About this family
Swap the oxygen of a polyester's ester for an N–H and you have a polyamide, and the properties change out of all proportion to the size of the edit. An ester oxygen accepts hydrogen bonds; an amide N–H both accepts and donates. Every repeat unit can therefore tie itself to the chain alongside it, and a polyamide behaves as though it were lightly crosslinked in a way the corresponding polyester is not. Nylon 6,6 melts at 265 °C where poly(hexamethylene adipate), the polyester with the identical carbon skeleton, is a low-melting wax.
That interchain bonding is the source of everything the nylons are used for – the melting points, the toughness, the abrasion resistance that puts them in gears and bearings, and the tensile strength that made nylon a fibre before it was a plastic. It is also the source of the one property that has to be designed around, because water hydrogen-bonds too.
What sets the properties
The numbering encodes the synthesis. A single number – nylon 6, nylon 11, nylon 12 – means an AB monomer, one molecule carrying both an amine and an acid (or the lactam that ring-opens to it), so the chain is built from one feedstock and stoichiometry looks after itself. Two numbers – nylon 6,6, nylon 6,10 – mean an AABB pair, a diamine of the first count condensed with a diacid of the second, where the ratio has to be controlled precisely for the chain to grow. The digits are simply the carbon counts.
Amide density sets the thermal properties, and diluting it with hydrocarbon lowers everything together. Nylon 6 melts at 220 °C and nylon 6,6 at 265 °C; stretch the diacid and nylon 6,10 falls to 215 °C; go to the long single-monomer nylons and nylon 11 melts at 190 °C and nylon 12 at 178 °C. The glass transitions move far less – they sit in a narrow band from about 41 °C to 57 °C across that whole range – because Tg reflects local backbone mobility while Tm reflects how well the crystal packs.
The same hydrogen bonds absorb water from the air, and absorbed water sits between chains and plasticises them. A dry nylon 6,6 moulding and the same moulding conditioned to equilibrium in a humid room are measurably different materials: the conditioned one is tougher and less brittle but lower in modulus and dimensionally larger. Nylons are therefore specified conditioned rather than dry, and the long-chain nylons 11 and 12 are chosen where dimensional stability matters precisely because their lower amide density takes up much less water. The aromatic polyamides at the far end of the family – the aramids – hydrogen-bond so effectively between rigid rods that they do not melt at all and have to be spun from solution.
All 112 in the library
Sorted by parent name, ignoring the leading "poly" and any locants – so poly(2-hydroxyethyl methacrylate) files under H. 108 of the 112 carry a note, and every one is searchable by drawn structure on the structure search page. 9 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.
A
Aggrecan
The bottlebrush that biology got to first. A protein backbone carries a hundred or so sulfated glycosaminoglycan chains, and many aggrecan molecules in turn attach to a single hyaluronan chain, so cartilage is packed with brushes hanging off brushes. The side chains are densely negatively charged, so they repel each other, hold water under load, and give cartilage its compressive stiffness - the same crowding argument as a synthetic brush, arrived at without a catalyst. Around cells the layer is thick enough to gate access to the surface: adding aggrecan to chondrocytes or mesenchymal stem cells thickened the pericellular matrix about two and a half times, from roughly 7 to 18 micrometres, and the layer sieves nanoparticles by size while trapping positively charged molecules on the sulfate. Chang, McLane and co-workers (Curtis group, Georgia Tech), Biophys. J. 2016.
Poly(amide-imide)
Half polyimide, half aromatic polyamide, and the compromise between them. The imide rings supply the heat resistance, the amide links supply enough chain flexibility that the polymer can actually be melt-processed - which the fully imide polymers cannot. It holds strength to about 275 C and is machined into bearings and valve seats that run hot and dry. Drawn with p-phenylenediamine, the simplest of the aromatic diamines used; commercial grades usually use a bridged one, which lengthens the repeat without changing the argument.
Poly(amidoamine) dendrimer
Not a chain but a tree, grown outward one exhaustive reaction at a time so that every molecule in a batch is identical - dispersity essentially one, which no chain polymerisation achieves. Each generation doubles the surface groups, so size, surface charge and the number of attachment points are all set by how many cycles were run. The interior develops cavities that hold guest molecules. Its problem is the surface: the amine-terminated generations are cytotoxic, so they are usually capped. Not drawn: a dendrimer has a core, generations and a surface, not a repeat unit.
Poly(aspartic acid)
The biodegradable answer to poly(acrylic acid), and a rare case of a green substitute that genuinely works: it inhibits scale, disperses pigment and superabsorbs water much as the acrylic does, but hydrolyses to a natural amino acid instead of persisting. Made by heating aspartic acid to polysuccinimide and hydrolysing that, so the chain is a mixture of alpha and beta linkages.
