Living free-radical polymerization of sterically hindered monomers: Improving the understanding of 1,1-disubstituted monomer systems

Zachary Szablan, Andrew Ah Toy, Lexandre Terrenoire, Thomas P. Davis, Martina H. Stenzel, Axel H E Müller, Christopher Barner-Kowollik

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The sterically hindered, 1,1-disubstituted monomers di-n-butyl itaconate (DBI), dicyclohexyl itaconate (DCHI), and dimethyl itaconate (DMI) were polymerized with reversible addition-fragmentation chain transfer (RAFT) free-radical polymerization and atom transfer radical polymerization (ATRP). Cumyl dithiobenzoate, cumyl phenyl dithioacetate, 2-cyanoprop-2-yl dithiobenzoate, 4-cyanopentanoic acid dithiobenzoate, and S- methoxycarbonylphenylmethyl dithiobenzoate were employed as RAFT agents to mediate a series of polymerizations at 60°C yielding polymers ranging in their number-average molecular weight from 4500 to 60,000 g mol-1. The RAFT polymerizations of these hindered monomers displayed hybrid living behavior (between conventional and living free-radical polymerization) of various degrees depending on the molecular structure of the initial RAFT agent. In addition, DCHI was polymerized via ATRP with a CuCl/methyl benzoate/N,N,N′N″N‴-pentamethyldiethylenetriamine/ cyclohexanone system at 60°C. Both the ATRP and RAFT polymerization of the hindered monomers displayed living characteristics; however, broader than expected molecular weight distributions were observed for the RAFT systems (polydispersity index = 1.15-3.35). To assess the cause of this broadness, chain-transfer-to-monomer constants for DMI, DBI, and DCHI were determined (1.4 × 10-3, 1.3 × 10-3, and 1.0 × 10 -3, respectively) at 60°C. Simulations carried out with the PREDICI program package suggested that chain transfer to monomer contributed to the broadening process, In addition, the experimental results indicated that viscosity had a pronounced effect on the broadness of the molecular weight distributions.

Original languageEnglish
Pages (from-to)3692-3710
Number of pages19
JournalJournal of Polymer Science, Part A: Polymer Chemistry
Issue number11
Publication statusPublished - 1 Jun 2006
Externally publishedYes


  • Atom transfer radical polymerization (ATRP)
  • Chain transfer to monomer
  • PREDICI modeling
  • Reversible addition fragmentation chain transfer (RAFT)
  • Sterically hindered monomers
  • Viscosity

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