Int J Thermophys (2009) 30:1411–1422 DOI 10.1007/s10765-009-0637-8 Rheological Investigation of Thermal-Induced Gelation of Polyacrylonitrile Solutions M. Bercea · S. Morariu · C.-E. Brunchi Received: 16 October 2008 / Accepted: 29 July 2009 / Published online: 13 August 2009 © Springer Science+Business Media, LLC 2009 Abstract In this article, thermal-induced gelation of polyacrylonitrile (PAN) solu- tions in dimethylformamide was studied through rheological measurements. The entangled and non-entangled states were delimited for an overlap parameter of mac- romolecular coils of 2.7. In temperature sweep experiments, two types of gelation processes were identified for PAN entangled solutions at: (1) a reversible gelation in the region of low temperatures (below 15 ◦ C) due to the formation of a crosslinked structure with a small region of order that dissolves completely in an excess of sol- vent, and (2) an irreversible gelation at high temperatures (above 60 ◦ C) and this gel is insoluble in an excess of solvent, due to the formation of a chemical three-dimensional network. Physical PAN gels with good elastic properties were also obtained by the freezing and thawing method. The gel properties depend on the thermal history of the solution (freezing time, aging time, and aging temperature), its composition (con- centration and molar mass of the polymer), and gelation conditions (freezing rate). The gelation was attributed to the formation of junction zones via an aggregation process between a certain number of chain segments due to attractive dipole–dipole interactions. Keywords Entangled solutions · Gel · Polyacrylonitrile (PAN) · Viscoelastic parameters M. Bercea (B ) · S. Morariu · C.-E. Brunchi “Petru Poni” Institute of Macromolecular Chemistry, 41-A Grigore Ghica Voda Alley, 700487 Iasi, Romania e-mail: bercea@icmpp.ro 123