About this family
A 1,3-diene has two double bonds, and polymerisation consumes only one of them. Add across carbons 1 and 4 and the remaining double bond ends up in the backbone; add across 1 and 2 and it ends up as a pendant vinyl group. Every polymer on this page therefore keeps unsaturation that the vinyl polymers do not have, and that surviving double bond is the whole story of the family – it is what lets these materials be vulcanised into rubbers, and it is also what makes them age.
The double bond in the chain has a geometry, and the difference between the two options is startling. cis-1,4-polyisoprene has a glass transition of −70 °C and melts at 28 °C: it is natural rubber, soft and highly elastic at room temperature. trans-1,4-polyisoprene is gutta-percha, a hard horn-like solid that melts at 74 °C. The molecular formula, the repeat unit, and the molecular weight can all be identical. The cis kink prevents the chain from packing; the trans chain is straight and crystallises readily.
What sets the properties
The same split runs through polybutadiene. The cis-1,4 polymer has a Tg of −100 °C, the lowest of the hydrocarbon rubbers and the reason it is blended into tyre treads for cold-weather grip; the trans-1,4 polymer sits at −83 °C and melts at 145 °C, behaving like a semicrystalline plastic instead. Controlling that ratio – and the fraction of 1,2 addition alongside it – is the central problem of diene polymerisation, and is why the catalyst matters far more here than in an ordinary vinyl polymerisation. Substituting the diene shifts the whole set: the chlorine in polychloroprene raises Tg to −43 °C and buys the oil and weather resistance that makes it a sealant and wetsuit rubber.
Because the backbone double bonds survive, these polymers can be crosslinked through them, which is what vulcanisation does – sulfur bridges struck between chains at the alkene sites, converting a tacky flowing material into an elastic network. A rubber's useful properties are properties of that network rather than of the chain, so crosslink density, not molecular weight, is the design variable. The same reactivity is the family's weakness: an alkene is attacked by ozone and by oxygen, so diene rubbers crack and harden on exposure unless they are protected by antiozonants, and the saturated elastomers on other pages exist largely to sidestep that.
All 22 in the library
Sorted by parent name, ignoring the leading "poly" and any locants – so poly(2-hydroxyethyl methacrylate) files under H. 20 of the 22 carry a note, and every one is searchable by drawn structure on the structure search page. 6 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
Poly(acrylonitrile-co-butadiene-co-styrene) high-rubber
Ordinary ABS is a blend; this is the graft concentrate it is made from, styrene and acrylonitrile polymerised in the presence of polybutadiene latex so that chains grow off the rubber particles. Those grafted chains are what anchor the rubber to the matrix - without them the particles would simply be filler and the toughening would not happen. Not drawn: it is a grafted particulate blend, not a repeat unit.
B
Polybutadiene (cis-1,4)
The trans-1,4 isomer is markedly more crystalline (Tg near -83 °C, Tm near 145 °C, Odian's Table 8-1). Sources spread on the cis Tg: Odian's Table 8-1 gives -95 °C where -100 °C is also widely quoted, and the real value moves with cis content, so treat anything in that range as the same material rather than a disagreement.
Polybutadiene (trans-1,4)
The same four carbons as butadiene rubber with the double bond the other way round, and a 139 C higher melting point for it: the trans chain is symmetric enough to crystallise, so this is a hard thermoplastic rather than an elastomer. Tg and Tm from Odian's Table 8-1. Commercial "polybutadiene rubber" is the cis isomer; the trans form turns up in golf-ball cores and as a crystallising component in tyre compounds.
Poly(butadiene) (1,2-vinyl)
Butadiene polymerised through only one of its double bonds, leaving the other hanging as a pendant vinyl instead of sitting in the backbone. That changes the polymer completely: where 1,4-polybutadiene is a rubber with a glass transition near -100 C, this is a crystallisable plastic, and the pendant vinyls are convenient handles for grafting and crosslinking.
Butyl rubber
Polyisobutylene with about one percent isoprene copolymerised in, purely to provide double bonds for vulcanisation - the parent has none and cannot be cured. What makes it irreplaceable is gas permeability roughly a tenth of natural rubber's: the crowded methyl pairs leave almost no free volume for a gas molecule to hop through, which is why it is the inner liner of every tubeless tyre. Not drawn: the isoprene fraction is deliberately tiny and random.
C
Carboxylated nitrile rubber
Nitrile rubber with a few percent of carboxyl groups, which zinc oxide then crosslinks into ionic clusters alongside the ordinary sulfur network. The ionic crosslinks are strong but exchangeable, so the rubber has unusually high tear strength and abrasion resistance - the reason disposable examination gloves are made of it. Undrawn: a random terpolymer.
Polychloroprene
D
Poly(2,3-dimethylbutadiene)
E
Ethylene propylene diene monomer rubber
Ethylene-propylene rubber with a diene added so it can be sulfur-cured, the diene chosen so that only one of its double bonds polymerises and the other is left pendant for crosslinking. With a fully saturated backbone it has no double bonds where ozone can attack, which is why every weather seal, roofing membrane and radiator hose is made from it rather than a diene rubber. Not drawn: a terpolymer whose composition is the specification.
