Polymers: Synthetic and Natural Polymers

Comprehensive vocabulary flashcards covering addition and condensation polymerization, plastic properties and cross-linking, industrial polymers (Teflon, Kevlar, Nylon-6,6, PET), and natural biological macromolecules.

Polymer

A large chain compound composed of many repeating units called monomers, with no theoretical limit to length (most consist of $1000$ to $10\,000$ monomers).

Monomer

The small molecular repeating unit that chemically links together to form a polymer chain.

Homopolymer

A polymer composed of only one type of monomer unit (e.g., polyethylene synthesized from ethene).

Copolymer

A polymer synthesized from two or more different monomers, characterized by alternating or mixed repeating sequences such as $-A-B-A-B-$ or $(-A-B-)_n$.

Addition Polymer

A polymer formed by addition reactions where the starting monomers contain alkene double bonds that open up without producing by-products.

Free Radical ($R^*$)

A highly reactive species containing an unbonded electron ($e^-$) used to initiate addition polymerization by attacking and breaking the carbon-carbon double bond of a monomer.

Polytetrafluoroethene (Teflon)

A synthetic addition polymer formed from tetrafluoroethene ($\text{CF}_2=\text{CF}_2$) monomers, known for its low friction and use in non-stick cookware coatings.

Polystyrene

An addition polymer formed from styrene monomers; its pure form is a hard plastic, and when air or $\text{N}_2$ is injected into it, it forms Styrofoam.

Plastics

Synthetic polymers derived from petrochemicals (usually substituted ethene or vinyl monomers) that can be moulded into specific shapes under high heat and pressure.

Biaxially Oriented Polypropylene (BOPP)

A durable polymer substrate used in currency notes that withstands high temperature ranges, resists counterfeiting, and lasts $2.5$ times longer than paper bank notes.

Low-Density Polyethene (LDPE)

A form of polyethene containing extensive branched chains that prevent polymer molecules from packing tightly together, producing flexible materials like plastic bags.

High-Density Polyethene (HDPE)

A form of polyethene consisting predominantly of straight, unbranched chains that pack closely together, producing rigid materials like plastic bottles.

Plasticizer

A substance (such as a phthalate) inserted between polymer chains to weaken intermolecular attractions and increase material flexibility.

Polymer Cross-Linking

The creation of covalent bond bridges between adjacent polymer chains, often accomplished using diene monomers that react at two locations to increase strength and rigidity.

Vulcanization

A chemical process that uses sulfur as an inorganic cross-linking agent to form disulfide ($-S-S-$) cross-links between polymer chains, converting soft latex into hardened rubber.

Thermoplastics

Plastics composed of linear polymer chains held by secondary forces that can be repeatedly melted, softened by heat, and remoulded (e.g., acrylic, PVC).

Thermoset Polymers

Plastics containing extensive covalent cross-links that do not soften upon heating and cannot be reshaped or melted into moulds (e.g., vulcanized rubber, fiberglass, polyurethanes).

Elastomers

Flexible, rubbery polymers that can be substantially stretched and automatically return to their original shape (e.g., silly putty).

Condensation Polymers

Polymers formed by step-growth reactions between monomers with bifunctional groups, releasing a small by-product molecule such as $\text{H}_2\text{O}$ or $\text{HCl}$.

Polyesters

Condensation polymers formed through the reaction between dicarboxylic acids and dialcohols, creating repeating ester linkages ($-\text{COO}-$) along the polymer backbone.

Polyethylene Terephthalate (PET / Dacron / Terylene)

A polyester synthesized from benzene-1,4-dicarboxylic acid (terephthalic acid) and ethane-1,2-diol (ethylene glycol) with the elimination of $\text{H}_2\text{O}$, widely used in shrink-resistant clothing.

Polyamides

Condensation polymers formed by reactions between carboxylic acids (or acyl chlorides) and amines, generating repeating amide linkages ($-\text{CONH}-$) along the chain.

Nomex

A synthetic aromatic polyamide (aramid) possessing high thermal stability and flame-resistant properties, used in protective gear for firefighters.

Kevlar

A high-strength synthetic polyamide whose mechanical toughness arises from tangled polymer chains and extensive intermolecular hydrogen bonding between parallel aromatic chains.

Nylon-6,6

A polyamide produced by reacting hexane-1,6-diamine and hexanedioyl dichloride (eliminating $\text{HCl}$), where each '$6$' indicates the number of carbon atoms contributed by the diamine and dioic derivative, respectively.

Carbohydrates (Polysaccharides)

Natural polymers of monosaccharides (simple sugars) with the empirical formula $\text{C}_x(\text{H}_2\text{O})_y$, serving as short-term energy stores, food sources, and structural materials.

Starch

A natural glucose polymer that functions as the principal energy storage macromolecule in plants.

Cellulose

A structural polymer composed of repeating glucose units that reinforces plant cell walls; recognized as the most abundant organic compound on Earth.

Glycogen

A branched polymer of glucose that acts as the primary short-term energy reserve in animals.

Proteins

Biological polymers composed of amino acid monomers joined in varying sequences by peptide bonds (amide linkages) to form functional polypeptides, enzymes, and structural components.

Amino Acids

The $20$ natural organic monomers that build proteins, each containing a carboxylic acid group ($-\text{COOH}$) and an amino group ($-\text{NH}_2$) bonded to the same alpha-carbon atom.

Peptide Bond

The covalent amide linkage formed by a condensation reaction between the amino group of one amino acid and the carboxyl group of another.

Nucleic Acids

Biological macromolecules (DNA and RNA) formed by the polymerization of nucleotide monomers to store and transmit genetic information.

Nucleotide

The repeating monomer unit of nucleic acids, consisting of a ribose sugar, an inorganic phosphate group, and one of four nitrogenous bases: adenine (A), thymine (T), cytosine (C), or guanine (G).

Denaturation

The permanent structural alteration and loss of native biological function in a protein or macromolecule caused by elevated heat, pH extremes, radiation, or chemical mutations.

Lipids

Non-polymeric biological macromolecules composed mainly of glycerol (propane-1,2,3-triol) and fatty acids (long-chain carboxylic acids), including fats, steroids, and cholesterol.