Bonds In Macromolecules Research Articles

Environmentally Degradable Polymers Incorporating Stimuli‐Triggered Cleavable Linkages toward Industrial Materials

AbstractPlastics designed to degrade upon exposure to ambient stimuli after use are emerging as promising alternatives to conventional plastics, considering environmental pollution. The so‐called “biodegradable polymers,” which can be degraded by enzymes or microbes, are the most reliable biodegradable polymers, and considerable effort is devoted to their practical application. Several other examples are also developed for the cleavage of chemical bonds in macromolecules, as one part of a vast variety of “stimuli‐responsive polymers,” especially for biomedical applications. These chemical insights provide a design concept that can even be extended to plastic materials. Here, stimuli‐cleavable linkages, drawing from the chemical insights cultivated in biomedical fields, intended for application in degradable plastics, are outlined. As stimuli for polymer degradation, pH changes, photoirradiation, and redox conditions are selected because polymers released in natural environments may inadvertently be exposed to these stimuli. The degradation pathways are grouped into five categories: 1) stimuli‐cleavable linkages, 2) self‐amplifying, 3) self‐immolative, 4) chain shattering, and 5) double responsive. The classification and organization of the stimuli‐cleavable linkages provide insights for designing new, degradable polymers.

Simulation of the processes of plasma modification and vacuum metallization of polymer materials by the method of molecular dynamics

The article presents the results of the development of molecular dynamics models of modifications of polypropylene (PP) material in the plasma of a radio-frequency (RF) discharge and a copper coating deposit by magnetron sputtering on the surface of a polyethylene (PE) material. The model of the RF plasma modification process describes changes in the surface layers of the PP material upon interaction with low-energy plasma ions: the nature of the breaking of covalent bonds in macromolecules, the chemical composition of sputtered particles, and changes in the ordering of the supramolecular structure. The model of the vacuum metallization process describes the processes of the introduction of metal atoms into the polymer structure, the change in the conformation of macromolecules, the formation of macroradicals with uncompensated chemical bonds, and the formation of an interfacial layer between the polymer and the metal coating.

Долговечность полимеров в переменном электрическом поле

An explanation of the difference in the electrical properties of polymers in the DC and AC electric fields is proposed. Energy release during recombination of electrons and holes injected into a polymer dielectric is considered as a factor accelerating the processes of electric aging of these dielectrics in an AC field. It is shown that nonradiative relaxation of electron excited states causes breaks of bonds in macromolecules and formation of free radicals. Due to the lower ionization energy of free radicals (compared to the original molecules), the rate of charge accumulation in the polymer dielectric increases, which leads to a decrease in its durability in an AC field compared to the durability of polymers in a DC field.

Neutron Crystallography for the Study of Hydrogen Bonds in Macromolecules.

The hydrogen bond (H bond) is one of the most important interactions that form the foundation of secondary and tertiary protein structure. Beyond holding protein structures together, H bonds are also intimately involved in solvent coordination, ligand binding, and enzyme catalysis. The H bond by definition involves the light atom, H, and it is very difficult to study directly, especially with X-ray crystallographic techniques, due to the poor scattering power of H atoms. Neutron protein crystallography provides a powerful, complementary tool that can give unambiguous information to structural biologists on solvent organization and coordination, the electrostatics of ligand binding, the protonation states of amino acid side chains and catalytic water species. The method is complementary to X-ray crystallography and the dynamic data obtainable with NMR spectroscopy. Also, as it gives explicit H atom positions, it can be very valuable to computational chemistry where exact knowledge of protonation and solvent orientation can make a large difference in modeling. This article gives general information about neutron crystallography and shows specific examples of how the method has contributed to structural biology, structure-based drug design; and the understanding of fundamental questions of reaction mechanisms.

Determination of the properties of modified phenol-formaldehyde oligomers and wood panels based on them

Results of studies of basic properties of the phenol-formaldehyde oligomer SFJ-3014 modified with the a furfurol acetone monomer FA are given. Strength tests of wood-based panels made using the modified adhesives have been performed. By means of IR spectroscopy, an increase in the strength of chemical bonds in macromolecules of a cured modified binder has been established. It has been shown that wood-based panels made on the basis of such a binder have improved physicomechanical properties.