Poly(azomethine)
Made by simply mixing a dialdehyde with a diamine and letting water leave - no catalyst, no metal, no purification. The imine bond is also reversible under acid, so these polymers depolymerise cleanly to their monomers and repolymerise, which has made them a favourite scaffold for covalent organic frameworks and self-healing networks.
B
Polybenzimidazole
The polymer used where nothing else survives: firefighters' and astronauts' suits, and high-temperature fuel cell membranes. Fused imidazole rings give one of the highest glass transitions of any thermoplastic, around 425 C, with no melting point and essentially no flammability. The N-H on the imidazole takes up phosphoric acid, which lets a PBI membrane conduct protons at 160 C without any water present - the property that made high-temperature PEM fuel cells possible.
Poly(benzoxazinone)
A heterocyclic backbone used mainly as a reactive intermediate: the benzoxazinone ring opens with an amine or an alcohol to give an amide or ester with a phenol left over, so it is a way of building a rigid chain and then modifying it at every repeat unit. Undrawn pending a checked structure.
Poly(benzoxazole)
The strongest organic fibre made, stronger than aramid by roughly half again, spun from a liquid crystalline solution of an essentially rigid rod. Its weakness is well documented and structural: the oxazole ring hydrolyses slowly in humid air under ultraviolet, so fibre strength decays with age - the reason body armour made from it was recalled.
Poly(gamma-benzyl-L-glutamate)
The classic synthetic alpha helix, and the first synthetic polymer shown to form a liquid crystalline phase in solution. Esterifying glutamic acid with benzyl alcohol removes the charge, so nothing disrupts the intramolecular hydrogen bonds and the chain holds a rigid helix in organic solvent - effectively a molecular rod whose length is set by the degree of polymerisation. Above a critical concentration the rods align into a cholesteric phase, which made it the model system for testing Onsager and Flory's theories of rigid-rod ordering.
Poly(bisbenzimidazobenzophenanthroline)
A true ladder polymer - two parallel strands of bonds all the way along, so no single bond breaking can sever the chain. It is one of the few n-type organic semiconductors stable in air indefinitely, and it survives 500 C. Not drawn: the fused ladder repeat is large and its ring fusion pattern is easy to draw wrongly in a way no mass check would catch.
Poly(2-butyl-2-oxazoline)
The hydrophobic member of the polyoxazoline set, insoluble in water at any temperature where the methyl and ethyl versions dissolve. It is used as the core-forming block of polyoxazoline micelles, whose unusual capacity for poorly soluble drugs - loadings approaching half the mass of the carrier - is the family's main claim in delivery.
C
Casein
Four related proteins that assemble into micelles carrying calcium phosphate - nature's way of holding far more calcium in milk than could ever dissolve. Acidifying or adding rennet strips the stabilising kappa fraction and the micelles aggregate, which is cheese. Dried and pressed it was also one of the first commercial plastics, moulded into buttons well before Bakelite. Not drawn: a mixture of proteins with no repeat unit.
Collagen
The most abundant protein in a mammal and the tensile element of skin, tendon and bone. Every third residue is glycine because the triple helix leaves room for nothing larger at that position, and the hydroxyproline that stabilises it requires vitamin C to make - which is why scurvy is a structural disease. Not drawn: a protein with a repeating motif but no fixed repeat unit.
Core-shell bottlebrush
A bottlebrush that is layered outward rather than along its length: every side chain is itself a diblock, so the molecule has an inner shell of one polymer and an outer shell of another around a single backbone. Make the inner block hydrophobic and the outer one hydrophilic and each molecule becomes a unimolecular micelle - a carrier that cannot fall apart on dilution the way an ordinary micelle does below its critical concentration, which is the usual reason a drug-loaded micelle fails in the bloodstream. One route couples pre-made polylactide-block-poly(ethylene glycol) side chains onto a poly(gamma-propyl-L-glutamate) backbone by azide-alkyne click chemistry. Compare the Janus bottlebrush, which divides the same two polymers along the molecule instead of around it. Reviewed by Verduzco, Li, Pesek and Stein, Chem. Soc. Rev. 2015, 44, 2405.
Cyanate ester network
Three cyanate groups cyclotrimerise into an aromatic triazine ring, so the crosslink itself is a stable aromatic heterocycle rather than a flexible junction. The result has the lowest dielectric loss of any structural thermoset, which is why radomes and high-frequency circuit boards use it, and it absorbs far less water than an epoxy of comparable temperature rating. A network, so no repeat unit is drawn.
Cyanophycin
A bacterial nitrogen store, and structurally a poly(aspartic acid) backbone with an arginine hung by an amide off every beta-carboxyl. That is a nitrogen-dense arrangement on purpose: five nitrogens per repeat, four of them in the arginine, which is why cyanobacteria use it as a reserve rather than as a structural polymer. It is made by a single enzyme rather than at the ribosome, so it is a genuine polymer with a repeat unit rather than a sequence-defined protein.
