Commercial Polymers

Polymers are giant macromolecules formed by the repetitive bonding of smaller units called monomers. The word 'polymer' comes from the Greek words 'poly' (many) and 'meros' (parts). Commercial polymers are synthetic or semi-synthetic materials manufactured on an industrial scale and have transformed modern life — from packaging and clothing to non-stick cookware and electrical insulation. Understanding their chemistry helps us appreciate both their remarkable versatility and their environmental impact. Polymers are broadly classified into addition polymers (formed by direct addition of monomers without any by-product) and condensation polymers (formed when monomers join with the elimination of small molecules such as water or HCl). Examples of addition polymers include polythene, PVC, and Teflon, while Nylon-6,6, polyester, and Bakelite are condensation polymers. Natural rubber is a naturally occurring polymer that is commercially improved through the process of vulcanization. The physical and chemical properties of a polymer — such as tensile strength, elasticity, melting point, and chemical resistance — depend on the nature of the monomers, the length of the polymer chain, the degree of branching, and the presence of cross-links between chains. By carefully controlling these factors, chemists can engineer polymers with specific properties for targeted applications in industry, medicine, and everyday life.

Key takeaways
  • Polythene (Polyethylene)
  • PVC (Polyvinyl Chloride)
  • Teflon (Polytetrafluoroethylene, PTFE)
  • Nylon-6,6
  • Polyester (Dacron / Terylene)
  • Bakelite
  • Rubber and Vulcanization

Polythene (Polyethylene)

Polythene is formed by the addition polymerization of ethylene (ethene, CH₂=CH₂). Low-density polyethylene (LDPE) is formed at high pressure (1000–2000 atm) and temperature (350–570 K) using trace oxygen or peroxide catalysts. It has a highly branched chain structure, making it soft and flexible — used for plastic bags and squeeze bottles. High-density polyethylene (HDPE) is formed at low pressure using Ziegler–Natta catalysts (TiCl₄ + Al(C₂H₅)₃). HDPE chains are linear with minimal branching, giving it greater rigidity and tensile strength — used for pipes, bottles, and toys. Repeat unit: —(CH₂—CH₂)ₙ—

PVC (Polyvinyl Chloride)

PVC is produced by addition polymerization of vinyl chloride (chloroethene, CH₂=CHCl). The repeat unit is —(CH₂—CHCl)ₙ—. PVC is hard and rigid in its pure form but becomes flexible when plasticizers are added. It is used for water pipes, flooring, electrical cable insulation, and raincoats. The C–Cl bond in PVC makes it inherently flame-retardant. However, incineration of PVC can release toxic hydrogen chloride and dioxins, raising environmental concerns.

Teflon (Polytetrafluoroethylene, PTFE)

Teflon is made by addition polymerization of tetrafluoroethylene (CF₂=CF₂). The repeat unit is —(CF₂—CF₂)ₙ—. The C–F bond is one of the strongest bonds in organic chemistry (bond energy ~485 kJ/mol), giving Teflon exceptional chemical inertness, thermal stability (up to ~260°C), and an extremely low coefficient of friction (non-stick property). Teflon was accidentally discovered by Roy Plunkett in 1938 at DuPont. Its uses include non-stick cookware coatings, gaskets, bearings, and electrical insulation.

Nylon-6,6

Nylon-6,6 is a condensation polymer (polyamide) formed from the reaction of hexamethylenediamine [H₂N—(CH₂)₆—NH₂] and adipic acid [HOOC—(CH₂)₄—COOH]. For each amide bond (—CO—NH—) formed, one molecule of water is eliminated. The numbers '6,6' refer to the six carbon atoms in each monomer. Nylon-6,6 has high tensile strength, elasticity, and resistance to heat and chemicals. It is used in making ropes, parachutes, toothbrushes, stockings, and gears. The amide linkages (peptide-like bonds) make Nylon structurally similar to proteins.

Polyester (Dacron / Terylene)

Polyester is a condensation polymer formed from ethylene glycol (HOCH₂CH₂OH) and terephthalic acid (benzene-1,4-dicarboxylic acid). Each ester linkage (—COO—) is formed with loss of water. The commercial product is poly(ethylene terephthalate) or PET. It is used in making fibres (Dacron/Terylene) for clothing, bottles (PET bottles), and films (Mylar). PET has excellent mechanical strength, chemical resistance, and transparency.

Bakelite

Bakelite is a thermosetting condensation polymer formed by the reaction of phenol (C₆H₅OH) and formaldehyde (HCHO) in the presence of an acid or base catalyst. Initially, an addition product (ortho- or para-hydroxymethylphenol) forms, which then condenses with more phenol, releasing water. Further condensation creates a three-dimensional cross-linked network — making Bakelite hard, infusible, and insoluble. It was the first fully synthetic plastic, invented by Leo Baekeland in 1907. Uses include electrical switches, handles, and billiard balls.

