Monomer Links Research Articles

Association Equilibrium and Gelation in Solutions of Cross-Associating Chains Containing Inactive Fragments

Solutions of two cross-associating chain molecular species (n-chains and p-chains) containing both associative (“sticky”) and non-associative monomer links have been simulated by molecular dynamics. The inactive monomers increase the stickers’ association equilibrium constant due to the excluded volume effect. In a wide concentration range, the equilibrium constant can be approximated as a simple function of the total volume concentration of the inert monomers, the volume effectively excluded by one inert monomer being about the same at different mixture compositions. Characteristics of molecular aggregates formed at pre-gelation and gelation conditions are examined, including effects of local cyclization.

Effects of the linear chain structure on the cross-association equilibrium between chainlike molecules in a good solvent

Molecular dynamics (MD) simulations have been performed for solutions of two cross-associating chain molecular species (n-chains and p-chains) one of which (p-component) may contain both associative (“sticky”) and inactive monomer links. The solutions of 63-mer chains show a crowding effect similar to that found in mixtures of short oligomers (J. Phys. Chem B, 2016, 120, 7234): the association equilibrium constant calculated from the stickers' concentrations increases with the volume fraction of the component with inactive fragments (“spacers”). For p-chains with inactive spacers of more than 3 monomer units, the equilibrium constant at a given concentration of p-component becomes almost independent of the spacer length. A simple mean field approximation for the excluded volume effect works reasonably well for the solutions of cross-associating chains except for mixtures with high concentration of p-component.

Adsorption of Polycomplexes at Solution/Air Interface

<p>The effect of complex formation of polyacids (polyacrylic (PAAc) and polymethacrylic (PMAAc)) with polyacrylamide (PAA) on their surface properties at solution/air interface has been studied by surface tension, electric conductivity and potentiometric measurements at 293±0.2 K. The relaxation time and surface activity of polycomplexes were calculated from kinetic data on the surface tension. It was found that during complex formation the relaxation time of a surface layer has a maximum and the surface activity of macromolecules is increased. Also the standard free energy of adsorption for PAA and polyacid-PAA polycomplexes were calculated. They are equal DadsG°<sub>293</sub> = - 19.1±0.1 kJ/base-mol. for PAA, DadsG°<sub>293</sub> = -21.2±0.1 kJ/basemol. for PMAAc-PAA polycomplex and DadsG°<sub>293</sub> = -23.0±0.1 kJ/base-mol. for PAAc-PAA polycomplex (calculation per base-mole of PAA monomer link). It is shown that the surface activity and ability to decrease of the water surface tension is less for PMAAc-PAA than for PAAc-PAA. Such anomalous behaviour of PMAAc-PAA polycomplex probably is caused by an excessive strengthening of inner- and intermolecular hydrophobic interactions in macromolecules of PMAAc- PAA polycomplexes due to the presence of α-methyl groups in PMAAc macromolecules. Because of the rebuilding of macromolecule segments of complex by polarity at the interface is becoming a difficult one.</p>

Hydrate hypothesis of living matter origination (LOH-hypothesis)

In the context of the LOH-hypothesis, the following questions are discussed: (1) Could N-bases and riboses originate from CH4-hydrocarbons and niter at the expense of internal energy? (2) How had methane-hydrate originated? (3) How had CH4 and NO 3 − met together? (4) Why are DNA and RNA monomer links similar and limited in size? (5) Why were N-bases and riboses limited in their chemical growth? (6) Why are the sequences of N-bases in DNA and RNA molecules not random? (7) Why do DNA and RNA compositions usually contain only five chemical elements? (8) Why do only five N-bases usually enter the DNA and RNA compositions, and why are other ones random? (9) Could D-ribose, desoxy-D-ribose, thymine, and uracil be simultaneously produced in the reaction of niter with methane? (10) Why did Nature select D-riboses for DNA and RNA construction?

