A new form of controlled growth free radical polymerization

Abstract

A new form of controlled growth free radical polymerization leading to narrow polydispersity polymers and/or block copolymers is described. The process is based on the polymerization of monomers in the presence of macromonomers of general structure CH2=C(Z)CH2(A)n [(A)n= radical leaving group, Z = activating group] and displays many of the characteristics of living polymerizations. The process is most suited to methacrylic monomers but with the appropriate choice of reaction conditions (high temperatures and/or low conversions) it can also be applied to acrylic and styrenic monomers. The macromonomers are conveniently prepared by catalytic chain transfer to alkyl cobalt(III) complexes or by addition‐fragmentation chain transfer. The factors which determine the efficiency of cobalt complexes for molecular weight reduction in free radical emulsion and solution polymerization of methyl methacrylate are also discussed.

Living Radical Polymerization by the RAFT Process

“…[31] We also reported that living characteristics (narrow polydispersities, block synthesis) could be achieved with the use of macromonomer RAFT agents in emulsion polymerization of methacrylate monomers in 1995 (the acronym RAFT was not used at that time). [34,35] Living radical polymerization using thiocarbonylthio RAFT agents was first described in a patent published in 1998. [14] The first paper and conference reports describing the process also appeared in 1998.…”

Living Radical Polymerization by the RAFT Process – A Third Update

“…[135][136][137] Macromonomer RAFT polymerization has been reviewed within larger reviews on catalytic chain transfer (CCT). [138,139] Similarities between the chemistry of RAFT polymerization and that seen in formation and reaction of acrylate mid chain radicals were highlighted in a recent publication.…”

Methacrylic block copolymers by sulfur free RAFT (SF RAFT) free radical emulsion polymerisation

“…25,26 The reaction starts with an inception of propagating radicals (P b ⦁ ) in the system after a normal free radical initiation. These radicals subsequently transfer to a macromonomer (P a m ), forming an intermediate low reactive radicals (addition), which then undergo the β-scission reaction (fragmentation).…”

“…24 The transfer constants were found to have some chain length dependence with the dimer a less effective chain transfer agent than the trimer or higher macromonomers with no polymerization retardation observed. This characteristic of these macromonomers allowed for their successful utilisation in the fabrication of well-defined block copolymers, 25,26 telechelic 27,28 and starshaped macromolecules. 29 The mechanism proceeds via chain transfer to macromonomer followed by a fragmentation to give a macroradical, as derived from the macromonomer, which is able to initiate a second monomer (monomer B) leading to block copolymers.…”

“…The propagating polymer, now propagating via monomer B addition, has competing chain transfer to residual macromonomer in a further additionfragmentation process similar to RAFT as mediated by S containing chain transfer agents. 25,[30][31] It is noted that this same research group discovered sulfur based RAFT fairly soon after first reporting this sulphur free process 25,26 . The resulting product from the addition-fragmentation is an AB block copolymer with a single terminal monomer B with residual unsaturation which can re-enter the polymerisation resulting in chain growth of block B in a process which is very similar to traditional RAFT.…”