Evaluation of RAFT Agents

Jeremy Bartels, Sebastian Grajales, Kaushik Patel, Kanth V. B. Josyula, Gangadhar Panambur and Scott Batcheller

RAFT polymerization process

In 1998, members of an Australian Commonwealth Scientific and Research Organization (CSIRO) team discovered the RAFT polymerization method.¹

Why use RAFT methods?

• The process allows radical-initiated growing polymer chains to degeneratively transfer reactivity from one to another through the use of key functional groups (dithioesters, trithiocarbonates, xanthates and dithiocarbamates).
• RAFT agents help to minimize out-of-control growth and prevent unwanted termination events from occurring, effectively controlling polymer properties like molecular weight and polydispersity.
• RAFT agents are commercially available.
• RAFT does not use any cytotoxic heavy metal components (unlike ATRP).

Classes of RAFT agents

• Dithiocarbamates Z₁ is typically -Me or other alkyl
  Z₂ is typically -Ph or other aromatic
• Xanthates Z is typically an alkyl chain (Et)
• Dithioesters Z can vary widely, but is typically -Ph
• Trithiocarbonates Z is typically an alkyl group (C₁₂H₂₅, etc.)

Versatility of RAFT

• RAFT is compatible with most functional groups and solvents, including water.
• RAFT polymerizations are often mildly tolerant to oxygen content, especially when compared to living anionic polymerizations.
• RAFT agents may be tuned to give polymers with telechelic functionality, for further processing/ binding events.
• The RAFT technique requires no special equipment or vacuum glassware.
• RAFT polymers can be applied to any field, from electronics to cell biology.

Compatibility table

RAFT efficacy

A series of five RAFT polymerizations were carried out using our RAFT agents, monomers, and initiators:

Polymer	Conv (%);	MnTheo (Da)	MnNMR (Da)	MwGPC (Da)	MnGPC (Da)	PDI
1. PtBA	33%	4,600	4,800	5,000	4,700	1.06
2. PtBA-b-PS	35%	7,400	7,200	7,200	6,300	1.15
3. PEO-b-PS	29%	7,300	7,400	7,000	6,300	1.04
4. PVAc	65%	12,300	12,300	18,000	14,800	1.21
5. PMMA	60%	15,400	15,000	16,400	14,900	1.10

New class of RAFT CTAs: Universal, pH-switchable RAFT agents

References

1. Chiefari J, Chong YK(, Ercole F, Krstina J, Jeffery J, Le TPT, Mayadunne RTA, Meijs GF, Moad CL, Moad G, et al. 1998. Living Free-Radical Polymerization by Reversible Addition?Fragmentation Chain Transfer:  The RAFT Process. Macromolecules. 31(16):5559-5562. https://doi.org/10.1021/ma9804951

Acknowledgements

• Shashi Jasty, Ph.D.
• John Radke
• Ilya Koltover, Ph.D.
• Angel Thompson