D
Poly(depsipeptide)
Alternating hydroxy acid and amino acid - lactic acid and glycine here - so it is half polyester and half polypeptide in strict alternation. The ester links set the degradation rate while the amino acid side chains provide functional groups, which is a degree of control neither poly(lactide) nor a polypeptide offers on its own.
Polydiketoenamine
Designed from the start to be taken apart: the diketoenamine bond that links triketone to diamine hydrolyses in strong acid at room temperature, releasing the monomers cleanly enough to be repolymerised without purification. It is one of the clearest answers yet to chemical recycling, in that the recovered monomer is indifferent to whatever dyes and fillers the original part contained. Left undrawn pending a structure I can check rather than infer.
DNA-grafted polypeptide bottlebrush
A bottlebrush built by grafting-onto, with a polypeptide backbone made by ring-opening polymerisation of an N-carboxyanhydride and DNA strands clicked onto it afterwards. Grafting-onto is the awkward one of the three strategies - the side chains have to find their attachment points against increasing crowding, so density is never guaranteed the way grafting-through guarantees it - but it is the only route when both blocks must be made under conditions the other would not survive, which is the case for a polypeptide and an oligonucleotide. Chen, Li, Liu and Li (Chinese Academy of Sciences and Tsinghua), Macromolecules 2012. Not listed as a copolymer of two library entries: the library has no polypeptide to point at, and naming a stand-in would put a component in the data that is not in the molecule.
E
Elastin
The protein that lets an artery and a lung recoil, and one that stores its elasticity in entropy rather than in bonds. Hydrophobic repeats stay disordered and hydrated; stretching them orders the chains and expels water, and it is the water's entropy driving back that restores the shape. It is crosslinked once during development and essentially never replaced, so the elastin in an adult artery is as old as the person. Not drawn: a crosslinked network with no repeat unit.
epsilon-Poly-L-lysine
A natural polylysine made by Streptomyces in which the amide runs through the side-chain epsilon-amine instead of the alpha, leaving the alpha-amine free and the chain cationic along its whole length. That charge lets it disrupt bacterial membranes, and it is approved as a food preservative in several countries - one of very few polycations considered safe to eat.
Poly(ester amide)
A backbone carrying both linkages, which is a deliberate compromise: amides supply hydrogen bonding and mechanical strength, esters supply the hydrolysable bonds that let the material degrade. Polyesters degrade but are weak, polyamides are strong but persist; mixing the two gives a degradable polymer with useful mechanics, which is why they appear in resorbable stents and sutures. Not drawn: the sequence and ratio are the design.
Polyetherimide
One repeat is a whole bisphenol A dianhydride residue joined to one m-phenylenediamine residue, which is why it is so large: two phthalimide rings, the two ether oxygens that give the "ether" in the name, the bisphenol A bridge, and a meta-linked benzene. The ether links and the meta substitution are what make it processable at all - a fully para, ether-free polyimide of this kind does not melt below its decomposition point, and Ultem trades a little heat resistance for the ability to be injection moulded.
Poly(2-ethyl-2-oxazoline)-graft chitosan
Chitosan's usefulness is limited by needing acid to dissolve; grafting a water-soluble polyoxazoline from its amines fixes that without removing the amines' charge entirely. The result stays soluble at neutral pH and keeps enough cationic character to bind nucleic acids and stick to mucosa. Not drawn: grafting density varies and the backbone itself has no fixed degree of deacetylation.
F
Fibrin
The polymer a blood clot is made of, and the fastest structural polymerisation in the body: thrombin clips two short peptides off fibrinogen, exposing knobs that fit holes on the next molecule, and the monomers self-assemble into fibres within seconds. Factor XIII then crosslinks them covalently. Its extraordinary extensibility - fibres stretch several times their length before breaking - comes from protein domains unfolding, not from chain slippage. Undrawn as a protein assembly.
G
Gelatin
Collagen that has been boiled until its triple helix falls apart. On cooling the chains partly re-form helices and physically crosslink, which is why gelatin sets on cooling and melts near body temperature - a thermoreversible gel with no chemistry involved. That reversibility, plus a sequence cells recognise and adhere to, makes it the default cheap scaffold in tissue engineering. Not drawn: it is a hydrolysed protein with no repeat unit.
Poly(gamma-glutamic acid)
The sticky, stringy polymer in fermented soybeans, and an oddity among polypeptides: the amide bond runs through the side-chain carboxyl rather than the alpha one, so the free acid hangs off the backbone and no protease that cuts ordinary peptides will touch it. Made by bacteria as a capsule, edible, and a strong water-holder, so it turns up as a moisturiser, a thickener and a flocculant.
Poly(gamma-glutamic acid) crosslinked hydrogel
The same gamma-linked glutamic acid chain, tied into a network by radiation or by a chemical crosslinker. The repeat unit does not change, and the carboxyl on every unit is still what does the work - it is what makes the network take up many times its own weight in water.
