Polymer Science, Series B最新文献

Poly(N-isopropylacrylamide) has been synthesized for the first time by reversible addition-fragmentation chain transfer polymerization in supercritical carbon dioxide. It has been shown that the molecular weight distribution of the polymer is narrower and its average molecular weights are lower than those of poly(N-isopropylacrylamide) synthesized in supercritical СО₂ (scСО₂) according to the conventional radical mechanism. Both polymers are branched and contain a minor proportion of the gel fraction. The form factors determined by light scattering are 1.35 (conventional polymerization) and 1.11 (reversible addition-fragmentation chain transfer polymerization), which is typical for branched and hyperbranched polymers, respectively. Aqueous solutions of the polymers are thermoresponsive and characterized by a cloud point of 30–31°С.

This paper is the first generalization of the material accumulated in the kinetic study of the ring-opening polymerization of cyclic ketene acetals. The main attention is focused on the difference between the kinetics of radical polymerization of these monomers and the kinetics of polymerization of vinyl monomers. The difference in the mechanisms of elementary events of chain initiation and termination is revealed. Kinetic features of the controlled polymerization of cyclic ketene acetals occurring by reversible inhibition, atom transfer, and reversible-addition fragmentation chain-transfer mechanisms are considered.

The synthesis of polyethersulfones of various chemical structures from commercially available starting materials is described. Quantitative characteristics of the dependences of the polycondensation degree and the molecular weight of the obtained polyethersulfones to the reactant ratio have been determined. The dependenses of the heat resistance of the obtained materials on the molecular weight and rigid-chain moieties introduced into the structure of the polymers have been revealed. The effect of the concentration and the reactivity of the end groups of macromolecules on the thermo-oxidative stability of the product polyethersulfones is shown. The particular attention is paid to the synthesis of polyethersulfones with phenolic end groups and a polycondensation degree of n = 25‒30. Such polymers have a high (up to 20 wt %) solubility in epoxy oligomers upon heating without a significant increase in the viscosity of the epoxy resins and do not form an insoluble phase upon binder cooling, thereby opening up broad prospects for their further use as epoxy modifiers.

The influence of external donor nature on propylene polymerization reactions with titanium-magnesium catalyst activated with AlEt₃ is studied. The use of cyclohexylmethyldimethoxysilane as the donor increases the content of isotactic polymer and the use of 2,6-dimethylpyridine promotes the formation of syndiotactic component in polypropylene. By combining different donors, it is possible to regulate the site distribution in catalytic system with respect to stereospecificity and to modify stereoregularity, molecular weight characteristics and mechanical properties of polypropylene.

Cross-linking of polymer is a simple way to improve stability of dyes into a polymer matrix according to using in different application. In this study spherical poly(methacrylic acid-ethylene glycol dimethacrylate) microparticles consisting of curcumin, rhodamine B and crystal violet were synthesized by precipitation polymerization to obtained possible synergistic effect and Förster resonance energy transfer in a single platform. The synthesized microparticles were characterized using scanning electron microscopy, X-ray diffraction, fluorescence spectroscopy, dynamic light scattering, and differential scanning calorimetry. Microparticles containing curcumin and crystal violet showed 2.7 times higher intensity than microparticles containing curcumin and rhodamine B and 14 times higher fluorescence intensity compared to microparticles containing curcumin only. Also, the most unpredictable result belonged to the microparticles containing crystal violet and rhodamine B. It showed approximately 5 and 2 times higher fluorescence intensity compared to microparticles containing curcumin and rhodamine B and microparticles containing curcumin and crystal violet, respectively. This finding enabled us to design microparticles with minimum toxic effect due to low contents of rhodamine B for bioimaging applications with high sensitivity.

