About this family
A bottlebrush carries a polymeric side chain on every repeat unit of its backbone, and the consequence is steric rather than chemical. The side chains are anchored too densely to avoid one another, so they push the backbone straight simply to make room. A linear chain of the same molecular weight is a random coil; a bottlebrush is an extended cylinder whose persistence length is far larger, set by how long and how dense the side chains are rather than by anything about backbone bond angles.
Nothing about the chemistry has changed – a poly(lactide) bottlebrush is made of the same ester as a linear poly(lactide). The architecture alone changes the physics, which is what makes this family interesting: it is a way to reach properties that are not otherwise available from the monomers you already have.
What sets the properties
The most useful consequence is that bottlebrushes barely entangle. Entanglement requires chains to thread past one another, and a thick, stiff cylinder cannot easily thread through its neighbours, so the entanglement molecular weight rises by orders of magnitude. A melt or network of bottlebrushes is therefore far softer than the same chemistry linear and crosslinked – soft enough to reach the moduli of biological tissue without adding any solvent, where a conventional elastomer would have to be swollen with oil that can leach out. That is the basis of the supersoft and solvent-free elastomer entries here.
The other consequence is size. Because the molecule is a cylinder tens of nanometres across, bottlebrush block copolymers microphase-separate at a spacing comparable to the wavelength of visible light, and self-assemble into photonic materials that reflect colour structurally rather than by pigment. The same bulk means a single molecule can carry a large, defined payload, which is what the drug-delivery and nucleic-acid conjugates in this list use it for.
Three synthetic routes appear here and the distinction matters when you read the entries. Grafting-through polymerises a macromonomer that already carries the side chain, most often by ROMP, and so guarantees exactly one side chain per backbone unit – the reason it dominates when the architecture has to be well defined. Grafting-from grows the side chains out of a backbone carrying an initiator on every unit, usually by ATRP, which reaches higher backbone molecular weights but leaves the grafting density to be measured rather than assumed. Grafting-to attaches finished chains to a reactive backbone, and is limited by how crowded the surface becomes as the reaction proceeds.
All 21 in the library
Sorted by parent name, ignoring the leading "poly" and any locants – so poly(2-hydroxyethyl methacrylate) files under H. 21 of the 21 carry a note, and every one is searchable by drawn structure on the structure search page. 0 have a CAS registry number for the polymer; most specialty polymers have never been assigned one, and the number you find in a catalogue is usually the monomer's, which is why the field is blank rather than borrowed here.
B
Bottlebrush poly(dimethylsiloxane) elastomer
A way to make a solid as soft as tissue with no solvent in it. An ordinary elastomer cannot be softened much below about 100 kPa, because softening means lengthening the strands between crosslinks and entanglements then take over. Grafting dense side chains onto those strands dilutes the entanglements from the inside: the side chains hold neighbouring backbones apart, and the network reaches a few kPa while staying completely dry. Conventional gels reach that softness only by holding solvent, which evaporates or leaches out. These match the stiffness of brain and fat tissue and stay where they are put.
Bottlebrush polyelectrolyte
A bottlebrush whose side chains repel each other electrically as well as sterically, so the molecule stretches further than crowding alone would manage and its size responds to salt and pH. Adding salt screens the charge and lets the corona collapse; removing it swells the molecule again. This is the synthetic version of what aggrecan does in cartilage and what neurofilament sidearms do in an axon - hold water, resist compression, and keep neighbours at a distance - and it is why charged brushes are studied as lubricants and as compression-resistant coatings. The listed components are representative: the same architecture is made with sulfonate, quaternary ammonium and zwitterionic side chains. Drawn through the exo-norbornene dicarboximide nitrogen, with the acrylic acid side chain attached there.
Bottlebrush prodrug
The argument for grafting-through in one line: the drug is attached to the macromonomer before polymerisation, so loading is fixed by the monomer rather than left to a post-polymerisation coupling that never quite goes to completion. Every repeat carries its drug, and the batch has one composition rather than a distribution of them. The first version carried doxorubicin and camptothecin on the same PEG-norbornene macromonomer through a photocleavable linker, and was about thirty times more toxic to cells after irradiation than before. The later work made the linker the design variable rather than the payload: tuning traceless linkers so that release kinetics measured in vitro predicted what the drug did in a tumour, which turned prodrug design into something you can calculate instead of screen. Johnson, Lu, Burts and co-workers, Macromolecules 2010, 43, 10326; Vohidov and co-workers (Johnson group, MIT), J. Am. Chem. Soc. 2021, 143, 4714.