Polyglycine
The simplest possible polypeptide - a nylon 2 with no side group at all. Having no substituent, the backbone can adopt conformations forbidden to every other residue, which is exactly why glycine appears at the tight turns of real proteins and at every third position in the collagen helix. As a homopolymer it packs into sheets and is insoluble in almost everything, so it is studied rather than used.
H
Poly(hexamethylene adipamide-co-terephthalamide)
Nylon with some of the adipic acid replaced by terephthalic, which lifts the melting point above 300 C and holds stiffness far better when hot and wet - the failing that keeps ordinary nylon out of under-bonnet parts. The aromatic content is kept below the level at which the polymer stops melting before it decomposes, which is the constraint the whole semi-aromatic family works inside. Not drawn: it is a random copolyamide and one repeat cannot represent it.
Poly(hexamethylene terephthalamide)
The fully aromatic-diacid nylon, and one that illustrates a hard limit: its melting point is around 370 C, above the temperature at which polyamides begin to decompose, so it cannot be melt-processed at all in pure form. Every commercial semi-aromatic nylon is therefore a copolymer of this with something that lowers the melting point into a workable window.
Poly(hydrazide)
Two nitrogens bonded to each other between the carbonyls. It is chiefly a precursor: heating it drives out water and closes each hydrazide into an oxadiazole ring, so a soluble, spinnable polymer can be made into fibre first and converted to an intractable heterocyclic one afterwards. The same trick as the poly(amic acid) route to polyimides.
Poly(hydroxyproline)
Proline with a hydroxyl on the ring - the post-translational modification that stabilises collagen's triple helix and requires vitamin C to install. As a homopolymer it is water-soluble where polyproline is marginal, and the hydroxyl gives an attachment point on a backbone that is otherwise chemically inert, which makes it a degradable alternative to PEG with handles.
I
Polyimide (PMDA-ODA)
The film that goes to space and into every flexible circuit. Fully aromatic with imide rings locking the backbone, it keeps its properties from about -270 C to over 400 C and does not melt at all. That intractability is handled by processing the soluble poly(amic acid) precursor first - cast it, then heat to close the imide rings in place - which is why polyimide is bought as a film or a varnish rather than as pellets.
Poly(2-isopropyl-2-oxazoline)
The polyoxazoline that behaves like poly(N-isopropylacrylamide): it dissolves cold and precipitates on heating, with a cloud point near body temperature. The isopropyl group is the same one that makes PNIPAM thermoresponsive, and it does the same job here - enough hydrophobic surface that the entropy of the hydrating water wins above a certain temperature. Unlike PNIPAM it also crystallises slowly from the collapsed state, so a solution held hot can turn irreversibly to a precipitate.
K
Keratin
Hair, horn, nail and feather, and a protein whose properties come from a crosslink rather than a sequence. Cysteine residues pair into disulfide bridges that lock coiled-coil helices into a network, and the crosslink density is what separates soft skin keratin from hard hoof. Those same bonds are what a perm breaks and reforms. Not drawn: a crosslinked protein network.
L
Poly(L-arginine)
The guanidinium side chain stays charged at every physiological pH and forms bidentate hydrogen bonds to sulfates and phosphates on a cell surface - which is why short arginine runs are the active element of cell-penetrating peptides. A polymer of it crosses membranes far more readily than an equally charged polylysine, so charge alone is not the explanation.
Poly(L-cysteine)
A thiol on every residue, so the polymer crosslinks itself into disulfides on exposure to air and comes apart again under a reducing agent. That reversibility is the point: a carrier crosslinked this way is stable in blood and falls open in the reducing interior of a cell. The thiol must be protected during polymerisation, which is most of the synthetic difficulty.
Poly(L-glutamic acid)
The polyanionic counterpart to poly(L-lysine), and a textbook helix-coil system: protonate the carboxylates at low pH and the chain folds into an alpha helix, deprotonate them and the charges repel it into a random coil. Degradable by proteases into a natural amino acid, which is why it has carried drugs into clinical trials as a conjugate backbone.
Poly(L-histidine)
The imidazole side chain has a pKa near 6, which is precisely the pH an endosome falls to - so a carrier built from it is neutral in blood and becomes cationic exactly where it needs to disrupt a membrane and escape. That coincidence of pKa with endosomal pH is why polyhistidine appears in so many delivery systems, and it also binds nickel, which is the basis of the histidine purification tag.
Poly(L-leucine)
A strongly helix-forming hydrophobic polypeptide - leucine has the highest helical propensity of the common residues - so it is the standard hydrophobic block when a self-assembling polypeptide needs a rigid rod rather than a coil. Also used as a heterogeneous asymmetric catalyst, where the helix itself is the chiral environment.
Poly(L-lysine)
A polypeptide that is also a polycation: the lysine side-chain amine is protonated at physiological pH, so the chain binds anything negatively charged - DNA, cell membranes, glass slides. That makes it the standard coating for getting cells to adhere to culture surfaces and one of the earliest non-viral gene delivery agents. Made by ring-opening the N-carboxyanhydride, which gives a synthetic polymer with a peptide backbone and therefore something proteases can cut.