Influence of chain-transfer reactions on the molecular-weight-distribution function of diene rubber on a neodymium-containing catalyst system

The numerical solution of a system of differential equations for the concentrations of the reaction system’s macromolecules, which describe the synthesis of diene rubber on a neodymium-containing catalyst system, has been obtained. The influence of the chain-transfer reactions on the number distributions of the monomer links of macromolecules with an assigned number of active sites has theoretically been investigated.

Electrical and optical properties of composites based on carbazole derivatives and silicon particles

The electrical and optical properties of polymer-silicon composites with particles incorporated by different means have been studied. It is shown that both when silicon particles are embedded in a carbazole-containing polymer matrix and in the case of a pure polymer, the I–V characteristics are nonlinear and asymmetric (the I–V characteristics of the carbazole-containing polyorganosiloxane, which has silicon atoms in the monomer link, behave in a more symmetric pattern). In all cases, the I-V characteristics can be fitted with power laws, I(V) ∼ Vp, with three different slopes for different voltage intervals, which remainds one of the pattern typical of the mechanism of space-charge-limited currents. It is shown that, in its luminescent properties, the carbazole-containing polyorganosiloxane is similar to a carbazole-containing polymer matrix with embedded silicon particles. The results obtained argue for charge transfer between the polymer and silicon nanoparticles if they are embedded in the matrix and for an formation of an interchain charge-transfer complex in the case of chemically bound silicon.

Radical copolymerization of maleic anhydride with organotin acrylates

Copolymerization of maleic anhydride (MA) with trialkylstannylmethacrylates has been studied. Copolymerization constants (r1r2) have been determined for maleic anhydride and trialkylstannylmethacrylates, the parameters Q2 and e2 have been calculated for (CH3)3Sn- (C2H7)3 Sn- and (n-C4H9)3Sn- and (n-C4H9)3Sn- methacrylic acid derivatives: Q2 = 0.31, 0.27, 0.23 and 0.18; e2 = − 0.64, − 0.75, − 0.81 and − 0.88. Kinetic regularities of the reaction have been studied. It has been shown that organotin copolymers composition, as well as their model compound structures, are characterized by the occurrence of coordinate bonds of type. There has been revealed the effect of internal complexation in radical copolymerization responsible for both monomer links laternation along macromolecular chain and possible stereodirection of the reaction. The reactivity of complexomers MA-TBSM and MA- Styrene (St) has been studied by means of terpolymerization.

Low Temperature Polymerization in p-Diethynylbenzene Crystal: Localization of Unpaired Electron in Poly-Conjugated System

Optical and ESR spectroscopy study has revealed that the stereo-regular polymer is formed under UV- or γ-irradiation of para-diethynylbenzene (DEB) crystals over a wide temperature range (77–300 K). It has been shown that the unpaired electron of the macro-radical of the propagating linear polymer chain (77–230 K) is localized on the terminal monomer link to give a doublet splitting in the ESR spectrum. Delocalization of unpaired electron in the poly-conjugated system takes place at 230–300 K by addition of the linear macro-radical to the double bond of the polymer. In this case, a normal polyene-type radical, observed during the polymerization of acetylenic monomers at elevated temperatures, is formed and shows singlet splitting with the width of ΔH = 1 mT in the ESR spectrum. The encounter of the macro-radical with the double bond probably occurs via polymer chain propagation.

Equations of motion for polymer chains in a thermostat

A constrained dynamics method suitable for molecular dynamics simulations is considered to study the long-time dynamics of polymer chains. The method is initially discussed on the basis of the Lagrangian and Hamiltonian formalisms for isolated polymer chains with fixed monomer–monomer links. Subsequently, the corresponding equations of motion are obtained for describing the dynamics of such polymer chains in the presence of a thermostat. The approach is applied to a few typical cases to illustrate how the formalism is implemented numerically and to elucidate its convergence properties when studying such systems in equilibrium. As an example, we consider the problem of reconstructing the backbone structure (chain of Cα atoms) of protein Rubredoxin from its contact matrix. It is shown that the target structure is succesfully reached after a long transient regime (typically in the range from 106 to 108 integration steps). A particular attractive extension of the algorithm presented here is to environment-dependent couplings, which could allow the study of the long-time polymer dynamics in realistic environments. The present method is thus expected to have useful applications in the modelling of the complex dynamics of bio-polymers such as proteins, and also in the context of nanoscale polymer materials.

