Synthesis And Self-Assembly Of Block Copolymers Containing Oligoaniline Or Polyaniline

Polyaniline (PANI), one of the most important conducting polymers, has received considerable attention due to its ease of synthesis, environmental stability, and unique acid/base doping/dedoping and oxidation/reduction chemistry. Nanostructured PANI offers an opportunity to applications on sensors, actuators, supercapacitors, etc., due to its large specific surface area. Many methods, including hard template, soft template and template-free methods, have been used to prepare nanostructured PANI as yet. On the other hand, self-assembly of block copolymers is an effective method to synthesize various polymer or metal nanostructures because its morphology can be conveniently tuned into various nanostutures such as spheres, cylinders, tubules, and vesicules. So, it is expected that various PANI structures could be produced by self-assembling of block copolymers containing PANI block.Due to the insolubity of PANI in most solvents, firstly, ABA triblock copolymers, where A and B were tetraaniline and poly(ethylene oxide) (PEO), repectively, were synthesized. Then, their electroactive properties, self-assembly behaviors in aqueous and organic solutions, and applications for detecting acid concentration in organic solvents were investigated. After that, diblock copolymers (mPEO-PANI) were prepared via a novel method of condensation between amines and aldehyde groups. At last, the dispersion of carbon nanotubes with the aid of diblock copolymers in solutions and polymer matrix, and self-assembly of diblock copolymers on the surface of carbon nanotube were investigated.A series of novel electroactive triblock copolymers, (ANI)4-b-(EO)n-b-(ANI)4 (n=13, 22,45,90), were successfully synthesized by a condensation reaction of PEO and tolylene 2,4-diisocyanate to afford the NCO-group-terminated PEO followed by further reacting with tetraaniline. Their chemical structures were confirmed by Fourier transform infra-red (FTIR), nuclear magnetic resonance (NMR), and ultraviolet-visible (UV-vis) spectroscopies. Results of cyclic voltammetry (CV) indicated that their intrinsic electroactivity was maintained, exhibiting one pair of redox peaks, which was attributed to the transition between LEB and EB states.Colloidal solutions of triblock copolymers were prepared by a selective solvent method. Effects of PEO chain length, acidity of selective solvent, and nature of common solvent on their self-assembled morphologies were investigated. (1) With the increase of PEO chain length, the morphologies changed from vesicles to sphere micelles. (2) When water was replaced by hydrochloric acid solution (HCl) as a selective solvent, the vesicular size of triblock copolymer with n=13 increased with the increasing of HCl concentration. As the HCl concentration increased to 1.0 mol/L, hollow spheres and bowl-like aggregates were obtained. (3) When N,N-dimethylfomamide (DMF) was used as a common solvent, the critical water content was lower than that of tetrahydrofuran (THF) and only spherical micelles were obtained which might be due to strong interaction of hydrogen bond between tetraaniline blocks and DMF.Doping behavior of tetraaniline block as a polyelectrolyte was employed to prepare reversed micelles by adding HCl/THF solution to triblock copolymer/THF solution. Without addition of HCl, bowl-like aggregates were obtained. When HCl concentration was between 10-4 and 10-1 mol/L, triblock copolymer with n=13 aggregates into large irregular net structure. While HCl concentration was higher than 1.0 mol/L, vesicles or rods were obtained. Meanwhile, the solution colors varied from deep purple to green, light purple, which indicated that the copolymer could be used as optical sensors for direct detection of acid concentration in organic solvents. For sulfuric acid and p-toluenesulfonic acid, it allowed concentration measurements from 1.0×10-6 to 1.0 mol/L.Diblock copolymers of mPEO-PANI were synthesized by esterification of PEO and p-formylbenzoic acid to obtain aldehyde group-terminated PEO (PEO-CHO) following by imination with PANI. The copolymers self-assembled into small spherical micelles in ethanol by selective solvent method and the diameter of micelles increased with the increasing of PEO chain length.The diblock copolymers were employed to disperse carbon nanotube (CNT) in aqueous and organic solutions. When CNTs were sonicated with mPEO-PANI in NMP, PANI chains were attached to the surface of CNTs due to specificπ-πinteraction between quinoid benzene and CNT and doping interaction of imine and sp2 carbon on CNT, and PEO blocks stretched into solvent to provide a steric hindrance to stable CNTs. As a result, CNTs were well dispersed in water and many organic solvents such as THF, DMF, and NMP, as well as in poly(vinyl alcohol) film matrix.Core-shell structures with CNT as a core and diblock copolymer as a shell were obtained via selective solvent method. These materials showed hydrophobic rather than the hydropholicity of both PANI and PEO homopolymers because a specific spike-like nanostructure of diblock copolymer on surface of CNT was formed.