Polymer-based soil ameliorants are considered effective tools to protect soil from wind and water erosion. In the article, five promising modern ameliorants were examined: hydrolyzed polyacrylonitrile (HYPAN, synthetic polyanion), two commercial humic products (potassium humates) and two binary mixtures composed of HYPAN and humates at 10/1 wt/wt ratio, with a special attention to their effects on soil structuring, anti-erosion and hydrophysical properties. The polymers were dissolved in water and the resulting aqueous formulations were 1) sprayed on the surface or 2) injected into the sandy loam soil. The obtained polymer-soil constructs were comprehensively tested for mechanical strength, aggregate composition, anti-erosion stability, water retention capacity and biocompatibility with the following main conclusions. When sprayed over the soil, the formulations penetrate the soil to a depth of 0.5 cm. Drying the soil with deposited polymers results in polymer-soil coatings with mechanical strength varied from 0.7–1.3 kg/cm² for humates to 4.1–6.7 kg/cm² for HYPAN-based formulations. HYPAN coatings provide a 100% soil resistance at an air flow speed of 72 km/h and only 5–7% loss of soil when re-watering. Treatment of soil with HYPAN-based formulations results in a higher water capacity, better retention of water and increased content of agronomically valuable aggregates 0.25–1 mm in size from 34 to 51 wt %. Addition of humates to HYPAN solutions stimulates plants growth. The results obtained are important to develop polymer ameliorants with anti-erosion, water-retaining and biostimulating properties.

Carboxylic polyelectrolytes, water-soluble copolymers of acrylic acid and N-substituted acrylamides, were synthesized for the first time by reactions in the chains of poly(acrylic anhydride) with aromatic amines. The structure, composition, and molecular weight characteristics of the copolymers were determined. The possibility of synthesizing alternating copolymers of acrylic acid was demonstrated. The copolymers of varying composition characterized by low cytotoxicity and activity against herpes simplex virus were prepared.

A novel catalyst system containing a complex of Ti⁴⁺ with a (O,N,O)-tridentate phenoxyimine ligand and a binary Al(C₂H₅)₂Cl/Mg(C₄H₉)₂ activator at a molar [Al]/[Mg] ratio of ~3 affords the synthesis of ethylene polymers with molecular weight in excess of 1 × 10⁶. Ethylene homopolymer produced at 35°C has M_w ~ 2.6 × 10⁶ and ethylene copolymers with small amounts (below 1 mol %) of 1-hexene, 1-octene and 1-decene have M_w ~ 1.5 × 10⁶. The polymers have a relatively narrow molecular weight distribution (M_w/M_n ratio from 3.5 to 5), their mechanical properties are similar to properties of commercial UHMW polyethylenes.

The peroxyoxalate chemiluminescent reaction is an excellent source of excitation for photosensitizers used in theranostics for identification and targeting of tumor cells that produce elevated amounts of hydrogen peroxide. However, the substrates of peroxyoxalate chemiluminescent reaction, aromatic oxalates, are highly susceptible to hydrolysis in aqueous surroundings. Solubilization of oxalates in nanoreactors with a hydrophobic core significantly reduces their degradation by water. In this study, we compared for the first time the efficiency of the peroxyoxalate chemiluminescent reaction in emulsion and micellar nanoreactors. Two oxalates were studied herein, i.e. a highly active bis(2,4,5-trichloro-6-(pentyloxycarbonyl)phenyl) oxalate (CPPO) and nearly 15-fold less active but bioinspired tyrosine-based oxalate (BTEE-ox), which differed significantly in the pK_a of the leaving phenolic group, cytotoxicity, and hydrophobicity. Encapsulation of both oxalates into emulsion nanoreactors increased stability of both oxalates approximately by two orders of magnitude as compared to a THF/water (4 : 1) homogeneous solution. However, the emulsion underwent colloidal destabilization due to Ostwald ripening. In contrast, polylactide-block-poly(ethylene glycol) micelles exhibited excellent colloidal stability and ensured low rate of oxalates hydrolysis. The chemiluminescence activity of BTEE-ox solubilized in micelles became even higher than that of CPPO indicating that solid nanoreactors influenced the peroxyoxalate chemiluminescent reaction efficiency.

MQ resins have proved to be promising fillers for obtaining molecular composites based on silicone and carbon-chain rubbers. In the present work, MQ copolymers play the role of a complex filler with an inorganic core (Q unit) and an organic shell (M unit). Copolymers, in which the ratio of M and Q units was 1 : 2, 1 : 3, and 1 : 4, were used as fillers. Grafted methyl and decyl groups made it possible to use the MQ copolymer as a reinforcing filler of a carbon-chain polymer, polyisoprene. The thermal and rheokinetic behavior of filled compositions during the transformation of elastomers into rubbers was studied. Using differential scanning calorimetry and rheology techniques, the temperature parameters of the crosslinked structure formation process were determined and the values of the apparent activation energy of the crosslinking process were calculated. Increasing the proportion of the inorganic component from 1 : 2 to 1 : 4 resulted in an increase in the storage modulus of the crosslinked composites.