Secondary structure of globules of copolymers consisting of amphiphilic and hydrophilic units: Effect of potential range

The relation of the coil-globule transition in macromolecules consisting of amphiphilic and hydrophilic monomer units to the radius of action of the interaction potential is investigated by the method of computer-assisted experiments. The internal structure of globules formed by such macromolecules is significantly dependent on the radius of action of the potential. In the case of the long-range potential, the globule is characterized by the blob structure, while in the case of the short-range potential, a quasi-helical structure forms. In this structure, the skeleton of a macromolecule forms a helical turn, and the direction of twisting may vary from one turn to another. The coil-globule transition in such macromolecules proceeds through formation of the necklace conformation from quasi-helical micelle beads. For sufficiently long macromolecules, the dimensions of such globules are linearly dependent on the degree of polymerization.     

Investigation of local density of monomer units and molecular dynamics in solutions of poly-4-vinyl-pyridine by the spin label technique

The local density of monomer units of the macromolecule (local density of the host molecule, ?_host) in poly-4-vinyl-pyridine solutions in ethanol was determined by the spin label technique. In dilute solutions, ?_host is considerably greater than the mean density of monomer units in the volume of the polymer coil; when the polymer concentration rises from 0.5 to 65 wt%, its increase does not exceed 30%. This indicates that the differences between polymer coil microstructure (mutual positions of monomer units close to a chosen unit) in dilute and concentrated solutions is small. The local density of monomer units of neighbouring macromolecules (guest macromolecules, ?_guest) is strongly dependent on the polymer concentration in solution. In dilute solutions, ?_host ? ?_guest; for polymer concentrations above 2–3 wt%, overlapping and interpenetration of macromolecular coils take place, local density of monomer units of neighbouring macromolecules rises and monotonously increases as polymer concentration grows. The concentration dependence of the local rotational and translational mobility of monomer units is determined by the local density of monomer units of the neighbouring macromolecules.     

Effect of ozone on poly(vinyl chloride) degradation

The influence of ozone on the kinetics and mechanisms of poly(vinyl chloride) degradation has been studied. The rate constants for reaction of ozone with saturated and unsaturated units of macromolecules have been measured. The products of the reaction of ozone with double bonds are inactive and do not influence the subsequent thermal dehydrochlorination of the polymer. The products of reaction of ozone with saturated units greatly increase dehydrochlorination.     

Some problems of nonequilibrium copolycondensation

The influence of the reactivity of the starting compounds and reaction conditions on the formation of the macromolecules of copolymers has been investigated for a nonequilibrium copolycondensation in solution by acceptor-catalytic polyesterification. In the nonequilibrium copolycondensation in solution, copolymers with different distributions of units may be formed, depending on various factors. Introduction of all amounts of acid chloride (intermonomer) in the beginning of the nonequilibrium copolycondensation leads to the formation of copolymers with statistical distribution of the units independent of the difference in reactivity of the comonomers used. For synthesis of copolymers with a block structure by one-stage nonequilibrium polycondensation in solution the initial comonomers must have different reactivities (r ≠ 1) and the rate of intermonomer introduction must be lower than that of its reaction with the more reactive comonomer. On varying the above factors, block copolymers with different lengths of block segments may be obtained.     

Synthesis and structure of built-up organic macromolecules containing helicene

Built-up macromolecules are acyclic molecules with molecular weights of several thousand daltons, which are synthesized by connecting small molecular units using stepwise methods. The chemical study of built-up macromolecules reveals some noteworthy properties that are different from those of conventional biological and synthetic macromolecules. A characteristic feature of built-up organic macromolecules is that their structures and properties are discontinuous at a certain molecular weight. For such macromolecules, variation in the small molecular units and the formation of cyclic structures substantially affect the structure and properties. The built-up organic macromolecules obtained by connecting helicenes with amide, acetylene, and amine groups are discussed in this paper. Some chiral built-up macromolecules are linked by covalent bonds, and the effects of linking on the structure are compared.     

Fabrication and Mechanical Performance of Non-Crimp Unidirectional Jute-Yarn Preform-Based Composites