Poly(L-proline)
The residue whose side chain loops back to its own nitrogen, so there is no amide hydrogen and the backbone cannot rotate freely. It forms two distinct helices interconvertible by solvent - the polyproline II helix being the same conformation each strand of collagen adopts - and because that helix is rigid and of known rise per residue, oligoproline is used as a molecular ruler for measuring distances in energy-transfer experiments.
Poly(L-tyrosine)
A polypeptide whose phenol side chains crosslink oxidatively into dityrosine - the same bond that stiffens insect resilin and the cuticle of a fertilised sea urchin egg. That makes it the synthetic route to a protein-like network formed without any added crosslinker, and the phenol is also the attachment point for iodination and for tyrosinase-triggered gelation.
Lubricin
The boundary lubricant of a joint, and a bottlebrush with grips on both ends. A heavily O-glycosylated mucin-like middle section forms the brush - hydrophilic, negatively charged, holding a water layer - while the end domains bind to the cartilage surface, so the molecule self-assembles into a telechelic brush anchored at both ends with the loop standing proud. Two such layers slide over each other without interdigitating, which is exactly the argument made for synthetic polymer brushes as lubricants, and it is why lubricin is copied by mimics for contact lenses, sensors and antifouling coatings. Losing it is associated with cartilage damage after joint injury.
M
Poly(m-phenylene isophthalamide)
Meta-linked aramid; flexible chains give flame-resistant fiber rather than high stiffness.
Poly(m-xylylene adipamide)
A nylon with an aromatic ring in the diamine, which raises the glass transition to about 85 C and drops the oxygen permeability roughly an order of magnitude below nylon 6's. It is blended or co-injected into PET bottles as a barrier layer for beer and juice, where the ring's stiffness restricts the segmental motion an oxygen molecule needs to diffuse.
Melamine-formaldehyde resin
The hard, colourless thermoset on laminate worktops and in unbreakable tableware. Melamine offers six reactive N-H sites, so the network is far denser than a phenolic's and the surface is correspondingly harder and more scratch resistant - and, unlike phenolics, it is not dark, so it takes any colour. Its known failure is slow hydrolysis of the amine linkages in hot water, which releases formaldehyde. Not drawn: a network with no repeat unit.
Poly(2-methyl-2-oxazoline)
The most hydrophilic of the polyoxazolines and the closest in behaviour to PEG, without the polyether backbone that eventually oxidises. Cationic ring-opening of the oxazoline is living, so the chain length is set by the monomer-to-initiator ratio and both ends can be functionalised - the initiator picks one and the terminating nucleophile the other. Its tertiary amide is a structural isomer of a peptide bond but has no N-H, so it cannot hydrogen-bond to itself and stays soluble.
Mucin
The other biological bottlebrush, and the reason mucus behaves as it does. Long stretches of the protein backbone are rich in serine and threonine, and each carries an O-linked sugar chain, so the glycosylated regions are brushes while the sparsely glycosylated regions between them stay flexible and can crosslink. The crowded glycans hold water, make the molecule extended and stiff, and give mucus its lubricity and its selectivity as a barrier - a synthetic brush is often justified by pointing at exactly these properties. Studied here as the natural template rather than from any single paper; treat the composition as variable, since mucins differ by tissue and their glycosylation is not a fixed structure.
N
Poly(naphthalene diimide)
Four carbonyls pulling on a naphthalene core make one of the strongest electron acceptors available from cheap starting material, and the reason the naphthalene diimides are the standard n-type unit in printed electronics. The same dianhydride is used to make ordinary high-temperature polyimides, so the unit works as both a structural and an electronic building block.
Neurofilament
The bottlebrush that fills the inside of an axon. A semiflexible filament core carries long unstructured polypeptide projection domains, heavily phosphorylated and so strongly charged, which stick out and hold neighbouring filaments apart. That spacing is what sets the calibre of an axon and therefore how fast it conducts, so the brush is doing a mechanical job with a direct physiological readout. Like other natural bottlebrushes they form lyotropic ordered phases, which is why synthetic semiflexible-core brushes are studied as models for them. Treat the composition as variable: the projection domains differ between the medium and heavy subunits and their phosphorylation state is not fixed.
Poly(2-nonyl-2-oxazoline)
A polyoxazoline with a side chain long enough to crystallise on its own, so the polymer shows a side-chain melting transition independent of the backbone in the same way the comb methacrylates do. It marks the point where the family stops behaving as a polyamide and starts behaving as a wax.
Nylon 10,10
A nylon made almost entirely from castor oil, both monomers deriving from ricinoleic acid, and one of the earliest bio-based engineering plastics - produced in China at scale since the 1960s. The long aliphatic runs make it flexible and nearly indifferent to water, with a melting point around 200 C.
