Polymers

• Natural • Synthetic • Semi-synthetic

• Proteins • Polysaccharides • Resins/gums

• Plastics • Elastomers • Rubber

• long chain molecule • constructed from many monomers that are covalently bonded together • can be linear, branched, cross-linked or colloidal

Comprised of all the same monomers

Made up of different monomers

• there are end groups • the nature of end groups allows method of synethsis to be analysed • it is possible for there to be no end groups = rings • useful for identifying a material • ratio of end groups to in-chain groups allows measuring of polymer length • reactive end groups allow further modification to control properties or add additional functionality

• type of end group is unique and will give a unique signature • ususally more reactive so can give a unique signature

• Thermoset • Thermoplastic • Elastomer

• burns when heated • irreversibly hardened once shaped • generally inflexible • chemical process called curing required

• epoxy resins • silicones • polyurethanes

• melts when heated • can be remelted and reshaped • generally more flexible • no chemical curing required

• polystyrene • nylon • polycarbonate

• can be thermoplastic or thermoset • has viscosity (can flow) and eslasticity (return to orignial shape)

• rubbers

• high density polyethylene • high crystalline content • less transparent than LDPE • stiffer and harder than LDPE • higher density • very low/no branching • less gas permeable

• low density polyethylene • low crystalline content • more transparent than HDPE • forms good films • lower density • highly branched • more gas permeable than HDPE

The regions of atomic ordering where intramolecular folding/stacking of adjacent chains occur

• crease • thermal behaviour • transparency • stiffness • impact resistance • tensile strength • young’s modulus

• 0 = completely amorphous • 1 = completely crystalline

how much something will stretch before it breaks * for polymers this increases with polymer chain length and crosslinking * easier to stetch smaller things - less matter to move = less force required

-ε = l/L * ε = strain (use this instead of stretch in solids * I = fractional change after stretching * L = initial starting length

-σ = F/A * σ = stress (used instead of force) * independant of sample size * F = force * A = distance stretched

How stiff a solid is