| Summary: | 博士 === 國立清華大學 === 化學工程學系 === 89 === Polyaniline, a low cost intrinsically conductive polymer, is stable under ambient conditions and its industrial applications have been investigated intensively. Due to its low solubility in most common solvents, commercialized products of polyaniline are limited. Grafting of protonic acid groups and alkyl groups onto polyaniline is formed to improve solubility in water and organic solvents, respectively. Two methods, copolymerization and grafting, are usually used for introducing these functional groups. However, the former usually results low molecular weight of polymers, low reaction yield and low electrical conductivity due to steric hindrance; While the latter provides polymers with controlled molecular weight and oxidation level and higher conductivity.
For the purpose of improving solubility in water and preventing migration of dopants, polyaniline has been modified in a self-doped form by introducing protonic acids into the side chains. For example, ring-substituted sulfonated polyaniline (SPAN) and nitrogen-substituted poly (aniline-co-N-propanesulfonic acid aniline) (PAPSAH), poly (aniline-co-N-propylbenzenesulfonic acid aniline), poly (aniline-co-N- (4-sulfophenyl) aniline), poly (aniline-co-o-anthranilic acid) and poly (o-aminobenzylphosphoric acid). However, some of these polymers are only soluble in aqueous alkaline solution but insoluble in pure water. The other polymers are soluble in water only after being purified by dialysis of its sodium salt in water and then further treatment with an H+-type ion exchange resin. All of the above polymers become insoluble in water after drying from their aqueous solution. Furthermore, during the synthesis and purification steps of all the above mentioned polyaniline derivatives, the use of inorganic acid such as, hydrochloric or sulfonic acid, can not be avoided. Thus additional purification steps are necessary for removing the free acids.
In this dissertation, we report the synthesis of a new water-soluble self-doped polyaniline derivative, poly (aniline-co-N-benzoylsulfonic aniline) (PABSAH), by direct reaction of polyaniline with o-sulfobenzoic anhydride. This synthetic route has no need of an inorganic acid in the synthesis or purification steps. The PABSAH so obtained with a grafting level of 30 % is completely soluble in water and can be redissolved after drying from its aqueous solution. Among these 30 % by more of sulfonic acid group, only 18 % act as dopant and the other 12 % act as free acid. Its solid form gives a symmetric ESR signal with Hpp, g-factor and spin density of 2.02G, 2.002980, 1.28×1020 spin/g, respectively, which are close to those of HCl doped polyaniline (g=2.002868 and spin density=2.2×1020 spin/g). Its electrical conductivity is 4.7×10-4 S/cm and can maintain at this level up to 105℃.
In the synthesis of PABSAH, pyridine is added as catalyst, almost all the quinoid units disappear and the grafting level can be as high as 85 %.
The same catalytic effect is also found in the grafting reaction of polyaniline with alkanoyl chlorides and the grafting level can be up to 90 %. The catalytic mechanisms for the two amidation reactions are proposed. The role of pyridine is to catch the protons on the polarons (radical cation) separated by the substituted nitrogen, which prevents the two unpaired electrons from recombination to yield quinoid unit. The two radicals then catch hydrogen atoms from solvent molecules or impurities (such as water) to yield amine hydrogen. Thus, amidation can then proceed further.
In the synthesis of water-soluble PAPSAH, starting from emeraldine base by suitable controlling the reaction condition and adjusting the dosage of reagents, various substitution levels up to 81 % are obtained. The reaction mechanism is proposed as follows. As NaH is added to the PAn solution, NaH reacts with PAn in two ways: (1) sodium substitution with amine nitrogen, and (2) sodium hydride addition to imine nitrogen. Path (1) dominates in the early stage and both paths occur simultaneously in the later stage. Thus PAn can be reduced to various levels and grafting with sultone can reach a level greater than 50 %. The electrical conductivity of the polymers with grafting levels 63% and 81% are 7.4×10-3 and 4.9×10-5 S/cm, respectively.
In this dissertation, we also report a new series of new organic soluble polyanilines, N-alkanoylated polyanilines, which were synthesized by reaction of n-alkanoyl chlorides with polyaniline. The resulting N-alkanoylated polyanilines are soluble in THF and dichloromethane.
The molecular weights determined using GPC are much lower than they are supposed to have in accordance with the high MW of PAn determined by NMP as carrier solvent. This result interprets that the PAn must be highly aggregated and its actual MW should be much lower than it appears.
For N-alkanoylated polyanilines, the degrees of alkanoylation can vary from 10% to 90%. Their electrical conductivity varies from 1 S/cm to 10-6 S/cm depending on degree of alkanoylation.
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