Nylon 10,12
A long-chain bio-based nylon used where dimensional stability in humid service matters more than stiffness.
Nylon 10,14
A long-chain bio-based nylon at the flexible end of the family, used where a polyamide has to survive repeated flexing.
Nylon 10,6
Castor-derived diamine with petrochemical adipic acid, a common half-bio-based engineering grade.
Nylon 10T
A bio-based semi-aromatic nylon, its diamine from castor oil, with the lowest moisture uptake of the aliphatic-aromatic family.
Nylon 11
Bio-based (castor oil); lower moisture uptake than nylon 6 or 6,6.
Nylon 11,10
Both halves from castor oil, making this one of the few fully bio-based engineering polyamides.
Nylon 12
Nylon 12,12
The most dilute common nylon, with twelve carbons on both sides of every amide. Amide density is low enough that it behaves nearly like polyethylene - very low water uptake, good impact strength when cold, and a melting point around 185 C - which is the point when a part must hold its dimensions in wet or cold service.
Nylon 12,6
A long diamine with a short diacid, giving a nylon with low water uptake and good impact at low temperature.
Nylon 13
A long-chain nylon whose amide groups are far enough apart that it behaves more like a polyethylene with occasional hydrogen bonds - low moisture uptake, good dimensional stability, and a melting point well under nylon 6.
Nylon 4
The most amide-dense nylon that can practically be made, one amide for every four backbone atoms. That gives it the highest moisture regain of the family - closer to cotton than to nylon 6 - which made it attractive as a comfortable synthetic fibre, but it also degrades near its melting point, so it has never been produced at scale.
Nylon 4,10
A bio-based engineering nylon: the diamine comes from castor oil and so does the sebacic acid, making it one of the few high-performance polyamides that is almost entirely from plants.
Nylon 4,12
A bio-based nylon combining the shortest practical diamine with a long diacid, giving high strength at low moisture uptake.
Nylon 4,6
The highest-melting aliphatic nylon in commercial use, near 295 C. Shortening the diamine from six carbons to four raises the amide density and lets every amide hydrogen bond, so the crystal is unusually perfect and stiffness is retained far closer to the melting point than nylon 6,6 manages - which is why it appears in gears and engine components that run hot.
Nylon 4,8
A short-diamine, medium-diacid nylon; the even-even pairing lets the chains hydrogen-bond antiparallel, which is what gives the even nylons their higher melting points.
Nylon 5
An odd nylon that has become interesting because cadaverine, its diamine relative, is now made by fermentation - putting a bio-based route to a five-carbon polyamide within reach where the petrochemical one never made sense. Odd-numbered nylons cannot hydrogen bond every amide in the crystal, so it melts lower than nylon 6 despite the higher amide density.
Nylon 5,10
Both halves bio-based - lysine-derived diamine, castor-derived diacid - with a lower melting point and better toughness than nylon 5,6.
Nylon 5,6
The pentamethylenediamine is made by decarboxylating lysine, which is why this nylon became the practical bio-based answer to nylon 6,6 rather than a curiosity.
Nylon 6
Nylon 6,10
Nylon 6,12
Nylon 6,6 with a much longer diacid, which dilutes the amides along the chain. Fewer amides means less water absorbed, so it holds its dimensions and stiffness in humid service where nylon 6,6 swells and softens - the reason it is chosen for toothbrush filament, fuel lines and precision mouldings.
Nylon 6,14
A long-chain nylon in the range where amide density has fallen far enough that the material machines and absorbs water more like a polyolefin.
Nylon 6,16
Among the most dilute of the hydrogen-bonded nylons, and correspondingly the most dimensionally stable in humid service.
Nylon 6,18
A long-chain nylon: eighteen carbons between amides dilutes the hydrogen bonding to roughly a third of nylon 6,6, which is what gives it the low moisture uptake these grades are bought for.
Nylon 6,36
Made with dimer fatty acid, a C36 diacid from oleic acid, which puts a long branched flexible segment between amides and gives a nylon that behaves as a thermoplastic elastomer.
Nylon 6,6
Nylon 6,9
The azelaic acid comes from ozonolysis of oleic acid, making this another partly bio-based polyamide. The odd nine-carbon diacid frustrates the crystal packing that even diacids allow, so it melts well below nylon 6,6 and absorbs less water - the usual trade for a nylon aimed at dimensional stability rather than strength.
Nylon 6I
The meta ring cannot pack into a crystal the way the para one does, so this is an amorphous, transparent polyamide - used as the barrier and clarity component in nylon blends.
Nylon 7
An odd-numbered nylon, and that parity matters: with an odd count between amides the chains cannot pair every carbonyl with a neighbouring N-H the way even nylons do, so the hydrogen bonding is frustrated and the crystal is different. It is the reason odd nylons show ferroelectric behaviour that even ones do not.
