Perfluorinated polymer film with functional group prepared by radiation-induced grafting

doi:10.1016/j.eurpolymj.2009.03.008

European Polymer Journal

Volume 45, Issue 6, June 2009, Pages 1668-1673

https://doi.org/10.1016/j.eurpolymj.2009.03.008 Get rights and content

Abstract

A perfluorinated vinyl ether monomer, 2-bromotetrafluoroethyl trifluorovinyl ether (BrTFF) was grafted into crosslinked poly(tetrafluoroethylene) (cPTFE) films by γ-rays irradiation under different conditions. The irradiation with absorbed doses more than 550 kGy gave the poly(BrTFF) grafted cPTFE membranes with grafting yields of more than 20%. FTIR spectra and SEM–EDS testified that BrTFF was successfully grafted into cPTFE films homogeneously in the film perpendicular direction. TGA analysis of the grafted films indicated that the perfluorinated poly(BrTFF) grafts were phase-separated from the PTFE region due to the crosslinked structure of the cPTFE based film, but the grafted films still had high thermal stability (above 300 °C). DSC measurements showed the decrease of melting temperature, but the increase of both heat of fusion and degree of crystallinity in cPTFE film after grafting. The grafted film, a new kind of perfluorinated polymer with bromine active groups and good mechanical properties, is expected to be modified for new applications.

Introduction

In the past few decades, a great interest has been focused on radiation modification of fluoropolymers [1], [2]. For example, radiation-grafted fluoropolymers are currently being used as electrolyte membranes for fuel cells, hydrophilic filtration membranes, matrix substrate materials for use in combinatorial chemistry, etc. [2], [3]. However, few studies on radiation-induced polymerization or grafting of perfluorinated vinyl monomers have been reported [4], [5]. Very recently, we investigated radiation-induced grafting of 2-bromotetrafluoroethyl trifluorovinyl ether (BrTFF) into poly(ethylene-co-tetrafluoroethylene) (ETFE), and found that the irradiation with absorbed doses more than 400 kGy gave the poly(BrTFF) grafted ETFE (ETFE-g-BrTFF) films with grafting yields of more than 20% [5]. The bromine of ETFE-g-BrTFF films could be utilized as an active group for further modification such as atom transfer radical polymerization, and novel polymer electrolyte membranes have been synthesized [6].

Among the fluoropolymers, poly(tetrafluoroethylene) (PTFE) is the most commercially available perfluorinated material with excellent chemical and thermal stability. Radiation effect of PTFE has been widely investigated. It was found that PTFE is extremely sensitive to radiation, resulting from the chain scission of PTFE main chain, while the PTFE can be crosslinked upon irradiation at its melting temperature under an oxygen-free condition in the film state [7], [8]. The crosslinked PTFE (cPTFE) film is quite stable towards the high-energy radiation and easily undergoes the styrene grafting modification compared with uncrosslinked PTFE film [9], [10]. In this work, we attempted the radiation-induced grafting of perfluorinated vinyl ether into cPTFE film, and expected to synthesize a new kind of perfluorinated polymer films with functional groups.

Section snippets

Materials

cPTFE film with a thickness of ca. 40 μm was kindly provided by Nitto Denko Co., Japan. It was crosslinked by electron-beam irradiation at 340 °C in argon with 100 kGy. The cPTFE film was washed with acetone to remove any impurity on its surface before use. BrTFF was purchased from Matrix Scientific Com. and used without further purification.

Irradiation of cPTFE with or without BrTFF

The grafting reaction was carried out by the simultaneous irradiation of the cPTFE in a BrTFF monomer at different temperatures and atmospheres (Scheme 1).

Simultaneous radiation-induced grafting of BrTFF into cPTFE films

A simultaneous radiation-induced grafting was investigated for the grafting of BrTFF into cPTFE films. Fig. 1 shows the results of the grafting of BrTFF into cPTFE films as a function of an absorbed dose in different conditions. When grafting reaction was carried out at room temperature, the grafting yield (GY) increased linearly with an increase in the dose up to 1000 kGy, and then leveled off. The surface area of the film increased as the grafting proceeded; this increase suggested that the

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Perfluorinated polymer film with functional group prepared by radiation-induced grafting

Abstract

Introduction

Section snippets

Materials

Irradiation of cPTFE with or without BrTFF

Simultaneous radiation-induced grafting of BrTFF into cPTFE films

Prog Polym Sci

Prog Polym Sci

Prog Polym Sci

J Fluorine Chem

J Fluorine Chem

Polymer

Radiat Phys Chem