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CH_318N_Lecture26-08_Spring_08 1
Chemistry 318N
Lecture 26
April 24, 2008
POLYMERS II
Chemistry 318N
Natural Polymers
Natural polymeric materials have been used
throughout history for clothing, decoration,
shelter, tools, weapons, and writing materials
Examples of natural polymers:
Cellulose (wood)
Hair
Silk
Rubber
Modified natural polymers
Nitrocellulose (lacquer, smokeless powder)
Rayon, etc 2
Chemistry 318N
Shellac
Chemistry 318N
Meyer
Baekeland
The History of Novolac
C.H. Meyer and/or L.H.
Baekeland Discovered
Novolac ca. 1907 - 1909
OH
CH
3 3
Chemistry 318N
Novolac Resin Production!!
Workers at Albert Co. in Wiesbaden, Germany
zerkleinert das Harz von Hand (ca. 1910)
Chemistry 318N
Bakelite and Shellac
Baekelands Phenol-formaldehyde
resins, which he called Bakelite. 4
Chemistry 318N
The Association People
Thomas Graham
1805-1869
Graham thought that cellulose and
other colloids consisted of large
numbers of structurally simple
molecules held together by
"association." .also called partial
valency ??!!
Chemistry 318N
Staudingers Heretic Proposal
Macromolecules
O
O
O
O
CH
3
CHCOCH
2
CH
3
O
OH
Polymer 5
Chemistry 318N
Hermann Staudinger
1881-1965
The statement of a German chemist after a debate with
Staudinger in 1926: We are shocked like zoologists would
be if they were told somewhere in Africa an elephant was
found who was 1600 feet long and 300 feet high.
Staudinger received the Nobel Prize in chemistry in 1953.
Chemistry 318N
If the total mass of dissolved material is known,
depresssion of freezing point, elevation of boiling
point, and osmotic pressure, colligative properties
give an easy way to estimate the molecular weight
of the substance. Eventually, the tiny osmotic
pressures and freezing point depressions seen in
polymer solutions could no longer be ignored, or
attributed to small amounts of a low molecular
weight impurity.
Science Wins 6
Chemistry 318N
Herman Francis Mark
May 3, 1895 April 6, 1992
Hans Mark
Chemistry 318N
X-Ray Crystal Structures
Mark and Staudinger fight over stiffness 7
Chemistry 318N
Wallace Hume Carothers 1896-1937
Synthesis of Polymers
Inventor of Nylon ... US patent 2,130,947
see
http://www.invent.org/hall_of_fame/28.html
Chemistry 318N
Commercializion of Nylon
ttp://www.chemheritage.org/EducationalServices/chemach/pop/whc.html
Nylon was first used for fishing line,
surgical sutures, and toothbrush
bristles. DuPont touted its new fiber
as being "as strong as steel, as fine
as a spiders web," and first
announced and demonstrated nylon
and nylon stockings to the American
public at the 1939 New York
Worlds Fair.
DuPont sold 5 million pairs of stockings across the U.S. on the
first day they were generally available, May 15, 1940. About
63 million were sold in their first year. 8
Chemistry 318N
Notation & Nomenclature
Show the structure by placing parenthesis
around the repeat unit
n = average degree of polymerization
CH
CH
2
n
Chemistry 318N
Notation & Nomenclature
To name a polymer, add the prefix poly to
the name of the monomer from which the
polymer is derived
if the name of the monomer is one word, no parentheses
are necessary ..like polystyrene
for more complex monomers or where the name of the
monomer is two words, enclose the name of the
monomer is parenthesis, as for example poly(vinyl
chloride) or poly(ethylene terephthalate)
Many common monomer names are used... 9
Chemistry 318N
Industrial Influence...
Poly(vinylidine chloride) Saran wrap
Poly(vinylidne Fluoride) Speaker membranes
Kevlar (Polyamide) bullet proof vests
Nylon (polyamide) rope and stockings
Delrin (polyacetal) bushings
Dacron (polyester) clothing, sails, etc.
Lexan (polycarbonate) aircraft windows
Polyethylene (bags, bottles, etc.)
etc..