Nylon 8
An even nylon between 6 and 10 in amide density, and therefore in water uptake and melting point. Every methylene added dilutes the hydrogen bonding that makes nylon 6 stiff and wet.
Nylon 8,6
The mirror of nylon 6,8 - same atoms, diamine and diacid swapped - and a reminder that the two numbers are not interchangeable: which half carries the amide hydrogens changes how the sheets stack.
Nylon 9
Made from oleic acid by ozonolysis, so its feedstock is vegetable oil rather than oil - one of the earliest bio-based nylons, produced in the Soviet Union as pelargon fibre. Nine carbons between amides means low moisture uptake and good dimensional stability, and being odd it shows the frustrated hydrogen bonding common to that half of the family.
Nylon 9,6
An odd-diamine nylon whose chains cannot register antiparallel, so it melts lower than either even neighbour.
Nylon 9T
The nine-carbon diamine drops the melting point into a processable window while keeping the low moisture uptake and high heat resistance the aromatic ring gives - the combination that puts these in engine bays and connectors.
O
Poly(1,3,4-oxadiazole)
A rigid heterocycle in place of the amide of an aramid, giving a fibre of comparable strength that is markedly more resistant to hydrolysis - the aramids' weakness. Spun from polyphosphoric acid and used where a high-temperature filter has to survive acid flue gas, though it never displaced the aramids commercially.
Poly(oxamide)
A nylon in which the two amide carbonyls are bonded directly to each other, the shortest possible diacid. The adjacent carbonyls force a rigid, planar linkage and the amide density is the highest of any polyamide, so it absorbs less water than nylon 6,6 despite having more amides - the hydrogen bonds are already fully satisfied within the crystal.
Poly(2-oxazine)
The six-membered ring counterpart of a 2-oxazoline, giving one extra methylene between amides. That single carbon lowers the amide density enough to change solubility and to raise drug loading in micelles substantially over the oxazoline analogue - one of the clearer cases where a homologue is not simply a slower version of its neighbour.
Poly(2-oxazoline) gradient copolymer
Because oxazoline polymerisation is living and different 2-substituents propagate at different rates, feeding two monomers together gives a chain whose composition drifts smoothly from one end to the other rather than forming blocks. A gradient copolymer has a broad, gentle phase transition where a block copolymer has a sharp one, which suits a thermoresponsive carrier meant to release gradually. Not drawn: the composition varies along the chain by design.
P
Peptide nucleic acid
DNA with the sugar-phosphate backbone replaced by a neutral peptide-like chain, the bases hanging off it in the same spacing. Because the backbone carries no charge there is no electrostatic repulsion between strands, so PNA binds DNA and RNA more tightly than they bind each other and does so at low salt. Nothing degrades it - neither nuclease nor protease - which makes it a durable probe and antisense agent, though getting it into a cell is its persistent problem. Not drawn: four bases means four repeat units and the sequence is the molecule.
Peptidoglycan
A single covalently closed molecule wrapped around an entire bacterium - sugar chains stitched together by short peptides, and the reason a cell holds its shape against several atmospheres of internal pressure. Penicillin blocks the enzyme that makes the peptide crosslink, which is why the drug kills growing cells and leaves resting ones alone. Undrawn: a two-dimensional network, not a chain.
Poly(perylene diimide)
The pigment behind automotive red paints and, in polymer form, the leading non-fullerene electron acceptor before the small-molecule acceptors overtook it. Its problem is its virtue: the flat perylene stacks so strongly that it crystallises into domains far larger than an exciton can cross. Not drawn - the fused perylene core is too easy to get wrong on paper, and I would not catch it by mass.
Poly(2-phenyl-2-oxazoline)
An aromatic polyoxazoline, glassy and water-insoluble, with a glass transition near 100 C where the alkyl versions sit far below room temperature. Because oxazoline polymerisation is living, it can be block-copolymerised with the water-soluble members to give amphiphiles in which every block comes from the same chemistry and the same reactor.
Poly(p-phenylene terephthalamide)
Rigid-rod liquid-crystalline aramid; does not melt (decomposes ~500 °C).
Polypropylenimine dendrimer
The other classical dendrimer, built by adding acrylonitrile to amines and hydrogenating the nitriles to new amines. Its interior is all amine and hydrocarbon with no amide, so it is more compact and more basic than PAMAM at the same generation - which makes it a better proton sponge and a worse host for polar guests. It reached commercial production earlier than PAMAM and at larger scale.
Poly(pyrrone)
A ladder polymer from the 1960s aerospace programmes, formed by condensing a dianhydride with a tetraamine so each junction closes two fused rings rather than one. It loses almost no mass below 600 C. It also proved impossible to process, which is the standard fate of ladder polymers and the reason polyimides won. Undrawn as a fused ladder.