F
Poly(beta-farnesene)
A sesquiterpene rubber produced at scale by engineered yeast fed sugarcane, and the first bio-based diene elastomer to reach commercial tyre compounds. The long branched side chain acts as a built-in plasticiser, dropping the glass transition to about -70 C and giving grip at low temperature without any added oil.
H
Halobutyl rubber
Butyl rubber halogenated at its few double bonds, which sounds minor and solves the practical problem: plain butyl cures too slowly to be co-vulcanised with the natural rubber alongside it in a tyre, so the layers do not bond. The allylic halide cures fast and by a different mechanism, letting the liner bond to the carcass while keeping butyl's gas barrier. Not drawn: halogenation is partial and positional.
Hydrogenated nitrile rubber
Nitrile rubber with the butadiene double bonds hydrogenated away while leaving the nitriles intact - a selective hydrogenation that is the whole technical achievement. Removing the unsaturation removes the sites where heat and ozone attack, so the oil resistance of nitrile survives to far higher temperature. It is what oilfield seals and timing belts are made of.
Hydroxyl-terminated polybutadiene
A liquid hydroxyl-terminated polybutadiene, Mn about 2800, and the classic example of why functionality is quoted as a number rather than an integer: at 2.4-2.6 there is roughly one extra hydroxyl along the chain for every two oligomer units, so it crosslinks with a diisocyanate instead of merely chain-extending. The hydroxyls are primary allylic alcohols. The hydrocarbon backbone gives hydrophobicity, a low Tg, low moisture permeability and resistance to aqueous acid and base, which is what puts it in potting and encapsulation, sealants, adhesives, waterproof membranes and cast polyurethanes.
I
Polyisoprene (cis-1,4)
Nearly amorphous at room temperature (crystalline Tm near 28 °C, Odian's Table 8-1). The trans-1,4 isomer, gutta-percha, is a harder, more crystalline, thermoplastic-like material (Tg near -58 °C, Tm near 74 °C).
Polyisoprene (trans-1,4)
Natural rubber's geometric isomer, and nothing like it. The trans double bond lets the chains pack into a crystal, so gutta-percha is a hard, non-elastic solid at room temperature where cis-polyisoprene is a rubber - the same atoms, the same connectivity, one double bond facing the other way. It was the insulation on the first transatlantic cables and is still used to fill root canals. Tg and Tm from Odian Table 8-1.
M
Poly(myrcene)
A bio-based diene rubber from a terpene found in hops and bay leaves. It polymerises through the conjugated diene exactly as isoprene does, leaving the isolated trisubstituted alkene of the tail untouched as a pendant group - so the chain is a rubber with a built-in second site for later crosslinking or functionalisation.
N
Nitrile rubber
An oil- and fuel-resistant rubber; acrylonitrile content sets the balance of oil resistance versus low-temperature flexibility.
Poly(norbornene dicarboximide)
The standard ROMP monomer for making bottlebrushes and precise block copolymers: the imide nitrogen carries whatever is to be grafted, and the strained norbornene opens fast and cleanly under a ruthenium catalyst without touching the imide. Almost every grafting-through bottlebrush in the literature is built on this unit or a close relative.
P
Polypentenamer
Made by ring-opening cyclopentene, and one of the earliest metathesis polymers taken seriously as a commercial rubber. It has one double bond every five carbons where polybutadiene has one every four, so it crystallises on stretching and gives high green strength - the property a tyre builder needs before vulcanisation. It lost out to butadiene on monomer cost, not on performance.
S
Styrene-butadiene copolymer
Styrene and butadiene arranged at random along the chain: the workhorse tyre rubber, made by emulsion (E-SBR) or solution (S-SBR) polymerisation and vulcanised in use. A random copolymer has one Tg between those of its components and no physical network, so it is not a thermoplastic elastomer - that is the ordered SBS triblock, which is a separate entry. A drawing shows the monomers, not whether the arrangement is random or block.
Styrene-ethylene-butylene-styrene
SBS with the butadiene block hydrogenated to an ethylene-butylene rubber, removing every double bond and with it the ozone and UV sensitivity that limits SBS to indoor use. The polystyrene domains still act as thermally reversible crosslinks, so it stays a thermoplastic elastomer - and being fully saturated it takes oil extension well, which is how the very soft grades used for overmoulded grips are made. Not drawn: a block copolymer.
V
Vulcanised natural rubber
cis-1,4-polyisoprene with sulfur bridges between chains. The repeat unit is untouched - vulcanisation consumes only a small fraction of the double bonds - and yet it is the whole difference between a tacky thermoplastic mass and an elastomer that returns to its shape, because the crosslinks stop chains from flowing past one another permanently. At high sulfur the same chemistry gives ebonite, a hard solid.