Hello and welcome to this new blog post in which we discuss the functional groups of polymers.
Introduction — why functional groups matter
Figure 1: Overview of the 11 functional groups of polymers.
Functional groups are the recurring atom clusters in organic molecules whose chemistry largely determines material properties (polarity, hydrogen-bonding, thermal stability, chemical resistance, chain rigidity, degradability, etc.).
In polymers, the functional group(s) present in the backbone or pendant positions control bulk properties and processing behaviour, so identifying the dominant functional group is a quick route to predicting performance during material selection.
What are the 11 functional groups we will discuss in this post:
- Imide group
- Sulfone Group
- Amide Group
- Ester Group
- Ketone Group
- Sulfide Group
- Ether Group
- Arene Group
- Alcohol Group
- Alkane Group
- Haloalkane Group
Let us get starting!
1) Imide group — structure: –CO–N–CO– (cyclic or linear imide)
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| Figure 1: Functional groups of polymers: Imide group. |
What it gives: outstanding high-temperature stability, good chemical resistance, high glass transition (rigid backbone), low creep.
Typical polymers / examples: Polyimides (e.g., Kapton®, Vespel®) used for high-T films, electrical insulation, aerospace parts. Polyimides are classic high-performance plastics made from dianhydride + diamine routes.
Notes: Alkyl groups (R-) are saturated, non-aromatic hydrocarbon chains derived from alkanes (e.g., methyl, ethyl).
Aryl groups (Ar-) are aromatic rings derived from compounds like benzene.
2) Sulfone group — structure: –SO2– (often between aryl groups)
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| Figure 2: Functional groups of polymers: Sulfone group. |
What it gives: high thermal stability, hydrolytic stability, rigidity and flame resistance; good dimensional stability and toughness in amorphous engineering resins.
Typical polymers / examples: Polysulfones / Polyethersulfones / Polyphenylsulfone (PSU, PES/PESU, PPSU — trade names include Ultrason®, Radel®). Widely used in medical devices, plumbing/valves, electrical components and under-the-bonnet automotive parts.
3) Amide group — structure: –CONH–
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| Figure 3: Functional groups of polymers: Amide group. |
What it gives: strong intermolecular hydrogen bonding resulting in high strength and toughness, relatively high melting point, moisture uptake (hydrophilicity increases with amide density), good abrasion resistance.
Typical polymers / examples: Polyamides (Nylons) — PA6, PA66, PA11, PA12; Semi-aromatic polyamides such as PPA, and fully-aromatic polyamides (aramids) such as Kevlar® for ballistic & high-strength uses. Use in fibers, gears, bearings, structural components.
4) Ester group — structure: –COO– (ester linkage in backbone)
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| Figure 4: Functional groups of polymers: Ester group. |
What it gives: backbone polarity (good mechanical strength), susceptibility to hydrolysis (hence biodegradability for some), good melt processability (thermoplastic polyesters).
Typical polymers / examples: Polyesters — PET (polyethylene terephthalate), PBT, PLA (polylactide). Used for fibers, bottles, films, engineering thermoplastics and (for some aliphatic esters) biodegradable medical devices.
5) Ketone group — structure: –CO– (ketone carbonyl in backbone or adjacent to aromatic units)
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| Figure 5: Functional groups of polymers: Ketone group. |
What it gives: increased backbone polarity and stiffness; when combined with ether linkages in high-performance families it confers elevated Tg and chemical resistance.
Typical polymers / examples: Poly(aryl ether ketone) family (PAEK) — includes PEEK, PEK, PEKK — used for high-temperature structural parts, bearings, medical implants, and additive manufacturing in demanding applications. PAEKs combine aryl, ether and ketone functionalities giving excellent thermo-oxidative stability.
6) Sulfide group — structure: –S– (or disulfide –S–S– / polysulfide –Sx–)
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| Figure 6: Functional groups of polymers: Sulfide group. |
What it gives: enhanced temperature resistance, chemical and solvent resistance; excellent flow for injection molding; inherent flame retardant properties; excellent dimensional stability;
Typical polymers / examples: Polyphenylene sulfide (PPS) trade names include Ryton®, Fortron®.