R
Resilin
The most efficient elastic material known, returning about 97 percent of stored energy - better than any synthetic rubber - which is what lets a flea jump and a wing beat for a lifetime without fatigue. Like elastin it stores energy in the entropy of disordered hydrated chains, but its crosslinks are dityrosine bridges formed by oxidation rather than the desmosine of elastin. Recombinant versions are made for exactly this resilience. Not drawn: a crosslinked protein network.
S
Poly(sarcosine)
The simplest peptoid and the leading candidate to replace PEG in circulating drug carriers. Being a polypeptide backbone it is degradable and non-immunogenic, while the N-methyl removes the amide hydrogen so it cannot fold or aggregate - it behaves as a random coil as PEG does. Its selling point is that anti-PEG antibodies, now measurable in a large fraction of the population, do not recognise it.
Poly(sarcosine-b-lactide)
The fully degradable answer to PEG-polyester micelles: both blocks break down, one to a natural amino acid and one to lactic acid, where a PEG block simply persists and accumulates. Nanoparticles from it circulate comparably to PEGylated ones without provoking the anti-PEG response, which is the argument for the whole polysarcosine field. Not drawn: a block copolymer.
Poly(semicarbazide)
A urea with an extra nitrogen inserted, made by reacting a diisocyanate with hydrazine rather than with a diamine. The four nitrogens per linkage give an exceptionally dense hydrogen-bonded network, so these are the hard segments in polyurethanes that must not soften - at the cost of being nearly insoluble once formed.
Silk fibroin
A protein whose strength comes from long runs of glycine alternating with alanine, small enough side groups that the chains pack into tight beta sheets - nanocrystals held in an amorphous matrix, which is a composite made at the molecular scale. Processing controls the sheet content and therefore everything else: the same protein gives a slow-degrading suture or a soft hydrogel depending only on how it is dried. Not drawn: it is a protein with a repetitive but not exactly periodic sequence.
Silk sericin
The other silk protein, the glue holding fibroin filaments together in a cocoon, and traditionally discarded as waste in the degumming step of silk production. It is about a third serine, so it is strongly hydrophilic and holds water, which has turned the waste stream into a moisturiser and a wound-dressing component. It is also the fraction blamed for silk suture's occasional allergic response. Not drawn: a protein with no repeat unit.
Poly(N-substituted glycine)
A peptide with the side chain moved from the alpha carbon to the amide nitrogen. That single relocation removes the backbone N-H, so no intramolecular hydrogen bonds form and no protease recognises it - the chains are far more flexible and essentially indefinitely stable in serum. Sequence-defined synthesis from cheap amine building blocks means any side chain can be placed anywhere, which is why peptoids are used as protease-resistant antimicrobials and as designed foldamers. Drawn with an ethyl side chain as the simplest representative.
T
Poly(thiosemicarbazide)
The sulfur analogue, and a powerful chelating polymer: the thiocarbonyl sulfur and the adjacent nitrogens form a pocket that grips soft heavy metals - mercury, lead, cadmium - far more tightly than a carboxylate resin does. It is used to strip those metals from water at concentrations where ion exchange stops working.
Poly(1,2,3-triazole)
A step-growth chain built by copper-catalysed azide-alkyne cycloaddition - the reaction that gave click chemistry its name and its 2022 Nobel. The triazole ring formed is aromatic, strongly dipolar and essentially inert once made, and because the coupling reaches high conversion without side reactions it is one of the few step-growth routes that reliably gives high molecular weight from ordinary difunctional monomers. Structure shown is the hexanediazide plus dipropargyl diethylene glycol pairing.
U
Polyurea
What you get when a diisocyanate meets a diamine instead of a diol. The urea linkage has two N-H donors to the urethane's one, so it hydrogen-bonds roughly twice as strongly and the hard phase is tougher and more heat-resistant. The reaction is also far faster - fast enough that polyurea is sprayed as a two-component mix that gels in seconds, which is how truck bed liners and blast-resistant coatings are applied.
Poly(urethane urea)
A polyurethane extended with a diamine rather than a diol, so the hard segments are urea rather than urethane - two hydrogen bond donors instead of one, which makes the hard domains far more cohesive. That is what allows the extraordinary recoverable extension of spandex, several hundred percent returning almost completely, and why the fibre keeps its shape where a urethane-extended elastomer would creep. Not drawn: a segmented block copolymer.
Z
Zein
A maize storage protein unusual for being soluble in aqueous alcohol but not in water, because it is dominated by hydrophobic and amide residues with almost no charge. That solubility makes it castable into a water-resistant edible film, used to coat confectionery and pharmaceuticals, and it was moulded into fibres and plastics before petrochemicals displaced it. Not drawn: a protein with no repeat unit.
Zein-oleic acid conjugate
Zein films are brittle because the protein has almost no chain flexibility; attaching a fatty acid to its lysines supplies internal plasticiser that cannot migrate out the way an added one does. That fixes the failure mode of every plasticised biopolymer film - the plasticiser leaving over time - at the cost of a synthesis step. Not drawn: a protein with a variable degree of acylation.