Dynamics of biomacromolecules in a coherent electromagnetic radiation field

It is shown that induced oscillations and periodic displacements of the equilibrium positions occur in biomacromolecules in the absence of electromagnetic radiation absorption, due to modulation of interaction potential between atoms and groups of atoms forming the non-valence bonds in macromolecules by the external electromagnetic field. Such "hyperoscillation" state causes inevitably the changes in biochemical properties of macromolecules and conformational transformation times.

Fabrication and characterization of dense Chitosan/polyvinyl-alcohol/poly-lactic-acid blend membranes

Dense membranes of Chitosan (CS)/Poly(vinyl alcohol) (PVA)/Poly(lactic acid) (PLA) blend were successfully fabricated using casting technique. The mechanical properties, moisture regain and water vapor permeability of polymer blend membranes were estimated by tensile test, moisture regain rate and dish method test respectively. The microstructures, morphology, chemical composition and thermal properties were also characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC) respectively. Results indicated that there were interactions and good compatibility among CS, PLA and PVA. And the blend membranes have good breaking elongation and slightly decreased breaking strength, and show best moisture regain at the case of CS60 (the content of CS in the blends is 60 %). They also have excellent porous structure, which is beneficial to their air permeability and may also contribute to cell regeneration. With the adding of PVA content, the melting peaks of blend membranes reduce and gradually close to that of PVA, demonstrating that the regularity of CS molecular chain may be destroyed and hydrogen bonds of macromolecules in polymers were newly formed. As a result, solution blending of the three polymers could complement their disadvantages and significantly improve the membrane performance of a single polymer, thus promote the mechanical and biological properties of blend membrane.

Is it possible to strengthen rigid polymers by adding low aspect ratio nanofillers?

twenty years ago, represented by the application of clay/nylon-6 nanocomposites at Toyota Central R&D Labs, they were considered as revolutionary alternative to microcomposites. As the interface between nanofillers and matrix would constitute large area within the bulk material, properties of polymer nano composites were expected to be greatly improved. With growing experience, however, it seems that enhancement of mechanical properties of rigid polymers (which are so named to distinguish them from rubbers and gels) resulting from addition of low aspect ratio nanofillers (e.g., clay, nanoparticles, etc.) is not so easy as people imagine. In general, stiffening characterized by increase of modulus can be acquired due to the inherent rigidity of inorganic nanofillers. Toughening is also possible when nanofillers are capable of highly mobile under applied stress, which leads to greater ability of energy dissipation and hence higher ductility of nano composites. The strategy has been evidenced by nanoclay/poly(vinylidene fluoride) or polystyrene (Adv. Mater., DOI: 10.1002/adma.200400984), nano-SiO2/polypropylene or polystyrene (Adv. Mater., DOI: 10.1002/adma.200602611), and carbon nanotubes/polypropylene (J. Mater. Chem., DOI: 10.1039/C1JM14474J). Nevertheless, the reported strengthening effect is far from satisfactory no matter how the composites are prepared. The poor loadbearing capability of the low aspect ratio nanofillers should take the main responsibility. It is worth noting that the results of our recent exploration indicate that the problem might be hopefully solved (J. Mater. Chem., DOI: 10.1039/ C2JM16097H). We found that when nano-SiO2 is present in drawn polypropylene, the aligned chains in amorphous regions can be tied by the well distributed nanofillers to share the stress together. Above the critical content of nanoparticles or drawing ratio, the nanoparticles form percolated network throughout the matrix, facilitating stress transfer in the amorphous phases during tensile test. Additionally, the nanoparticles favor microfibrillation of matrix polymer in the late stage of tensile testing (note: the microfibrils are mainly constituted by the crystalline phases). As a result, the high strength covalent bonds of macromolecules in both amorphous and crystalline phases are brought into full play. The matrix acts as the key load-bearer, while nano-SiO2 gives indispensable assistance. This is different from the mechanism involved in conventional fiber/ polymer composites. Our approach is not a total solution for the aforesaid problem and needs optimization for specific polymers, but it demonstrates the possibility of strengthening rigid linear polymers with low aspect ratio nanofillers. Continuous efforts are needed in this aspect to find out new strengthening mechanism.