Brush block copolymer photonic crystal
Colour from architecture rather than from any dye. Two bottlebrush blocks of different composition segregate into layers, and because a crowded brush is forced into an extended cylinder rather than a coil, the layer spacing lands in the hundreds of nanometres where visible and near-infrared light is reflected. Brushes also order in minutes rather than the long annealing a linear block copolymer of the same period would need, because there are no entanglements to unpick. The polymers that established this used rigid helical polyisocyanate side chains from hexyl and 4-phenylbutyl isocyanate, reached molar masses of 1.5 to 7 MDa, and reflected across the ultraviolet, visible and near-infrared - the near-infrared version was proposed as a heat-rejecting paint. Miyake, Weitekamp, Piunova and Grubbs, J. Am. Chem. Soc. 2012, 134, 14249.
Brush-arm star polymer
The brush-first route, and the reason a bottlebrush can be turned into a nanoparticle without a template. Macromonomers are polymerised first to give living bottlebrushes; a bis-norbornene crosslinker is then added and couples those brushes together through their living chain ends, so the arms of the resulting star are themselves bottlebrushes rather than linear chains. Particle size is set by how much crosslinker is added, which makes a size series a matter of pipetting rather than of new synthesis. The original report used a photodegradable o-nitrobenzyl crosslinker and nitroxide labels, so the core could be cut with UV light and the core and shell environments distinguished by EPR. Liu, Burts and co-workers (Johnson group, MIT), J. Am. Chem. Soc. 2012, 134, 16337.
C
Cationic bottlebrush polymer
A polycation shaped as a brush instead of a chain, made to carry plasmid DNA into cells. Backbone length was varied over degrees of polymerisation of 13, 20, 26 and 37 while every side chain was held at 57 units, which separates the effect of architecture from the effect of chemistry - the linear macromonomer is the control, and it is the same molecule that makes up the arms. The complexes with DNA, called bottleplexes, gave up to about sixty times more cells expressing the delivered gene than the linear building block, and expression rose with backbone length. Both architectures got the DNA inside cells about equally well, so the advantage lies after uptake rather than in it. Dalal, Kumar, Ohnsorg, Brown and Reineke, ACS Macro Lett. 2021, 10, 886. Drawn through the exo-norbornene dicarboximide nitrogen, with the methacrylate side chain attached there.
Core-shell cyclic bottlebrush
A macrocyclic bottlebrush whose side chains are themselves diblocks, hydrophobic polystyrene next to the backbone and hydrophilic poly(acrylic acid) outside, so each molecule is a core-shell cylinder closed into a ring. Exchanging the solvent from tetrahydrofuran to water walks the assemblies through spheres, then porous spheres, then nanobowls - spheres with a single large opening. A linear bottlebrush of matched backbone and side-chain lengths stops at porous spheres under the same conditions, so the ring topology is doing the work, apparently by changing how fast the aggregate's interior stiffens as solvent leaves. Pal, Garrison, Miao, Diodati, Veige and Sumerlin, Macromolecules 2022, 55, 7446.
D
DNA bottlebrush
A bottlebrush with DNA as one of its two components, either as side chains grafted from a synthetic backbone or as a main chain wearing a synthetic corona. The corona stiffens the DNA substantially: effective persistence lengths near 250 nm have been measured by nanopore and by AFM, against 50 nm for bare duplex DNA. The stiffening does not translate into a more rod-like molecule, because the corona thickens it faster than it rigidifies it, so the effective aspect ratio of persistence length over diameter falls. It does not follow that liquid crystallinity is lost: a measured case still formed lyotropic phases, and at a lower concentration than bare DNA, because what the corona costs in aspect ratio it more than repays in excluded volume. See the Chain Dimensions tool, where those numbers appear and a persistence length can be turned into a real chain size, and the self-assembled DNA bottlebrush entry for the measurement.
DNA-backbone bottlebrush
The inverse of the usual arrangement: the DNA is the backbone and the synthetic polymer is the corona. PEG chains are attached at chosen positions along an oligonucleotide hairpin, so the sequence still does its job - the hairpins undergo hybridisation chain reaction essentially as well as unmodified ones - while the crowded PEG shell keeps nucleases off. The result resists enzymatic digestion, melts at a higher temperature, and stays in the blood longer, which is what a DNA nanostructure needs before it can be a therapeutic rather than a demonstration. Jia, Wang, Lu and co-workers (Ke Zhang group, Northeastern), Nano Lett. 2018, 18, 7378.
