the achievements in precision polymer synthesis via living and controlled covalent polymerization processes, supramolecular chemists have only just learned how to developed strategies that allow similar control over polymer length, (co)monomer sequence and morphology (random, alternating or blocked ordering). This highlight article discusses the unique opportunities that arise when coassembling multicomponent supramolecular polymers, and focusses on four strategies in order to control the polymer architecture, size, stability and its stimuli‐responsive properties: (1) end‐capping of supramolecular polymers, (2) biomimetic templated polymerization, (3) controlled selectivity and reactivity in supramolecular copolymerization, and (4) living supramolecular polymerization. In contrast to the traditional focus on equilibrium systems, our emphasis is also on the manipulation of self‐assembly kinetics of synthetic supramolecular systems. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 34–78     

The Effect of –(C6F4)– on the Surface Free Energy of Main‐Chain Liquid Crystalline and Crystalline Polymers

Novel fluorinated main‐chain liquid‐crystalline/crystalline polymers were prepared through thin film polymerization to investigate the effect of –(C₆F₄)– on the surface free energy. The fluorine in the phenyl rings does not lower the total surface free energy of the thin copolymer films, compared to those without fluorine. Interestingly, the Lewis acid components (γ⁺) of the surface free energy of the fluorine‐containing polymers increase with an increase in the –(C₆F₄)– content, indicating the increasing electron accepting character of the surface.     

Synthesis and study of new phenolic antioxidants with nitroaromatic and heterocyclic substituents

New polyfunctional aromatic, nitroaromatic, and heterocyclic compounds linked to the 2,6-di-tert-butylphenol moiety via –NH–, –C(O)NH–, –S–, or–C=N– spacers were synthesized. These structures provide intramolecular charge transfer (ICT) and exhibit antioxidant activity. The structures of the new compounds were established by X-ray diffraction. The novel compounds were evaluated for antioxidant activity using the DPPH assay. The presence of the 2,4,6-trinitrophenyl moiety in combination with the –NH– spacer leads to a considerable increase in the antioxidant activity of 2,6-di-tert-butylphenols. These compounds are also weak lipoxygenase inhibitors. The results of this study provide an opportunity to search for new types of antioxidants with ICT.     

Synthesis and structural elucidation of 1-D silver(I) aliphatic carboxylate coordination polymers with 1,3,5-triaza-7-phosphaadamantane/N-methyl-1,3,5-triaza-7-phosphaadamantane

Reactions of silver(I) salts of acetate and trifluoroacetate with 1,3,5-triaza-7-phosphaadamantane (PTA) afforded 1-D coordination polymers [Ag(μ₂-PTA-κ²P?-:N)(μ₂-O₂CCH₃-κ²O:O′)]_n·2nH₂O (1) and [Ag(μ₂-PTA-κ²P:N)(μ₂-O₂CCF₃-κO)]_n·nH₂O (2), while a reaction of silver(I)trifluoroacetate with N-methyl-1,3,5-triaza-7-phosphaadamantane (PTAMe) afforded the coordination polymer [Ag(PTAMe)(μ₃-O₂CCF₃-κ³O:O:O’)(μ₂-O₂CCF₃-κ²O:O′)]_n (3). The coordination polymers were characterized using single-crystal X-ray diffraction. Nuclear magnetic resonance, infrared, and electron spray ionization mass spectrometries were used to initially establish complexation of Ag(I) to the PTA or PTAMe before recrystallization. In the crystal structures of 1 and 2, coordination of the PTA moieties to Ag(I) is via P and N forming chains that are linked through bridging carboxylates. The resulting structural motif can be described as ladder-like in which –[PTA–Ag–PTA]– chains are the strands while the bridging carboxylates comprising of –[Ag–O–C–O]₂– or –[Ag–O]₂– metallacycle rungs of the ladder. Compound 3 forms single-stranded coil-like coordination polymers with two non-equivalent Ag(I) centers, both tetrahedrally coordinated by four oxygens from four trifluoroacetates in one and by three oxygens from the trifluoroacetates and in each by the P of the PTAMe with alternating Ag?Ag interactions. The crystal structures of all three coordination polymers have a variety of fairly strong hydrogen bonds and intermolecular interactions which contribute stabilization of the crystal lattices.     