P-LINCS: A Parallel Linear Constraint Solver for Molecular Simulation.

By removing the fastest degrees of freedom, constraints allow for an increase of the time step in molecular simulations. In the last decade parallel simulations have become commonplace. However, up till now efficient parallel constraint algorithms have not been used with domain decomposition. In this paper the parallel linear constraint solver (P-LINCS) is presented, which allows the constraining of all bonds in macromolecules. Additionally the energy conservation properties of (P-)LINCS are assessed in view of improvements in the accuracy of uncoupled angle constraints and integration in single precision.

IR spectroscopic identification of chemical bonds in macromolecules of polyacrylonitrile and carbon fibres

A hypothesis concerning the orbital mechanism of formation of the IR absorption spectra of polyacrylonitrile and carbon fibres was advanced and quantitatively substantiated. The previously advanced hypothesis concerning the gravitational mechanism of formation of chemical bonds for a gravitational constant of ∼1028 cm3/g·sec2) was confirmed.

On the possible effect of a magnetic field on the breaking of mechanically loaded covalent chemical bonds

It was established using the EPR method that a magnetic field (B=0.6 T) does not affect the process of the appearance of free radicals that are formed as a result of the breaking of covalent chemical bonds in macromolecules of mechanically loaded fibers of polycaproamide. On this basis, as well as on the basis of some other data, doubts were cast on the possibility of using the assumption (frequently discussed in the literature) on the influence of a magnetic field on the rate of transformation of defect complexes due to singlet-triplet transitions upon the fluctuational lengthening of covalent bonds in such complexes for explaining some manifestations of the magnetoplastic effect in ionic crystals.

Oxidative Destruction of Chitosan During Ozonization

Ozonization of water suspension of chitosan leads to oxidation of amino groups which accompanied by deamination and crosslinkihg of macromolecules. The clearing of 1,4-β-v-glucoside bonds in macromolecule is a basic process in the protection of amino groups by protonation with acid. The polymerization degree of ozonolysis products in acidic medium can be varied in wide ranges depending on reaction conditions. The rate of the interaction of ozone with chitosan depends on the conformation of polysaccharide macromolecules.

Oxidative destruction of chitosan under the effect of ozone and hydrogen peroxide

AbstractIn the present work the results of the study of oxidative destruction of chitosan effected by ozone and hydrogen peroxide are listed. The results obtained verify the rupture of 1,4‐β‐D‐glucoside bonds in macromolecule to be the basic process during amino groups of chitosan protection by acids. The rate of ozone with chitosan interaction depends on the concentration of ions in reaction mass. Destruction of chitosan by hydrogen peroxide leads to the formation of oligosaccharides in contrast to ozonolysis. Hydrogen peroxide oxidizes functional groups of chitosan only under tough conditions. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 875–881, 2001

Reactions and stability of fluorinated poly(vinyl trimethylsilane) in electrochemical systems

Fluorinated poly(vinyl trimethylsilane) (FPVTMS) unlike virgin PVTMS is able to participate in electrochemical reactions and undergoes direct and indirect electrochemical reductive degradation. Specifically, its perfluorinated units are reduced irreversibly at a glass carbon electrode in a 0.05-M (C 4H 9) 4ClO 4 solution in dimethylformamide with subsequent splitting of C–F bonds and formation of conjugated double bonds in macromolecules at the polymer surface. On the other hand, the incompletely fluorinated units at the FPVTMS surface interact with the previously electrochemically reduced background solution to be dehydrofluorinated. This is accompanied by the formation of conjugated double bonds and dissolution of the dehydrofluorinated layer also. The data obtained allowed distinguishing the incompletely fluorinated units from the perfluorinated ones in the fluorinated layer of FPVTMS. Moreover, the quantity of the incompletely fluorinated units in FPVTMS can be determined. It was found that the strengthening of fluorination conditions led to an enhancement of the electrochemically induced FPVTMS transformations.

