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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Tuning the molecular weight distributions of vinylketone-based polymers using RAFT photopolymerization and UV photodegradation
The choice of chain transfer agent in reversible addition/fragmentation chain transfer polymerization has proven to be instrumental in modulating the dispersity of a certain polyphenyl vinyl ketone (PVK). The monomer, PVK, which can self-initiate when exposed to blue light, was used to synthesize homopolymers, block copolymers by extending with a different monomer and gradient polymers. Regardless of the polymer architecture or degree of polymerization, a consistent trend in polymer dispersity was quantified, with higher loadings of the less active chain transfer agent xanthate leading to higher dispersities. The dispersity could be further modulated by photodegradation of vinyl ketone polymers under UV irradiation.
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- PAR ID:
- 10317567
- Date Published:
- Journal Name:
- Polymer Chemistry
- Volume:
- 12
- Issue:
- 46
- ISSN:
- 1759-9954
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract In typical cyclic polymer synthesis via ring‐closure, chain growth and cyclization events are competing with each other, thus affording cyclic polymers with uncontrolled molecular weight or ring size and high dispersity. Here we uncover a mechanism by which Lewis pair polymerization (LPP) operates on polar vinyl monomers that allows the control of where and when cyclization takes place, thereby achieving spatial and temporal control to afford precision cyclic vinyl polymers or block copolymers with predictable molecular weight and low dispersity (≈1.03). A combined experimental and theoretical study demonstrates that cyclization occurs only after all monomers have been consumed (when) via conjugate addition of the propagating chain end to the specific site of the initiating chain end (where), allowing the cyclic polymer formation steps to be regulated and executed with precision in space and time.
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Abstract In typical cyclic polymer synthesis via ring‐closure, chain growth and cyclization events are competing with each other, thus affording cyclic polymers with uncontrolled molecular weight or ring size and high dispersity. Here we uncover a mechanism by which Lewis pair polymerization (LPP) operates on polar vinyl monomers that allows the control of where and when cyclization takes place, thereby achieving spatial and temporal control to afford precision cyclic vinyl polymers or block copolymers with predictable molecular weight and low dispersity (≈1.03). A combined experimental and theoretical study demonstrates that cyclization occurs only after all monomers have been consumed (when) via conjugate addition of the propagating chain end to the specific site of the initiating chain end (where), allowing the cyclic polymer formation steps to be regulated and executed with precision in space and time.
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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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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.
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D1PY01129D