Complex formation of polyethyleneimine with copper(II), nickel(II), and cobalt(II) ions

AbstractAn influence of the structure of a globule of polyethyleneimine on the complex formation of one with the copper(II), nickel(II), and cobalt(II) ions is described. A change of the coordination number from the pH of solution for complexes of ethylenediamine, diethylenetriamine, and polyethyleneimine with metal ions was found. The fraction of monomer links, bound with metal ions, depends on the volume of the globule of macromolecule as well as the condition of the proceeding reaction. The reaction of complex formation is controlled by the diffusion of metal ions into the polymer globule in solution. The effective equilibrium constants of complex formation were found. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 914–922, 2002; DOI 10.1002/pola.10157

Calculations of the intrinsic constant of an ideal polymer from spectrophotometry data using factor analysis

A new procedure for the mathematical processing of the data of spectrophotometric titration using factor analysis was considered. Both the intrinsic constant of an ideal polymer and the concentration profiles of spectral forms in equilibrium can be calculated by the proposed procedure. Examples of spectrophotometric titrations of ideal polymers that simulate the behavior of polyuridine acid and differ in the number of monomer links in the polymer chain were considered. It was shown that the results of calculations using the proposed procedure are theoretical values of the intrinsic constant in the case when the system possesses high selectivity. In the case of insufficient selectivity, the agreement between the calculated and actual constants can be improved using normalization.

Dynamics of the electron structure of phthalide derivatives at the interaction with low-energy electrons

By means of negative ion mass spectrometry (resonant electron capture spectra) the interaction of electrons (0–15 eV) with molecules of phthalide and its substitutes has been studied. These molecules model monomer links of polymers in which phenomena of charge instability are observed. An instability of CO-bond under interaction of molecule with low-energy electrons and, consequently, high probability of the bond cleavages have been found. It may explain unusual electrophysical properties of polyphthalidilidenarylenes.

Temperature Effects on Thermodestructive Processes

Abstract Temperature effects on thermodestructive processes in polymers are considered. The logarithm of lifetime of a linear polymer thin film on 1/T (inverse temperature) was found to be a smooth increasing curve tending to a limit at definite values of 1/T, characteristic of each polymer. Temperatures above which avalanche-like decomposition of polymers occurred were called “limiting.” To explain the dependence i t was assumed that associated and nonassociated monomer links are destroyed with different rate constants, the sequence of chemical acts in the process being the same. The rate constant of destruction of nonassociated monomer links is higher than that of associated links. Equilibrium of concentrations of associated and nonassociated monomer links is established much more quickly than the chemical reactions run. At rather low temperatures the reaction presumably runs at chain ends. As the temperature increases, the number (concentration) and the length of blocks consisting of nonassociated mono...

On the localization of the unpaired electron in a macroradical of a propagating polymer chain during low-temperature, solid-phase polymerization of p-diethynylbenzene

An electron spin resonance (ESR) study of the UV- or γ-induced polymerization of p-diethynylbenzene (DEB) crystals over a wide temperature range (77–300 K) has revealed that the unpaired electron of the macroradical of the propagating polymer chain (77–230 K) is localized on the terminal monomer link to give a doublet splitting in the ESR spectrum. Delocalization in the polyconjugated system takes place at 230–310 K by addition of the linear macroradical to the double bond of the polymer. In this case, a normal polyene-type radical, observed during the polymerization of acetylenic monomers at elevated temperatures, is formed and shows a singlet splitting with a width of ΔH ∼ 1 mT in the ESR spectrum. The encounter of the macroradical with the double bond probably occurs via polymer chain propagation.