This work developed novel jute-yarn, non-crimp, unidirectional (UD) preforms and their composites, with three different types of warp jute yarns of varying linear densities and twists in the dry UD preforms, in order to present a possible solution to the detrimental effects of higher yarn twists and crimp at the warp–weft yarn interlacements of traditional, woven, preform-based composites on their mechanical properties. In the developed UD preforms, warp jute yarns were placed in parallel by using a wooden picture-frame pin board, with the minimal number of glass weft yarns to avoid crimp at the warp–weft yarns interlacements, which can significantly enhance the load-bearing ability of UD composites compared to traditional, woven, preform composites. It was found that an optimal combination of jute warp yarn linear densities and twists in the UD preforms is important to achieve the best possible mechanical properties of newly developed UD composites, because it encourages a proper polymer-matrix impregnation on jute fibres, leading to excellent fibre–matrix interface bonding. Composites made from the 25 lb/spindle jute warp yarn linear density (UD25) exhibited higher tensile and flexural properties than other UD composites (UD20, UD30). All the UD composites showed a much better performance compared to the traditional woven preform composites (W20), which were obviously related to the higher crimp and yarn interlacements, less load-carrying capacity, and poor fiber–matrix interfaces of W20 composites. UD25 composites exhibited a significant enhancement in tensile modulus by ~232% and strength by ~146%; flexural modulus by 138.5% and strength by 145% compared to W20 composites. This reveals that newly developed, non-crimp, UD preform composites can effectively replace the traditional woven composites in lightweight, load-bearing, complex-shaped composite applications, and hence, this warrants further investigations of the developed composites, especially on long-term and dynamic-loading mechanical characterizations.     

Effect of stability of nanosized catalyst-polymer substrate complex on hydrolysis of poly(<Emphasis Type="Italic">N</Emphasis>-vinylpyrrolidone) in copper sols

The causes of a high total conversion and the S-shaped pattern of the time dependence of conversion for copper sol-catalyzed hydrolysis of the lactam rings of poly(N-vinylpyrrolidone) have been studied. The high conversion of the hydrolusis is achieved via replacement of modified macromolecules in shields of catalyst particles with less modified macromolecules from the dispersion medium of a sol in the course of reaction owing to a decline in the stability of copper nanoparticle complexes with macromolecules with an increase in the degree of hydrolysis. A reduction in the complex stability leads to an increase in the lability of bonding of shielding polymer chains with the catalyst surface and to the growth of the rate of rearrangement and the overall rate of reaction after the induction period. This situation is also responsible for the enlargement of nanosized catalyst particles in the course of reaction and the destruction of the sol after a limiting conversion of units of ～40–50% is attained.     

Relationships of graft polymerization of vinyl monomers onto cellulose. Reaction kinetics and polymer structure

Graft polymerization of acrylamide and sulfuric salt of 2-methyl-5 vinylpyridine onto cellulose using CO(III) salts was studied. It was shown that graft polymerisation of water-soluble polymers can be described by general relationships of radical reaction. The relation between elementary reaction constants of the formation and termination of active centers in cellulose, as well as relation between constants of the propagation, transfer and termination of chains were determined for different cellulose materials and monomers. The translational diffusion, sedimentation, viscosity, and flow birefringence of copolymers have been investigated in different solvents. Experimental data showed that the copolymers obtained are graft copolymers with two to five grafted chains onto macromolecules. The minimum distance between the branch points is 100 ± 20 glucoside units. The peculiarity of these copolymers is relatively low polydispersity. The conformation of macromolecules of such copolymers in solution depends on the compatibility of the copolymer components and the thermodynamic properties of the solvent.     

Synthetic strategies for the preparation of proton-conducting hybrid polymers based on PEEK and PPSU for PEM fuel cells

Synthetic strategies for the preparation of proton-conducting hybrid polymers based on Poly-Ether-Ether-Ketone (PEEK) and Poly-Phenyl-Sulfone (PPSU) are presented. Sulfonation reactions are discussed as a function of sulfonating agents and reaction conditions. Metalation reactions are also described, specifically the introduction of silanol units into the macromolecules. The objective is to improve the proton conductivity of the hybrid polymers by sulfonation, and the mechanical and thermal stabilities by introduction of silicon moieties. Examples of NMR spectra and thermogravimetric curves are shown and discussed in view of the macromolecular structure.     

The general theory of irreversible processes in solutions of macromolecules

The general theory of irreversible processes in solutions of macromolecules, previously formulated by the author, is reviewed. The theory is based upon the Oseen method for determining the perturbation in the hydrodynamic flow pattern produced by the frictional forces exerted by the macromolecule on the solvent, and on a generalized theory of Brownian motion in molecular configuration space. Applications of theory to viscoelastic behavior, flow birefringence, and the Kerr effect, and to dielectric dispersion are presented in outline.     

