Conducting Properties of Iodine-Doped Low-Density Polyethylene–Poly(4-Vinylpyridine) Blends Sidnei Luis Andrade da Silva, 1 Marcia Laudelina Arruda Temperini, 2 Glaucione Gomes de Barros 1 1 Chemistry Institute, Brası ´lia University, Brasilia, Brazil 2 Chemistry Institute, Sa ˜o Paulo University, Sa ˜o Paulo, Brazil Received 29 September 2001; accepted 8 November 2001 ABSTRACT: The conductivities of blends of low-density polyethylene and poly(4-vinyl pyridine) (P4VP) were stud- ied. The blends were synthesized by in situ sorption and thermal polymerization of 4-vinylpyridine in low-density polyethylene. They showed, after iodine doping, conductiv- ities of 1.7 to 5.0  10 -7 S cm -1 at 298 K, depending on the P4VP mass increment into the matrix. Their conductivities were one order of magnitude higher for measurements at 338 K. The optimum ratio of iodine to pyridine (n) which gave the highest conductivity was 0.21. The thermal stability of doped blends was acceptable for their uses as electro- chemical devices. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 939 –944, 2003 Key words: conducting polymer blends; iodine doping; poly(4-vinyl pyridine); low-density polyethylene INTRODUCTION In general, most polymers are insulating because they possess low conductivity. The conductivity depends on the thermally generated carriers and also on the addition of suitable dopants. 1,2 Because of the complexity of the chemical and phys- ical structures of polymers, the role of dopants in the conduction process is not well understood. 3 However, a considerable amount of work has been reported on steady-state electrical conduction in impurity-doped polymers. 4–6 The introduction of a dopant into a poly- mer can considerably modify the charge storage prop- erty of the polymer or it can improve the charge carrier mobility. 1,7 Many of the presently available doped conductive polymers possess some undesirable characteristics such as environmental instability, poor processibility, or poor physical properties. Attempts have been made to improve the physical properties of these conductive polymers. A large number of studies have been carried out with the objective of preparing microphased polymer systems, in the form of either blends or block/graft copolymers. One of the phases is formed by a polymer capable of being doped to achieve electrical conduc- tivity, and the second phase, by a polymer segment or a host matrix capable of improving the mechanical and thermal properties of the conducting struc- ture. 8 –10 It is known that poly(4-vinylpyridine) (P4VP) doped with iodine results in an electronic semicon- ductor. 11 Block copolymers based on P4VP and poly- (dimethyl siloxane) (PDMS) have been reported in the literature. 9 The presence of an isolating PDMS seg- ment in these materials does not greatly affect the conductivity but it does improve the physical proper- ties of the conducting system. Blends of low-density polyethylene (LDPE) and P4VP have been prepared. 12 They are synthesized by in situ by sorption of 4-vinylpyridine (4VP) followed by thermal polymerization. LDPE was chosen as the P4VP host matrix because of its ready availability as a film and its good mechanical properties. The same method has been used to synthesize LDPE/poly- (acrylic acid) and LDPE/poly(methyl methacry- late). 13,14 The blends exhibit new properties such as ion exchange, ionic conduction, and fluorescence. 15–17 This work details our findings concerning the changes that occur in the properties and structure of LDPE/P4VP blends upon iodine doping. EXPERIMENTAL Characterization of LDPE films LDPE sheets [d = 0.918 g/cm 3 , melt index = 1.15 g/min] were supplied by Poliolefinas (Sa ˜o Paulo, SP, Brazil). The films (3  4 cm) were cleaned and the charac- teristics of polymer checked by FTIR spectroscopy. 13 The degree of crystallinity was 50% as measured by X-ray diffraction. 18 Correspondence to: G. Gomes de Barros (gbarros@unb.br). Contract grant sponsor: Brazilian Research Council; con- tract grant sponsor: District Capital Foundation. Journal of Applied Polymer Science, Vol. 87, 939 –944 (2003) © 2002 Wiley Periodicals, Inc.