Production of Materials 1.4-2

Question 1

what is a monomer

Answer 1

small chained chemical unit that is linked over and over to form a larger chain (polymer).
e.g. ethylene

Question 2

What is a polymer

Answer 2

larger molecules made up of many repeating monomers.

e.g. polyethylene

Question 3

Ethylene as a monomer

Answer 3

double bond in ethylene can be broken and other ethylene molecules join to form polyethylene chain
n(CH2=CH2) –> -(H2C-CH2)-n
ethene –> polyethene

Question 4

polymerisation

Answer 4

• as the size of the molecule increase, the effect of dispersion forces if greater since they have a greater molecular S.A in contact.
• adding side chains and other functional groups to the HC chain allows chemists to fine tune the physical properties and chemical reactivities of the compounds allowing for many synthetic compounds to be tailored for specific uses.

Question 5

what are dispersion forces

Answer 5

weak forces of attraction between uncharged molecules with full electron shells. Strength of the force increase as total # electrons in the molecule increase.

Question 6

What is an addition polymer

Answer 6

a large chain molecule that can be formed from an addition reaction involving many molecules of monomers with double bonds

Question 7

addition polymerisation

Answer 7

requires 2 or more functional groups to join together by simple addition

Question 8

Steps in production of HDPE

Answer 8

produced using zeiger-natta catalytic process:
* low pressure (20atm)
* low temp (80-100C)
* Ionic catalyst (usually transition metal such as titanium chloride)
polymerisation is carried out on the surface of the ion

Question 9

Steps in production of LDPE

Answer 9

1. INITIATION: ethylene and an organic peroxide catalyst (benzoyl peroxide) heated at 80-300C @ high pressure (1500-3000atm).
   Catalyst initiates the reaction and covalent bond splits to form free radicals
   Free radicals contain unpaired electrons which are very reactive.
   R-O-O-R –> R-O* * O-R
2. ACTIVATION: free radicals react with and open the double bond in ethylene monomers. This forms an activated monomer radical.
3. PROPOGATION: activated monomer radicals attack double bonds in other ethylene molecules and the chain grows to form a polymer. As chain grows backbiting occurs (curls back on itself) and radical removes H from CH2 group within the chain which forms side chains (branching)
4. TERMINATION: chain length stops due to free H atoms attaching to free radicals, free radical ppoymers react to form covalent bonds or temp/pressure decreases.

Question 10

what is a free radical

Answer 10

formed when a covalent bond is broken, producing an atom with unpaired electrons in its outer shell. Ethene free radicals readily join with other Ethene molecules by reacting with the double bond. This promotes rapid growth of the polyethylene chain

Question 11

what does the catalyst do for production of LDPE and HDPE

Answer 11

LDPE ( organic peroxide) HDPE (transition metal catalyst)
Allow reactions to occur @ lower temps and pressure by lowering the activation energy required for the reaction to occur. It can affect arrangement of the units

Question 12

LDPE

Answer 12

extensive branching --> weak dispersion forces
chains not packed tightly 
soft
flexible 
non crystalline

Question 13

HDPE

Answer 13

Little branching (mostly straight chains) --> strong dispersion forces
tightly packed chains 
hard
not as flexible 
crystalline

Question 14

common features of LDPE and HDPE

Answer 14

thermoplastics
non toxic
waterproof
excellent insulators 
Resistant to most chemicals

Question 15

Vinyl Chloride

• systematic name
• monomer form
• polymer
• uses and properties

Answer 15

systematic name: chloroethane
monomer form: CH=CHCl
Polymer: polyvinylchloride (PVC) 
                (-CH2-CHCl-)n
Uses: toys, films for car interiors 
properties: rigid, flexible, non toxic, weather and fire resistant

Question 16

Styrene

• systematic name
• monomer form
• polymer
• uses and properties

Answer 16

systematic name: phenylethene
monomer form: CH2=CH(C6H5)
benzene ring =(C6H5)
polymer: polystyrene (-CH2-CH(C6H5))n
uses and : cups, eskies and flotation devices
properties: light weight, insulator, cheap, low density

Question 17

importance of simulators

Answer 17

• some experiments are too dangerous to perform without specialised equipment/personnel.
• too difficult
• too expensive
  therefore we use molecular model kits or simulations which allow us to see in a simplified form what happens at a molecular level so we can obtain an understanding of the processes involved.