Thermal Behavior of Poly(acrylonitrile-co-1-vinyl imidazole) During Stabilization

Melt-Spinnable Polyacrylonitrile—An Alternative Carbon Fiber Precursor

“…The information about the effect of VIM on the glass transition temperature is contradictory. Thus, its decrease is observed with an increase in the content of VIM in the copolymer [ 84 ], while the opposite observation is described in [ 87 ]. The molecular weight distribution plays a minor role in the thermal behavior of the copolymers of AN and VIM, while the copolymer composition plays an important role.…”

“…Therefore, it is very difficult to synthesize copolymers of AN and VIM in water (emulsion, suspension, precipitation copolymerization). In this regard, copolymerization of AN and VIM is performed in organic solvents typical for PAN, e.g., DMF or DMSO [ 84 , 85 , 86 , 87 ]. A specific feature of the copolymerization of AN and VIM is the broadening of the MWD at high monomer conversions up to Đ > 2.5, which manifests itself in solution polymerization and is suppressed in the presence of a chain transfer agent.…”

“…The rate of the formation of a ladder structure at a constant temperature differs sharply in argon atmosphere and in air. Thus, 10% conversion of nitrile groups into –C = N– groups is achieved after 2.5 h of heat treatment in argon at 225 °C or after 15 min in air at the same temperature [ 87 ]. This difference made it possible to find the optimal composition of the copolymer (18 mol.% VIM), at which the copolymer forms melt (190–200 °C) in an inert atmosphere before the onset of cyclization.…”

“…If the polymer is melted at a temperature before the start of cyclization, then the fiber will lose its shape completely or partially turn into a melt during TOS. As mentioned above, attempts were made to solve this problem by introducing a small amount of a third comonomer containing an acid group into PAN at the synthesis stage [ 84 , 85 , 86 , 87 ]. As a result, TOS in the spun fiber proceeds at a high speed although it starts above the melting point.…”