ENME307 Polymer Structure

The whole lot :,(

Bonds within polymer molecules

covalent

Bonds between polymer molecules

van der walls

Aliphatic

linear, less stable derived from methane

Aromatic

ring, more stable, derived from benzene

Radicals

species that have 1 or more unpaired e-, initiates polymerisation but remains unchanged

Functional group

group responsible for chemical characteristics

Electro Negativity

ability to pull e- towards nucleus

Polarity

amide > carboxylic acid > alcohol > ketone/aldehyde > amine > ester > ether > alkane

Monomers

repeating units

Isomers

same composition, different structure, different properties

Cis

rigid

Trans

flexible

Polyethylene (PE)

CH4

Polyvinyl chloride (PVC)

CH3Cl

Teflon

CF4

Polypropylene (PP)

CH3CH3

Polystyrene (PS)

CH3 benzene ring

Addition/Chain

add mer group (Teflon, PP), faster weight growth

Condensation/Step

chem reaction with H2O byproduct (epoxy, PE), slower weight growth

Monofunctional

1 functional group

Difunctional

2 functional groups, needed for polymerisation

Short DP

softer material

HD

high density

LD

low density

LLL

linear low density

UHMW

ultra high molecular weight

A

amorphous

X

cross linked

Ligamers

like monomers but longer

Reactants

unsaturated polymer, styrene, curing agent

Curing agent

opens up double bonds, contains radicles

Crosslinked polymers

thermoset (resin), elastomers

Gel point

where resin becomes unworkable and every component is crosslinked

Vitrification

rubber to glassy/rigid

Glass transition

increases as cross link and temp increase. Amount of entanglement and resistance to flow.

Above Gt

rubbery

Below Gt

stiff

Composition

side and end functional groups, bond type

Configuration

spatial arrangement of atoms/groups

Conformation

special arrangement of chain

Thermoset bonding

covalent

Thermoplastic bonding

secondary

Solvent and chain structure

swells polymer structure

Plasticisers

makes material more ductile, separates chain, reduces stress

Degradation

break molecule into sperate pieces

Secondary bonding strength

dispersion < induction < dipole-dipole < hydrogen

Dipole – dipole

large EN difference leads to permanent dipole formation (PVC)

Induction

permanent dipoles induce dipole in neighbouring atoms

Dispersion

momentary dipole formed by electron movement

Hydrogen bonds

highly positive charged hydrogen with high EN atoms (F,O,N)

Polarity

water > PA > POM > PET > OVC > PMMA > PS > PE > PP

Atactic

random side groups

Isotactic

same side side groups

Syndiotactic

regular alternating side groups

Trans configuration

electrons aligned

Gauche configuration

electrons alternate

Helix

molecule twisting to avoid overlap

Linear structure

secondary bonding (PE, PVC, PS, nylon, fluorocarbons)

Branched structure

lower packing, lower density

Crosslinked structure

all chains covalently bonded (rubber, PE, Epoxy, polyester)

Network structure

3D network, 3 active covalent binds (structure, epoxy, phenol formaldehyde)

HDPE properties

higher crystallinity, more secondary bonding, higher Tm, strong, brittle

LDPE properties

lower crystallinity, branching interferes with chain packing

High Mw properties

solid, higher density, higher viscosity

Low Mw properties

gas, lower density

Degree of polymerisation

repeated units along backbone

Melt flow rate indicates viscosity, more material, higher viscosity

Higher entanglement

more stretch before failure

Low shear rate

higher viscosity

Higher shear rate

lower viscosity, shear elongates chains allowing them to slide past each other easier

More chain branching

decreased viscosity

Bimodal

best from HM and LM

Low Mw

assist flow, higher crystallinity, less creep

High Mw

improves toughness, strength, stress crack propagation

Macromolecular motion

main chain rotation, molecular vibration, translational motion

Theory of reptation

wriggling motion, contained within a tube, motion restrained laterally

Physical entanglement

no crosslinking

Chemical entanglement

crosslinking

Below Mc

no entanglement as chains are too short

Viscosity below Mc

M α n no entanglement as chains are too short

Viscosity above Mc

M^3.5 α n higher M more entanglement

Amorphous

lacks repeatability, not consistent distances, not spatially identical

Driving force

increased entropy reduces free energy of system

Enthalpy

controls crystallinity

Heating crystal

energy absorbed (endotherm)

Cooling crystal

energy required (exotherm)

Ease of crystallisation

determined by length of unordered chain segments

Nuclei formation

requires extra energy

Crystallinity over time

harder crystallisation due to stress builds up within lamella duto increase in chain folds

Energy over time

Rapid decrease as loose segments become ordered.

More crystalline

less volume, more shrinkage, more symmetric

Atactic

harder to crystallize

Lower vibration

lower secondary binding, lower energy, crystals!

Undercooling

barrier to form new crystals as surface at a higher energy state, energy needed to form surfaced for nucleation

Epitaxial growth

laterally growing upward

Optimum growth rate

Tg+30 < Topt < Tm-19

Below Tg

structure rigid and molecules can’t diffuse easily

Rapid cooling

favour nucleation, smaller crystals

Slow cooling

favour growth, larger crystals

Chain folding

chain exit and renter elsewhere in the same crystallite