Polymer Science, Series A最新文献

The morphology and tensile properties of reactor polymer compositions based on ultrahigh molecular weight polyethylene (UHMWPE, M_w = 10⁶) with different contents of modifying polyolefin fractions have been studied. The compositions were obtained directly during the polymerization of ethylene using homogeneous catalysts. Modifying polyolefin fractions differed in their structure, molecular weight, and thermophysical properties and included linear HDPE with M_w = 5 × 10⁴ and 1.5 × 10⁵, as well as branched ethylene/hexene-1 copolymers with a 1-hexene content of 3, 10, and 20 mol %. The melting temperatures, the degrees of crystallinity of the materials and the dimensions of the crystallites were determined using the DSC and WAXS. The influence of morphology, physical and mechanical properties of modifying polyolefin fractions, their content on the stress-strain curves and tensile characteristics of reactor polymer compositions have been studied.

The specific free surface energy has been determined by the contact angle measurements for thin films of glassy polymers and dense membranes based on rubbery polymers. The obtained surface energy values have been compared with the coefficient of gas permeability towards nitrogen for the membranes based on investigated polymers. Regardless of the relaxation state of the polymers, linear correlation dependences have been found between the logarithm of the gas permeability coefficient and the nonpolar (dispersive) component of the surface energy of the films (membranes). For the films of glassy polymers, two parallel correlation dependences with close values of the slope tangent have been revealed. For the films of rubbery polymers, these dependences have been individual for each class of the substances. The slope tangents of the correlation dependences for glassy and rubbery polymers are opposite in sign, which is probably due to the difference in their relaxation states and, accordingly, the different nature of the free volume of these types of polymers. For the films based on poly[1-(trimethylsilyl)-1-propyne], the influence of the sample history on the value of the nonpolar component of the surface energy and gas permeability coefficient has been shown. The obtained results allow us to assume that the dispersive component of the surface energy of polymer films and dense polymer membranes can serve as a parameter for comparative evaluation of their gas permeability, and the contact angle measurements make it possible to trace the influence of the history on their surface and bulk properties.

A series of stereoregular linear polymers of alpha-methylstyrene have been synthesized by low-temperature cationic polymerization in solution. Molecular weight distribution functions of the synthesized poly(alpha-methylstyrenes) are determined by gel permeation chromatography. Depending on the synthesis conditions, the average molecular weight of the polymers varies in the range from 140 × 10³ to 490 × 10³. According to X-ray phase analysis, the polymers under study are X-ray amorphous. The syndiotactic structure of polymer chains is established by proton magnetic resonance spectroscopy. Hypercrosslinked alpha-methylstyrene polymers are prepared in a 1% polymer solution in dichloroethane by crosslinking phenyl groups of the polymers with 4,4'-bis(chloromethyl)-1,1'-biphenyl in an amount of 0.5 to 2.0 mol per mol of the monomer unit by the Friedel–Crafts reaction. Low-temperature nitrogen adsorption measurements show that the hypercrosslinked poly(alpha-methylstyrenes) possess a well-developed micro–mesopore system. With increasing the degree of crosslinking of the polymers, the volume of ~2 nm micropores doubles but the average size of mesopores decreases from 8 to 4 nm and their volume fraction decreases from 80 to 60%. The specific pore surface area at the maximum degree of crosslinking is 900 m²/g, and the total volume of pores up to 150 nm is 0.94 cm³/g. Hypercrosslinked alpha-methylstyrene polymers are characterized by a bimodal pore system with predominant micropore fractions of ~2 nm and mesopore fractions of 4–8 nm. The synthesized hypercrosslinked polymers are promising for biomedical applications as adsorbents of toxic organic compounds.

