Download Organic Polymers Synthetic and Natural

Organic Polymers
Synthetic and Natural
1
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A polymer is a high molar mass molecular compound made up
of many repeating chemical units.
Naturally occurring polymers
• Proteins
• Nucleic acids
• Cellulose
Tyvek
• Rubber
Synthetic polymers
• Nylon
• Dacron
• Lucite
Silverstone®: polytetrafluoroethylene
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The simple repeating unit of a polymer is the monomer.
Homopolymer is a polymer made up of only one type of
monomer
( CF2
CF2 )n
Teflon
( CH2
CH2 )n
Polyethylene
( CH2
CH )n
Cl
PVC
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Copolymer is a polymer made up of two or more monomers
( CH
CH2
CH2
CH
CH
CH2 )n
Styrene-butadiene rubber
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Stereoisomers of Polymers
R groups on same
side of chain
Isotactic
R groups alternate
from side to side
Syndiotactic
R groups disposed
at random
Atactic
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Polymerization: Addition reactions
•  Involve unsaturated compounds containing double or
triple bonds
•  Particularly C=C and C≡C
•  Examples:
−  Hydrogenation
−  Reactions of hydrogen halides and halogens with
alkenes and alkynes
−  Polymerization
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Mechanism of addition polymerization
initiator
repeating unit (monomer)
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Vulcanization: Properties of rubber
sulfur cross-links
before vulcantization
after vulcantization
stretched
relaxation after stretching
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Polymerization: Condensation reactions
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Conduc'ng Polymers Introduction
Polymers (or plastics as they are also called) are
known to have good insulating properties.
" 
•  Polymers are one of the most used materials in the modern world. Their uses and applica'on range from containers to clothing. •  They are used to coat metal wires to prevent electric shocks. What is conduc-vity? Conduc'vity can be defined simply by Ohms Law. V= IR Where R is the resistance, I the current and V the voltage present in the material. The conduc'vity depends on the number of charge carriers (number of electrons) in the material and their mobility.In a metal it is assumed that all the outer electrons are free to carry charge and the impedance to flow of charge is mainly due to the electrons "bumping" in to each other. Insulators however have 'ghtly bound electrons so that nearly no electron flow occurs so they offer high resistance to charge flow. So for conductance free electrons are needed. What makes the material conduc've? Three simple carbon compounds are diamond, graphite and polyacetylene. They may be regarded as three-­‐ two-­‐ and one-­‐dimensional forms of carbon materials . Diamond, which contains only σ bonds, is an insulator and its high symmetry gives it isotropic proper'es. Graphite and acetylene both have mobile π electrons and are, when doped, highly anisotropic metallic conductors. Polyenes Polyacetylenes Ethylene
C 2 H4
H-(CH=CH)-H
Butadiene
C 4 H6
H-(CH=CH)-(CH=CH)-H
Hexatriene
C 6 H8
H-(CH=CH)-(CH=CH)-(CH=CH)-H
Octatetraene
C8H10
H-(CH=CH)4-H
...
-103,7 °C
- 169 °C
- 4,4 °C - 108,9 °C
78 °C
- 12 °C
+ 50 °C
1° J.C.S. Chem. Comm., 1977 received, 16th May 1977 2° P.R.L., 1977
received, 23 June, 1977 3° J.A.C.S., 1978 received, September 6, 1977 Yet Alan J. Heeger, Alan G. MacDiarmid and Hideki Shirakawa have changed this view with their discovery that a polymer, polyacetylene, can be made conduc've almost like a metal. Two condi'ons to become conduc've: 1-­‐The first condi'on for this is that the polymer consists of alterna'ng single and double bonds, called conjugated double bonds. In conjuga'on, the bonds between the carbon atoms are alternately single and double. Every bond contains a localised “sigma” (σ) bond which forms a strong chemical bond. In addi'on, every double bond also contains a less strongly localised “pi” (π) bond which is weaker. Basis of Soliton Theory Coulson-­‐Rushbrooke Theorem The π-­‐molecular orbitals of non-­‐zero binding energy (ε ≠ 0) appears in pair (conjugate molecular orbitals) with opposite energies. Polyacetylenes with even number of carbon atoms C.A. Coulson aPolyacetylenes nd G.S. Rushbrooke, Proc. Cambridge, hil.Soc. 3o
6, f 1c93 (1940) atoms with odd nPumber arbon Mol. Phys. 5, 15 (1962) Such unpaired electrons may be detectable by electron spin resonance. The defect is able to travel through the molecule since its mo?on depends only on a small displacement of The existence of m
isfits hould by nin o Fm
eans 3b. e limited one carbon atom. This is isllustrated igure (p.19) to odd polyenes. One can conceive of a series of such misfits, at regular distances, in a large even polyene. A strong concentra'ons of spins – one per 5000 atoms at room temperature has been observed by ESR in extremely long even conjugated polymers [M. Nechstein, J. Polymer Sci. C1, 1367-­‐1376 (1963)] 2-­‐The second condi'on is that the plas'c has to be disturbed -­‐ either by removing electrons from (oxida'on), or inser'ng them into Doping. (reduc'on), the material. The process is known as •  There are two types of doping: 1-­‐oxida'on with halogen (or p-­‐doping). (CHn) + 3x/2 I (CHn)+ + I3-­‐ 2-­‐ Reduc'on with alkali metal (called n-­‐doping). (CHn) + xNa (CHn)x-­‐ + xNa+ " e"
+ e"
#$
$$
##
#$
!!! If mobile, conduc'vity without spin !
!
