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The direct-growth technique was used to synthesize several macromonomers (MMs) employing reversible addition–fragmentation chain transfer (RAFT) polymerization by growing directly from a norbornene-functionalized chain transfer agent (CTA). We aimed to investigate the formation of bisnorbornenyl species resulting from radical termination by combination ( i.e. , coupling) during RAFT polymerization at different monomer conversion values in four types of monomers: styrene, tert -butyl acrylate, methyl methacrylate and N -acryloyl morpholine. Ring-opening metathesis polymerization (ROMP) of these MMs using Grubbs' 3rd generation catalyst (G3) at an MM : G3 ratio of 100 : 1 resulted in the formation of bottlebrush polymers. Analysis by size-exclusion chromatography (SEC) revealed high molar mass shoulders of varying intensities attributed to the incorporation of these bisnorbornenyl species to generate dimeric or higher-order bottlebrush polymer oligomers. The monomer type in the RAFT step heavily influenced the amount of these bottlebrush polymer dimers and oligomers, as did the monomer conversion value in the RAFT step: We found that the ROMP of polystyrene MMs with a target backbone degree of polymerization of 100 produced detectable coupling at ≥20% monomer conversion in the RAFT step, while it took ≥80% monomer conversion to observe coupling in the poly( tert -butyl acrylate) MMs. We did not detect coupling in the poly(methyl methacrylate) MMs, but broadening of the SEC peaks and an increase in dispersity occurred, suggesting the presence of metathesis-active alkene-containing chain ends created by disproportionation. Finally, poly( N -acryloyl morpholine) MMs, even when reaching 90% monomer conversion in the RAFT step, showed no detectable coupling in the bottlebrush polymers. These results highlight the importance of monomer choice and RAFT polymerization conditions in making MMs for ROMP grafting-through to make well-defined bottlebrush polymers.
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Orthogonal Cationic and Radical RAFT Polymerizations to Prepare Bottlebrush Polymers
Abstract An orthogonal combination of cationic and radical RAFT polymerizations is used to synthesize bottlebrush polymers using two distinct RAFT agents. Selective consumption of the first RAFT agent is used to control the cationic RAFT polymerization of a vinyl ether monomer bearing a secondary dormant RAFT agent, which subsequently allows side‐chain polymers to be grafted from the pendant RAFT agent by a radical‐mediated RAFT polymerization of a different monomer, thus completing the synthesis of bottlebrush polymers. The high efficiency and selectivity of the cationic and radical RAFT polymerizations allow both polymerizations to be conducted in one‐pot tandem without intermediate purification.
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- PAR ID:
- 10138974
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Angewandte Chemie International Edition
- Volume:
- 59
- Issue:
- 18
- ISSN:
- 1433-7851
- Page Range / eLocation ID:
- p. 7203-7208
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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