polymers 1 Flashcards
what are polymers (basic, structurally)
organic materials containing carbon
what is polymerisation?
joining up of many small molecules (mers/monomers), bonded together with strong covalent, intramolecular bonds, producing long, chain-like structures (or three dimensional structures
why are polymers called macromolecules?
can be the order of 10^5-10^7 monomers making up a single polymer chain/network molecule, can treat one chain as a macromolecule
draw diagram of linear, branched, crosslinked, and network molecular structures
nice!
what is the ‘backbone’ of polymers often made of? (‘frame’ for network structures)
carbon
draw a polymer chain with a carbon backbone and H side groups
go
when are three dimensional polymer structures formed?
when there are more than two active bonding sites (see Phenol formaldehyde/Bakelite)
what is a homopolymer vs a copolymer?
homopolymers: when all the repeating units are the same type
copolymers: polymers made from more than one type of monomer (see slide 7)
what are the two mechanisms of polymerisation?
addition and condensation
what are the stages of addition polymerisation?
1) initiation: R* + C2H4 -> RC2H4* where R* is the initial/radical electron. The double bond breaks (see slide 14)
2) growth: RC2H4* + C2H4 -> RC4H8*
3) termination: occurs either by meeting another growing chain or reacting with the initiator
write an addition polymerisation reaction
see slide 15
what is addition polymerisation?
polymer that forms by simple linking (addition) of monomers without generating byproducts
what is condensation polymerisation?
requires reactive groups at the end of the monomer units. commonly water is given off in condensation reactions. slide 16
what does the molecular weight of a polymer affect? and why?
properties eg melting/softening temperature. due to not all chains growing to be the same length, causes distribution of molecular lengths and thus weights. usually characterise polymers with their average weights
what is the effect of molecular weight on the softening point?
as molecular weight increases, softening temperature increases. (eg @ room temp, short chain polymers are lliquid or gas. 1000 g/mol are waxy solids, and 10,000 g/mol or above are rigid solids)
what is significant about the covalent bonds in polymers?
very very strong, and directional (ie angled at 109deg). backbone carbon atoms in a chain can lie anywhere on a cone with respect to their neighbours (slide 19)
what are some different types of conformations?
formed due to bond rotation. can have twisted, coiled, or tangled conformations. end to end distance much smaller than actual chain length, good for large extensions of rubber materials
think how intestines are inside body, stretch out really long. bryony explained this well.
why are mechanical/thermal properties affected by restriction of bond rotation?
chain segments’ ability to rotate in response to mechanical stresses or thermal vibrations. dependent on monomer structure. (double bonds give rigidity, as well as bulky side groups reduce chain mobility)
why are additives used in plastics?
can increase strength, hardness, resilience, toughness, flexibility, stiffness. commonly serve multiple purposes, can use more than one additive
examples of additives to polymers?
heat stabilisers, antioxidants, crosslinking agents, lubricants, flame retardants, colourants, UV absorbers, fillers
why are fillers added to polymers?
to increase compressive and tensile strength, toughness, and hardness. synergistic effect is obtained, ie the mixture of filler and plastic gives better strength than the things on their own (eg wood flour + resin)
examples of types of fillers?
wood flour (effectively a polymer. same density as phenol formaldehyde so remains low density).
silica flour (harder than wood flour, good with abrasion resistance, adds thermal stability but increase density)
fibrous fillers (good for adding strength to product)
what are colourants?
change colour of polymer, may be added as dyes or pigments. dye - molecules dissolve and become part of polymer structure. pigments - do not dissolve and remain separate phase. usually prepared in masterbatch
what are flame retardants?
interfere with the combustion process of the polymer, control gases present during combustion, or by initiation of chemical reactions which cool the combustion reaction
