A novel thermosensitive soluble polypyrrole composite

Electrically conducting PPy/DBSA/poly(NiPAAm-co-AMPS) composites were synthesized by chemical oxidation of pyrrole using ammonium persulfate (APS) as the oxidant in an aqueous solution. Dodecylbenzene sulfonic acid (DBSA) and a copolymer, poly(NiPAAm-co-AMPS), of N-isopropyl acrylamide (NiPAAm) and 2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS) were used as a primary dopant and a co-dopant, respectively. We figured out poly(NiPAAm-co-AMPS) was incorporated into the PPy composite as the co-dopant through sulfate anion of AMPS. When more poly(NiPAAm-co-AMPS) was fed into the polymerization solution, more poly(NiPAAm-co-AMPS) existed in the resulting composite. Most of the composites showed good solubility in chloroform with extra DBSA. From the composite solutions, we cast free-standing films with excellent quality whose electrical conductivities were in the range of 10(-2) to 5 S/cm. We found the PPy composites exhibited moisture-dependent electrical conduction behavior. Electrical conductivity of the PPy composite increased with increase of moisture concentration in air, which resulted from the moisture absorbed by hydrophilic NiPAAm moiety in the composite. Moisture absorption by NiPAAm was confirmed by higher swelling ratio in water of the composites containing more NiPAAm moiety. We also found PPy/DBSA/poly(NiPAAm-co-AMPS) composites showed thermosensitive swelling behavior in water. The swelling ratios of PPy composites gradually decreased with temperature until 35 degreesC, which is known as the lower critical solution temperature (LCST) of poly(NiPAAm). We, therefore, concluded the decrease of swelling ratio with temperature was caused by release of water from the composite by coagulation of the thermally sensitive NiPAAm moiety in the composite. We expect the moisture-dependent electrical conductivity and thermosensitive swelling behvior of the composite synthesized in this study may be useful for diverse attractive applications. (C) 2001 Elsevier Science B.V. All rights reserved.