polymers ansh verma
TRANSCRIPT
-
8/3/2019 Polymers Ansh Verma
1/29
polymers- a brief up.ansh verma - 10208025, mechanical a.
-
8/3/2019 Polymers Ansh Verma
2/29
2
Polymers: Introduction
Polymer: molecules can be linked in repeatingunits to make longer.
High molecular weight molecule made up of asmall repeat unit (monomer).
A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A
Monomer: Low molecular weight compound thatcan be connected together to give a poymer
Oligomer: Short polymer chain
Copolymer: polymer made up of 2 or moremonomers
Random copolymer: A-B-B-A-A-B-A-B-A-B-B-B-A-A-B
Alternating copolymer: A-B-A-B-A-B-A-B-A-B-A-B-A-B
Block copolymer: A-A-A-A-A-A-A-A-B-B-B-B-B-B-B-B
-
8/3/2019 Polymers Ansh Verma
3/29
3
Types of Polymers
Polymer Classifications
Thermoset: cross-linked polymer that cannot bemelted (tires, rubber bands)
Thermoplastic: Meltable plastic
Elastomers: Polymers that stretch and then return totheir original form: often thermoset polymers
Thermoplastic elastomers: Elastic polymers that canbe melted (soles of tennis shoes)
Polymer Families Polyolefins: made from olefin (alkene) monomers
Polyesters, Amides, Urethanes, etc.: monomerslinked by ester, amide, urethane or other functional
groups
-
8/3/2019 Polymers Ansh Verma
4/29
4
Common PolyolefinsMonomer Polymer
Ethylene
H3C CH3
nRepeat unit
Polyethylene
CH3CH3
n
CH3 CH3 CH3 CH3 CH3 CH3CH3
Propylene
Polypropylene
PhCH3
n
Ph Ph Ph Ph Ph PhPhStyrene
Polystyrene
Cl
CH3
nCl Cl Cl Cl Cl ClCl
Vinyl ChloridePoly(vinyl chloride)
F2C CF2
Tetrafluoroethylene
F3C
F2C
CF2
F2C
CF2
F2C
CF2
F2C
CF2
F2C
CF2
F2C
CF2
CF3n
Poly(tetrafluoroethylene): Teflon
-
8/3/2019 Polymers Ansh Verma
5/29
5
Polyesters, Amides, and UrethanesMonomer Polymer
CO2HHO2CHO
OHO O
HO OH2C
H2C O
nTerephthalic
acidEthylene
glycol
Poly(ethylene terephthalate
H
Ester
HO OH
O O
4 H2N NH24Adipic Acid 1,6-Diaminohexane Nylon 6,6
HO NH
NH
H
O O
4 4n
CO2HHO2C
Terephthalic
acid
NH2H2N
1,4-Diamino
benzene
Kevlar
O
HO
OHN
HN H
n
Amide
HOOH
Ethyleneglycol
H2COCN NCO
4,4-diisocyantophenylmethaneSpandex
H2
C
H
N
H
N
O
HO
O
O
H2
C
H2
C O Hn
Urethane linkage
-
8/3/2019 Polymers Ansh Verma
6/29
6
Natural PolymersMonomer Polymer
Isoprenen
Polyisoprene:Natural rubber
O
H
HO
H
HO
H
HOHH
OH
OH
Poly(-D-glycoside):cellulose
O
H
O
H
HO
H
HOHH
OH
OH
H
n
-D-glucose
H3N
O
O
R
Polyamino acid:protein
H3N
OHN
R1
OHN
Rn+1
O
OH
Rn+2n
Amino Acid
BaseO
OH
OP
O
O
O
oligonucleic acidDNA
NucleotideBase = C, G, T, A
BaseO
O
OP
O
O
O
DNA
DNA
-
8/3/2019 Polymers Ansh Verma
7/29
7
What Makes Polymers Unique?
Really big molecules (macromolecules) likepolymers have very different properties thansmall molecules Chain entanglement: Long
polymer chains get entangled with
each other. When the polymer is melted, the chains
can flow past each other.