J
Janus bottlebrush
A bottlebrush that is two-faced along its own length rather than divided into blocks down the backbone. The trick is where the polymerisable group sits: a diblock side chain is made first and the norbornene is installed at the junction between the two blocks, so on polymerisation each repeat projects one polystyrene arm and one polylactide arm from the same point. The backbone then runs down the middle of a molecule that is polystyrene on one side and polylactide on the other, which is a shape that cannot be reached by making the two side chains separately. Kawamoto, Zhong and co-workers (Johnson group, MIT, with Ross and Alexander-Katz), J. Am. Chem. Soc. 2016, 138, 11501.
L
Linear-bottlebrush-linear triblock hydrogel
An injectable gel that solves two opposite problems with one architecture. The middle block is a PEG bottlebrush, which is compact and barely entangled, so the solution stays thin enough to push through a needle; the linear poly(N-isopropylacrylamide) ends are thermoresponsive and aggregate the moment they reach body temperature, so it sets on arrival with no crosslinking chemistry and nothing to leach. The result matches the deformation response of adipose and brain tissue, stays below about 1 kPa in modulus while surviving 700 percent deformation, and does not expel its water on gelling, which is the usual failure of a physically set gel. Vashahi, Martinez and co-workers (Sheiko and Matyjaszewski groups), Sci. Adv. 2022. See also the dry analogue, the PMMA-bottlebrush-PDMS-PMMA thermoplastic elastomer that this work uses as its comparison.
M
Poly(methyl methacrylate)-bottlebrush poly(dimethylsiloxane) thermoplastic elastomer
The dry counterpart of the injectable bottlebrush gel, and the reason that architecture works at all. A bottlebrush poly(dimethylsiloxane) middle block supplies a network strand that is soft and barely entangled; glassy poly(methyl methacrylate) end blocks aggregate into hard domains that act as physical crosslinks, so the material is an elastomer that can still be melted and reshaped. No solvent is present, so there is nothing to evaporate or leach - the softness comes from the architecture rather than from a plasticiser. It is mechanically the weaker of the pair: the aqueous PNIPAM-bottlebrush-PEG version reaches about 3.5 MPa at break against roughly 0.6 MPa here, which is the comparison the injectable work used to make its case.
Mikto-brush-arm star polymer
What happens when two different bottlebrushes are crosslinked into the same star. Each macromonomer is polymerised separately to a living bottlebrush, the two are mixed in a chosen ratio, and only then is the crosslinker added, so composition is set by a mixing ratio rather than by making a new macromonomer for every point in the series. Because the arms are homopolymer brushes rather than brushes with mixed side chains, the domains inside one particle can be large. Hydrodynamic diameters were 28-32 nm in THF at every composition, both blocks being solvated; in water the polystyrene-rich particles aggregate instead, reaching about 166 nm, while PEG-rich ones stay single molecules with the polystyrene arms shielded. Irradiating the photocleavable core at 365 nm releases the arms as roughly 10 nm bottlebrushes. Shibuya, Nguyen and Johnson (MIT), ACS Macro Lett. 2017, 6, 963.
Molecular bottlebrush by ATRP grafting-from
The other route, and the one that inverts the trade-off. Rather than polymerising a pre-made side chain, a backbone is built carrying an initiator on every repeat - typically by esterifying poly(2-hydroxyethyl methacrylate) with a bromoisobutyryl group - and the side chains are grown outward by atom transfer radical polymerisation. The backbone can be made very long, which grafting-through struggles with, but the side chains grow crowded together where radicals sit close, so termination between neighbours becomes the limiting problem and conversion is deliberately kept low. Grafting-through buys certainty about grafting density; grafting-from buys backbone length. Neither gives both.
N
Poly(norbornene)-graft-poly(2-ethyl-2-oxazoline)
A bottlebrush whose side chains are polyoxazoline rather than PEG. Polyoxazoline is water-soluble and stealthy like PEG but is a polyamide, so it is not degraded by the oxidative chemistry that eventually cuts a polyether, which matters for anything meant to circulate. The side chains are made by cationic ring-opening polymerisation from methyl tosylate and terminated onto a norbornene acid, then that macromonomer is polymerised through its strained ring by a Grubbs third-generation catalyst. Crosslinking those brushes brush-first gave stars of 21-27 nm. Their point was metal-free MRI contrast: a nitroxide radical carried at the core-shell interface gave transverse relaxivities of 1.83-2.28 per mM per s, against 0.14-0.19 for the longitudinal - an organic contrast agent that avoids gadolinium entirely. Alvaradejo and co-workers (Johnson group, MIT), ACS Macro Lett. 2019, 8, 473. Drawn through the exo-norbornene dicarboximide nitrogen, the same macromonomer linkage as the PEG brush; other norbornene acids appear in the literature and would change only the junction.
