Producción CyT
Artículo
Autoría
Maria C. Miras,
;
ACEVEDO, DIEGO FERNANDO
;
Natalia Monge,
;
Evelina Frontera
;
Claudia R. Rivarola
;
Cesar A. Barbero*
Fecha
2008
Editorial y Lugar de Edición
Benthan science publisers
Revista
The Open Macromolecules Journal,
vol. 1
(pp. 58-73)
- ISSN 1874-3439
Benthan science publisers
Benthan science publisers
ISSN
1874-3439
Resumen
Información suministrada por el agente en
SIGEVA
Polymers have been traditionally considered as insulators. However, since the discovery by Shirakawa, Heeger and MacDiarmid that the conductivity of polyacetylene increases significantly upon doping with electron acceptors, a large effort has been devoted to make new intrinsically conductive polymers (ICP) and/or improving the properties of those materials. Conductive polymers could have a variety of applications:corrosion protection coatings and conductive coatings for antistatic and/or RF shi...
Polymers have been traditionally considered as insulators. However, since the discovery by Shirakawa, Heeger and MacDiarmid that the conductivity of polyacetylene increases significantly upon doping with electron acceptors, a large effort has been devoted to make new intrinsically conductive polymers (ICP) and/or improving the properties of those materials. Conductive polymers could have a variety of applications:corrosion protection coatings and conductive coatings for antistatic and/or RF shielding purposes. An obvious requirement to produce such coatings is processability trough solubility of the conductive polymers in common solvents, including aqueous solutions. One of the promises of the conducting polymers is that, unlike inorganic metals and semiconductors, both the synthesis and chemical modification of organic materials offer unlimited possibilities. Soon enough it was recognized that few monomers render polymer chains with high conductivity. Two factors made difficult to produce truly conducting chains. On one hand the formation of high molecular weight polymer could be impeded by low reactivity of the monomer. On the other hand, conjugated polymer backbones could have low conductivity due to electronic and/or steric effects. This constrain is intrinsic and it remains unsolved to this day. On the other hand, synthetic obstacle to the synthesis of novel conducting polymers can be solved producing simple conducting backbones which are then post-modified. Another possibility is the copolymerization of non reactive monomers with more reactive monomers. However, the different reactivity of each comonomer results in a composition of the copolymer different to the ratio of comonomers in the feed and the formation of block copolymers. Moreover, since usually the reaction is carried out to maximum conversion, a drift of composition occursduring reaction producing a mixture of different copolymers. Both effects imply that the material has domains with different properties (e.g. conductivity) and the effective value of the property is different than the one observed in a homogenous material [5]. Another advantage is that the chain length of the modified polymer is similar to that of the parent polymer while copolymers have different chain lengths depending on the reactivity of the comonomers. Therefore, the influence of the chain length could be ruled out when considering new properties such as increased solubility. Polyaniline (PANI) has attracted great attention because of its electronic, electrochemical and optical properties and especially good environmental and thermal stability. The bad procesability of the pristine polymer, make necessary to introduce a wide variety of functional groups on the polymer backbone. The synthetic problems are more acute in the case of polyanilines because the reactivity of the monomer is adversely affected by substitution, both in the ring and in the nitrogen, due to electronic and steric effects. Therefore, unlike other conducting polymer families like polypyrroles and polythiophenes, it is only possible to obtain relatively high molecular weight polymer from a limited set of substituted anilines. Almost all the reactions are carried out with PANI in its insoluble solid form. An important point is how to know if the reaction has occurred and the structure of the modified polymer. To that effect, infrared spectroscopy is usually used because it is easily performed in solids. Raman spectroscopy has also been used to that effect [11]. A more quantitative assessment of the degree of modification is usually made by X-ray photoelectron spectroscopy (XPS) [12], Electron dispersion-absoprption (EDAX), or plain chemical analysis. Using those techniques it is possible to measure the degree of modification. This value is defined as the ratio between the moles of functional groups with respect to the moles of repetitive units in the polymer (aniline units in the case of PANI).
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