Facile synthesis and intrinsic conductivity of novel pyrrole copolymer nanoparticles with inherent self-stability

Intrinsically self-stabilized nanoparticles of a copolymer from 4-sulfonic diphenylamine (SD) and pyrrole (PY) were facilely synthesized in HCl solution at 10 degrees C by a chemically oxidative polymerization. The critical reaction parameters such as SD/PY ratio, polymerization time, and oxidant species were studied to significantly optimize the polymerization yield, size, conductivity, and solubility of the final copolymer particles. The molecular structure, size, size distribution, and morphology of the particles were analyzed by IR spectroscopy, laser particle-size analysis (LPA), atomic force microscopy, and transmission electron microscopy (TEM). It was found that the polymerization yield of the SD/PY (50/50) copolymers increased dramatically in the initial 2 h of polymerization and then slowly enlarged in the subsequent 22 h. However, the copolymerization yield for the polymerization time of 24 h exhibited a nonlinear dependence on the SD/PY molar ratio, i.e., a maximum at 10/90 and a minimum at 80/20. The number-average diameter, Dn, of the copolymer particles strongly depended on the SD/PY ratio, decreasing rapidly from 6402 to 291 nm as the SD/PY molar ratio changed from 30/70 to 50/50, whereas the polydispersity index, PDI = Dw/Dn (where Dw is the weight-average diameter), surprisingly maintained very small values, decreasing slightly from 1.21 to 1.08. The SD/PY (80/20) copolymer particles prepared with (NH4)2S2O8 as the oxidant had the smallest size of ca. 10 nm by TEM and the lowest Dw/Dn value of 1.03 by LPA, whereas the copolymer particles prepared with FeCl3 as the oxidant exhibited the second smallest size of ca. 20 nm by TEM and the highest conductivity. The conductivity of the SD/PY (50/50) copolymers rose first and then decreased with increasing polymerization time from 10 min to 24 h, exhibiting a maximum (0.217 S/cm) at 12 h. It is of interest that the copolymer particles with SD/PY molar ratios in the range between 50/50 and 80/20 surprisingly exhibited the smallest size, the narrowest size distribution, and the highest conductivity at the same time. In particular, the copolymer nanoparticles exhibited high purity, clean surfaces, good self-stability, high conductivity, and strong chemoresistance that were very important to nanomaterial processibility and application. The obtained copolymers were partially soluble in concentrated H2SO4, demonstrating a new direction for synthesizing a soluble pyrrole copolymer.