Hasell - case studies and basics Flashcards

Question

How does Tg change with chain length?

Answer 1

longer chains = higher Tg

Answer 2

greater than 150C

Answer 3

retain desirable mechanical, thermal, and chemical properties when under harsh conditions (high temp, pressure, corrosive chemicals)

Answer 4

crystalline

Answer 5

crystalline

Answer 6

crystalline

Answer 7

crystalline

Answer 8

same as polyethylene but 4F instead of 4H

Answer 9

1) very unreactive (strong C-F bonds) 2) repels water and hydrocarbons (due to fluorination) 3) very resistant to solvents and corrosion so used for scientific and medical components 4) semicrystalline

Answer 10

1) no known solvents for it 2) too high viscocity to melt, doesn't flow but decomposes if heated more 3) to be shaped it needs to be granulated and compressed at high temp

Answer 11

Tm = 320-330C Tg = 120-130C Xc = high (60-80%)

Answer 12

semicrystalline

Answer 13

teflon (polytetrafluoroethylene)

Answer 14

1) semicrystalline 2) high temp thermoplastic 3) made by step condensation at ~300C in polar aprotic solvents

Answer 15

Tg = 143C Tm = 343C

Answer 16

1) temperature stable to be used upto 250C 2) good chemical resistance except to strong acids 3) can be melt processed

Answer 17

for bearings, piston parts, HPLC columns, valves, electrical insulation, medical implants bc it doesn't wear down easily

Answer 18

aromatic polyamides

Answer 19

1) aramid 2) not melt-processable - decomposes below its melting point 3) requires conc sulfuric acids and specialist equipement for processing 4) very strong temp resistance ~500C 5) normally spun into fibres 6) high strength and lightweight

Answer 20

the chains are all directed into the trans conformation, cis would be sterically hindered by the phenol hydrogens trans conf allows hydrogen bonding between linear chains

Answer 21

bulletproof vests and military armour, ropes, sails and sport equip, fireproof clothing, in composites with epoxy resin

Answer 22

1) heterocyclic polyimide - strong, good thermal and chemical resistance 2) soluble intermediate but insoluble product 3) product is thermoset so doesn't melt and is hard to process 4) stable upto 400C

Answer 23

1) heterocyclic polyimide - strong, good thermal and chemical resistance 2) soluble intermediate but insoluble product 3) product is thermoset so doesn't melt and is hard to process 4) stable upto 400C 5) linear

Answer 24

intermediate = polyamic acid: the O=C-NH is bent so gives some flexibility

Answer 25

the electron acceptors are the carbonyl groups on the ONE SIDE of the rings, the nitrogen atoms inside are the electron donors the other carbonyl groups the other side of the ring pull electron density away from the acceptor units the polyimides stack to arrange so the electron acceptor is above the electron donor, allowing the electron donor/acceptor groups to interact with the adjacent other group

Answer 26

1) thermal and electrical insulation 2) circuit boards 3) x-ray diffraction windows (doesn't diffract) 4) insulating heat shields when coated with Al for spacecraft 5) thermal blankets

Answer 27

1) chemically stable and inflammable 2) Bakelite = electrically insulating and resistant to damage 3) forms a 3D network 4) once melted cannot be molded - only cut

Answer 28

1) e- from O on the phenol goes back into the bond while the double bond next to it attacks the H2C of the methanol 2) proton transfers and methanol is now attached to the double bond next to the phenol whihc has been regenerated 3) attached methanol is protonated until the H2O leaves it and Ch2+ remains attached 4) the H2C+ is attacked by another new phenol molecule to add the whole molecule to it so it is a double ring structure ACID CATALYSED SO REACTS AT ORTHO OR PARA POSITIONS

Answer 29

- the epoxy group is strained and very reactive which allows reaction with many hydrogen donors - often use multifunctional (so not linear) amines to crosslink - most are based on bisphenol A and epichlorohydrin

Answer 30

1) bisphenol is made from 2 phenols and acetone (condensation reaction) 2) bisphenol A then reacts under basic conditions with epichlorohydrin

Answer 31

by controlling the ratio of bisphenol A to epichlorohydrin

Answer 32

they have two sets of NH2 so reaction can occur at any of the 4 proton positions to produce a highly crosslinked structure

Answer 33

- natural rubber is polyisoprene - synthetic rubber can be made from isoprene, butadiene, or often copolymer of styrene and butadiene -vulcanised to crosslink

Answer 34

- the reactive sites are unsaturated groups, sulfur bridges for inbetween these (can be one or many S atoms)

Answer 35

makes the linear rubber into a cross-linked thermoset

Answer 36

lower crosslinking = elastic & durable higher crosslinking = hard and brittle

Answer 37

depolymerises back into the rings bc of the radicals on each end

Answer 38

replacement for ivory electrical items, jewellery

Answer 39

car tyres, soles of shoes, rubber bands

Answer 40

1) 50% or more S8 = polymeric sulfur crosslinked by small organic molecule 2) first crosslinker reported was DIB 3) no solvents, simple synthesis, atom efficient

Answer 41

1) more stable LiS batteries 2) IR- transparent lenses 3) recyclable/repairable crosslinked polymers (vitrimers) 4) heavy metal capture 5) thermal/electrical insulation 6) antimicrobial materials