MHT-CET Chemistry · Free notes
Introduction to Polymer Chemistry — MHT-CET Chemistry
Polymers is about two questions a paper in MHT-CET Chemistry and almost never HARD — one of its 142 past-year questions. It is a chapter of named pairs: a polymer and its class (fibre, elastomer, thermoplastic, thermoset; homo- or copolymer), a polymer and its monomers, a polymer and the linkage that holds it, and a polymer and the household article it is made into. The only reasoning is in the polymerisation method — addition, condensation or ring-opening — and in telling LDPE from HDPE. Four pages in the book's order. Every PYQ is tagged.
The handout has every subtopic, worked example, formula and trap with answers shown. The formula sheet is the chapter’s formulas and traps alone, on one page.
Subtopic notes
Classification of Polymers
41 PYQsPolymers are classed four ways — by source (natural, semisynthetic, synthetic), by chain structure (linear, branched, cross-linked), by the number of monomer kinds (homopolymer, copolymer) and by the strength of the intermolecular forces (elastomer, fibre, thermoplastic, thermosetting) — and the same polymer answers a different question under each.
Polymerisation Methods: Addition, Condensation, Ring-Opening
14 PYQsAddition (chain-growth) polymerisation joins C=C monomers with nothing lost, usually through a free radical from a peroxide initiator; condensation (step-growth) joins two functional groups with loss of a small molecule such as water; ring-opening polymerisation unrolls a cyclic monomer — caprolactam to nylon 6 — with nothing lost and no C=C.
Polymers and Their Monomers
49 PYQsEvery named polymer is one or two monomers: isoprene for natural rubber, chloroprene for neoprene, butadiene with styrene for Buna-S and with acrylonitrile for Buna-N, acrylonitrile for PAN, styrene for thermocol, methyl methacrylate for perspex, adipic acid with hexamethylenediamine for nylon 6,6, caprolactam for nylon 6, ethylene glycol with terephthalic acid for dacron and with phthalic acid for glyptal, two 3-hydroxy acids for PHBV, phenol or urea with formaldehyde for the resins — and the linkage between them (amide, ester, or plain C–C) is what the paper asks next.
Properties and Applications of Polymers
38 PYQsLow-density polythene is branched, amorphous and made at 1000 to 2000 atm with an oxygen or peroxide initiator; high-density polythene is linear, crystalline and made at low pressure over a Ziegler–Natta catalyst; rubber is vulcanised with sulphur and an accelerator; and each commercial polymer has a household use the paper asks by name — PVC for pipes and floor tiles, polystyrene for disposable cups, polypropylene for straws, nylon 6 for tyre cords, nylon 6,6 for bristles and sutures, Teflon for oil seals, glyptal for paints.
Formula & revision sheet
4 formulas · 3 reference tables · 7 gotchas across all subtopics — the exam-eve cheat-sheet
Formula & revision sheet
4 formulas · 3 reference tables · 7 gotchas across all subtopics — the exam-eve cheat-sheet
Reference tables (1)
Elastomer, Fibre, Thermoplastic, Thermosetting: Ranked by Intermolecular Force4 rows
| Class | Intermolecular force | Heating | Examples |
|---|---|---|---|
| Elastomer | Weakest (a few cross-links) | Stretch and recover | Natural rubber, Buna-S, Buna-N, neoprene |
| Thermoplastic | Intermediate | Softens, remouldable | Polythene, PVC, polystyrene, Teflon, PMMA Thermoplastics have NO extensive cross-linking. |
| Thermosetting | Cross-linked network | Sets once, cannot remelt | Bakelite, urea-formaldehyde, melamine-formaldehyde |
| Fibre | Strongest (H-bond / dipole) | High tensile strength, drawn to thread | Nylon 6, nylon 6,6, terylene, PAN |
Watch out for (2)
- Nylon 6,6 as the copolymer→ By Source, by Chain Structure, by Number of Monomers
