A metal-free method for ultra-high molecular weight polyacrylonitrile under dimethyl sulfoxide

A convenient method for preparing high molecular weight polyacrylonitrile (PAN)/poly (acrylonitrile- co -methyl acrylate) (P(AN- co -MA)) using a Lewis base (LB)/dimethyl sulfoxide (DMSO) system for controlled anionic polymerization was explored. Nine systems were shown to achieve high conversion and high molecular weight polymerization while maintaining low molecular weight distribution (polydispersity index, PDI = 1.03–1.57). Among them, the 1,8-Diazabicyclo [5,4,0] undec-7-ene (DBU)/DMSO and P(OEt) 3 /DMSO systems, notably, exhibited quasi-living polymerization allowing us to prepare PAN with ultra-high MW (1,110,000 g/mol), with high linearity while maintaining low PDI (1.49). Evidence has been shown that DMSO can interact with monomers, LB catalysts, and propagating chains during polymerization, unlike other aprotic solvents. Such interactions are found to increase the rate of chain initiation, stabilize chain propagation, and prevent chain transfer, branching and chain termination. P(AN- co -MA) was also prepared with this new method resulting in high M w (880,000 g/mol) and better spinnability. Because of the good scalability of this method, it can be applied to other anionic monomers. Thermogravimetry analysis (TGA) shows lower cyclization temperatures and high thermal stability providing promise towards in the development of high-performance carbon fibers. • A metal free method to produce UHMW-PAN and P(AN-co-MA) in DMSO has been demonstrated. • UHMW-PAN with the Mw over 1,000,000 g/mol with better thermostability was obtained. • HMW P(AN-co-MA) with the Mw over 880,000 g/mol with good processability was obtained.