polymers 2 Flashcards
what are the four types of molecular structure?
linear, branched, cross-linked, networked
describe linear polymers
monomer units joined in single chains. covalent bonding occurs along the backbone, secondary bonding (Van der Waals) occurs between different chains
describe branched polymers
monomer units joined in chains with branching. covalent bonds along chains and branches. secondary/van der waals bonds between chains. lower density than linear
describe cross-linked polymers
neighbouring molecules get joined at various positions by covalent bonds (can occur during polymer synthesis or later at higher temp using additive atoms). secondary bonding can still occur between polymer chains since they can be coiled
draw cross linked polymer with long tangled chains like how bryony did
nice
describe 3d networked structure
higher functionality monomer units having at least three active bonds. (if polymer is highly cross linked it could be regarded as a network polymer). some secondary bonding could occur however properties and behaviour almost fully influenced by the excessive covalent bonding.
what is the difference between thermoplastics, elastomers, and thermosets?
thermoplastics melt, thermosets don’t (think sets with temperature). elastomers are bouncy elastic polymers.
structure of thermoplastics
linear polymers, sometimes can be branched. can be amorphous or partially crystalline, could be drawn into fibres. as the temperature increases, the secondary bonds break and the polymer melts. (thermoplastics can be reformed)
structure of thermosets
amorphous. networked, often have high degree of cross-linking. basically fully covalent bonds so do not soften with temperature. tend to be brittler than thermoplastics, but have better thermal stability.
structure of elastomers
neighbouring molecules joined at occasional points by covalent bonds. generally more like thermosets than thermoplastics as crosslinked covalently.
what is isomerism
different atomic configurations for the same configuration (butane and isobutane, see slide 21)
draw example of head to tail and head to head configurations
yep
is head to head more common or head to tail configurations?
head to tail due to polar repulsion between R groups
what are stereoisomers
molecules which are linked in the same order (head to tail) but differ in spacial arrangement
what are forms of stereoisomer configurations?
isotactic (R on same side of chain). syndiotactic (R alternates side of chain). atactic (random positioning of R groups) (slide 25)
what is cis vs trans isomerism?
cis is same side, trans is opposite side. cis and trans isomers can result in very different properties (trans isoprene easily crystallises into a rigid material. cis isomer is unsymmetrical and unable to crystallise under stress, rubbery) *slide 27
what are the four types of copolymers?
random, alternating, block, graft
what is degree of crystalinnity of a polymer affected by?
size of side groups, intermolecular forces, steric regularity (atactic difficult to crystallise unlike isotactic and syndiotactic)
what properties does crystallinity of a polymer affect?
density, strength, youngs modulus, toughness, deformation
what are spherulite structures?
chain folded lamellae crystals, separated by amorphous material, held together by tie chains. (folded lamellae form spherically shaped structures that grow outwards, impinge on other growing spherulites and form planar boundaries)
how does drawing into fibres affect properties?
drawn (think tensile test we did). very strong as covalently bonded chains are aligned in direction of fibre, hard to break. drawing increases degree of crystallinity, and anisotropy is introduced
