Phase separation of polyisoprene-polyacetylene copolymers

Polyacetylene can be solubilized by making copolymers with polyisoprene via anionic polymerization of isoprene using n-BuLi as the initiator, followed by Ziegler-Natta copolymerization of acetylene onto the polyisoprenyllithium chains using either Ti(OBu)4 or CoCl2. We have previously demonstrated that diblock copolymers of polyisoprene and polyacetylene (PI-PA) prepared by the cobalt catalyst form worm-like micelles in solution, which transfer into a lamellar structure upon I2-doping. In the present study, the effects of temperature and I2-doping on the phase behavior of PI-PA diblock copolymers in solution and in the solid state are investigated. We found that I2-doping of the PI-PA copolymer films leads to the formation of a pseudo interpenetrating polymer network (PIPN) due to the strong self-association of polyacetylene segments and thermodynamic immiscibility between the polyisoprene and polyacetylene chains. The PIPN network thus formed plays an important role in regulating the electrical properties of the I2-doped copolymer films.