Macromolecular Chemistry and Physics最新文献

Hydrogels are used widely in healthcare disciplines due to factors such as their high water content and safety profile. However, the materials are typically soft and may not be suitable for applications under stress, such as implantation into load-bearing sites. It has been shown that tough hydrogels may be formed by combining brittle chemically-cross-linked polymers with a physically-entangled system to give “double-network” hydrogels. However, the process for chemically cross-linking polymers typically requires reactive species, which are unsafe to use outside of specialised facilities. Furthermore, once the chemical network is formed, the material cannot be remolded. In this study, double-network hydrogels have been formed from two physical networks, namely agar and PVA hydrogels. Agar forms a helical polymer network supported by non-covalent interactions, whereas PVA can form a so-called “cryogel” by freeze-thaw cycling to induce crystallites, which cross-link the network. It has been shown that this approach to producing double-network hydrogels gives tough materials without harsh cross-linking agents. Relationships between PVA molecular weight and gel mechanical properties are probed by approaches including needle-injection, tensile testing, and shear rheometric methods. Formulation factors such as concentration, freeze time, and storage time are also explored.

Recent interest in manipulating the chemistry of block copolymers (BCPs) to manage the covarying properties necessary to meet manufacturing criteria in nanolithography has resulted in the development and expansion of the A-block-(B-random-C) BCP architecture, where the random block allows for the decoupling of thermodynamic and wetting properties. Previous reports of such BCPs have used click chemistry to create the desired random block, but all such instances possess additional functional groups that are susceptible to undesirable side reactions upon annealing, such as cross-linking and surface grafting. This study reports the substitution reaction of polystyrene-block-poly(pentafluorophenyl methacrylate) (PS-b-PPFMA) with primary amines. The resulting methacrylamide structure of the functionalized random block has only an amide linkage between the attached functional group and the polymer backbone, thereby omitting any sources of side reactions within the BCP. The outcomes of this report also demonstrate the enhanced thermal stability of these materials by virtue of their stable amide bonds. A range of random copolymer compositions is assessed to develop BCPs in which the random block has approximately the same surface energy as the PS block. These BCPs can self-assemble into perpendicular lamellae and are therefore promising candidates for directed self-assembly.

Surface and interface engineering of heterogeneous catalysts requires an understanding of structure-activity relationships to enhance catalytic activity and selectivity. Herein, we elaborate on the role of (bio)polymer supports on catalytic activity in polyaniline-chitosan nanocomposites (NCs) that contain Ag nanoparticles (Ag@PNI-(x)-CHT). These NCs can be tailored to enhance selectivity in reductive transformations of model dyes: methylene blue (MB) and p-nitrophenol (PNP). Adjusting the composition (x) of the (bio)polymer fraction is shown to regulate the catalyst structure, stability, activity, and selectivity. The findings herein underscore the critical role of chitosan content and surface modification in governing the interaction with the dye to yield improved catalyst performance and selectivity. The greater Langmuir binding affinity (K_L = ∼68 L mmol⁻¹) and monolayer adsorption capacity (q_m = 0.63 mmol.g⁻¹) of Ag@PNI-(25)-CHT with MB versus PNP reveal that modification of catalysts with chitosan led to surface accumulation of hydrophilic substrates onto the catalyst. Greater catalyst activity parallels the greater rate constant and values of K_L between the catalyst with dyes, and higher q_m values correlate with enhanced catalytic performance. The structure-property relationships reveal a unique reduction mechanism for MB over the PNP dye system, wherein polyaniline serves as the surface-active reduction site.

This study presents an innovative approach to synthesizing multi-reprocessable materials by combining acrylates with dynamic dioxaborolane chemistry. The presented method enables a rapid, solvent-free, and cost-effective synthesis with a tetrafunctional linker to create highly crosslinked materials. The optically transparent vitrimers exhibit a glass transition temperature (T_{g,DMA(6.28 rad s}⁻¹₎) of 58°C and a low activation energy of 33.4 kJ mol⁻¹, allowing for robust thermosetting polymers with exceptional thermal stability—demonstrated by a thermal degradation temperature of 305°C. The stress-relaxation dynamics show a rapid relaxation in 18 s at 110°C. Static stress-relaxation experiments are analyzed using a stretched exponential fit. Furthermore, frequency sweep measurements are used to determine the stress-relaxation properties and to discuss the applicability of two models to fit the stress-relaxation data after annealing. In the tensile test, the materials display an elastic modulus of 1.9 GPa and a tensile strength at maximum elongation of 58 MPa at room temperature after 20 recycling cycles. Finally, potential applications as matrix material for carbon fiber mesh composites or titanium dioxide nanoplates (50 wt.%) are presented.

Chemical stability is a key property for polymeric hot-melt adhesives (HMAs) used in industrial settings. The chemical stability of an HMA and its polyamide base resin (obtained from bio-based dimer acids) is assessed after immersion in various solvents. Visual observation and gravimetry show that they resist alkaline conditions better than acidic conditions and are susceptible to dispersion in organic solvents. The organic solvents’ impact can be predicted using Hansen parameters. Infrared (FTIR) and solid-state NMR spectroscopies confirm the degradation of the polyamide resins and HMA at the molecular level. Solution-state NMR allows the identification of the type of degradation, such as aromatic substitution. Aromatics and vinylics (from the dimer acid) are quantified with solution-state NMR, including benchtop NMR. The precision of the quantification does not depend on the sensitivity of the instrument but rather on the user-dependent data treatment. The degradation occurs via amide hydrolysis, leading to chain scission, without imide formation. Degradation does not affect the relative amount of vinylics but surprisingly affects that of the aromatics. Free-solution capillary electrophoresis (CE) allows the detection and separation of the most hydrophilic degradation products, including monomers, during the degradation in highly acidic or alkaline conditions without any sample preparation.

This research investigated the impact of gamma, e-beam, and X-ray irradiation on medical-grade polypropylene (PP). A comprehensive array of analytical methods was employed to assess the chemical and physical changes in irradiated PP. The main findings revealed that irradiation did not significantly affect the mechanical properties, as tensile strength and elongation at break remained unaltered across all irradiation types and doses. Thermal analysis using DSC indicated a slight reduction in melting temperature at higher doses. ESR identified peroxyl radicals, which decayed similarly regardless of dose or irradiation type. Colorimetric analysis revealed yellowing in PP samples, particularly with gamma and X-ray irradiation, likely associated with specific additives. HPLC analysis showed that the oxidation potential was more influenced by the PP formulation than by the irradiation technology.