Download WATKINS - Chabot College

Engineering 45
Polymer
Structures
Bruce Mayer, PE
Licensed Electrical & Mechanical Engineer
[email protected]
Engineering-45: Materials of Engineering
1
Bruce Mayer, PE
[email protected] • ENGR-45_Lec-29_PolyMer_Structures.ppt
Learning Goals – Polymer Structure
 Learn The Basic Electronic Structure of
Very Long Organic Molecules
 Understand Basic MicroStructural
Features of Polymers
 Calculate Molecular Weights for LongChain Polymers
 Learn the Difference between
ThermoSETTING and ThermoPLASTIC
Polymers
Engineering-45: Materials of Engineering
2
Bruce Mayer, PE
[email protected] • ENGR-45_Lec-29_PolyMer_Structures.ppt
Ancient Polymer History
 Originally natural polymers were used
• Wood, Cotton, Leather, Rubber, Wool, Silk
 Early Human-History Uses for the
Natural PolyMers
• Rubber balls used by Incas
• Noah used pitch (a natural polymer)
for Sealing the Ark
Engineering-45: Materials of Engineering
3
Bruce Mayer, PE
[email protected] • ENGR-45_Lec-29_PolyMer_Structures.ppt
Organic Chemistry
 Recall PolyMer  Many Mers
 Mer  a Single Chemical Unit
 Almost All Solid Polymer Materials are
“Organic” in Nature
 Organic → Based on CARBON
 Almost All Organic Chemicals are a
combination of Carbon And
HYDROGEN
Engineering-45: Materials of Engineering
4
Bruce Mayer, PE
[email protected] • ENGR-45_Lec-29_PolyMer_Structures.ppt
C-H Bond
 ReCall from Periodic Table the Valences for
C&H
• C → Grp IVa → 4 Valence e−
• H → Grp 1A → 1 Valence e−
 Thus in a C-H molecule Both can Attain the
Noble-Gas Configuration if
• 4 H’s Give their e−’s
to 1 Accepting C
 Four-H’s and 1-C Yield the
METHANE molecule
Engineering-45: Materials of Engineering
5
Bruce Mayer, PE
[email protected] • ENGR-45_Lec-29_PolyMer_Structures.ppt
Single, Double, Triple Bonding
 First Note That the
Methane Molecule is
NOT Planer in 3D
• As Might be Expected the
H’s Take Equal
Separation to Form a
Tetrahedral Structure
 In Methane, Each H
Atom Shares ONE e−
• This Configuration is
Shown Schematically as
H
|
H

C
 H
|
H
• Each C-H is connected by
a SINGLE Bond as
depicted the Single-Line
Connection
Engineering-45: Materials of Engineering
6
Bruce Mayer, PE
[email protected] • ENGR-45_Lec-29_PolyMer_Structures.ppt
1X, 2X, 3X Bonding cont.1
 Another Electronic
Configuration, Ethylene,
Has the two adjacent
Carbons sharing TWO
e− to achieve the Neon
Configuration
H
H
|
|
C

H
 C  C  H
C
|
|
H
H
Engineering-45: Materials of Engineering
7
 In this case the C=C
connection is termed a
DOUBLE Bond
 Similarly, in Acetylene
two Carbons Share 3 e−
to form a TRIPLE Bond
Bruce Mayer, PE
[email protected] • ENGR-45_Lec-29_PolyMer_Structures.ppt
The C-H Chain Basic-Mer
 Consider the Base
Methane Molecule with
the end-H’s Removed

