Into the era of electrified packaging (on)

Since the polymer was invented in the 1970s more than 100 years ago, it has always prided itself on the great advantages of insulation, and has been widely used in the industry, especially in the packaging field. In the 1980s, due to the high-tech injection, the conductive polymer was greatly developed, and its application area was broader.
The conductive polymer material has a special structure and excellent physical and chemical properties, so that it has a wide range of uses in the field of optoelectronics, information industry, aerospace and other fields. In the anti-electromagnetic, anti-static, stealth packaging (anti-infrared, anti-radar), smart packaging, etc., has an attractive application prospects. Therefore, conductive polymers are the focus of research, development and application of new materials in the 21st century.
Conductive polymer (polymer) refers to a polymer whose main chain structure has a conductive function and is generally prepared by doping electron-highly delocalized conjugated polymers with appropriate electron acceptors (or donors). of.
Conductive polymers are classified into three types: composite, structure (intrinsic), and ionic. The former is obtained by adding a conductive material such as carbon black, fine metal powder, or metal-plated oxide to an insulating polymer to obtain electrical conductivity. The ionic type is made by adding salt ions such as lithium perchlorate to conduct electricity, and the structural type is based on the fact that the polymer main chain structure has a conductive gene and imparts conductivity, and the three are fundamentally different.
1. Characteristics and Synthesis of Conductive Polymers Conductive polymers are basically unsaturated polymers and are generally synthesized by electrolytic polymerization. And after a certain doping treatment to make it conductive conductive polymer. Its conductive properties have the following characteristics.
1 By controlling the degree of doping, the conductivity of the conductive polymer can be varied in the insulator-metal range (10 negative 9th power S/cm-10 5th power S/cm), which is any other material incomparable. At present, the highest room temperature conductivity can reach 10 5 S/cm, which can be comparable to the conductivity of copper, while the weight is only about 8% of copper; typical conductive polymers generally have a conductivity of 10 5th power S /cm. 2 Conductive polymers can be oriented in a stretched manner, with the electrical conductivity increasing with the degree of stretching along the stretching direction, while the electrical conductivity in the perpendicular stretching direction is substantially constant, showing a strong electrical conductivity direction anisotropy; 3 despite the conductive polymer Conductivity up to the metal level, but its conductivity - temperature curve does not show the metal properties; 4 conductive polymer with the carrier (soliton), polaron (polaron), bipolaron (bipolaron ) The concept description is not only different from the free electrons of metals, but also different from the electrons or holes of semiconductors. 5 Conductive polymers have a doping/dedoping, completely reversible process, which is a unique and unique property of conductive polymers; 6 Conductive polymers have the characteristics of doping with color changes and high third-order nonlinear optical effects, making it a wider range of applications.
The above-mentioned conductive polymer is generally made by doping a conjugated polymer. According to the principle of “green chemistry”, there are currently five types of conductive polymer synthesis methods.
(1) Chemical synthesis method: According to the principle of polymer synthesis, a polymer with a main chain conjugate is prepared. Japanese Xia Yingying uses a Ziegler-Nand catalyst at a low temperature, and polymerization of acetylene to polyacetylene (PAC) is a typical example.
(2) Electrochemical synthesis: According to the principle of organic electrochemical synthesis, conjugated polymers are obtained. Many heterocyclic conductive polymers, such as polypyrrole PPY and polythiophene PTP, are produced by electrochemical synthesis. The electrochemical synthesis method can not only simultaneously perform the polymer and the doping, but also easily obtain a conductive film of a desired thickness.
(3) Plasma polymerization method: polymerization of monomers under glow discharge, the process of this method is complicated, and the structure of the obtained polymer is relatively complex, and there are not many practical examples at present.
(4)Conjugation conversion method: conversion from non-conjugated polymers to conjugated polymers, such as the dehydrochlorination of polyvinyl chloride to obtain polyacetylene PAC, polyphenylene vinylene PPV and polythiophene acetylene PTV, etc. Preparation. and many more.