PA+ Oxida've p-­‐doping Conduc'on without spin PA-­‐ Reduc've n-­‐doping Conduc'on without spin !
3x
x+
I2 " [CH]n + x I#3
[CH]n +
2
[CH]n + x
x#
Na " [CH]n + x Na+
Undoped PA Doped PA !!! Red shiq upon doping Doping process •  The halogen doping transforms polyacetylene to a good conductor. Oxida'on with iodine causes the electrons to be jerked out of the polymer, leaving "holes" in the form of posi've charges that can move along the chain. DOPING - FOR BETTER
MOLECULE PERFORMANCE
•  Doped polyacetylene is, e.g., comparable to good conductors such as copper and silver, whereas in its original form it is a semiconductor. Conduc-vity of conduc-ve polymers compared to those of other materials, from quartz (insulator) to copper (conductor). Polymers may also have conduc-vi-es corresponding to those of semiconductors. Factors that affect the conduc'vity 1-­‐ Density of charge carriers. 2-­‐ Their mobility. 3-­‐ The direc'on. 4-­‐ Presence of doping materials (addi'ves that facilitate the polymer conduc'vity) 5-­‐ Temperature. Applications
Conduc'ng polymers have many uses. The most documented are as follows: •  an'-­‐sta'c substances for photographic film •  Corrosion Inhibitors •  Compact Capacitors •  An' Sta'c Coa'ng •  Electromagne'c shielding for computers "Smart Windows" A second genera'on of conduc'ng polymers have been developed these have industrial uses like: •  Transistors •  Light Emitng Diodes (LEDs) •  Lasers used in flat televisions •  Solar cells •  Displays in mobile telephones and mini-­‐format television screens Shield for computer screen against electromagne'c "smart" windows radia'on smart" windows Solar cell Photographic Film Light-­‐emitng diodes Examples of Conduc'ng Polymers Prac-cal Applica-ons Conduc-ve plas-cs used in, or being developed industrially for: -­‐ an'-­‐sta'c substances for photographic films -­‐ shields for computer screens against electromagne'c radia'on -­‐ "smart" windows that can exclude sunlight Semi-­‐conduc-ve polymers recently developed in: -­‐ light-­‐emitng diodes (LEDs) -­‐ solar cells
-­‐ displays in mobile telephone and mini-­‐format televisions screens Applica-ons ⇒ Plas'c Electronics Polyaniline
conductor electromagne'c shielding of electronic circuits corrosion inhibitor Poly(ethylendioxythiophene) – PEDOT an'sta'c coa'ng material on photographic emulsions hole injec'ng electrode material in PLED Poly(phenylene vinylidene) ac've layer in electroluminescent displays (GSM) Poly(dialkylfluorene)
emissive layer in full-­‐colour video matrix displays Poly(thiophene) field-­‐effect transistor Poly(pyrrole)
microwave-­‐absorbing "stealth" (radar-­‐invisible) screen coa'ngs ac've thin layer of sensing devices Conclusion •  For conductance free electrons are needed. •  Conjugated polymers are semiconductor materials while doped polymers are conductors. •  The conduc'vity of conduc've polymers decreases with falling temperature in contrast to the conduc'vi'es of typical metals, e.g. silver, which increase with falling temperature. •  Today conduc've plas'cs are being developed for many uses. Proteins
Proteins are polymers of amino acids
•  Termed polypeptides
•  Play a key role in nearly all biological processes
−  Enzymes, the catalysts of biochemical reactions
−  Transport of materials
−  Storage of vital substances
−  Coordinated motion
−  Mechanical support
−  Protection against diseases.
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Amino acids are the basic structural units of proteins.
•  Contain at least one amino group (-NH2)
•  And at least one carboxyl group (-COOH)
•  Existing form is pH dependent
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Amino acids are joined in a protein by the formation of a
peptide bond
H O
H O
+H
3N
C C O- + +H3N C C OR1
H O
+H
R2
Peptide (amide) bond
planar
H O
- + H O
N
C
C
N
C
C
O
3
2
R1
H R2
Dipeptide – contains two amino acid residues
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20 amino acids can form 202 or 400 dipeptides.
Protein with 50 amino acid residues can be arranged in
2050 or 1065 ways.
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Polypeptide chain: repeating amide bonds
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Protein Structure: α-helix
Carbon
Nitrogen
Oxygen
R group
The structure is
held in position by
intramolecular
hydrogen bonds
(………)
Hydrogen
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Protein Structure: β-Pleated Sheets
Hydrogen bonds in parallel and antiparallel β-pleated sheets
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Protein Structure
tertiary
structure
quaternary
structure
primary
structure
secondary
structure
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Protein Structure
Intermolecular Forces in a Protein Molecule
ionic forces
hydrogen
bonds
dispersion
forces
ionic forces
dispersion
forces
dispersion
forces
dipole-dipole
forces
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Protein Structure
The structural changes that occur when oxygen binds to the
heme group in hemoglobin.
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Denatured proteins: no longer exhibit normal biological
activities.
Denaturation can be caused by pH, denaturants (special
reagents) or temperature
Can be reversible
or irreversible
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Nucleic Acids
Nucleic acids are high molar mass polymers that play an
essential role in protein synthesis.
1.  Deoxyribonucleic acid (DNA)
2.  Ribonucleic acid (RNA)
DNA molecule has 2 helical strands.
Each strand is made up of nucleotides.
Electronmicrograph of DNA
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The Components of the Nucleic Acids DNA and RNA
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Base-Pair Formation by Adenine and Thymine and by
Cytosine and Guanine
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