H
H
H
|
|
|
C

C

C
|
|
|
H
H
H

 The Central Carbon Can
Connect to Similar
Fragments with a 1X
Bond to form a CHAIN
Engineering-45: Materials of Engineering
8
 The CH2 Fragment, or
Mer, can Repeat Almost
endlessly, creating very
large PolyMer Chain
Molecules
 There can be Many
basic Mers consisting of
• 2X or 3X bonded C’s
• Other Atoms, or Ions
(Molecule Fragments)
may Substitute for H
Bruce Mayer, PE
[email protected] • ENGR-45_Lec-29_PolyMer_Structures.ppt
PolyMer MicroStructure
 Some Typical Repeating-Mer (PolyMer) Structures
 C-C Forms a Very Strong intRAmolecular Bond
• The CoValent IntERmolecular Bond Strength Varies with the
Form of the Chain-to-Chain Electronic interaction
Direction of increasing strength
Engineering-45: Materials of Engineering
9
Bruce Mayer, PE
[email protected] • ENGR-45_Lec-29_PolyMer_Structures.ppt
Mer Forms in 3D
PE: polyethylene
Phenol-formaldehyde
(Bakelite)
Engineering-45: Materials of Engineering
10
PVC: polyvinyl chloride
PET: polyethylene
terephthalate (a polyester)
Bruce Mayer, PE
[email protected] • ENGR-45_Lec-29_PolyMer_Structures.ppt
Example → PolyEthylene
 Poly (many) Mer (parts): A large
molecule made up of one or more
repeating units (mers) linked together
by covalent chemical bonds.
 The PolyEthylene Chemical Reaction
n  CH 2  CH 2  CH 2  CH 2 n
Temp, Press
• n = number of monomers reacting >> 1
Engineering-45: Materials of Engineering
11
Bruce Mayer, PE
[email protected] • ENGR-45_Lec-29_PolyMer_Structures.ppt
Effect of Molecular Weight
on the Properties of PolyEthylene
Engineering-45: Materials of Engineering
12
Bruce Mayer, PE
[email protected] • ENGR-45_Lec-29_PolyMer_Structures.ppt
PolyMer Chemistry
 Polymer MACROmolecules Produce NONcrystalline
Solids by the interMolecular Bonding
 The Chain-Creating “PolyMerization” Chemical Reaction
usually Proceeds with the aid of a catalyst, R
monomers + catalyst (initiator) = polymer chain
Poly
Ethylene
H
polyethylene
(C2H4 Mer)
Engineering-45: Materials of Engineering
13
C
Bruce Mayer, PE
[email protected] • ENGR-45_Lec-29_PolyMer_Structures.ppt
Molecular Geometry
 As indicated in the Previous Slide Any Three
Carbons in the “BackBone” form Something
near the Classic Tetrahedral Angle (109.471°)
 However the Molecules are NOT constrained
to TWO Dimensions
 The BackBones can Rotate, Kink, or Coil to
Generate Randomly Complex Shapes
Engineering-45: Materials of Engineering
14
Bruce Mayer, PE
[email protected] • ENGR-45_Lec-29_PolyMer_Structures.ppt
Isomerism
 IsoMerism  two compounds with same
chemical formula can have quite
different structures
• Example: C8H18
– n Octane
H H H H H H H H
H C C C C C C C C H
= H3C CH2 CH2 CH2 CH2 CH2 CH2 CH3
H H H H H H H H
– 2-methyl-4-ethyl
pentane
(IsoOctane)
CH3
H3C CH CH2 CH CH3
CH2
CH3
Engineering-45: Materials of Engineering
15
Bruce Mayer, PE
[email protected] • ENGR-45_Lec-29_PolyMer_Structures.ppt
Cross-linking
 Generally, amorphous polymers are weak.
 Cross-linking adds strength: vulcanized
rubber is polyisoprene with sulphur-based
cross-links:
Engineering-45: Materials of Engineering
16
Bruce Mayer, PE
[email protected] • ENGR-45_Lec-29_PolyMer_Structures.ppt
PolyMer Size Characterization
 MOLECULAR WEIGHT, Mw  Mass of a mol of
chain-molecules
 Average CHAIN SIZE, n  Number of Mers per Chain
• Also Called the “Degree of PolyMerization”
 Some Consequences: Mw↑  Tmelt↑
• short chains (~100 g/mol): liquid or gas
• long chains (1000 g/mol): waxy solid, soft resin
• “high polymer” (>10,000 g/mol): solid
 Also Mw↑  TS↑
• Longer chains are entangled (anchored) better
Engineering-45: Materials of Engineering
17
Bruce Mayer, PE
[email protected] • ENGR-45_Lec-29_PolyMer_Structures.ppt
MOLECULAR WEIGHT
• Molecular weight, Mi: Mass of a mole of chains.
Lower M
higher M
total wt of polymer
Mn 
total # of molecules
M n  x i M i
M w  w i M i
Mw is more sensitive to
higher molecular
weights
Engineering-45: Materials of Engineering
18
Bruce Mayer, PE
[email protected] • ENGR-45_Lec-29_PolyMer_Structures.ppt
Molecular Weight Calculation
 Example: average mass of a class
Ni
Mi
xi
wi
# of students
mass (lb)
1
1
2
3
2
1
100
120
140
180
220
380
0.1
0.1
0.2
0.3
0.2
0.1
0.054
0.065
0.151
0.290
0.237
0.204
Σ=10
Σ=1860
Mn
186 lb
Mw
216 lb
Engineering-45: Materials of Engineering
19
M n   xi Mi
M w   w i Mi
Bruce Mayer, PE
[email protected] • ENGR-45_Lec-29_PolyMer_Structures.ppt
Tacticity
 isotactic – all R
groups on same
side of chain
 syndiotactic – R
groups alternate
sides
 atactic – R groups
random
Engineering-45: Materials of Engineering
20
H H H H H H H H
C C C C C C C C
H R H R H R H R
H H H R H H H R
C C C C C C C C
H R H H H R H H
H H H H H R H H
