Reversible addition–fragmentation chain transferbased copolymers of acrylonitrile and alkyl acrylates as possible precursors for carbon fibers: synthesis and thermal behavior during stabilization

Abstract

Copolymers of acrylonitrile and alkyl acrylates with various alkyl substituents (methyl, ethyl, butyl, 2‐ethylhexyl and lauryl) were synthesized via reversible addition–fragmentation chain transfer polymerization in dimethylsulfoxide. It is demonstrated that reactivity of alkyl acrylate in copolymerization decreases with increase of the length of the alkyl substituent. The molar fractions of homodiads and homotriads of acrylonitrile and the number‐average sequence length of acrylonitrile units decreases with a decrease in the acrylate content in the copolymer or with an increase in the length of the alkyl substituent in the acrylate. The copolymer composition was held constant throughout copolymerization in all the studied systems resulting in the formation of copolymers with high compositional homogeneity. Additionally the reversible addition–fragmentation chain transfer mechanism provides low dispersity of the copolymers. Both factors enable the effect of the alkyl substituent in alkyl acrylate on the thermal behavior of acrylonitrile copolymers to be carefully revealed. Being inert in the cyclization reaction, alkyl acrylates have no effect on the activation energy of the reaction. However, increase of the length of the alkyl substituent is followed by a slower evolution of the ladder structure. In contrast, in conditions of oxidative stabilization, the stabilization index increases in the order of increase of the number‐average sequence length of the acrylonitrile units in the copolymers. Thus, the use of alkyl acrylates with longer alkyl substituents provides an increase of chain flexibility and the formation of an enhanced ladder structure during oxidative stabilization which is profitable for carbon fiber production. © 2021 Society of Industrial Chemistry.

Melt-Spinnable Polyacrylonitrile—An Alternative Carbon Fiber Precursor

“…Their advantages include the ease of the synthesis based on radical polymerization in aprotic organic solvents (DMSO, DMF, etc. ), concentrated water-salt media (NaSCN, ZnCl 2 ), and water (emulsion, suspension, and precipitation polymerization) [ 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 ]; the variability of comonomers with different functionalities [ 36 , 37 , 38 , 39 , 40 , 41 ]; and controlling the molecular characteristics by changing the polymerization conditions [ 42 , 43 , 44 , 45 ].…”

Special Issue: Functional Polymers and Composites: From Synthesis to Applications (Dedicated to the 80th Anniversary of Professor George S. Georgiev)

“…Subsequent papers present synthetic approaches, some of which are based on controlled (reversible deactivation) radical polymerization. The work by Chernikova and coworkers 21 describes the application of addition‐fragmentation chain transfer (RAFT) copolymerization of acrylonitrile with various acrylates leading to materials suitable for the preparation of carbon fibers. The article that follows, by Zubov and collaborators, 22 deals with the preparation of dispersions with narrow particle size distributions by the radical copolymerization of silicon‐containing monomers.…”