A Novel Characterization Method for Graft‐Polymer Structures Chemically Attached on Thermally Stable Polymer Films

Abstract

Most polymer grafts in grafted polymer fi lms obtained by radiation-induced solid graft polymerization are not analyzed in detail due to diffi culties in isolation of the grafts without structural decomposition. Herein, a novel structural and molecular weight characterization method is reported for polymer grafts that are chemically attached to thermally and chemically stable polymer substrates, based on a swelling-induced graft detachment in hot water. Polymer grafts prepared by the radiation-induced polymerization of alkyl acrylate into poly(ethylene-co -tetrafl uoroethylene) (ETFE) followed by a sulfonation reaction are found to have a ternary copolymer structure whose monomer units contain -COOH or -SO 3 H groups, or both. fuel-cell polymer-electrolyte membranes for mobile power, vehicles and domestic cogeneration systems. [ 2 , 3 , 6-16 ] The analysis of the chemical structures and molecular weights of the grafts in grafted fi lms prepared by radiationinduced graft polymerization and the subsequent solidstate chemical transformations is restricted to degradable or soluble polymer substrates, such as poly(ethylene oxide), poly(butylene oxide) and natural polymers. [17][18][19] However, grafts introduced into practical polymer substrates are generally thermally and chemically stable, and, thus, cannot be isolated from the substrates for detailed analysis. Recently, we found that the poly(styrenesulfonic acid) (PSSA) grafts in fl uorinated polymer substrates can be successfully isolated in water at 85 ° C by the swellinginduced detachment of the hydrophilic grafts from the hydrophobic polymer substrates without decomposition of the side chains and main chains (thus maintaining the molecular weights). These results were confi rmed by performing UV-vis and NMR spectroscopy. [ 20 ] We have reported previously that graft-type polymerelectrolyte membranes (PEMs) consisting of alkylsulfonic acids were synthesized by the radiation-induced graft polymerization of methyl acrylate (MA) into a poly(ethylene-co -tetrafl uoroethylene) (ETFE) fi lm,

Counter‐Anion Effect on the Properties of Anion‐Conducting Polymer Electrolyte Membranes Prepared by Radiation‐Induced Graft Polymerization

“…The OH − conductivity and water uptake of AEM‐Cl films with GDs of 34–95%, along with the corresponding values for AEM‐OH and AEM‐HCO 3 films, are plotted in Figure 4, for comparison with other PEMs with the same IEC levels. AEM‐Cls with IECs ranging from 1.53 to 2.68 mmol g −1 showed conductivity (8.3–29 mS cm −1 ) and water uptake (19–57%) values similar to those of PEMs such as Nafion and graft‐type PEMs with poly(styrenesulfonic acid) grafts 3, 16–23. The AEM‐HCO 3 films showed conductivity (6.1–25.1 mS cm −1 ) and water uptake (22–67%) nearly similar to those of the AEM‐Cl films, even though bicarbonate ions possess a pH (dissociation degree) much lower than that of chloride ions.…”

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

“…Enomoto et al. argued that when ETFE was grafted with methyl acrylate, the long‐term swelling in hot water (85 °C) resulted in the detachment of the grafts from the base polymer, and the length of the grafted chains could be measured via gel permeation chromatography . The swelling approach, however, is reported to result in additional chain‐scission mechanisms, which questions the accuracy and selectivity of the analysis .…”

Cleavage of the Graft Bonds in PVDF–g–St Films by Boiling Xylene Extraction and the Determination of the Molecular Weight of the Graft Chains

“…For example, a hydrophilic monomer can be grafted onto a hydrophobic backbone [6,7,8,9], and an ionic monomer can be grafted onto an insulating film [10,11,12]. Due to these versatile advantages, the radiation grafting has been used to modify existing films, fibers, and particles for applications such as ion-conductive membranes [13,14,15,16,17,18], adsorbents [19,20,21], sensor materials [9], and compatibilizers for polymer blends [22]. This radiation grafting is a “graft from” process in which free radicals that are produced on the backbones by irradiation initiated the polymerization of graft chains, forming C–C chemical bonds between graft chains and backbones, namely graft bonds [23,24,25].…”

“…Recently, the separation of materials chains from fluoropolymer-based grafted films has been achieved by immersion in hot water or solvents [17,18]. Nevertheless, in these cases, it is difficult to ascertain whether the separated materials correspond to graft chains or homopolymer.…”