A novel thermosensitive soluble polypyrrole composite

Electrically conducting PPy/DBSA/poly(NiPAAm-co-AMPS) composites were synth esized 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 an ion of AMPS. When more poly(NiPAAm-co-AMPS) was fed into the polymerization solution, more poly(NiPAAm-co-AMPS) existed in the resulting composite. Mo st of the composites showed good solubility in chloroform with extra DBSA. From the composite solutions, we cast free-standing films with excellent qu ality whose electrical conductivities were in the range of 10(-2) to 5 S/cm . We found the PPy composites exhibited moisture-dependent electrical condu ction behavior. Electrical conductivity of the PPy composite increased with increase of moisture concentration in air, which resulted from the moistur e absorbed by hydrophilic NiPAAm moiety in the composite. Moisture absorpti on by NiPAAm was confirmed by higher swelling ratio in water of the composi tes containing more NiPAAm moiety. We also found PPy/DBSA/poly(NiPAAm-co-AM PS) composites showed thermosensitive swelling behavior in water. The swell ing 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 wi th temperature was caused by release of water from the composite by coagula tion of the thermally sensitive NiPAAm moiety in the composite. We expect t he moisture-dependent electrical conductivity and thermosensitive swelling behvior of the composite synthesized in this study may be useful for divers e attractive applications. (C) 2001 Elsevier Science B.V. All rights reserv ed.