ENME207 L24

Polymer Structure

Polymers

many repeating units

saturated polymers

bonded to 4 other atoms, less reactive

unsaturated polymers

bonded or triple bonded carbon (unstable)

Molucular characteristics

chemistry, molecular weight, shape, structure

PE

H, clear bottle/film

PVC

1 Cl, pipe

PTFE / teflon

4 F, non stick

PP

1 CH3, pipe, container

PS

1 benzyne, container, foam

low Molecular weight

short chain

high molecular weight

long shain

Degree of polymerisation

average repeating units per chain

Molecular shape

linear, branched, crosslinked, network

linear

single chain, high density

Branched

small side chane, less dense

Crosslinked

parallel chains linked with covalent bonds, high strength and stiffness

Network

excessively linked 3D structure, high strength and rigidity

Sterioisoner

saturated bonds (where R groups are bonded)

isostatic

R groups on same side of chain

syndiotactic

R groups on alternate sides periodically

Atactic

R groups random

Geometric isomer

unsaturated (cis, trans)

cis

H and CH3 on same side

trans

H and CH3 on different side

copolymers

monomers polymerised together (random, block, alternating, graphed)

Crystalinity

how aligned are grain boundaries

High crystalinity

low cool, simple chains, linear, regular copolymer

low crystallinity

high cool, large groups, branched/crosslinked, random copolymer

brittle

alligned, crosslinked, network

plastic

semicrystaline

elastomer

amorphous shain, very kinked, lighly cross linked

Drawing

stretched polymer, aligns chain ( strain hardening)

drawing properties

Increases E, TS, Decreases %EL

Annealing

decreases allignment (cold work)

Annealing properties

Increases % EL, Decreases E, TS

Decreasing temperature and increasing strain rate

Increases E, TS, Decreases %EL

Increasing stiffness

increases Tm, Tg

Increasing regularity

Increases Tm

Increasing Molecular weight

increases Tm, Tg

Glass transition tempe

glass to rubber on heating

Increase degree crystallization

Tg closer to Tm (more stable)

Low to high Tg

PE (low density), PE (high density), PVC, PS, PC

relaxation

apply tensile strain, hold, observe stress

relaxation modulus (Er)

large decrease in Er for temp above Tg

thermoplastic

linear, secondary, ductile, soft on heating, little cross linking, high KC, Low E, yield, T

Thermoset

hard, brittle, lots of cross link, high E, yield, T, low Kc

craze

fracture of thermoplastic, network microvous and fibrillar bridges join