Polymers Flashcards
what are polymers?
not plastics! they’re synthetic materials made up of repetition of high weight molecules in the form of a flexible chain. they are soft and moldable during manufacture. repeating molecules are called monomers polymerization is when monomers link together
what are the two main types of addition polymerization and describe them
homogeneous: same monomers over and over again - polyethylene
copolymer: alternation of 2 types of monomers
what is condensation polymerization?
polymerization reaction between two monomers with the loss of water (a simple by-product). problem in recycling because you can’t put the by-product back in. addition polymerization is more easily recyclable because easy to break apart and put back together
how does polymer structure coincide with its strength?
Linked length-wise most of the time. If only links in one direction- only strong in which direction
You can’t push on a rope
Polymers are strong in tension (in direction of chain) but very weak in compression
Some can link off in other directions and you get chains in other directions called branches
Fully cross-linked has strength in all direction
Lots of variability we can make all types of polymers (high uniformity within material)
what is a monomer that is widely used in manufacture of other monomers and polymers?
ethylene
what are some of the advantages of polymers?
lightweight and can be used to replace steel!
recyclable because you can heat them up and reform them
usually not very expensive (except for carbon fibre)
can be transparent
corrosion resistant, electrical insulators, moldable
what are some disadvantages of polymers?
some types aren’t recyclable (eg. thermosets)
not suitable for high temp environments
low in strength
what are the three groups of polymers?
thermoplastics
thermosets
elastomers
what are thermoplastics?
branched chain polymers usually obtained by addition polymerization. Easily recyclable because easily reformed when heated up. very ductile
what are thermosets?
three-dimensional cross-linked or network polymers. stronger and harder than linearly structured thermoplastics. usually products of condensation polymerization and will undergo setting and hardening when heated and cooled. are isotropic. NOT REFORMABLE AND NOT RECYCLABLE
brittle so no deformation before failure so bad as rebar. low fracture energy
what are elastomers/rubbers?
linear polymer structures with some cross-linking between molecules. low elastic modulo. ability to elastically deform under low loads without permanently changing shape. no definite elastic modulus in stress-strain curve.
what are some important properties of elastomers?
Pritef
elasticity (stretch a lot but shape can be recovered)
flexibility
toughness (due to high deformability)
massive amount of strain capability
impermeability to water and air
resistance to corrosion
plasticity and easy of molding
what are silicones?
not carbon based, silicon based. don’t tear easily. a special type of elastomer. high dimensional and thermal stability. good electrical and anti-adhesive properties
how is functionality used to classify different polymers?
defined as the number of bonding sites and how good it is for cross-linking. if polymer has three sites at which molecules may be attached - trifunctional.
how does increasing polymer molecule size change the properties of the polymer?
increased melting point, increased strength, increased stiffness
explain why polymers are used for insulators
they have low thermal conductivity so they are used for thermal insulators
they do not have interconnected pores so they have low permeability. great for science
explain polymers in terms of durability
no corrosion (could replace steel in terms of durability and for strength)
bad under oxidation and uv exposure
don’t break down by acid or alkalis or harsh conditions
do polymers break down by bacteria or fungal attack?
no! only exceptions are natural polymers. some polymer additives to increase vulnerability to biological degradation.
some polymers become toxic when temperature is increased (decompose and release toxic substances)
name the additives profs without the o
plasticizers (improve flow, reduce brittleness, lower transition temp in amorphous polymers)
fillers (reduce cost, less pure polymer)
reinforcement agents (improve mechanical properties)
stabilizers (improve heat, UV, and oxidation resistance)
describe amorphous polymers
atoms held together in loose manner. decreased polymer chain mobility with decrease in temp. below glass transition they become a rigid solid. above, they are a viscous solid (like elastomer)
describe crystalline polymers
similar structure to that of metallic or ionic crystals. lattice structure. more likely to break then to bend and then break. like diamonds
describe the amorphousness in crystalline structures
the crystalline structure of a polymer has lamellar morphology of the crystalline phase and amorphous nature of chain segments between the crystallites.
what are foamed polymers?
low density polymers. they can be rigid or flexible. styrofoam is an example as well as polymers in mattresses.