“Recognition” of copolymers and stereoisomers in macromolecule complexation reactions in dilute solutions

Theoretical relationships have been obtained describing the dependence of selectivity (or molecular “recognition”) on the length of reacting polymer chains in reactions between complementary macromolecules. The possibility of highly efficient separation of mixtures of macromolecules, differing little in chemical structure, was predicted as well as of fractionation of compositionally inhomogeneous copolymers by means of polymer-polymer interactions. Experimentally it has been found that polyethylene glycol mixed with polymethacrylic acid stereoisomers is selectively bound in a polycomplex with macromolecules enriched with iso-triads; polyvinylpyrrolidone is selectively bound to those poor in iso-triads. Polyvinylpyrrolidone selectively binds polymethacrylic acid in mixtures with copolymers of acrylic and methacrylic acids. The degree of “recognition” of a macromolecule of given chemical structure by an oligomer increases with increasing oligomer chain length and is in a quantitative agreement with the theoretical equation. It has been shown that, in aqueous solution for interaction of polyacrylic acid with compositionally inhomogeneous copolymer of 4-vinylpyridine and N-ethyl-4-vinylpyridinium bromide (partially quaternized polyvinylpyridine), the polyacrylic acid binds selectively the fractions rich in non-alkylated units. This result can be explained quantitatively in terms of the theory.     

Synthesis and characterization of cyanoethyl hemicelluloses and their hydrated products

A novel type of hemicellulosic derivative, cyanoethyl hemicelluloses (CEH), derived from xylan-rich hemicelluloses and acrylonitriles was successfully prepared in aqueous sodium hydroxide. The reaction was performed under various reaction conditions such as temperature, time, the amount of sodium hydroxide, and the molar ratio of acrylonitrile to anhydroxylose units in hemicelluloses, and the relationship between reaction condition and DS of the CEH was investigated in detail. A series of CEH with degree of substitution of cyanoethyl (DS_C≡N) ranging from 0.23 to 1.64 were obtained. Importantly, CEH can undergo various reactions and convert into other macromolecules with functional groups like carboxylic acids, amine, aldehyde etc. In this work, H₂O₂/K₂CO₃/DMSO was used to hydrate CEH into carbamoylethyl hemicelluloses at room temperature. FT-IR, ¹H and ¹³C NMR spectra confirmed the introduction of cyanoethyl groups into the hemicelluloses backbone and the presence of carbamoylethyl groups in the hydrated product. In addition, in the nucleophilic addition reaction, the hydroxyl groups at C-3 position of the anhydroxylose units were more active than these at C-2. TGA/DTG showed that CEH had lower thermal stability than hemicelluloses. This work provided a new macromolecule which can be used as a versatile platform for producing other functional macromolecules.     

Mechanism of action of some stabilizers in the thermal degradation of poly(vinyl chloride)

The dehydrochlorination of PVC under vaccum has been studied at 170–200°C by a volumetric method. The accelerating effect of HCl is related to its interaction with the forming polyene units of macromolecules. A mechanism is proposed. The effects of various stabilizers, such as organic salts of Ca, Ba, Cd, trialkyl- and dialkyltin, trialkyl phosphites, and mixtures of phosphites with metal salts upon the rate of dehydrochlorination, polymer crosslinking, and electron absorption spectra of PVC during degradation in evacuated ampoules were investigated. The stabilizing activity of these compounds depends primarily on the effectivity of absorption of HCl and destruction of polyene units by these compounds.     

Controlled adsorption-desorption of cationic polymers on the surface of anionic latex particles

The complexation of anionic latex particles with two series of cationic copolymers is studied. The copolymers of the first series contain cationic and electroneutral (zwitter ion) hydrophilic units. The electrostatic adsorption of these copolymers on the surface of latex particles is accompanied by the formation of multiple salt bridges between cationic copolymer units and surface anionic groups. The dependence of ultimate adsorption on the molar fraction of cationic groups in copolymer α is described by a bell-shaped curve with a maximum at α = 0.05−0.10 and a long horizontal portion at α > 0.24. In terms of the adsorption theory of polyampholytes, such a pattern of the adsorption curve results from the compromise between the attraction of polymer chains to the surface induced by their polarization in the electric field of particles and the repulsion of like charged macromolecular units. The stability of complexes with the copolymers of the first series in water-salt media increases with an increase in α. The copolymers of the second series contain cationic and hydrophobic units. In this case, an increase in α is accompanied by a decrease in the amount of the adsorbed polymer throughout the studied α range (0.24–1). The complexes are stabilized not only via electrostatic interactions but also via hydrophobic interactions. A decrease in α decreases the role of electrostatics in stabilization of the complexes; however, this effect is compensated for by an increase in the number of hydrophobic contacts. This allows the stability of complexes to be preserved in concentrated water-salt solutions. The results of this study indicate that the stability of interfacial layers with the participation of cationic copolymers can be changed in a wide range by varying the ratio of ionic and electroneutral (hydrophilic or hydrophobic) comonomers in macromolecules.     

