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11 SCHOOL OF MECHANICAL ENGINEERINGLECTURER: PROF. SEUNGTAE CHOI
Chapter 5. Structures of Polymers
ISSUES TO ADDRESS...
22 SCHOOL OF MECHANICAL ENGINEERINGLECTURER: PROF. SEUNGTAE CHOI
Polymers & Hydrocarbon Molecules
Naturally occurring polymers
Synthetic polymers
Most polymers are hydrocarbons, i.e., made up of Hydrogen and Carbon.Intramolecular bonds are covalent.
Unsaturated hydrocarbons
Saturated hydrocarbons
33 SCHOOL OF MECHANICAL ENGINEERINGLECTURER: PROF. SEUNGTAE CHOI
Definitions
Term “polymer”: greek poli (many) + meros (unit) = many units
Polymer:
Repeating unit:Monomer: rOligomer:
Single repeat unit: MONOMERMany repeat units: POLYMERDegree of polymerization:
44 SCHOOL OF MECHANICAL ENGINEERINGLECTURER: PROF. SEUNGTAE CHOI
Hydrocarbon Molecules
Paraffin family
55 SCHOOL OF MECHANICAL ENGINEERINGLECTURER: PROF. SEUNGTAE CHOI
Hydrocarbon Groups
66 SCHOOL OF MECHANICAL ENGINEERINGLECTURER: PROF. SEUNGTAE CHOI
Isomerism
Hydrocarbon compounds with the same chemical formula can have differentatomic arrangements.
For example: C4H10 (butane), C8H18 (octane)
77 SCHOOL OF MECHANICAL ENGINEERINGLECTURER: PROF. SEUNGTAE CHOI
Polymer Molecules
Polymers = Macromolecules
Monomer Repeat Unit
Poly mer= many = repeat unit
88 SCHOOL OF MECHANICAL ENGINEERINGLECTURER: PROF. SEUNGTAE CHOI
Polymerization and Polymer Chemistry
Free radical polymerization
Initiator: example benzoyl peroxide
99 SCHOOL OF MECHANICAL ENGINEERINGLECTURER: PROF. SEUNGTAE CHOI
Chemistry and Structure of Polyethylene
Callister & Rethwisch 9e.
110 SCHOOL OF MECHANICAL ENGINEERINGLECTURER: PROF. SEUNGTAE CHOI
Various Polymers
Homopolymer: All the repeating units along a chain are of the same type.Copolymer: Chains are composed of two different repeat units.Terpolymer: Chains are composed of three different repeat units.
Functionality: The number of bonds that a given monomer can form
••
111 SCHOOL OF MECHANICAL ENGINEERINGLECTURER: PROF. SEUNGTAE CHOI
Bulk or Commodity Polymers
H
112 SCHOOL OF MECHANICAL ENGINEERINGLECTURER: PROF. SEUNGTAE CHOI
Volatile Organic Compounds (VOCs):
Volatile organic compounds (VOCs) are organic chemicals that have a highvapor pressure at ordinary room temperature. Their high vapor pressureresults from a low boiling point, which causes large numbers of molecules toevaporate or sublimate from the liquid or solid form of the compound andenter the surrounding air, a trait known as volatility. For example,formaldehyde, which evaporates from paint, has a boiling point of only –19 C.
VOCs are numerous, varied, and ubiquitous. They include both human madeand naturally occurring chemical compounds. Most scents or odors are ofVOCs. VOCs play an important role in communication between plants,[1] andmessages from plants to animals. Some VOCs are dangerous to human healthor cause harm to the environment. Anthropogenic VOCs are regulated by law,especially indoors, where concentrations are the highest. Harmful VOCstypically are not acutely toxic, but have compounding long term health effects.Because the concentrations are usually low and the symptoms slow to develop,research into VOCs and their effects is difficult.
113 SCHOOL OF MECHANICAL ENGINEERINGLECTURER: PROF. SEUNGTAE CHOI
5.5 Molecular Weight
Molecular weight, M: Mass of a mole of chains.
