Polymer flash cards

1. 1.What is a polymer?

   A high molecular mass macromolecule formed by the repetitive joining of a large number of small structural units called monomers, linked by covalent bonds.

   Hint: Greek: poly = many, mer = unit.

2. 2.Define monomer.

   The simple, small, low-molecular-mass reactive molecule (the repeating structural unit's precursor) from which a polymer is built, e.g. ethene for polythene.

   Hint: The building block.

3. 3.What is polymerisation?

   The process by which a large number of monomer molecules combine (with or without loss of small molecules) to form a polymer.

   Hint: Monomers → macromolecule.

4. 4.What is the degree of polymerisation ($n$)?

   The number of repeating (monomer) units present in one polymer chain. High polymers have $n$ running into hundreds or thousands.

   Hint: Count of repeat units per chain.

5. 5.Classify polymers based on their source.

   Natural polymers (cellulose, starch, proteins, natural rubber), semi-synthetic polymers (cellulose acetate, cellulose nitrate) and synthetic polymers (polythene, nylon, PVC, Buna-S).

   Hint: Three origins.

6. 6.Give three examples of natural polymers.

   Cellulose, starch (polysaccharides), proteins, nucleic acids and natural rubber (cis-polyisoprene).

   Hint: Found in nature/biological.

7. 7.What are semi-synthetic polymers? Give examples.

   Polymers derived by chemical modification of natural polymers, e.g. cellulose acetate (rayon) and cellulose nitrate (gun cotton).

   Hint: Natural backbone, man-made tweak.

8. 8.Classify polymers based on structure.

   Linear polymers, branched-chain polymers and cross-linked (network) polymers.

   Hint: Chain geometry: three types.

9. 9.Describe linear polymers and give examples.

   Long straight chains packed closely; high density, high tensile strength and high melting point. Examples: high-density polythene, PVC, nylon.

   Hint: Well-packed straight chains.

10. 10.Describe branched-chain polymers and give an example.

    Linear chains bearing side branches; irregular packing gives lower density, lower tensile strength and lower melting point. Example: low-density polythene, amylopectin, glycogen.

    Hint: Chains with side twigs; LDPE.

11. 11.Describe cross-linked (network) polymers and give examples.

    Monomers linked by strong covalent bonds into a 3-D network; hard, rigid, brittle. Examples: bakelite, melamine, vulcanised rubber.

    Hint: 3-D covalent network; thermosets.

12. 12.Classify polymers based on the mode of polymerisation.

    Addition (chain-growth) polymers and condensation (step-growth) polymers.

    Hint: Two mechanisms of joining.

13. 13.What is an addition polymer?

    A polymer formed by repeated addition of monomer molecules possessing double or triple bonds, with NO loss of any small molecule. Repeat unit has the same composition as the monomer.

    Hint: Unsaturated monomers; nothing eliminated.

14. 14.What is a condensation polymer?

    A polymer formed by repeated condensation between two bi/poly-functional monomers, usually with elimination of small molecules like $H_2O$, $HCl$ or $NH_3$.

    Hint: Small molecule split out each step.

15. 15.Give the key difference between addition and condensation polymers regarding mass.

    In addition polymers, polymer mass = an exact whole-number multiple of the monomer mass. In condensation polymers, mass is less than the sum of monomers because small molecules are eliminated.

    Hint: Multiple-of-monomer vs. mass lost.

16. 16.What is chain-growth polymerisation?

    Polymerisation in which reactive centres (free radicals, cations or anions) add monomer units one at a time to a growing chain; each chain grows rapidly to full size. Same as addition polymerisation.

    Hint: One monomer at a time onto an active chain end.

17. 17.What is step-growth polymerisation?

    Polymerisation in which bifunctional monomers react in steps; any two species (monomer, dimer, oligomer) can combine, and high molecular mass builds up only late in the reaction. Same as condensation polymerisation.

    Hint: Any-two-can-react; mass builds slowly.

18. 18.Distinguish homopolymer and copolymer.

    A homopolymer is made from a single type of monomer (e.g. polythene). A copolymer is made from two or more different monomers (e.g. Buna-S from butadiene + styrene).

    Hint: One monomer vs. two-plus.

19. 19.Give two examples of copolymers.

    Buna-S (1,3-butadiene + styrene), Buna-N (1,3-butadiene + acrylonitrile), nylon-6,6 (hexamethylenediamine + adipic acid).

    Hint: Two different repeating units.

20. 20.What is the repeating pattern in an alternating copolymer?

    The two monomers A and B alternate regularly along the chain: $-A-B-A-B-A-B-$.

    Hint: Strict ABAB.

21. 21.Classify polymers based on molecular forces / mechanical behaviour.

    Elastomers, fibres, thermoplastic polymers and thermosetting polymers.

    Hint: Four classes by intermolecular force strength.

22. 22.What are elastomers? Give an example.

    Polymers with weak intermolecular forces and coiled chains held by a few cross-links; they stretch greatly and return to original shape. Example: natural rubber, Buna-S, Buna-N, neoprene.

    Hint: Weakest forces; rubbery, stretchy.

23. 23.What are fibres? Give examples.

    Polymers with strong intermolecular forces (H-bonding, dipole-dipole) and close chain packing; high tensile strength, thread-like, crystalline. Examples: nylon-6,6, terylene, silk.

    Hint: Strongest forces; thread-forming.

24. 24.What are thermoplastic polymers? Give examples.

    Linear/slightly branched polymers with intermediate intermolecular forces that soften on heating and harden on cooling; can be remoulded repeatedly. Examples: polythene, PVC, polystyrene.

    Hint: Soften-remould reversibly.

25. 25.What are thermosetting polymers? Give examples.

    Heavily cross-linked (3-D network) polymers that set irreversibly into a hard, infusible mass on heating and cannot be remelted or remoulded. Examples: bakelite, melamine, urea-formaldehyde resin.

    Hint: Set once; cannot remould.

26. 26.Rank elastomers, plastics and fibres by intermolecular force strength.

    Elastomers (weakest) < plastics/thermoplastics (intermediate) < fibres (strongest). Thermosets have covalent cross-links (essentially the strongest, network).

    Hint: Elastomer → plastic → fibre increasing.

27. 27.Why can thermoplastics be recycled but thermosets cannot?

    Thermoplastics have only weak intermolecular forces between separate chains that reversibly weaken on heating; thermosets have permanent covalent cross-links, so heating only degrades them.

    Hint: Reversible forces vs. permanent covalent net.

28. 28.Name the three mechanisms of chain-growth (addition) polymerisation.

    Free-radical, cationic and anionic polymerisation, depending on the type of initiator and monomer.

    Hint: Radical / cation / anion.

29. 29.What type of initiator is used in free-radical addition polymerisation?

    A free-radical initiator such as benzoyl peroxide, acetyl peroxide or tert-butyl peroxide (or by heat/light).

    Hint: Peroxides generate radicals.

30. 30.Name the three steps of the free-radical polymerisation mechanism.

    Chain initiation, chain propagation, and chain termination.

    Hint: Start, grow, stop.

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