Modeling analysis of chain transfer in reversible addition‐fragmentation chain transfer polymerization

Abstract

The validity of simplifying the reversible addition-fragmentation chain transfer (RAFT) polymerization as a degenerative chain transfer process was verified in this work. The simplified chain transfer mechanism enabled the direct modeling investigation of chain transfer coefficient in the RAFT polymerization. It also gave the analytical expressions for concentration, chain length, and polydispersity of various chain species. The comparison between the simulations based on chain transfer mechanism and those from general RAFT mechanism showed that this simplified mechanism can accurately predict RAFT polymerization in the absence of side reactions to adduct radicals other than fragmentation. However, significant errors are introduced at high conversion when side reactions to adduct are present. The chain transfer coefficient of RAFT agent is the key factor in RAFT polymerization. The polydispersity is more sensitive to chain transfer coefficient at low conversion. At high conversion, however, the polydispersity is mainly determined by termination, which can be controlled by RAFT agent concentration and the selection of initiator. At last, an analytical equation is derived to directly estimate chain transfer coefficient of RAFT agent from the experimental data.

Chain Transfer in Degenerative RAFT Polymerization Revisited: A Comparative Study of Literature Methods

“…An important extension of Equation ( 10) was reported by Gao and Zhu, [ 4 ] who included conventional radical initiation and termination reactions in their analytical derivations to eventually obtain a more complex expression for Ð as a function of x : …”

“…[1][2][3][4] In particular, the presence of thiols and halocarbons under conventional free radical polymerization (FRP) conditions, leading to intermolecular transfer, has been shown effective in regulating the polymer number average chain length ( x n ), as they act as irreversible conventional chain transfer agent (CTA) species. [1][2][3][4] This discovery has revolutionized especially the synthetic rubber industry, since the lower average chain length polymers obtained by FRP with addition of a CTA exhibit a much higher processability.…”

“…[1][2][3][4] In particular, the presence of thiols and halocarbons under conventional free radical polymerization (FRP) conditions, leading to intermolecular transfer, has been shown effective in regulating the polymer number average chain length ( x n ), as they act as irreversible conventional chain transfer agent (CTA) species. [1][2][3][4] This discovery has revolutionized especially the synthetic rubber industry, since the lower average chain length polymers obtained by FRP with addition of a CTA exhibit a much higher processability. [ 5 ] The intermolecular transfer reaction with CTA can be formally written as [1][2][3][4] + → + R A P A n k n * tr (1) in which R n is a macroradical of length n , A the CTA, P n a dead polymer molecule of length n , A * the resulting radical after transfer to CTA, and k tr the corresponding intrinsic rate coeffi cient (L mol −1 s −1 ).…”

“…[1][2][3][4] This discovery has revolutionized especially the synthetic rubber industry, since the lower average chain length polymers obtained by FRP with addition of a CTA exhibit a much higher processability. [ 5 ] The intermolecular transfer reaction with CTA can be formally written as [1][2][3][4] + → + R A P A n k n * tr (1) in which R n is a macroradical of length n , A the CTA, P n a dead polymer molecule of length n , A * the resulting radical after transfer to CTA, and k tr the corresponding intrinsic rate coeffi cient (L mol −1 s −1 ).…”

“…Table 1 ), including those from approximate analytical correlations for the polymer dispersity ( Ð ) profi le. [ 4,[23][24][25] In the present work, the different direct experimental methods to determine the RAFT exchange reactivities ( C tr,0 , C −tr,0 , and C tr ) are briefl y discussed, focusing on their model assumptions. Next, the accuracy of the most important methods which are based on an analytical expression is assessed for a wide range of representative conditions, focusing on their inherent limitations in the absence of experimental error.…”