2. Conductive Polymer Polyamide PPY
The first conductive polymer was Polypyrroles, which was introduced as early as 1916. Due to the limited use, it is almost forgotten. Until 1977, Japan and the United States successively made high-conductivity polyacetylene (PAC) to attract people's attention to conductive polymers. Over the past 10 years, the research and application of polyfluorene have been highly valued, and especially the 3 substituted polypyrrole derivatives have attracted widespread attention.
In order to increase the electrical conductivity and processability of polypyrrole PPY, in-situ polymerization methods are usually used. That is, the PPY monomer swells and diffuses into the flexible polymer matrix, and then the indium is polymerized in-situ to obtain a high-performance and high-functional molecular composite material.
In the last 10 years, polyxanthene derivatives have developed rapidly. Poly(3-alkyl)pyrroles, poly(3-alkyl)pyrroles, poly(dialkylated benzene) pyrroles, poly(3-alkyl) pyrroles have been synthesized. Dihydrobenzo) dipyrroles, as well as the theoretical design of PPY derivatives with small gaps and substituted PIYs for use in solid state lithium batteries. It is worth pointing out that poly-opened ring porphyrin polymers can be obtained by the polycondensation reaction of pyrrole and aldehydes. That is, the pyrrole and formaldehyde are dissolved in an appropriate solvent, and the acid catalyst is added thereto under stirring to polymerize. First, the polymethane and its derivatives are formed, the formed polymer is separated, and then dissolved in an appropriate solvent and electrolyzed. Oxidation or enzyme-catalyzed oxidation processes move the reaction toward the formation of polypyrrolylene and its derivatives. Using such reactions, a large number of new conductive polymers can be obtained.
3. Polythiophene PTP
Polythiophenes, abbreviated as PTP or PTH, developed by chemists in 1989 is yet another useful conductive polymer. For technical reasons, polyalkylthiophene was synthesized early because the introduction of the alkyl group at the 3-position of thiophene increased the solubility in general organic solvents, but weakened the interaction between PTP molecular chains. With the increase of alkyl R, the solubility of PTP increases, but the conductivity decreases. When R is -CH3, -C2H5, PTI conductivity can reach 10 square s/cm. However, the low concentration of dissolved polymers in the doping of these polymers is a disadvantage.
Structural conductive polymers are insoluble. The water-soluble polythiophene synthesized by the 3-sulfonic acid alkyl thiophene can overcome this disadvantage and has self-doping, ie the combination of metal ions M+. With the relative humidity, the conductivity is negative at the 7th power of 10. -10 quadratic s/cm change. Doping with Br2 increases the conductivity to 10 cubic s/cm, and the band gap is higher than that of polythiophene. The polymer is easily made into a film with an aqueous solution, and for the sake of ease of preparation, a series of problems such as high molecular weight, mechanical strength, stability, reasonable production cost, and production process have been solved, and finally the conductive polymer has entered a practical stage. Today, polythiophene and derivatives have become novel conductive polymers that are soluble, have high electrical conductivity and good stability.
Poly(p-phenylene) PPP
Another type of conductive polymer with high conductivity, good stability, and heat resistance is PPP-polyparaphenylene, which shows electrochemically interesting properties and has been reportedly used by the United States. In smart packaging.
In general, there are mainly two methods for synthesizing PPP. One is chemical condensation polymerization and the other is electrochemical polymerization.
In order to obtain a PPP film-like product, electrolytic polymerization of benzene is generally used. However, because benzene is extremely stable, it is electrolytically oxidized in the presence of a supporting electrolyte; only the addition of Lewis acid additives allows benzene to be converted into a complex before electrolytic oxidative polymerization. In addition, benzene can also undergo oxidative polymerization in H2SO4 and liquid sulfurous acid. However, the PPP film obtained by this type of polymerization method has a deep color and also has some structural defects. In order to increase the degree of polymerization and processability of PPP, a soluble prepolymer conversion process must be used. That is, it can be formed in the prepolymer stage of its molding process, and then converted into poly-p-phenylene structure, which is a new method of synthesizing PPP from soluble intermediates. (To be continued)