7) Ether group — structure: –O– (alkyl or aryl ether linkages)
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| Figure 7: Functional groups of polymers: Ether group. |
What it gives: flexibility (aliphatic ethers), good low-temperature toughness, and for aromatic ether linkages (polyarylethers) increased thermal stability and oxidative resistance. Ethers reduce crystallinity when in backbone and improve chain mobility.
Typical polymers / examples: Polyethers (polyethylene glycol PEG/PEO; polypropylene oxide PPO), polyetherimide (PEI), polyethersulfone (PES), epoxy networks (contain ether linkages after cure). Applications span elastomers, polyurethanes (polyether polyols), and engineering plastics. Trade names include Noryl® PPE, Ultem® PEI, Veradel® PESU.
8) Arene (aromatic ring) group — structure: –Ar– (phenyl, substituted phenyl rings in backbone or pendant)
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| Figure 8: Functional groups of polymers: Arene group. |
What it gives: backbone rigidity (high modulus), thermal stability, UV interaction (often poor UV resistance unless stabilized), pi-stacking that influences mechanical and barrier properties. Aromatic content generally increases glass transition and heat resistance.
Typical polymers / examples: Polystyrene (PS) — aromatic pendant phenyls on a saturated backbone; poly(phenylene), polyaryls and many high-performance polymers with aromatic repeat units (e.g., polyimides, PAEK family). Polystyrene is a major commodity aromatic polymer used for foams, rigid packaging and consumer products.
9) Alcohol (hydroxyl) group — structure: –OH (pendant or chain-end hydroxyls)
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| Figure 9: Functional groups of polymers: Alcohol group. |
What it gives: hydrogen bonding, polarity, water solubility (if dense), reactivity for crosslinking (e.g., with isocyanates to form polyurethanes) or functional modification. Hydroxyls raise surface energy and adhesion.
Typical polymers / examples: Polyvinyl alcohol (PVA, PVOH) — water-soluble, used in films, adhesives and hydrogels; alcohol endgroups in polyols (polyether or polyester polyols) are core building blocks for polyurethanes.
10) Alkane group (saturated hydrocarbon backbone) — structure: –CH2–CH2– etc. (non-functional hydrocarbon chain)
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| Figure 10: Functional groups of polymers: Alkane group. |
What it gives: low polarity results in low surface energy, excellent chemical resistance to polar solvents, high flexibility (especially in low Tg aliphatic polyolefins), good electrical insulating properties and very high production volumes (commodity plastics).
Typical polymers / examples: Polyethylene (PE), Polypropylene (PP). These are the polyolefin family used for films, containers, piping, and fibers. Expect low density, good toughness, and simple processing.
11) Haloalkane group (alkyl halide pendant or backbone) — structure: –C–X (X = Cl, Br, F)
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| Figure 11: Functional groups of polymers: Haloalkane group. |
What it gives: increased flame retardance (e.g., chlorinated polymers), increased polarity and density, and ready sites for nucleophilic substitution or further modification; halogens can also raise refractive index and change dielectric properties.
Typical polymers / examples: Polyvinyl chloride (PVC) — chlorine on backbone carbons; fluoropolymers (e.g., PTFE — where fluorine dominates) are extreme cases with outstanding chemical resistance and low friction. PVC is used in construction, pipes, cable insulation and flooring; fluoropolymers are used where chemical inertness and high T performance are needed.
Mixed-functionality polymers & location of the group
- Backbone vs pendant vs endgroup: a functional group in the backbone (repeat unit) typically dominates bulk mechanical/thermal behaviour. Pendant groups (e.g., the phenyl in polystyrene or the chloro in PVC) tune Tg, polarity and solubility. Endgroups mainly affect surface chemistry and reactivity.
- Combinations are common: many engineering polymers combine functional groups (for example, PAEKs include arene, ether and ketone motifs; polysulfones include aryl, ether and sulfone units), which gives the unique combined property sets.
Overview of all the 11 functional groups of polymers
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| Figure 12: Overview of the functional groups of polymers. |
Check out my video on functional groups too:
Thanks for reading and #findoutaboutplastics
Greetings,
Herwig
Literature:
[1] Lodge, Tim: Polymer Chemistry, 2007, CRC
[2] https://www.polymermaterialselection.com
[3] https://www.justerexpertwitness.com/case-directory
[4] https://www.findoutaboutplastics.com/2025/04/nature-is-built-on-5-polymers-modern.html
