Polythiophene Grafted on Polyethylene Film
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2University,
Brooklyn, New York 11201 Department of Physics, Queens College of CUNY, Flushing New York 11367 Institute for Polymer Research, Hohe Str. 6, D-0 1069 Dresden, Germany
3
4
The NSF MRSEC for Polymers at Engineered Interfaces.
5 Department of Materials Sciences and Engineering, State University of New York at Stony
Brook, NY 11794-2275. ABSTRACT We have successfully grafted polythiophene on polyethylene (PE) film with a three reactions step: gas phase bromination on PE, yielding PE-Br; substitution reaction of PE-Br with 2-thiophene thiolate anion, following by chemical oxidative polymerization. The polymerization was carried out in a suspension solution of anhydrous FeCI3 in CHCI3, yielding a reddish PE-PT film after dedoping with ethanol. ATR-FTIR shows that the polythiophene (PT) was grafted on PE in the 2,5-position; on the other hand, PT homopolymer shows a small amount of 2,4 coupling. XPS reveals higher intensity of the S2p, including neutral and positive sulfur. SEM image reveals the island of PT on the PE film. AFM analysis found the thickness of the island is in the range of 120-145 nm. The conductivity of these thin films is in the range of 10-6 S/cm. INTRODUCTION During the past 10 years, there has been growing interest in electrically conducting polymers due to their potential applications. Among these polymers, polythiophene (PT) has
attracted interest because of its high magnetic and optical properties, electrical conductivity, and environmental stability (both to oxygen and to moisture). PT can be prepared both by electrochemical
and
by
oxidative
polymerization
of thiophene.
The
electrochemical
polymerization of PT is carried out in an organic solvent such as acetonitrile, nitromethane, nitrobenzene, or propylene carbonate [1]. Polyethylene (PE) is one of the most interesting commodity polymers. However, it exhibits low surface energy, and different methods were developed to increase surface energy. Among those, hydrophilic polymers were successfully grafted on PE surface by direct plasma polymerization [2], pretreatment of PE surface with corona or Ar plasma prior to polymerization in the monomer solution [3], pre-swell organic initiator on the PE surface prior to polymerization in the hydrophilic monomer solution [4]. In addition, other monomers such as styrene, glycidyl methacrylate (GMA), 2-hydroxyethylmethacrylate (HEMA), can be grafted on PE surface by photo-irradiation [5], which the later products can be used in medical application. Recently we reported that bromination of PE films improves their wettability [6]. Furthermore, the bromopolyethylene films (PE-Br) could be altered to amino terminated PE film (PE-S-Ph-NH 2) using nucleophilic substitution reaction. In addition, we also reported substitution reaction with other aromatic thiols [7]. Among others, we have successfully grafted thiophene thiol on PE films (PE-S-T). In principle, these films can be used as substrates in oxidative polymerization with thiophene, yielding polythiophene grafted on PE film. Here we
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