Thermo-oxidative degradation of some elastomers with a high content of 3,4 isoprene units

New elastomers with high content of 3,4 isoprene units have been developed during the last decades in an attempt to ensure superior performances of the final products and the present study is devoted to the investigation of some peculiarities of their ageing behaviour. On thermo-oxidative degradation, 3,4 isoprene units are less affected in comparison to cis-1, 4 and trans-1, 4 isoprene units. The degradation process consists mainly in splitting of the main chains at temperatures of 80–100 °C while at higher temperatures (120–130 °C) branching becomes a significant modification and this reaction is enhanced for the polymers containing preponderantly 3,4 units. Such behaviour leads to the fact that the processability of polymers containing high amounts of 1,2 and 1,3 isoprene units is less affected by thermo-oxidative degradation in comparison with cis-1, 4-polyisoprene, which could be explained by the fact that large amounts of double bonds are not present in the backbone of macromolecules but in the pendent groups.     

Synthesis and Catalytic Studies of Thermoresponsive Copper (I) Complex towards Click Reactions

Click reaction or copper-assisted azide–alkyne cycloaddition (CuAAC) reaction can conveniently synthesize desired organic molecules or functionalize biological macromolecules. In many cases, trace amounts of residual copper from the reaction mixture are not trivial to remove when the exhaustive purification step is avoided to fulfill the essential criteria of a click reaction. It is often detrimental, particularly for biochemical applications or when it involves biological macromolecules. Herein, we have reported the synthesis of a new type of copper (I) complex as a smart catalyst for click reaction, which can be separated from the reaction mixture very easily by the slight elevation of temperature, thanks to its thermoresponsive behavior. The click reactions using a thermoresponsive catalyst were first studied in an aqueous medium using various organic molecules containing alkyne and azide functional groups. Later, the strategy was extended to biological macromolecules like collagen.     

An analysis of fractal geometry of macromolecular gelation

With fractal geometry theory and based on experiments, an analysis of fractal geometry behavior of gelation of macromolecules was carried out. Using the cross-linking copolymerization of styrene-divinylbenzene (DVB) as an example, through the determinations of the evolution of the molecular weight, size and the dependence of scattering intensity on the angle of macromolecules by employing laser and synchrotron small angle X-ray scattering, respectively, this chemical reaction was described quantitatively, its fractal behavior was analyzed and the fractal dimension was also measured. By avoiding the complex theories on gelation, this approach is based on modern physical techniques and theories to perform the analysis of the behavior of fractal geometry of macromolecular gelation and thus is able to reveal the rules of this kind of complicated gelation more essentially and profoundly.     

Stab resistance of UHMWPE fiber composites impregnated with thermoplastics

Compared with aramid fabrics, ultrahigh molecular weight polyethylene fiber unidirectional (UHMWPE UD) composites have higher ballistic limited velocity at the same areal density, making UHMWPE UD composites better candidate materials for the design of body armor against ballistic and stab impact. In this study, UHMWPE UD composites impregnated with thermoplastic films were prepared, and a novel methodology was proposed to evaluate the stab‐resistant performance of these composites using the concept of stab impact. Stab‐resistant performance is strongly affected by stab impact parameters, such as stab velocity or impact energy, layers of UD, and stab angle. Results show that the stab‐resistant performance of composites can be significantly improved by thermoplastic films, particularly polyethylene terephthalate and polypropylene films. The structure of UD composites functions importantly in enhancing stab resistance. Copyright © 2014 John Wiley & Sons, Ltd.     

Mode of photocatalytic bactericidal action of powdered semiconductor TiO2 on mutans streptococci.

Powdered semiconductor TiO2 has a photocatalytic bactericidal capacity on some kinds of bacteria, but its mechanism still remains unclear. The mode of its photocatalytic bactericidal action on the mutans group of streptococci was investigated. Powdered TiO2 had a bactericidal capacity on all serotypes of mutans streptococci. Streptococcus sobrinus AHT was mainly used for these experiments. The most effective concentration of TiO2 was about 1 mg ml-1 and, at this concentration, 10(5) colony-forming units of S. sobrinus AHT per millilitre were completely killed within 1 min. In order to search for the mechanism of this effect, a high bacterial cell density (10(9) colony-forming units ml-1) was used in the following studies. "Rapid" leakage of potassium ions from the bacteria occurred parallel to the decrease in cell viability. Protein and RNA were "slowly" released from bacterial cells for a reaction time up to 120 min. The pH of the reaction mixture decreased continuously to 4.5 after 120 min. Co-aggregation of S. sobrinus AHT and powdered TiO2 occurred at high bacterial densities (above 10(8) colony-forming units ml-1). Aggregates gradually decomposed with light irradiation. Transmission electron microscopy of S. sobrinus AHT after photocatalytic action for 60-120 min indicated complete destruction of bacterial cells. From these results, bacterial death appears to be caused by a significant disorder in cell membranes and finally the cell walls were decomposed.