Addition Polymers — Key Points

• HDPE: Ziegler-Natta catalyst (TiCl4 + Al(C2H5)3) + low pressure → linear chains → high density, strong, rigid containers.
• LDPE: free radical initiator + high pressure (1000–2000 atm, 350–570 K) → branched chains → low density, flexible bags.
• PVC: monomer = vinyl chloride (CH2=CHCl, C=CCl); free radical; uses = pipes, cables, flooring.
• Teflon: monomer = tetrafluoroethene (CF2=CF2, FC(F)=C(F)F); chemically inert, non-stick; strong C–F bonds.
• PAN (Orlon): monomer = acrylonitrile (CH2=CHCN, C=CC#N); synthetic wool; warm fabrics.
• Polystyrene: monomer = styrene (C6H5CH=CH2, C=Cc1ccccc1); packaging, Styrofoam.

Condensation Polymers — Key Points

• Nylon-6,6: TWO monomers — hexamethylenediamine (6C, NCCCCCCN) + adipic acid (6C, OC(=O)CCCCC(=O)O). Polyamide (–CO–NH–). Thermoplastic.
• Nylon-6: ONE monomer — caprolactam (O=C1CCCCCN1). Ring-opening. Polyamide. Thermoplastic.
• Dacron (PET): ethylene glycol (OCCO) + terephthalic acid (OC(=O)c1ccc(C(=O)O)cc1). Polyester (–COO–). Thermoplastic. Clothing + bottles.
• Bakelite: phenol + formaldehyde → novolac (linear) → cross-linked 3D network. Thermosetting. Electrical switches.
• Buna-S: butadiene + styrene (tires). Buna-N: butadiene + acrylonitrile (oil-resistant).
• PHBV: biodegradable polyester (bacteria). Nylon-2-nylon-6: biodegradable polyamide.

Rubber — Key Points

• Natural rubber = cis-1,4-polyisoprene (monomer: isoprene, C=CC(=C)C). Elastic because cis coils chains.
• Gutta-percha = trans-1,4-polyisoprene. Same formula. Hard, non-elastic (trans = straight chains, close packing).
• Vulcanization: + 2–3% S + heat → S–S cross-links → harder, more elastic, less tacky, better temperature resistance.

Polymer Classification Table