The growth and interaction of conjugated polymer chains, the unpaired electron localization

AbstractAn ESR method was used to study the structure of the macroradical of the propagating chain Rp in the low‐temperature, solid‐phase polymerization of p‐diethynylbenzene (DEB). The ESR spectra for γ‐irradiated DEB samples and those of DEB deuterated in the ethynyl group showed that in the range 77–230 K, the unpaired electron of the macroradical was localized on one of the monomer links. At 230–310 K, its delocalization in a polyconjugated system took place because of addition of a linear macroradical to a double bond of a polymer molecule. The encounter of the macroradical with double bond probably occurs as polymer chain propagation. © 1994 John Wiley & Sons, Inc.

A 13C NMR study of polyflavonoid tannin adhesive intermediates. I. Noncolloidal performance determining rearrangements

AbstractChemical and heat treatments introduce noticeable modifications on the structure of four different polyflavonoid tannin extracts during their modification for use as tannin‐form aldehyde polycondensates. Such modifications are performance determining and account for the profound differences in behaviour of the four tannin extracts when used as tanninformaldehyde adhesives. Such modifications are directly followed by 13C NMR on the tannin extracts. Although some of the modifications observed by 13C NMR appear to correlate well with previous findings by model compounds studies, others could only be observed by 13C NMR of the modified tannin extracts themselves. Structural rearrangements to phlobatannins, depolymerization, recyclation, rearrangement of the type of interflavonoid monomer links, and autocondensation have been followed by 13C NMR and found to occur to different extents in the four tannins accounting for many of their differences in adhesive performance and characteristics. A novel reaction of autocondensation was observed for pecan nut pith tannins, which is different in applied characteristics from other polyflavonoid tannin adhesives. © 1994 John Wiley & Sons, Inc.

Poly(Amide‐Arylates) based on polycyclic bisphenols

AbstractThe microstructure of poly(amide‐arylate) based on cardotype polycyclic bisphenol can be changed by heating it at high temperatures at the expense of interchain exchange reactions. In this case, the block segments in polymer chains reduce in size, tending to form copolymers with statistically distributed monomer links in a polymer chain.

Polymerization of isoprene adsorbed on kaolin from gaseous phase

Polymerization of isoprene adsorbed on kaolin from gaseous phase was investigated. In the polymerization process that part of polyisoprene which is in the closest contact with the substrate surface is crosslinked and cannot be extracted by solvents. The extractible polymer fraction is a mixture of macromolecules of normal structure and of polymer chains which carry OH and/or C = O groups in each monomer link. Oxygen-containing groups are also present in the insoluble polyisoprene fraction. The incorporation of oxygen-containing groups into polymer chains is probably due to the reaction of water molecules bonded to the exchangeable cations in kaolin with double bonds in the polyisoprene molecules. The microstructure of the polyisoprene has been elucidated.

A theoretical analysis of the flexibility of polyimides and polyamido-acids

The flexibility of isolated chains of a wide group of polyimides and certain polyamido-acids has been calculated theoretically. It has been shown that polyimides mostly have individual chains with a high flexibility: in the equivalent freely jointed chain the Kuhn segment contains 5–6 linear bonds and the persistent length varies chiefly in the range 10–20 Å. Equally the flexibility depends on the presence and number of angular discontinuities in the diamine and dianhydride fragments of the monomer link. In the case of the polyamido-acids, the experimental values for the unperturbed dimensions of the molecular coils may be obtained only with the supposition that the amide groups are predominantly in the meta-position.

Hydrogen bonding and structure formation of molecules of unsaturated carboxylic acid polymers in organic solvents

IR spectroscopy has been used to investigate the processes involved in the formation of hydrogen bonds in solutions of unsaturated carboxylic acid polymers in dioxane and in mixtures of dioxane with small additions of methanol. It has been shown that the poly-acid macromolecules have a secondary structure formed by intra-chain hydrogen bonds (COOH-dimers) between monomer links that are both remote and also neighbouring in the chain. The degree of intra-chain ordering is determined by the chemical structure of the polyacid. Structure formation of the solutions has been studied close to the phase separation temperature.