Polymers have changed the world
Chemistry 318N
Morphology
Many polymers tend to crystallize as they precipitate
or are cooled from a melt
But, they are very large molecules, often with
complicated and irregular shapes, which inhibits
crystallization and tends to prevent efficient packing
into exactly ordered structures
As a result, polymers in the solid state tend to be
composed of ordered crystalline domains and
disordered amorphous domains 10
Chemistry 318N
Polymer Morphology
Crystalline and semi crystalline
Amorphous
Chemistry 318N
Morphology
Polymers with regular, compact structures and
strong intermolecular forces, such as hydrogen
bonds have high degrees of crystallinity.
as crystallinity increases, the polymer becomes more
opaque due to scattering of light by the crystalline
regionsfor example, teflon -(CF
2
CF
2
)-looks white
Melt transition temperature, T
m
: the temperature
at which crystalline regions melt
as the degree of crystallinity increases, T
m
increases 11
Chemistry 318N
Polymer Crystals
Chemistry 318N
Crystallinity
some spontaneously form crystalline regions (micelles)
proportion of crystalline / amorphous strong influence on properties
PE carrier bag - amorphous, toughened pipe 95% crystalline
amorphous
crystalline 12
Chemistry 318N
Morphology
Amorphous polymers are referred to as glassy
polymers
they lack crystalline domains that scatter light and are
transparent.Poly(methyl methacrylate)
they are weaker polymers and generally more flexibility
on heating, amorphous polymers are transformed from
a hard glass to a soft, flexible, rubbery state
Glass transition temperature, T
g
: the temperature
at which a polymer undergoes a transition from a
hard glass to a rubbery solid
(ca. 100 degrees for
polystyrene)
Chemistry 318N
Differential Scanning Calorimetry 13
Chemistry 318N
A DSC Plot
Chemistry 318N
Morphology
Example:
poly(ethylene terephthalate),
abbreviated PET can be made with crystalline
domains ranging from 0% to 55% depending on
how it is processed. It can have the properties of
drink bottles or Dacron fiber.
O
O
O
O
n
Poly(ethylene terephthalate) 14
Chemistry 318N
Morphology
Amorphous PET is formed by cooling the melt
quickly
plastic beverage bottles are PET with a low degree of
crystallinity
By cooling slowly, more molecular diffusion
occurs, chains become more ordered and crystalline
domains form
PET with a high degree of crystallinity can be drawn into
textile fibers and tire cords (dacron)
Chemistry 318N
Wallace
Hume
Carothers
Our friend appears again
Condensation Polymerization
Addition Polymerization and 15
Chemistry 318N
A d d itio n
Carothers Definition
Additon Polymerization
CO
2
H
HO
2
C
HO
OH
O
O
O
HO
O
H
+
(
(
Condensation
- H
2
O
Condensation Polymerization
Loss of a small molecule
Emperical formula retained
Chemistry 318N
N C O
N C O
HO
OH
OCN
H
N
O
O
O
N
H
O
Ar
+
Condensation?
O
O
O
O
O
O
Condensation?
Addition?
Problems with Carothers Definition
Same product by two paths??? 16
Chemistry 318N
Paul J Flory
1910-1985
The Nobel Prize in Chemistry 1974
"for his fundamental
achievements, both theoretical
and experimental, in the physical
chemistry of macromolecules"
Chemistry 318N
Flory Clears Things Up
Polymer Structure is distinct from Polymerization Process.
O
O
O
O H
HO
O
O H
HO
Addition
Polymerization
Condensation
Polymerization
Condensation
Polymer
Release of small molecules
Degradation gives different
composition
New functional groups
Condensation
Same composition
(monomer = polymer)
Similar connections
Ring-opening
No by-products
Addition
Structure
Process 17
Chemistry 318N
Basic Types of Polymerization Mechanisms
Chain-growth
Step-growth
Ring-opening
O
O
O
-
O
RO
-
O
O
RO
H
+
CH
2
C
O
HO
CH
2
OH
CH
2
C
O
O
CH
2
O H
H
H
2
O
Dimer
Tetramer
Octamer
Hexamer
...