Below the melting point, the chains canmove, but only slowly. Thus the plastic isflexible, but cannot be easily stretched.
Below the glass transition point, the chainsbecome locked and the polymer is rigid
-
8/3/2019 Polymers Ansh Verma
8/29
8
Physical Properties
Stretch
Linear Polymer
The chains can be stretched, which causesthem to flow past each other. When released,the polymer will not return to its original form.
Stretch
Cross-Linked Polymer
The cross-links hold the chains together.When released, the polymer will return to it'soriginal form.
Relax
-
8/3/2019 Polymers Ansh Verma
9/29
9
Polymer Synthesis
There are two major classes of polymerformation mechanisms
Addition polymerization: The polymer grows bysequential addition of monomers to a reactive site
Chain growth is linear
Maximum molecular weight is obtained early in the reaction
Step-Growth polymerization: Monomers reacttogether to make small oligomers. Small oligomersmake bigger ones, and big oligomers react to give
polymers. Chain growth is exponential
Maximum molecular weight is obtained late in the reaction
-
8/3/2019 Polymers Ansh Verma
10/29
10
Addition Polymerization
In* AInitiation
In A* A
-
8/3/2019 Polymers Ansh Verma
11/29
11
Addition PolymerizationPropagation
In*A
InitiationIn A A* A
-
8/3/2019 Polymers Ansh Verma
12/29
12
Addition PolymerizationPropagation
AIn*A
InitiationIn A A A*
-
8/3/2019 Polymers Ansh Verma
13/29
13
Addition Polymerization
Propagation
nA
In A A A AnA*
A A A A Am
In A A A AnA
*A A A A Am
Combination
*A A A A Am
In A A A A n A
B A A A Am
Disproportionation
Termination
Reactive site is consumed
A
In A A A AnA
A*
Chain TransferNew reactive siteis produced
MW kpropagation
ktermination
MW
% conversion0 100
In*A
InitiationIn A A A A*
-
8/3/2019 Polymers Ansh Verma
14/29
14
Types of Addition Polymerizations
Ph
Anionic
C3H7 LiC4H9
Ph
Li+ Phn
C4H9
Ph Ph
Li+
n
Ph
Radical
PhCO2Ph
n
Ph
Cationic
Cl3Al OH2H
PhHOAlCl3
PhnH
Ph Phn
HOAlCl3
PhCO2
Ph
PhCO2
Ph Phn
-
8/3/2019 Polymers Ansh Verma
15/29
15
Step-Growth Polymerization
Stage 1
Consumptionof monomer
n n
Stage 2
Combinationof small fragments
Stage 3
Reaction ofoligomers to givehigh molecularweight polymer
-
8/3/2019 Polymers Ansh Verma
16/29
16
Step-Growth Polymerization
Because high polymer does not form until the
end of the reaction, high molecular weightpolymer is not obtained unless high conversion ofmonomer is achieved.
Xn 1
1 p
Xn=Degree of polymerizationp= mole fraction monomerconversion
-
8/3/2019 Polymers Ansh Verma
17/29
Thermoplastics
No cross links between chains.
Weak attractive forces between chains
broken by warming.
Change shape - can be remolded.
Weak forces reform in new shape when
-
8/3/2019 Polymers Ansh Verma
18/29
Thermosets
Extensive cross-linking formed by
covalent bonds.
Bonds prevent chains moving relativeto each other.
-
8/3/2019 Polymers Ansh Verma
19/29
Longer chains make stronger
polymers.Critical length needed beforestrength increases.
Hydrocarbon polymers averageof 100 repeating units necessarybut only 40 for nylons.
Tensile strength measures theforces needed to snap a
polymer.
More tangles + moretouching!!!
-
8/3/2019 Polymers Ansh Verma
20/29
20
Crystalline polymers Areas in polymer where
chains packed in regular way.
Both amorphous and
crystalline areas in samepolymer.
Crystalline - regular chain
structure - no bulky side
groups. More crystalline polymer -
stronger and less flexible.
-
8/3/2019 Polymers Ansh Verma
21/29
21
Cold-drawing
When a polymer is stretched a neck forms.