Tandem mass spectrometry of synthetic polymers

The detailed characterization of macromolecules plays an important role for synthetic chemists to define and specify the structure and properties of the successfully synthesized polymers. The search for new characterization techniques for polymers is essential for the continuation of the development of improved synthesis methods. The application of tandem mass spectrometry for the detailed characterization of synthetic polymers using the soft ionization techniques matrix‐assisted laser desorption/ionization mass spectrometry (MALDI‐MS) and electrospray ionization mass spectrometry (ESI‐MS), which became the basic tools in proteomics, has greatly been increased in recent years and is summarized in this perspective. Examples of a variety of homopolymers, such as poly(methyl methacrylate), poly(ethylene glycol), as well as copolymers, e.g. copolyesters, are given. The advanced mass spectrometric techniques described in this review will presumably become one of the basic tools in polymer chemistry in the near future. Copyright © 2009 John Wiley & Sons, Ltd.     

Polypeptoids: A perfect match for molecular definition and macromolecular engineering?

Precision synthesis of polymers has been a hot topic in recent years. While this is notoriously difficult to address for polymers with a C? C backbone, Merrifield has discovered a way many decades ago for polypeptides. Using a similar approach, N‐substituted polypeptides, so‐called polypeptoids have been synthesized and studied for about 20 years. In contrast, the living ring‐opening polymerization (ROP) of N‐substituted N‐carboxyanhydrides was among the first living polymerizations to be discovered. More recently, a surge in new synthetic approaches led to the efficient synthesis of cyclic or linear multiblock copolypeptoids. Thus, polypeptoids can be synthesized either by solid phase synthesis to yield complex and exactly defined oligo‐ and small polymers or by ROP of appropriately N‐substituted N‐carboxyanhydrides (NNCA) to give linear, cyclic, or star‐like polymers. Together with an excellent biocompatibility, this polymer family may have a bright future ahead as biomaterials. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2731–2752     

Biodegradable Polymers: Prospects,Problems, and Progress

Abstract

At different times in the history of polymer science specific subjects have come to center stage; for intense investigation because they represent new and important intellectual challenges as well as technological opportunities. In past years the chief incentive for the scientific study of biodegradation of polymers was concern with the problem of preventing or retarding attack on such products by microorganisms, insects, rodents, and other animals. Many research efforts in synthetic polymer chemistry were directed toward the synthesis of polymers resistant to biodegradation. The paramount feature sought by polymer chemists and engineers was stability, and the production of such materials has been very impressive. This is still a very important factor in many applications such as paints, protective coatings, textiles, electrical insulation, and plastic films and sheets used for many applications such as upholstery and floor covering. Fortunately, most synthetic polymers are resistant to biological attack and many of these studies were concerned with choosing additives which would be bioresistant, or with providing protection for the susceptible ingredients in the plastic formulation by the use of fungicides and other biocides. In recent years, however, the picture has changed and there has been a raft of publicity about degradable plastics [1–10].     

β-cyclodextrin modified xanthan gum as an eco-friendly corrosion inhibitor for L80 steel in 1 M HCl

The development of eco-friendly corrosion inhibitors is a subject of several investigations, especially natural polymers. Aimed at suppressing the corrosion of L80 steel in 1 mol/L hydrochloric acid (HCl), a novel natural polymer inhibitor was developed based on xanthan gum (XG) and β-Cyclodextrin (β-CD) in this work. The corrosion inhibition effect of β-cyclodextrin modified xanthan gum (β-CD-XG) on L80 steel was evaluated by electrochemical methods, and surface analysis technology. Adsorption isotherm studies, Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS) were used to explore the corrosion inhibition mechanism of β-CD-XG on L80 steel. The results suggested that β-CD-XG was classified as a mixed-type inhibitor, and mainly suppressed the anode metal dissolution by a tight adsorption film. The formation of the film was attributed to the chemisorption of –OH, –COO-, –CH₂–O–, and –CH₂–O–CH₂– groups on the surface of L80 steel, which conformed to the Langmuir adsorption model. The experimental results illustrated that the maximum corrosion inhibition efficiency of 94.74% was acquired at 200 mg/L β-CD-XG at 293 K.

Graphic abstract

     

Recent progress on cyclic polymers: Synthesis,bioproperties, and biomedical applications

Polymer topologies exert a significant effect on its properties, and polymer nanostructures with advanced architectures, such as cyclic polymers, star‐shaped polymers, and hyperbranched polymers, are a promising class of materials with advantages over conventional linear counterparts. Cyclic polymers, due to the lack of polymer chain ends, have displayed intriguing physical and chemical properties. Such uniqueness has drawn considerable attention over the past decade. The current review focuses on the recent progress in the design and development of cyclic polymer with an emphasis on its synthesis and bio‐related properties and applications. Two primary synthetic strategies towards cyclic polymers, that is, ring‐expansion polymerization and ring‐closure reaction are summarized. The bioproperties and biomedical applications of cyclic polymers are then highlighted. In the end, the future directions of this rapidly developing research field are discussed. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1447–1458