Transcript Lecture_26_(1)_Polymers

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Synthetic and Biological Polymers
Polymers: Macromolecules formed by the covalent
attachment of a set of small molecules termed monomers.
Polymers are classified as:
(1)
Man-made or synthetic polymers that are
synthesized in the laboratory;
(2)
Biological polymer that are found in nature.
Synthetic polymers: nylon, poly-ethylene, poly-styrene
Biological polymers: DNA, proteins, carbohydrates
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Methods for making polymers
Addition polymerization and condensation polymerization
Addition polymerization: monomers react to form a
polymer without net loss of atoms.
Most common form: free radical chain reaction of
ethylenes
n monomers
one polymer molecule
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Example of addition polymers
4
Free-Radical AdditionPolymerization of
Ethylene
H2C
CH2
200 °C
2000 atm
CH2
CH2
CH2
CH2
O2
peroxides
CH2
polyethylene
CH2
CH2
Free-Radical Polymerization of Propene
H2C
CH
CH
CH3 CH3
CHCH3
CH
CH
CH
CH
CH
CH3
CH3
CH3
CH3
CH3
polypropylene
..
•
RO
..
H2C
Mechanism
CHCH3
Mechanism
..
RO:
H2C
CHCH3
•
..
RO:
H2C
Mechanism
CHCH3
•
H2C
CHCH3
..
RO:
H2C
Mechanism
CHCH3
H2C
CHCH3
•
..
RO:
H2C
Mechanism
CHCH3
H2C
CHCH3
•
H2C
CHCH3
..
RO:
H2C
Mechanism
CHCH3
H2C
CHCH3
H2C
CHCH3
•
..
RO:
H2C
Mechanism
CHCH3
H2C
CHCH3
H2C
CHCH3
•
H2C
CHCH3
Likewise...
•H2C=CHCl
•H2C=CHC6H5
•F2C=CF2
polyvinyl chloride
polystyrene
Teflon
Important
constitutions
for synthetic
polymers
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Supramolecular
structure of
polymers
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Structural
properties of
linear
polymers:
conformationa
l flexibility
and strength
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Cross linking adds
tensile strength
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Condensation polymerization
Condensation polymerization: the polymer grows from
monomers by splitting off a small molecule such as
water or carbon dioxide.
Example: formation of amide links and loss of water
Monomers
First unit of polymer + H2O
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Polymers in the movies
In the 1967 movie, "The Graduate”,
a smug Los Angeles businessman takes aside the
baby-faced
Dustin Hoffman and declares,
"I just want to say one word to you -- just
one word -- 'plastics.' "
In 2005 we can replace ‘plastics’ with
another word: ‘synthetic polymers’
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Rembember from GChem?
Nylon is a condensation polymer
made of the monomers adipic acid
and hexamethylene diamine.
O
OH
O
OH
Q uickTim e™ and a
Phot o - JPEG decom pr essor
ar e needed t o see t his pict ur e.
They're nylons, Benjamin.
adipic acid
+
NH2
H2N
hexamethylene diamine
nylon
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Hydrogen bonds between chains
Supramolecular
Structure of
nylon
Intermolecular
hydrogen bonds
give nylon
enormous tensile
strength
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Biopolymers
Nucleic acid polymers (DNA, RNA)
Amino acids polymers (Proteins)
Sugar polymers (Carbohydrates)
Genetic information for the cell: DNA
Structural strength and catalysis: Proteins
Energy source: Carbohydrates
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Proteins: amino acid monomers
The basic structure of an amino acid monomer
HO
NH2
H
O
R
The difference between amino acids is the R group
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Proteins: condensation polymers
Formed by condensation polymerization of amino acids
Monomers: 20 essential amino acids
General structure of an amino acid
NH2
H
R
CO2H
R is the only variable group
Glycine (R = H) + Glycine
First step toward poly(glycine)
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Representation of the
constitution of a protein
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Three D representation of the structure of a protein
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DNA
Thymine (T)
The monomers:
Adenine (A)
Cytosine (C)
Guanine (G)
PhosphateSugar (backbone) of
DNA
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Phosphatesugar
backbone
holds the DNA
macromolecule
together
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One strand
unwinds to
duplicate its
complement via a
polymerization of
the monomers
C, G, A and T
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Carbohydrates
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