polymers 2

Question 1

what are the four types of molecular structure?

Answer 1

linear, branched, cross-linked, networked

Question 2

describe linear polymers

Answer 2

monomer units joined in single chains. covalent bonding occurs along the backbone, secondary bonding (Van der Waals) occurs between different chains

Question 3

describe branched polymers

Answer 3

monomer units joined in chains with branching. covalent bonds along chains and branches. secondary/van der waals bonds between chains. lower density than linear

Question 4

describe cross-linked polymers

Answer 4

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

Question 5

draw cross linked polymer with long tangled chains like how bryony did

Answer 5

nice

Question 6

describe 3d networked structure

Answer 6

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.

Question 7

what is the difference between thermoplastics, elastomers, and thermosets?

Answer 7

thermoplastics melt, thermosets don’t (think sets with temperature). elastomers are bouncy elastic polymers.

Question 8

structure of thermoplastics

Answer 8

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)

Question 9

structure of thermosets

Answer 9

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.

Question 10

structure of elastomers

Answer 10

neighbouring molecules joined at occasional points by covalent bonds. generally more like thermosets than thermoplastics as crosslinked covalently.

Question 11

what is isomerism

Answer 11

different atomic configurations for the same configuration (butane and isobutane, see slide 21)

Question 12

draw example of head to tail and head to head configurations

Answer 12

yep

Question 13

is head to head more common or head to tail configurations?

Answer 13

head to tail due to polar repulsion between R groups

Question 14

what are stereoisomers

Answer 14

molecules which are linked in the same order (head to tail) but differ in spacial arrangement

Question 15

what are forms of stereoisomer configurations?

Answer 15

isotactic (R on same side of chain). syndiotactic (R alternates side of chain). atactic (random positioning of R groups) (slide 25)

Question 16

what is cis vs trans isomerism?

Answer 16

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

Question 17

what are the four types of copolymers?

Answer 17

random, alternating, block, graft

Question 18

what is degree of crystalinnity of a polymer affected by?

Answer 18

size of side groups, intermolecular forces, steric regularity (atactic difficult to crystallise unlike isotactic and syndiotactic)

Question 19

what properties does crystallinity of a polymer affect?

Answer 19

density, strength, youngs modulus, toughness, deformation

Question 20

what are spherulite structures?

Answer 20

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)

Question 21

how does drawing into fibres affect properties?

Answer 21

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