Polymer Technology
Core concepts
Polymer technology spans synthesis, structure, properties and processing. Know step-growth (condensation) vs chain-growth (addition) polymerisation, including free-radical, ionic and coordination (Ziegler–Natta, metallocene) mechanisms. Understand molecular weight distributions, number- and weight-average molecular weights, polydispersity, and their effect on properties. Crystallinity, glass transition temperature and melting point govern mechanical behaviour. Copolymers (random, block, graft), crosslinking, and tacticity matter. Processing methods: extrusion, injection moulding, blow moulding, compression moulding, calendering and fibre spinning. Degradation, stabilisers and recycling are increasingly tested. Commodity polymers (PE, PP, PVC, PS, PET) and engineering polymers (nylon, PC, PMMA) have characteristic properties.
Traps
Mn < Mw always; polydispersity = Mw/Mn ≥ 1. Thermosets cannot be remelted; thermoplastics can. Do not confuse Tg (amorphous transition) with Tm (crystalline melting). Higher crystallinity raises stiffness and density but lowers clarity. Free-radical polymerisation gives broad MWD; living/controlled methods give narrow distributions.
Worked rule of thumb
For a mixture of equal masses of two monodisperse fractions, Mw = (ΣwiMi²)/(ΣwiMi) and Mn = 1/(Σwi/Mi). Equal masses of 10⁴ and 10⁵ g/mol give Mn ≈ 18,200 and Mw ≈ 55,000, so polydispersity ≈ 3.0 - a useful sanity check.
Exam strategy
Identify the polymerisation mechanism first, then link structure (branching, crystallinity, MWD) to processing and end-use properties.