Detailed analysis on thermal,microstructural, mechanical,and morphological features of side chain liquid crystalline polymer/isotactic polypropylene graft copolymers: Effect of grafted and ungrafted polymer units

The main scope of this comprehensive study is to investigate the effects of poly(p-benzophenoneoxycarbonylphenyl acrylate), poly(BPOCPA), which presenting as only graft units or both graft and ungrafted units in the matrix, on the fundamental features of isotactic polypropylene (IPP). The graft copolymerization of BPOCPA onto IPP was performed with the aid of bulk melt polymerization at varying monomer content levels ranging from 5% to 40%. The thermal behavior, crystal quality, mechanical performance, and surface morphology of the samples were investigated by means of differential scanning calorimeter, X-ray diffractometer (XRD), universal mechanical test, and scanning electron microscope (SEM) techniques. Thermal analyses depicted that there existed the noteworthy enhancements in both crystalline melting temperatures and percent crystallinities of matrix polymers. Furthermore, according to XRD results, a and b parameters increased significantly at low percentages of the graft units, while the parameter c decreased in all products in consistence with the content. As for the mechanical characterization, the grafting led to remarkable improvements in modulus, tensile and impact strength of the products. SEM micrographs indicated that the samples were completely homogeneous without any phase separation and the products exhibited brittle nature with some ductility.     

Preparation and characterization of highly stable protic-ionic-liquid membranes

A highly durable proton exchange membranes (PEM)s based on covalently supported ionic liquid (IL) bearing sulfonic acid imidazolium groups were successfully fabricated. The membrane preparation involved radiation induced grafting of 1-vinyl imidazole (1-VIm) onto poly(ethylene-co-tetraflouroethene) (ETFE) film, followed by covalent immobilization of 3-sulfopropyl and subsequent treatment with trifluoromethanesulfonic acid. The ionic conductivity of the supported IL membranes was increased with the increase in the concentration of IL and reached a maximum value of 138 mS cm⁻¹ in a fully hydrated state with an ion exchange capacity of 4.82 mmol g⁻¹ that is higher than Nafion with a similar thickness. The membranes displayed excellent chemical and mechanical stability. In addition, the dimensional and thermal stability of supported IL-membranes were significantly higher than commercial Nafion membranes.     

Separators for alkaline water electrolysis prepared by plasma-initiated grafting of acrylic acid on microporous polypropylene membranes

Highly hydrophilic separators for alkaline water electrolysis were prepared by plasma-initiated grafting of acrylic acid on porous polypropylene (PP) membranes. The membranes were activated in a low-pressure radio-frequency discharge in oxygen and subsequently graft polymerization of acrylic acid was performed in aqueous solution. The membranes were characterized by gravimetric grafting degree (GD), SEM, FTIR, critical wetting surface tension (CWST) test, mechanical strength, and electrolytic conductivity. Moreover, the membranes were applied as separators in alkaline electrolysis cell, and content of hydrogen in the produced oxygen was measured to determine membrane permeability to hydrogen dissolved in the electrolyte. It was observed that increasing GD improves performance of membranes as separators in alkaline electrolysis, although the particular effects on the electrolytic conductivity and hydrogen permeability strongly depend on structure the of initial PP substrate. Ageing test conducted in 30 wt% KOH at 60 °C revealed that although considerable degrafting took place at beginning of the test, the remaining polyacrylic acid provided highly hydrophilic character to membrane for 7000 h of the test.     

High-performance sodium polyacrylate nanocomposites developed by using ionic liquid covalently modified multiwalled carbon nanotubes

Ionic liquids grafted with multiwalled-nanotubes (CNT Br/NTf₂), involving hydrophilic bromide salt and hydrophobic bis(trifluoromethanesulphonyl)imide salt, were prepared by amidation, followed by an easy solution-casting method of blending CNT Br/NTf₂ with sodium polyacrylate (PAA) as well as crosslinking agent (XR-100) to form PAA hybrid nanocomposites. The uniform dispersion of CNT Br/NTf₂ were analyzed by TEM. The defects and physical properties of fillers were characterized by Raman spectroscopy, Contact angle test, and TGA. Furthermore, microstructures of hybrid nanocomposites were characterized by SEM, from which it can be found that fillers were homogeneously distributed in the PAA matrix. CNT Br/NTf₂ significantly improved the mechanical properties and tensile fatigue resistance, as well as offered tunable swelling behavior of PAA nanocomposites without wasting too much of thermal stability. This study offers a simple approach to develop multifunctional materials based on ionic liquids covalently modified MWCNTs PAA nanocomposites.     

Copolymer synergistic coupling for chemical stability and improved gas barrier properties of a polymer electrolyte membrane for fuel cell applications

A novel radiation grafted ETFE based proton conducting membrane was prepared by double irradiation grafting of two different monomers. The intrinsic oxidative stability of the ETFE-g-poly(styrene sulfonic acid-co-divinylbenzene) membrane was improved by reducing the gas crossover through incorporation of polymethacrylonitrile (PMAN) containing the strong polar nitrile group. A fuel cell test was carried out at 80 °C under constant current density of 500 mA cm⁻² for a time exceeding 1′900 h. The incorporation of PMAN considerably improves the interfacial properties of the membrane-electrode assembly. No significant change in the membrane hydrogen crossover and performance over the testing time was observed, except for a measured decrease in the membrane ohmic resistance after 1′000 h. The combination of the double irradiation induced grafting with the use of the PMAN as gas barrier in addition to its chelating abilities (e. g. Ce³⁺) offers a promising strategy to develop more durable membranes for fuel cells.     

Polymer on Top: Current Limits and Future Perspectives of Quantitatively Evaluating Surface Grafting

Well‐defined polymer strands covalently tethered onto solid substrates determine the properties of the resulting functional interface. Herein, the current approaches to determine quantitative grafting densities are assessed. Based on a brief introduction into the key theories describing polymer brush regimes, a user's guide is provided to estimating maximum chain coverage and—importantly—examine the most frequently employed approaches for determining grafting densities, i.e., dry thickness measurements, gravimetric assessment, and swelling experiments. An estimation of the reliability of these determination methods is provided via carefully evaluating their assumptions and assessing the stability of the underpinning equations. A practical access guide for comparatively and quantitatively evaluating the reliability of a given approach is thus provided, enabling the field to critically judge experimentally determined grafting densities and to avoid the reporting of grafting densities that fall outside the physically realistic parameter space. The assessment is concluded with a perspective on the development of advanced approaches for determination of grafting density, in particular, on single‐chain methodologies.     

Effects of modified silica on the co-vulcanization kinetics and mechanical performances of natural rubber/styrene–butadiene rubber blends

Rubber blends are widely used for combining the advantages of each rubber component. However, to date, how to determine and distinguish the vulcanization kinetics for each single rubber phase in rubber blends during the co-vulcanization process is still a challenge. Herein, high-resolution pyrolysis gas chromatography–mass spectrometry (HR PyGC-MS) was employed for the first time to investigate the vulcanization kinetics of natural rubber (NR) and styrene–butadiene rubber (SBR) in NR/SBR blends filled with modified silica (SiO₂). The reaction rates of crosslinking of each rubber phase in NR/SBR were calculated, which showed that the crosslinking rates of NR were much lower than those of SBR phase in the unfilled blends and blends filled with unmodified and silane modified silica. Interestingly, the vulcanization rates of NR and SBR phase were approximately same in the vulcanization accelerator modified silica filled blends, showing better co-vulcanization. In addition, the vulcanization accelerator modified silica was uniformly dispersed and endowed rubber blends with higher mechanical strength compared to the untreated silica. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48838.