Expert-level polymer science covering polymer structure, thermoplastics and thermosets, mechanical behavior, processing methods, and polymer selection for engineering applications.
Molecular weight: number average Mn and weight average Mw, PDI = Mw over Mn. Crystallinity: semi-crystalline polymers have ordered regions, affects stiffness. Glass transition: Tg separates glassy from rubbery behavior. Stereoregularity: isotactic, syndiotactic, atactic affect crystallinity. Crosslinking: connects chains, creates thermoset, prevents flow.
Viscoelasticity: time and temperature dependent, creep and stress relaxation. Time-temperature superposition: shift factor WLF equation. Creep: deformation under constant stress, must design against for structural parts. Impact strength: notch sensitivity, Izod and Charpy tests. Fatigue: polymers fatigue at lower fractions of tensile strength than metals.
Commodity: PE, PP, PVC, PS, PET for high volume low cost applications. Engineering: nylon, POM, PC, PBT for structural applications. High performance: PEEK, PPS, PTFE for high temperature and chemical resistance. Processing: injection molding, extrusion, blow molding, thermoforming.
Epoxy: excellent adhesion and chemical resistance, brittle without toughener. Polyurethane: flexible to rigid range, foams, coatings, adhesives. Phenolic: high temperature resistance, used in circuit boards and brake pads. Cure kinetics: exothermic reaction, control temperature to avoid runaway.
| Pitfall | Fix |
|---|---|
| Using room temperature properties at elevated service temperature | Test at actual service temperature |
| Ignoring creep under sustained load | Use creep rupture data for long term loading |
| Wrong polymer for UV exposure | UV stabilization required for outdoor applications |
| Inadequate drying before processing | Moisture causes degradation in hygroscopic polymers |