Rubber and Vulcanization

Natural rubber is a polymer of isoprene (2-methylbuta-1,3-diene, CH₂=C(CH₃)—CH=CH₂). The repeat unit is cis-1,4-polyisoprene: —(CH₂—C(CH₃)=CH—CH₂)ₙ—. Raw rubber is sticky when hot and brittle when cold, making it unsuitable for most applications. Vulcanization (discovered by Charles Goodyear, 1839) involves heating natural rubber with sulfur (2–3% for soft rubber, up to 30% for ebonite) at 140–160°C. Sulfur atoms form cross-links (—S—S— bridges) between adjacent polymer chains at the double bond sites. This dramatically improves elasticity, strength, hardness, and resistance to heat and chemicals. Vulcanized rubber is used in tyres, hoses, footwear, and gaskets.

The Key Equation

\cen H2N−(CH2)6−NH2+n HOOC−(CH2)4−COOH−>[−NH−(CH2)6−NH−CO−(CH2)4−CO−]n+n H2O\ce{n\, H2N-(CH2)6-NH2 + n\, HOOC-(CH2)4-COOH -> [-NH-(CH2)6-NH-CO-(CH2)4-CO-]_n + n\, H2O}
  • \ce{H2N-(CH2)6-NH2} — Hexamethylenediamine (mol): Diamine monomer contributing 6 carbons and two amine groups to the polymer chain
  • \ce{HOOC-(CH2)4-COOH} — Adipic acid (mol): Dicarboxylic acid monomer contributing 6 carbons and two carboxyl groups
  • \ce{-CO-NH-} — Amide linkage (peptide bond) (—): The characteristic bond formed between amine and carboxyl groups in polyamides
  • \ce{H2O} — Water (by-product) (mol): One molecule of water is eliminated per amide bond formed

Worked Example

Problem. Identify the type of polymerization (addition or condensation), the monomer(s), and the linkage present in: (a) Teflon, (b) Polyester (PET), (c) Nylon-6,6. Also write the repeat unit for Teflon.

Teflon repeat unit: \ce−(CF2−CF2)n−\text{Teflon repeat unit: } \ce{-(CF2-CF2)_n-}

Answer. Teflon: addition polymer (C–C linkage); PET: condensation polymer (ester linkage, –COO–); Nylon-6,6: condensation polymer (amide linkage, –CO–NH–). Repeat unit of Teflon: –(CF₂–CF₂)ₙ–

Figure
Diagram
Vulcanization: Cross-linking of Rubber Chains by SulfurCCCCCH₃ side groupChain 1: cis-polyisopreneCCCCChain 2: cis-polyisopreneSS–S–S–cross-linkBefore VulcanizationChains slide past each other→ sticky, weak, thermoplasticAfter VulcanizationS–S bridges lock chains together→ elastic, strong, heat-resistant→ used in tyres, hoses, gasketsYellow circles = sulfur atoms forming –S–S– cross-links between polymer chains
Origins · 1 minLeo Hendrik Baekeland and how this was discovered
LH
Leo Hendrik Baekeland
1863–1944 · Belgian-American

Leo Baekeland invented Bakelite in 1907 — the world's first fully synthetic plastic. He reacted phenol with formaldehyde under controlled temperature and pressure in his 'Bakelizer' reactor to produce a hard, thermosetting resin. Bakelite was called 'the material of a thousand uses' and launched the modern plastics industry, revolutionizing electrical insulation, consumer goods, and manufacturing. Baekeland originally set out to find a synthetic substitute for shellac (a natural resin secreted by insects). Instead, he accidentally created something far more revolutionary. He sold the rights to his earlier invention — photographic paper (Velox) — to George Eastman for $750,000 in 1899, funding his subsequent polymer research.

  • Addition Polymerization — Commercial polymers like polythene, PVC, and Teflon are all made by addition polymerization of alkene monomers — understanding the mechanism is essential context for this topic.
  • Condensation Polymerization — Nylon-6,6, Polyester (PET), and Bakelite are all condensation polymers — the concept of ester and amide bond formation with loss of water is fundamental to understanding their synthesis.
  • Proteins and Peptide Bonds — The amide (peptide) linkage in Nylon-6,6 is identical to the peptide bond found in proteins, making the comparison between synthetic and biological polymers educationally valuable.
  • Functional Groups in Organic Chemistry — Identifying ester, amide, and hydroxyl functional groups in monomers is the foundation for predicting the type of polymer formed and the nature of the linkage.
  • Polysaccharides (Natural Polymers) — Comparing synthetic commercial polymers with natural biopolymers like starch and cellulose reinforces the universal concept of polymer chain formation from monomer units.