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Abstract Cationic bottlebrush homopolymers are polymerized using a grafting‐through approach by ring‐opening metathesis polymerization (ROMP) to afford well‐defined polymers. Quaternary ammonium macromonomers (MMs) are prepared by quaternizing tertiary amine MMs synthesized by reversible addition‐fragmentation chain transfer (RAFT) polymerization. The quaternary ammonium MMs undergo ROMP to target molecular weights (Mn= 30 000–100 000 g mol−1) and a low dispersity (Đ= 1.10–1.30). Halide‐ligand exchange between the third generation Grubbs catalyst (G3) and halide counter ions (bromide and iodide ions) of MMs changes the catalyst activity throughout ROMP, causing it to deviate from pseudo‐first order kinetic behavior; however, the polymerization still follows controlled behavior without significant catalyst termination. Increasing steric bulk of the MMs decreases the polymerization rate as well. Amphiphilic block copolymers are synthesized by sequential polymerization of quaternary ammonium MMs and polystyrene (PS) MMs. Using a PS macroinitiator affords block copolymers with lowerĐvalues as compared to the less active cationic macroinitiator.
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Synthesis of bottlebrush polymers based on poly( N -sulfonyl aziridine) macromonomers
We synthesized bottlebrush polymers with polyaziridine brushes and a polynorbornene backbone by a grafting-through approach. Polyaziridine macromonomers were synthesized by aza-anoinic polymerization of an N -tosylaziridine, initiated with a norbornene-functionalized sulfonamide anion. These macromonomers were then polymerized by ring-opening metathesis polymerization (ROMP) in dichloromethane to produce bottlebrush polymers with molecular weights of 136–456 kDa. To investigate potential macromonomer aggregation that would hinder grafting-through polymerization, we used dynamic light scattering (DLS) to measure the change in macromonomer aggregation and the growth of bottlebrush chains during ROMP. We observed that the macromonomers aggregate in solution, but once ROMP is initiated, these aggregates disperse over the course of the polymerization. This solution behavior appears to be an example of polymerization-induced deaggregation.
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- Award ID(s):
- 1933525
- PAR ID:
- 10406393
- Date Published:
- Journal Name:
- Polymer Chemistry
- Volume:
- 13
- Issue:
- 43
- ISSN:
- 1759-9954
- Page Range / eLocation ID:
- 6134 to 6139
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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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.more » « less
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Bottlebrush polymers, macromolecules consisting of dense polymer side chains grafted from a central polymer backbone, have unique properties resulting from this well-defined molecular architecture. With the advent of controlled radical polymerization techniques, access to these architectures has become more readily available. However, synthetic challenges remain, including the need for intermediate purification, the use of toxic solvents, and challenges with achieving long bottlebrush architectures due to backbone entanglements. Herein, we report hybrid bonding bottlebrush polymers (systems integrating covalent and noncovalent bonding of structural units) consisting of poly(sodium 4-styrenesulfonate) (p(NaSS)) brushes grafted from a peptide amphiphile (PA) supramolecular polymer backbone. This was achieved using photoinitiated electron/energy transfer-reversible addition–fragmentation chain transfer (PET-RAFT) polymerization in water. The structure of the hybrid bonding bottlebrush architecture was characterized using cryogenic transmission electron microscopy, and its properties were probed using rheological measurements. We observed that hybrid bonding bottlebrush polymers were able to organize into block architectures containing domains with high brush grafting density and others with no observable brushes. This finding is possibly a result of dynamic behavior unique to supramolecular polymer backbones, enabling molecular exchange or translational diffusion of monomers along the length of the assemblies. The hybrid bottlebrush polymers exhibited higher solution viscosity at moderate shear, protected supramolecular polymer backbones from disassembly at high shear, and supported self-healing capabilities, depending on grafting densities. Our results demonstrate an opportunity for novel properties in easily synthesized bottlebrush polymer architectures built with supramolecular polymers that might be useful in biomedical applications or for aqueous lubrication.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/d2py01125e
