of 24
7/27/2019 web 11-11-05
1/24
The phenol + formaldehyde rxn
7/27/2019 web 11-11-05
2/24
Network formation Further reaction under heat & pressure builds up denselycross-linked network. This is Bakelite, a thermosetting polymer. Once reaction is complete, material cannot bereheated and/or reformed
Bakelite
7/27/2019 web 11-11-05
3/24
Bakelite telephone
Bakelite microphone Bakelite camera
Clear Bakelite items
Bakelite radio
Phenolic resin/celluloid clock
Bakelite - Material of a Thousand Uses
7/27/2019 web 11-11-05
4/24
Crosslinking
Take linear polymer chains & link using covalent bonds
7/27/2019 web 11-11-05
5/24
Crosslinking
Ex: rxn of natural rubber or poly(isoprene)
with sulfur - interconnects the chains by reacting with the double bonds
(vulcanization)
H
CH 2 -
CH 3 C = C
- CH 2
H
CH 2 -
CH 3 C = C
CH 2
H
CH 2 -
CH 3 C = C
CH 2
7/27/2019 web 11-11-05
6/24
Crosslinking
7/27/2019 web 11-11-05
7/24
3 types isotactic syndiotactic
atactic
Tacticity
7/27/2019 web 11-11-05
8/24
Tacticity
CH3
propylene monomer: CH2=CH
Ex: polypropylene
CH3
upon polymerization: CH2C
H
7/27/2019 web 11-11-05
9/24
isotactic
Tacticity
CH3
propylene: CH 2=CH
7/27/2019 web 11-11-05
10/24
Tacticity
atactic
syndiotactic
7/27/2019 web 11-11-05
11/24
Tacticity
Polypropylene - largely isotactic
isotactic character of PP allows "crystallization"
as a result, material can be stiffer
7/27/2019 web 11-11-05
12/24
Tacticity
Polystyrene - atactic
Polypropylene - largely isotactic
PVC - largely atactic(some syndiotactic sequences)
PMMA -atactic
7/27/2019 web 11-11-05
13/24
Copolymers
Graft Copolymers
-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-
A - A - A - A - A - A
- A - A -
A
- A - A - A - A - A - A - A
- A - A -
A - A - A - A
- A - A -
Block Copolymers
-A-A-A-A-A-A-B-B-B-B-B-B-B-B-B-B-A-A-A-A-A-A-
Random Copolymers-A-B-B-B-A-A-B-A-B-A-A-A-B-A-B-B-A-B-B-A-A-A-B-
Alternating Copolymers
-A-B-A-B-A-B-A-B-A-B-A-B-A-B-A-B-A-B-A-B-A-B-
7/27/2019 web 11-11-05
14/24
Blends
miscible immiscible
single phase phase separated
blend
7/27/2019 web 11-11-05
15/24
Molecular weight
Gases
Liquids
Increasing Molecular Weight
16
30
44
58
114
450
420030
CH 4
CH 3 - CH 2 _ CH 3
CH 3 - CH 3
CH 3 - CH 2 - CH 2 - CH 3
CH 3 - (CH 2 )6 _ CH 3
CH 3 - (CH 2 )30 _ CH 3
CH 3 - (CH 2 )30000 _ CH 3
--------------------------------------------------------
-----------------------------------------
---------------
---------------
---------------
----------
"Semi-solid"
Solids
increasing molecular weight
7/27/2019 web 11-11-05
16/24
7/27/2019 web 11-11-05
17/24
Molecular weight
Is it important?
Mol. Wt.
Melt ViscosityTensile Strength
Mol. Wt.
7/27/2019 web 11-11-05
18/24
Molecular weight
Is it important?
Very important in processing
If viscosity too high, polymerdifficult to process
If too low, an extruded materialwon't hold together until itsolidifies
7/27/2019 web 11-11-05
19/24
Blow molding
Step 1: make preform byextrusion or injectionmolding
7/27/2019 web 11-11-05
20/24
Blow molding
Step 1: make preform byextrusion or injectionmolding
Step 2: use air pressureto inflate preform inside
closed, hollow mold.Polymer expands to takeshape of cooled mold &solidifies under pressure
7/27/2019 web 11-11-05
21/24
Polymers are different
7/27/2019 web 11-11-05
22/24
Polymers are different
Normal crystalline materials Either crystalline (~100 %, neglecting
defects ) or amorphous at a particular temperature
Melt at a sharp, well-defined temperature
Crystallizable polymers Never 100% crystalline Melt over a range of temperatures
7/27/2019 web 11-11-05
23/24
7/27/2019 web 11-11-05
24/24