What happens to the chains in the neck? Cold drawing is used to increase a polymers
strength. Why then do the handles of plastic carrier
bags snap if you fill them full of tins of beans?
-
8/3/2019 Polymers Ansh Verma
22/29
22
Nylon-6,6
Cl Cl
O O
4H2N NH24
Adipoyl chloride 1,6-Diaminohexane
Cl NH
NH
H
O O
4 4
NaOH
HO NH
NH
H
O O
4 4n
6 carbondiacid
6 carbondiamine
Nylon-6,6Diamine, NaOH, in H2O
Adipoyl chloridein hexane
Nylon 6,6
-
8/3/2019 Polymers Ansh Verma
23/29
23
Nylon-6,6
Diamine, NaOH, in H2O
Adipoyl chloridein hexane
Nylon 6,6
Since the reactants are in differentphases, they can only react at the
phase boundary. Once a layer ofpolymer forms, no more reactionoccurs. Removing the polymer allowsmore reaction to occur.
-
8/3/2019 Polymers Ansh Verma
24/29
24
Molecular Weight of PolymersUnlike small molecules, polymers are typically a mixture of differentlysized molecules. Only an average molecular weight can be defined.
Measuring molecular weight
Size exclusion chromatography
Viscosity
Measurements of average molecular
weight (M.W.) Number average M.W. (Mn): Total
weight of all chains divided by # ofchains
Weight average M.W. (Mw): Weighted
average. Always larger than Mn Viscosity average M.W. (Mv): Average
determined by viscositymeasurements. Closer to Mw than Mn
# of molecules
Mn
Mw
increasing molecular weight
Mv
-
8/3/2019 Polymers Ansh Verma
25/29
25
What the Weights MeanMn: This gives you the true average weight
Let's say you had the following polymer sample:2 chains: 1,000,000 Dalton 2,000,000
5 chains: 700,000 Dalton 3,500,000
10 chains: 400,000 Dalton 4,000,000
4 chains: 100,000 Dalton 400,000
2 chains: 50,000 Dalton 100,00010,000,000
10,000,000/23 = 435,000 Dalton
1 Dalton = 1 g/mole
-
8/3/2019 Polymers Ansh Verma
26/29
26
Weight Average Molecular Weight
Mw: Since most of the polymer mass is in the heavier fractions, this
gives the average molecular weight of the most abundant polymerfraction by mass.
2,000,000
10,000,000 0.20 1,000,000 200,000
3,500,00010,000,000 0.35 700,000 245,000
4,000,000
10,000,000 0.40 400,000 160,000
400,000
10,000,000 0.04 100,000 4,000
100,000
10,000,000 0.01 50,000 500
Total 609,500
-
8/3/2019 Polymers Ansh Verma
27/29
27
Polymer Microstructure
Polyolefins with side chains have stereocenters on every other carbon
CH3n
CH3 CH3 CH3 CH3 CH3 CH3CH3
With so many stereocenters, the stereochemistry can be complex.
There are three main stereochemical classifications for polymers.Atactic: random orientation
Isotactic: All stereocenters have same orientation
Syndiotactic: Alternating stereochemistry
-
8/3/2019 Polymers Ansh Verma
28/29
28
How to Determine Microstructure?13C NMR is a very powerful way to determine the microstructure of a
polymer.
13C NMR shift is sensitive to the two
stereocenters on either side on sptectrometers
> 300 MHz. This is called pentad resolution.
r mm rmr
mmrm pentad
m = meso (same orientation)r = racemic (opposite orientation)
12 1 2
13C NMR spectrum of CH3 regionof atactic polypropylene
-
8/3/2019 Polymers Ansh Verma
29/29
29
Why is this important?
Tacticity affects the physical properties
Atactic polymers will generally be amorphous, soft,flexible materials
Isotactic and syndiotactic polymers will be morecrystalline, thus harder and less flexible
Polypropylene (PP) is a good example
Atactic PP is a low melting, gooey material
Isoatactic PP is high melting (176), crystalline, tough
material that is industrially useful Syndiotactic PP has similar properties, but is very
clear. It is harder to synthesize