Scaling the Graft Length and Graft Density of Irradiation‐Grafted Copolymers

Abstract

Graft CopolymersIrradiation-induced graft copolymerization is often the easiest route to combine the functionality of two polymers and, furthermore, the average composition of the copolymer is straightforward to control. However, control of the graft length and the graft density is more difficult and has been considered to be infeasible. To test the hypothesis that the graft density and graft length may be increased or decreased via increasing or decreasing the dose of irradiation and graft level, polymer electrolytes are characterized in terms of water sorption, proton conductivity, and nanostructure. Based on the premise that graft density and graft length define ion transport and phase segregation, impedance spectroscopy and small-angle scattering support the hypothesis. The method therefore represents a novel degree of freedom in the design and synthesis of radiation grafted copolymers. 2 of 7) www.advancedsciencenews.com www.mcp-journal.de (

Unique Structural Characteristics of Graft-Type Proton-Exchange Membranes Using SANS Partial Scattering Function Analysis

“…The scattering intensity profiles, I ( q ), for representative f D 2 O are shown in Figure . In agreement with previously reported scattering profiles, − three typical features in the scattering profiles of ETFE-g-PSSA PEMs can be observed in three specific regions. Thus, we defined the corresponding regions in the figure as follows: A small- q upturn in the low- q region at q < 0.12 nm –1 (region I), a broad shoulder-like scattering peak in the middle- q region at 0.12 < q < 1.5 nm –1 (region II), and a distinct scattering peak in the high- q region at q > 1.5 nm –1 (region III).…”

“…This difference might be the reason for the low swelling of the ETFE-g-PSSA PEM under fully hydrated conditions, whereas lower conductivity under the low relative humidity (RH) conditions as compared to Nafion . This new finding is remarkably more advanced than the traditional structural analysis based on the scattering intensity profile, which specifies only the information of ionomer peaks but not the accurate assignment of each component. − This study demonstrates for the first time the repulsive behavior between GPs and water on a small length scale (molecular level) by the delicate PSF analysis using the contrast-variation SANS technique. This structural factor is believed to affect the membrane conductivity significantly and requires special attention for future PEM design.…”

“…Thus, the proton conductivity and fuel-cell performance are controlled by not only the density of the SA groups but also the morphology and connectivity of ion channels . Small-angle X-ray scattering (SAXS) and neutron scattering (SANS) are the most potent techniques for investigating morphology in PSSA-grafted PEMs, such as crystalline structures and phase-separated hydrophobic/hydrophilic regions. − In conventional scattering analysis, the scattering intensity profile, I ( q ), is plotted as a function of the scattering vector, q . The I ( q ) profiles of these PEMs usually show two scattering characteristics: a broad peak in the low- q range at 0.1 < q < 0.3 nm –1 (20–60 nm), corresponding to the microphase separation between graft polymer (GP) domains and the BP matrix due to their immiscibility − and a second peak in the high- q range at 1.5 < q < 3 nm –1 (2–4 nm), so-called the “ionomer peak”, associated with hydrophilic water domains and channels. ,,− The structures of PEMs are usually obtained by the best fitting of appropriate structural models to their I ( q ) profiles; for example, a low- q peak is generally regarded as a distance characteristic determined by a complex combination of interdomain distances, domain form, and effective interaction between adjacent domains. − However, the low- q peak-related structures such as shape, size, and chemical components of the origin are rarely studied, with the exception of a recent report by Narimani et al, where the hard-sphere fluid-structure model (HS-fluid model) originally developed by Kinning and Thomas was introduced to describe the morphology at the low- q range for PEMs composed of a high content (at least 64% vol) of PS polymer chains grafted to the poly-(vinylidene difluoride- co -chlorotrifluoroethylene) backbone.…”

Positron annihilation lifetime spectroscopic analysis of Nafion and graft‐type polymer electrolyte membranes for fuel cell application

“…It was reported that the amorphous ETFE zones and PSSA chains in ETFE-PEM are immiscible. [53,60] Moreover, the higher-order microstructures of ETFE-PEM revealed by SAXS indicate that the PSSA chains were generated mainly inside the lamellae with a GD of 0%-34% and outside with a GD higher than 34%. [8,10,11] Thus, these different amorphous arrangements include the lamellar amorphous within the lamellae and mobile amorphous regions outside of the lamellar as well as the PSSA layers.…”

“…All materials, reagents, and detailed procedures for the preparation of ETFE-PEMs are similar to those described previously. [7,9] Briefly, the ETFE films (50 μm) (Asahi Glass Co. Ltd., Japan) were irradiated using gamma rays from a 60 Co radioisotope source at a dose and dose rate of 15 kGy and 15 kGy/h, respectively. The graft polymerization was conducted by immersing the irradiated film in a styrene solution of toluene at 60 C. The grafting degree (GD) is determined by the following equation: GD (%) = 100(W g À W o )/W o , where W g and W o are the weights of the films after and before graft polymerization, respectively.…”