Effect of Polymer Matrix on Kinetics and Mechanism of Carbene Reactions

The features of kinetics and mechanism of the cage radical reactions initiated by carbenes in solid polymers has been considered. The peculiar low temperature reaction of arylcarbenes is their interaction in clusters with formation of biradicals (BR). The yield of BR is a measure of the distribution non-homogeneity of the carbene precursors in polymers. The reaction of BR formation allows us to study the molecular dynamics at cryogenic temperatures. The main factor determining the kinetic non-equivalence of triplet carbenes in low temperature reaction of the hydrogen atom abstraction is the dispersion of the cage distances between carbenes and C—H bonds of macromolecules. The strong effect of structural modifications in filled polymers on the thermal decay of carbenes has been established. The matrix effect on the mechanism of the product formation in the carbene reactions, associated with the relaxation processes, has been recognized by the example of the polyvinylalcohol cross-linkage. The advantage of polyisoprene stabilization against thermoxidation by the phenol grafting in carbene synthesis has been shown.

Influence of Structure-Physical Properties of Polymer Matrix on Kinetics of Inside Cell Radical Reactions

Abstract In polymethylmethacrylate and cellulose acetate the kinetics of triplet cyclohexadienone carbenes decay by 77–135 K including a hydrogen atom transfer from C[sbnd]H bonds of macromolecules with the radical pair formation was examined. The kinetics of this process reflects the influence of peculiarities on a level of cells. The influence of external magnetic field on the decay of carbenes was established. The character of the magnetic is different in two polymers. It's determined by the cell recombination efficiency of radicals and the exchanged energy in radical pairs depending on mutual radical configurations. The structure-physical modification of polymers by aerosil filling connected with the formation of interfaces influences strong on the rate of carbenes conversions.

Physico-Chemical Principles Governing the Ageing of Elastomers Under the Action of Atmospheric Ozone

Abstract Complex process of ozone degradation of elastomers have been considered as phisico-chemical system. It was shown that reaction of ozone with double bonds in macromolecules was a limiting stage of process. Sensitive methods studying of cracks formation and growth were used in combination with ozone absorption control. It was given basic dependences of cracks growth and stress relaxation upon time and ozone concentration.

Influence of “weak” bonds in macromolecules on the activation energies of fracture of oriented polymers

As a model of the amorphous interlayer of an oriented polymer a study is made of a system of quasi-elastic chains of various lengths and of two types, viz. “normal” ones, and those that contain “weak” chemical bonds. The dependence of the activation energy of fracture U0 on the number of “weaker” chains has been calculated. The value of U0 may be changed not only by altering the number of weak bonds in polymer, but also by mechanical and thermal treatment leading to change in the length of the amorphous interlayer. Predicted changes in U0 in this case are rather small, but may be detected experimentally.

Autoionization mechanism of the rupture of chemical bonds in macromolecules

It was shown that thermofluctuation fracture of bonds may be accompanied by the separation of electrons from macromolecules. Ionization of macromolecules is regarded as the tunnel transition of electrons from local donor levels formed during fluctuation elongation of bonds in macromolecules into deep traps. As a result macromolecules break down into macroions and free macroradicals.

Use of laser radiation in field-electron and field-ion microscopy for observation of biological molecules

An analysis is made of the possibility of using laser radiation in field-electron and field-ion projectors for the selective detachment of electrons or ions from macromolecules. It is proposed to photoionize selectively certain molecular bonds in macromolecules by a multistage process involving several laser pulses at different frequencies. A different laser variant of a field-ion projector is also considered: In this variant it is possible to reduce drastically the electric field intensity necessary for the field ionization of atoms in the imaging gas. It is proposed to use laser radiation in the excitation of atoms of the imaging gas to quantum states near the ionization threshold.