Molecular weight distribution
Low M high M
xi i
molecules ofnumber totalpolymer of weight total
nM
iiW
iin
MwMMxM
Callister & Rethwisch 9e.wi i
Mi i
114 SCHOOL OF MECHANICAL ENGINEERINGLECTURER: PROF. SEUNGTAE CHOI
Degree of Polymerization, DP
Degree of Polymerization (DP) = average number of repeat units per chain
i
iimfm
C C C C C C C CH
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
C C C C
H
H
H
H
H
H
H
H
H( )
DP
115 SCHOOL OF MECHANICAL ENGINEERINGLECTURER: PROF. SEUNGTAE CHOI
5.6 Molecular Shape
Molecular Shape (or Conformation) – chain bending and twisting are possibleby rotation of carbon atoms around their chain bonds
Chain End to End Distance, r
Callister & Rethwisch 9e.
116 SCHOOL OF MECHANICAL ENGINEERINGLECTURER: PROF. SEUNGTAE CHOI
5.7 Molecular Structure of Polymer
Linear chains:Branched chains:
Hyper branched polymer
Cross linked polymer:Net work polymer:
Callister & Rethwisch 9e.
117 SCHOOL OF MECHANICAL ENGINEERINGLECTURER: PROF. SEUNGTAE CHOI
5.8 Molecular Configurations for Polymers
Stereoisomerism: Atoms are linked together in the same order (head to tail)but differ in their spatial arrangement.Stereoisomers are mirror images: can’t superimpose without breaking a bond.Tacticity – stereoregularity or spatial arrangement of R units along chain
C C
H
H
H
R R
H
H
H
CC
R
H
H
H
CC
R
H
H
H
CC
C CR
HH
HC C
H
H
H
R
or C C
H
H
H
R
EB
A
D
C C
D
A
BE
118 SCHOOL OF MECHANICAL ENGINEERINGLECTURER: PROF. SEUNGTAE CHOI
Stereoisomerism (continued)
C C
H
H
H
R R
H
H
H
CC
R
H
H
H
CC
R
H
H
H
CCC C
H
H
H
R
C C
H
H
H
R
C C
H
H
H
R R
H
H
H
CC
119 SCHOOL OF MECHANICAL ENGINEERINGLECTURER: PROF. SEUNGTAE CHOI
Geometrical Isomerism
Cis/Trans Isomerism
C CHCH3
CH2 CH2
C CCH3
CH2
CH2
H
220 SCHOOL OF MECHANICAL ENGINEERINGLECTURER: PROF. SEUNGTAE CHOI
5.9 Thermoplastic and Thermosetting Polymers
Polymers may be classified as follows, according to the mechanical response atelevated temperatures:
a) Thermoplastics:
221 SCHOOL OF MECHANICAL ENGINEERINGLECTURER: PROF. SEUNGTAE CHOI
5.9 Thermoplastic and Thermosetting Polymers
b) Thermosets
222 SCHOOL OF MECHANICAL ENGINEERINGLECTURER: PROF. SEUNGTAE CHOI
5.10 Copolymers
Homopolymers:
Copolymers:
Several classes of copolymer are possibleStatistical copolymer (Random)
Alternating copolymer
Block copolymer
Graft copolymer
Callister & Rethwisch 9e.
223 SCHOOL OF MECHANICAL ENGINEERINGLECTURER: PROF. SEUNGTAE CHOI
5.10 Polymer Crystals
Crystalline regions
Polymers rarely 100% crystalline
Callister& Rethwisch 9e.
Callister 6e.The Structure and Properties of Materials
Mechanical Behavior
224 SCHOOL OF MECHANICAL ENGINEERINGLECTURER: PROF. SEUNGTAE CHOI
Polymer Single Crystals
Electron micrograph– multilayered singlecrystals (chain folded layers) of polyethyleneSingle crystals – only for slow and carefullycontrolled growth ratesSpherulite
