The success of conjugated polymers as components in anticorrosion coatings, charge-injection layers in organic lightemitting diodes, electromagnetic shielding, plastic circuitry, and biosensors, among others, is due to their high conductivity, low density, and reasonably high processability. 1 Polyaniline (PANI) is particularly attractive because of its easy synthesis, low cost, and high degree of environmental stability in both the doped and undoped states. One drawback is its low solubility, caused by π-stacking of the highly conjugated backbone, resulting in low processability of the final materials. Replacing mineral acid dopants such as HCl or H 2 SO 4 with functionalized organic acids such as 10-camphorsulfonic acid (CSA) and 2-acrylamido-2methyl-1-propanesulfonic acid (AMPSA) 2 increases the overall solubility by way of the large organic groups attached to the acidic moiety. Doping PANI with CSA and processing from a polar solvent such as m-cresol has resulted in films with conductivities as high as 400 S/cm. 3 Other sulfonic acids are effective as dopants, including polyelectrolytes such as polystyrenesulfonic acid, 4-6 diesters of sulfophthallic acid, 7 or sulfosuccinic acid, 8 particularly in association with polar solvents such as m-cresol or 2,2-dichloroacetic acid (DCAA).A more difficult problem to address is the highly brittle nature of PANI. One solution to this problem is preparing block copolymers with a conducting polymer segment and a low-T g amorphous polymer segment. Such attempts are most successful with systems like poly(3-hexylthiophene), where the conducting
A method was developed for utilizing block copolymers that combine an acidic block, 2acrylamido-2-methyl-1-propanesulfonic acid (AMPSA), and an acrylate block, n-butyl, ethyl, or methyl acrylate, as templates for acid-doped conducting polymers such as polyaniline (PANI) or polypyrrole (PPY). PANI templated with diblock copolymers dissolved in dichloroacetic acid results in the formation of highconductivity materials (30 S/cm) that possess a greater degree of flexibility than pure PANI (between 20% and 50% elongation at ∼4 MPa). Triblock copolymers were used as templates for the oxidative polymerization of PANI and PPY to form in situ conducting polymer composites with conductivities of ∼0.1 S/cm.
2-Acrylamido-2-methyl-N-propanesulfonic acid (AMPSA) was successfully polymerized via atom transfer radical polymerization (ATRP) using a copper chloride/2,2 0 -bipyridine (bpy) catalyst complex after in situ neutralization of the acidic proton in AMPSA with tri(n-butyl)amine (TBA). A 5 mol % excess of TBA was required to completely neutralize the acid and prevent protonation of the bpy ligand, as well as to avoid side reactions caused by large excess of TBA. The use of activators generated by electron transfer (AGET) ATRP with ascorbic acid as reducing agent resulted in both increased conversion of the AMPSA monomer during polymerization (up to 50% with a 0.8 [ascorbic acid]/[Cu(II)] ratio) and much shorter polymerization times (\30 min). Block copolymers and molecular brushes containing AMPSA side chains were prepared using this method, and the solution and surface behavior of these materials were investigated.
[reaction: see text] At 275 degrees C, 8-exo-methylbicyclo[4.2.0]oct-2-ene (1a) undergoes a [1,3] sigmatropic rearrangement to 5-methylbicyclo[2.2.2]oct-2-enes, of which the orbital symmetry-allowed si product is only marginally favored over the forbidden sr product; that is, si/sr is 2.4. Accompanying the [1,3] shift are significant amounts of epimerization and fragmentation. The 8-endo epimer 1b, which yields no [1,3] product, experiences primarily direct fragmentation and secondarily epimerization. A diradical intermediate can account for all such observations.
At 300 degrees C, bicyclo[4.2.0]oct-2-ene (1) isomerizes to bicyclo[2.2.2]oct-2-ene (2) via a formal [1,3] sigmatropic carbon migration. Deuterium labels at C7 and C8 were employed to probe for two-centered stereomutation resulting from C1-C6 cleavage and for one-centered stereomutation resulting from C1-C8 cleavage, respectively. In addition, deuterium labeling allowed for the elucidation of the stereochemical preference of the [1,3] migration of 1 to 2. The two possible [1,3] carbon shift outcomes reflect a slight preference for migration with inversion rather than retention of stereochemistry; the si/sr product ratio is approximately 1.4. One-centered stereomutation is the dominant process in the thermal manifold of 1, with lesser amounts of fragmentation and [1,3] carbon migration processes being observed. All of these observations are consistent with a long-lived, conformationally promiscuous diradical intermediate.
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