Polymers Flashcards
What is a polymer?
A polymer is an organic material made by joining many Mers with covalent bond to produce chain like structures.
What is a homopolymer?
homopolymers are when all the repeating units are the same type.
What is a copolymers?
Is a Polymers made from more than one type of monomer.
What is a functional group?
A functional group is a specific group of atoms within a molecule that is responsible for a characteristic chemical reaction of that molecule.
What are the mechanisms of Polymerisation and what do they require?
Addition which required unsaturated bond and a catalyst and Condensation which requires reactive groups at the end of the monomer.
Why is molecular weight important?
Not all chain grow to the same length so the properties of the polymers will be affected by its molecular weight.
How does bond rotation affect polymers?
The covalent bond in a polymer is directional so they can like any direction as long as they are angled at 109 degrees meaning the polymer can form in different shapes.
Why are additives used in polymers?
Additives are used to improve the mechanical properties of the polymer.
What are fillers?
Fillers are a group of additives usually used to increase the compressive and tensile strength, hardness and toughness.
What are some types of additives?
Colourants, Flame Retardants and Plasticiser.
What are the different polymer chains?
Linear, Branched, Cross linked, Networked.
What is the difference between thermoplastics, thermosets and Elastomers?
Thermoplastics do melt, Thermosets do not melt and elastomers are special in that they are highly elastic.
What is isomerism?
Different atomic configuration for the same composition.
What are Stereoisomers?
Molecules linked in the same order but differ in spacial arrangement.
What are the stereoisomers configurations?
Isotactic (R on same side), Syndiotactic ( R alternate sides), Atactic( R is Random)
What are the types of copolymers?
Random, Alternating, Block and Graft.
What is Crystallinity?
The arrangement of atoms or molecules into an ordered structure.
How is the degree of crystallinity affected?
Size of the side groups, intermolecular forces, steric regularity.
streic regularity is how difficult different stereoisomer configeration are to crystallise
What is the glass transition temperature?
The glass transition temperature (Tg) is the temperature at which an amorphous material transitions from a hard, brittle state into a softer, more rubbery state.
What are the stages of deformation?
Crystalline lamellae ‘shear’ past each other, lamellae orientate to the load direction, lamellae segments separate from the bulk connected by tie chains, Blocks and tie chains align with the loading direction.
What are the effects of crosslinking in a structure?
increased strength and stiffness, reduced ductility
What increases the melting point of a material?
Reducing branching, increased molecular weight, crystallite size and larger/stiffer backbone units and side groups.
What is the difference between purely elastic behaviour and purely viscous behaviour?
An elastic material will “spring” back to it original form when the load is removed, when the load is applied to a viscous material the strain will increase over time until it is removed.
What are the steps in a general shaping process?
Production of liquid, placement of material/liquid, hardening
How does the shaping process differ for thermoplastic and thermosets?
For thermoplastics we heat above Tg, shape, then cool. For thermosets we have a low viscosity liquid when mixed, shape and then possibly have to heat to cure.
What is shaping by extrusion?
Extrusion is use to make continuous products of constant cross section (eg, sheets of pipes).
What is shaping by moulding?
There are many forms of moulding but generally moulding is get a material/liquid and putting is around a shape in a specific way.
What is shaping by joining?
Joining can be done mechanically, by welding or by adhesive bonding.
What is Exotherm?
Is the process of thermoset curing and there is a large amount of heat released?
What are macromolecules
Because there is a very large amount of monomers making up a polymer chain, polymers are commonly termed macromolecules.
What are the main differences between condensation polymerisation and addition polymerisation
Condensation produces a byproduct of H20 each time a monomer joins the chain, Addition reactions involve radicals and a change of boding instead of a loss of atoms to by-products.
What is the viscoelastic behaviour in a leathery state?
Small instantaneous elastic strain followed by a much larger time-dependent elastic strain along with a small amount of viscous flow
What is the viscoelastic behaviour in a rubbery state?
More instantaneous elastic strain, negligible primary creep, and increased viscous flow
Explain the 5 stages of a more realistic viscoelastic behaviour.
1) Rapid elastic loading
2) Primary and secondary creep occurring
3) Rapid elastic recovery
4) Slow recovery of primary creep
5) No recovery of secondary creep
What happens to a semi-crystalline thermoplastic polymer material when a polymer is heated past the Tg, Tm, Td.
Tg: amorphous regions get out of their glass-like state, and secondary bonds break.
Tm: The secondary bond holding the crystalline region together breaks.
Td: the primary covalent bond break.
How does the addition of plasticisers affect the mechanical properties of a polymer?
Plasticisers are used to reduce the stiffness and increase the “flexibility” and/or “softness” of a polymer. They work by lowering the glass transition temperature of the polymer.