Poly(norbornene)-graft-poly(caprolactone)
The slow-degrading member of the polyester bottlebrush family. Polycaprolactone side chains are made by ring-opening a lactone from an alcohol on the norbornene, then the macromonomer is polymerised through its ring, the same route as the polylactide brush. The difference is timescale: caprolactone esters hydrolyse far more slowly than lactide ones, so where a polylactide brush is chosen to disappear over weeks to months, a caprolactone brush is chosen to persist and then go, which suits a scaffold or a depot that has to hold its shape first. It is also semicrystalline and much softer, so the two are not interchangeable even before degradation starts. Drawn through the exo-norbornene dicarboximide nitrogen, with the caprolactone chain grown from the hydroxyl on that linker.
Poly(norbornene)-graft-poly(ethylene glycol)
The workhorse bottlebrush, and the reason ring-opening metathesis is the default route to this architecture. A PEG chain is capped with a norbornene and that macromonomer is polymerised through its strained ring by a fast-initiating Grubbs catalyst, so every backbone repeat carries a side chain by construction rather than by chance. Grafting-through guarantees the grafting density instead of hoping for it, which is why it dominates despite the macromonomer being the expensive part. The crowded PEG corona forces the backbone to extend, so the molecule behaves as a soft cylinder rather than a coil, and a drug attached to the backbone sits shielded inside a stealth shell.
Poly(norbornene)-graft-poly(lactide)
The degradable bottlebrush, and the one that makes the architecture visible to the eye. Bottlebrush block copolymers assemble into lamellae with periods of hundreds of nanometres against the tens a linear block copolymer manages, because the crowded side chains stretch the backbone and there are no entanglements to slow the ordering. Those periods fall in the range of visible wavelengths, so the films are structurally coloured photonic crystals whose reflected colour is set by molar mass alone. The polylactide side chains then hydrolyse, which a polystyrene brush will not.
Poly(norbornene)-graft-polystyrene
The hydrophobic counterpart to the PEG bottlebrush, and the block that supplies the high-refractive-index or glassy half of most bottlebrush assemblies. Polystyrene is made first by a controlled radical polymerisation and then joined to a norbornene, commonly by copper-catalysed azide-alkyne coupling of an azide-terminated chain to a norbornene alkyne, before being polymerised through the ring. Because the side chains are glassy and immiscible with PEG, the two brushes segregate rather than mix, which is what makes them useful together. Drawn through the exo-norbornene dicarboximide nitrogen, the same macromonomer linkage as the PEG brush; the alkyne precursors used elsewhere would change only the junction.
O
Oligonucleotide macromonomer bottlebrush
A way of deciding where in a bottlebrush the DNA sits. Protecting an oligonucleotide so it dissolves in organic solvent lets it be built into a macromonomer alongside PEG, and a custom norbornene phosphoramidite puts the polymerisable group wherever it is wanted along that macromonomer. Put the norbornene at the far end and the result is a linear norbornene-DNA-PEG arm with PEG at the periphery; put it at the junction and the arm is Y-shaped, with DNA and PEG both projecting from the backbone. The same components therefore give a brush with the PEG buried or exposed, which is an unusual amount of control over where each block ends up. Lu, Cai and co-workers (Ke Zhang group, Northeastern), Macromolecules 2022, 55, 2235.
V
Poly(vinyl alcohol)-graft-poly(ethylene oxide)
The model system for asking what a bottlebrush actually looks like in water, chosen because both blocks are simple, water-soluble and well parameterised for simulation. Atomistic molecular dynamics on cyclic and linear versions found the side-chain length to be the variable that matters most: short side chains leave the backbone flexible and the molecule coil-like, and only past a certain length does the crowding force the extended cylinder that the word bottlebrush implies. The cyclic and linear forms converge as side chains lengthen, because a long enough corona hides what the backbone is doing. Chen and Dormidontova, Macromolecules 2023, 56, 3286. Drawn as a direct ether from a poly(vinyl alcohol) hydroxyl; preparations that derivatise the hydroxyl first would insert a linker here.