C C C C C C C C
H R H R H H H R
Bruce Mayer, PE
[email protected] • ENGR-45_Lec-29_PolyMer_Structures.ppt
Cis/Trans IsoMerism
cis Form
CH3
H
trans Form
CH3
C C
CH2
C C
CH2
cis-isoprene
(natural rubber)
 Bulky groups on
same side of chain
Engineering-45: Materials of Engineering
21
CH2
CH2
H
trans-isoprene
(gutta percha)
 bulky groups on
opposite sides of
chain
Bruce Mayer, PE
[email protected] • ENGR-45_Lec-29_PolyMer_Structures.ppt
CoPolyMers
Adapted from Fig.
14.9, Callister 7e.
random
 Two or More MonoMers
PolyMerized ToGether
• random – A and B
randomly vary in chain
• alternating – A and B
alternate in polymer chain
• block – large blocks of A
alternate with large blocks
of B
• graft – chains of B grafted
on to A backbone
Engineering-45: Materials of Engineering
22
alternating
block
B
A
graft
Bruce Mayer, PE
[email protected] • ENGR-45_Lec-29_PolyMer_Structures.ppt
PolyMer Crystallinity
 % Crystalinity 
% of Material that
is crystalline
crystalline
region
amorphous
region
 TS and E often
increase with % crystallinity
 Annealing causes crystalline regions to grow.
• % crystallinity increases
Simulated conformation of a polymer
chain consisting of 100 main chain
repeat units and 50 side chains, each
consisting of 20 repeat units.
Engineering-45: Materials of Engineering
23
Bruce Mayer, PE
[email protected] • ENGR-45_Lec-29_PolyMer_Structures.ppt
PolyMer Xtals - Spherulites
 Polymer Single Xtals
Often Form Plate-like,
or Lamellar, Structures
by Folding Back on
themselves
Lamellae
Tie
Molecules
 In Bulk Material,
Amorphous regions of
Twisted & Kinked “Tie
Molecules:”connect the
Lamellae
Engineering-45: Materials of Engineering
24
 Upon Heating the Layered
Structures Become
Spherical with an “OnionLayer”, or Spherulitic,
Structure
Bruce Mayer, PE
[email protected] • ENGR-45_Lec-29_PolyMer_Structures.ppt
ThermoPlastic
25
Polymer-Chain
Structure v. Heating
ThermoSetting
Engineering-45: Materials of Engineering
Bruce Mayer, PE
[email protected] • ENGR-45_Lec-29_PolyMer_Structures.ppt
ThermoPlastic Polymers
 Polymers which melt and solidify withOUT
chemical change are called thermoplastics.
 They support hot-forming methods such as
injection-molding
Engineering-45: Materials of Engineering
26
Bruce Mayer, PE
[email protected] • ENGR-45_Lec-29_PolyMer_Structures.ppt
ThermoSet Polymers
 Polymers which irreversibly change when
heated are called thermosets.
 Most often, the change involves cross-linking
which strengthens the polymer (setting).
 Thermosets will not melt, and have
good heat resistance.
 They are often made from multi-part compounds
and formed before setting (e.g. epoxy resin)
 Setting accelerates with heat or, for some
polymers, with UV light.
Engineering-45: Materials of Engineering
27
Bruce Mayer, PE
[email protected] • ENGR-45_Lec-29_PolyMer_Structures.ppt
ThermoSets vs ThermoPlastics
 ThermoPlastics
• little cross linking
• ductile
• Soften, then Melt
with heating
• Examples
– polyethylene (PE)
– Polypropylene (PP)
– Polycarbonate
(Lexan)
– polystyrene
(StyroFoam)
Engineering-45: Materials of Engineering
28
 ThermoSets
• large cross linking
– 10 to 50% of mers
• hard and brittle
• do NOT soften with
heating
– Decompose Instead
• Examples:
vulcanized rubber,
epoxies, polyester
resin, phenolic resin
• 1st Synthetic Polymer
Bruce Mayer, PE
[email protected] • ENGR-45_Lec-29_PolyMer_Structures.ppt
WhiteBoard Work
 Prob 14.9
• For the Kinked & Twisted
Polymer at right Find
– Total Length, L
– End-to-End distance, r
• Given
– Eqns 14.11 & 14.12
– Mn for Linear
PolyPro = 300 kg/mol
Simulated conformation of a polymer
chain consisting of 100 main chain
repeat units and 50 side chains, each
consisting of 20 repeat units.
Engineering-45: Materials of Engineering
29
Bruce Mayer, PE
[email protected] • ENGR-45_Lec-29_PolyMer_Structures.ppt
Appendix - BakeLite




The First Synthetic Polymer
Invented by Leo Beakeland (1863 - 1944) in 1907 in Yonkers, NY
Chemical Name → phenol formaldehyde (Phenolic)
Historic Products
• 1912 - A Bakelite record invented by Edison. (USA)
• 1912 - Bakelite billiard balls invented by Hyat Burroughs. (UK)
• 1914 - The telephone receiver made of Bakelite by Western Electric.
(USA)
• 1915 - Photo camera from Kodak by Eastman gets a Bakelite case.
(USA)
• 1923 - Philips radio company starts with its own Bakelite production,
called Philite. (Netherlands)
• 1926 - First Bakelite chair
• 1927 - First Philite radio speaker made by Philips. (Netherlands)
– See also
 http://www.mbzponton.org/valueadded/maintenance/bakelitehist.htm
Engineering-45: Materials of Engineering
30
Bruce Mayer, PE
[email protected] • ENGR-45_Lec-29_PolyMer_Structures.ppt