- Neoprene as a fibre, bakelite as a thermoplastic→ Elastomer, Fibre, Thermoplastic, Thermosetting: Ranked by Intermolecular Force
Watch out for (1)
- Nylon 6 as an addition polymer because nothing is lost→ Which Method Makes Which Polymer
Reference tables (1)
Polymer to Monomer: the Table the Paper Draws From14 rows
| Polymer | Monomer(s) | Type |
|---|---|---|
| Natural rubber | Isoprene (2-methylbuta-1,3-diene) | Addition, homo |
| Neoprene | Chloroprene (2-chlorobuta-1,3-diene) | Addition, homo A homopolymer — the 'copolymer' statement about it is the false one. |
| Buna-S / Buna-N | Buta-1,3-diene + styrene / + acrylonitrile | Addition, co |
| PAN (orlon) | Acrylonitrile CH₂=CHCN | Addition, homo — wool substitute |
| Thermocol | Styrene | Addition, homo |
| Perspex (PMMA) | Methyl methacrylate | Addition, homo |
| Teflon | Tetrafluoroethene CF₂=CF₂ | Addition, homo |
| Nylon 6,6 | Adipic acid + hexamethylenediamine | Condensation, polyamide |
| Nylon 6 | Caprolactam | Ring-opening, polyamide |
| Nylon 2-nylon 6 | Glycine + ε-aminocaproic acid | Condensation, biodegradable polyamide |
| Dacron / terylene | Ethylene glycol + terephthalic acid | Condensation, polyester Phthalic acid instead of terephthalic gives glyptal. |
| Glyptal | Ethylene glycol + phthalic acid | Condensation, polyester |
| PHBV | 3-Hydroxybutanoic + 3-hydroxypentanoic acid | Condensation, biodegradable polyester |
| Novolac / bakelite | Phenol + formaldehyde | Condensation resin |
Watch out for (2)
- Terephthalic acid for glyptal→ Polymer to Monomer: the Table the Paper Draws From
- PAN as a polyamide→ The Linkage in the Repeat Unit: Amide, Ester or None
Reference tables (1)
Which Polymer Makes Which Article13 rows
| Article | Polymer | Why |
|---|---|---|
| Water pipes, floor tiles | PVC | Rigid, chemically resistant |
| Disposable cups and plates | Polystyrene | Cheap, foamable; leaches styrene |
| Drinking straws | Polypropylene | Rigid, heat-resistant |
| Toys, buckets | HDPE | Tough, crystalline |
| Tyre cords | Nylon 6 | High tensile strength Nylon 6 → tyre cords; nylon 6,6 → bristles and sutures. |
| Brush bristles, surgical sutures | Nylon 6,6 | Stiff, strong polyamide |
| Wool substitute | Polyacrylonitrile | Soft, warm fibre |
| Terycot | Dacron + cotton | Wrinkle-free blend |
| Oil seals, gaskets | Teflon | Inert, low friction |
| Rubber belts, shoe soles | Buna-N | Oil- and abrasion-resistant |
| Paints | Glyptal | Alkyd resin |
| LCD screens | Perspex | Transparent PMMA |
| Plastic dinner ware | Melamine-formaldehyde | Hard thermoset |
Watch out for (2)
- Reading '6–7 atm' as LDPE→ LDPE against HDPE, and Vulcanisation
- Nylon 6 for bristles→ Which Polymer Makes Which Article
PYQ weightage by concept
7 concepts · 142 PYQs — where the marks actually sit, so you know what to drill first
PYQ weightage by concept
7 concepts · 142 PYQs — where the marks actually sit, so you know what to drill first
| Concept | PYQs | Share |
|---|---|---|
| By Source, by Chain Structure, by Number of Monomers | 11 | 8% |
| Elastomer, Fibre, Thermoplastic, Thermosetting: Ranked by Intermolecular Force | 11 | 8% |
| Concept | PYQs | Share |
|---|---|---|
| Which Method Makes Which Polymer | 9 | 6% |
| Concept | PYQs | Share |
|---|---|---|
| Polymer to Monomer: the Table the Paper Draws From | 19 | 13% |
| The Linkage in the Repeat Unit: Amide, Ester or None | 10 | 7% |
| Concept | PYQs | Share |
|---|---|---|
| Which Polymer Makes Which Article | 19 | 13% |
| LDPE against HDPE, and Vulcanisation | 6 | 4% |
Test yourself on Introduction to Polymer Chemistry
20 past MHT-CET questions from this chapter, timed at 18 minutes and marked the way the exam marks it. You see your score and every answer the moment you finish. Free to start.