Molecular weight polyaniline synthesis

Synthesis of High-Molecular-Weight Polyaniline for Fiber Spinning... 

Adams, P.N., P.J. Laughlin, A.P. Monkman, and A.M. Kenwright. 1996. Low temperature synthesis of high molecular weight polyaniline. Polymer 37 3411. 

Mattoso, L.H.C., A.G. MacDiarmid, and A.J. Epstein. 1997. Controlled synthesis of high molecular weight polyaniline and poly(o-methoxyaniline). Synth Met 68 1. 

P. N. Adams, P. J. Laughlin, A. P. Monkman, Synthesis of high molecular weight polyaniline at low temperatures, Synthetic Metals 1996, 76,157. 

Leclerc [125] has shown that poly(2-methyl aniline) has properties similar to that of polyaniline. Dao et al. [127] have carried out extensive investigations on chemical and electrochemical polymerization of substituted polyanilines. These authors report that chemical synthesis yields a polymer having a higher molecular weight. Some of their results are given in Table 12.13. Their study further shows that there is no polymer film on an electrode surface in the presence of the following substitutions ... 

Parameters such as, synthesis medium (HCl, camphor sulfonic add (CSA) or dodecylbenzene sulfonic acid (DBSA)), molar ratio aniline/oxidant, method for oxidant addition, temperature, polymerization duration, dedoping conditions will have effects on polymer properties in terms of yield, chain length, effective conjugation, defects rate, and electrical properties. Temperature was kept to 0 C, -30 C or -40 C and reactions were stopped after various durations in order to control the molecular weight of samples. Polymerization durations were varied from 1 hour to 5 days and depended on the reaction temperature. The inherent viscosities of the polyanilines (Pani) were determined at 25 °C in 0.1%w solutions in concentrated sulfuric acid (95 %), using an Ubbelohde viscometer. For instance, high viscosity samples (1.4 dl/g) were obtained after 3 days at -40 °C vsMe low viscosity samples (0.6 dl/g) were obtained after 1 hour at 0 A relationship was found between polymerization duration and inherent viscosity for polymers synthesized at low temperature (- 40 °C). Inherent viscosity increases from 0.6 to 1.4 when duration of polymerization increases from one to five days. In the case of synthesis at 0°C no correlation was obtained between duration of polymerization and inherent viscosity. A careful control of other parameters (synthesis medium, molar ratio aniline/oxidant, method for oxidant addition) have permitted to get samples with inlierent viscosities ranging from 0.55 to 2.1 dl/g in a reproducible way. 

In the case of low tenq)erature synthesis polyaniline samples, conductivity was found to be related to inherent viscosity (Figure 10). Such a correlation is not found for sanq)les synthesized at O C. This may be related to the fact that low tenoperature synthesis leads to defect fi-ee materials ere conjugation length increases with molecular weight of the polymer. In the case of 0 °C sanples, defects content is high and limits the conjugation length whatever the molecular wei t is. 

A major application is the synthesis of high molecular weight water-soluble polymers (e.g., polymers and copolymers of acrylamide, acrylic acid, and its salts) for flocculants and tertiary oil recovery. Other uses are the synthesis of polyaniline/CdSe quantum dots composites [49], hybrid polyaniline/carbon nanotube nanocomposites [50], polyani-line-montmorillonite nanocomposites [51], or in reversible addition-fragmentation chain-transfer-controlled radical polymerization (RAFT) [52]. 

Ohtani, A., Abe, M., Ezoe, M., Doi, T., Miyata, T., and Miyake, A., Synthesis and properties of high-molecular-weight soluble polyaniline and its applications to the 4MB-capacity barium ferrite floppy disk s antistatic coating, Synth. Met., 57, 3696, 1993. 

Based upon the comparison of the experimental results with theory, it is clear that for polyaniline increased molecular weight will lead to enhanced electrical conductivities. Furthermore, since the transport is currently limited by disorder, it may be possible to achieve a major increase in electrical conductivity (by a factor of order N, the number of monomers in a typical macromolecular chain) with improved chain extension and alignment as a result of post-synthesis processing. 

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