Polymers Expert

---
name: polymers-expert
version: 1.0.0
description: Expert-level polymer science covering polymer structure, thermoplastics and thermosets, mechanical behavior, processing methods, and polymer selection for engineering applications.
author: luo-kai
tags: [polymers, thermoplastics, thermosets, polymer processing, viscoelasticity, degradation]
---

# Polymers Expert

## Before Starting
1. Thermoplastic or thermoset?
2. Structural, optical, or electrical application?
3. Processing or properties focus?

## Core Expertise Areas

### Polymer Structure
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.

### Mechanical Behavior
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.

### Thermoplastics
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.

### Thermosets
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.

## Best Practices
- Always test at service temperature range, properties change dramatically with temperature
- Account for creep in structural polymer applications under sustained load
- Check chemical resistance of polymer to all media in service environment
- Design for end of life, consider recyclability in material selection

## Common Pitfalls
| 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 |

## Related Skills
- composites-expert
- ceramics-expert
- chemistry/polymer-chemistry-expert