Thermal degradation of polyarylene ketone of the general formula –[–O–C₆H₄–C(=O)–C₆H₄–O–C₆H₄–R–C₆H₄]_n– containing two species differing in chemical structure (R₁ = –C(CH₃)₂– and R₂ = ‒[(C₆H₄–C(=O)O)]–) and in the stability of the units, analyzed within the framework of a kinetic model that includes two parallel reactions involving units and products of their transformation. The predicted kinetic curve of mass loss was obtained by adding the experimental curves of degradation of individual polymers, taking into account the mass fraction of their units in the copolymer. This makes it possible to predict a relatively low temperature resistance of the copolymer, which is consistent with experimental data. The contributions of the three stages of degradation and their activation energies were estimated by the method of nonlinear regression analysis, which includes simultaneous processing of all kinetic information obtained at different heating rates. The correspondence of the found values of the activation energies of the copolymer to the activation energies of the degradation of individual polymers confirms the adequacy of the proposed process model.

Three polyethylene terephthalate glycol (PETG) resins with different molecular structures were used, and their molecular structures (comonomer types, comonomer content), fluidity, and crystallinity were comparatively studied. They were further molded into cast films and subjected to tensile tests at different temperatures, and a series of samples stretched to different ratios were prepared. The tensile behavior and morphological evolution mechanism of PETG cast films during stretching process were revealed by means of differential scanning calorimetry (DSC), two-dimensional small angle X-ray scattering (2D-SAXS), X-ray diffraction (XRD), polarized IR spectra, and tensile performance test. The results showed that the tensile stress-strain curves of the three PETG cast films are quite different, and PETG-A and PETG-C undergo more obvious stretch-induced crystallization behavior during the stretching process. With the increase of the stretching ratio, PETG-B is most likely to be oriented under the external force; while PETG-C is less likely to be highly oriented. Although PETG-A will also be oriented under stretching, its degree of orientation is significantly lower than that of PETG-B. After pre-stretching, the three PETG cast films were stretched again in different directions respectively, and the stress-strain curves of the secondary stretching was investigated. It was found that the secondary stretching behavior was closely related to the orientation and crystallization behavior during the initial pre-stretching. The related mechanism was discussed.

It has been shown that there is a significant difference in the stoichiometry of the complexes of fully and partially saponified poly(vinyl alcohol) (PVA) with lithium chloride and bromide. This phenomenon is explained based on the concept of hybrid interpolymer complexes. In the Raman spectra of the complexes, a single band is observed at 1445 cm^–1.

Properties of compositions based on polycaprolactone, chitosan, and antibiotic ceftriaxone, which are designed for the protection and treatment of long nonhealing wounds, have been studied. It is shown that despite the fact that the film materials are obtained by melt processing at a temperature of 80°C, they possess microbiological activity against Staphylococcus aureus and Pseudomonas aeruginosa. It is demonstrated that varying the content of ceftriaxone and chitosan in the composition makes it possible to control the moisture absorption capacity of the material and the release of drug substance from the film coating, as well as the values of elastic modulus, tensile strength, and elongation at break.

Polyimide exhibits high optical transparency, exceptional thermal properties, robust mechanical characteristics, and dimensional stability. However, conventional polyimides typically do not possess luminescent properties, which significantly restricts their applicability in the domain of optoelectronic devices. A viable approach to address this limitation involves the incorporation of fluorescent powders into polyimide films, thereby ensuring that the films maintain their practical utility while also exhibiting certain fluorescent properties. In this study, we synthesized yttrium oxide (Y₂O₃), which possesses fluorescence characteristics, and incorporated it into polyimide films. The introduction of Y₂O₃ not only imparts fluorescence to the films but also enhances their thermal stability while preserving their mechanical integrity. The glass transition temperature of the modified films is approximately 300°C, and the tensile strength exceeds 85 MPa, surpassing the industry application standards.

In this paper, carboxymethyl cellulose/polyacrylamide single network hydrogel was immersed in ferric ion solution to prepare dual-network ionic conductive hydrogel. The tensile strength, elongation, and conductivity of the hydrogel can reach 1.01 MPa, 411%, and 3.11 S/m respectively. Its super mechanical properties, excellent electrical conductivity, and stable sensing properties can convert external mechanical signals into stable electrical signal output. Carboxymethylcellulose-based double network ion-conducting hydrogels were further used as flexible substrates to assemble flexible sensor devices. Hydrogel sensors can monitor both simple joint movements and complex spatial movements and have potential application value in the research fields of intelligent response electronic devices such as flexible wearable devices and soft robots.