Transcript Polymer Classifications - LSU Macromolecular Studies Group

Polymer Classifications:
Foreword.
This presentation is to be used with Chapter 2
of the Virtual Book. Students can complete
their virtual book thusly:
1. Make simple sketches and write ideas
during the class when this material is
presented.
2. Improve that by making better sketches
and editing a downloaded copy of
Chapter2.
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Linear polymers can be represented by a
simple sequence such as: A-A-A-A-A
CH
.
CH2
Polystyrene
n
Styrene monomer
Nylon
Two monomers
make one
repeating unit.*
HOOC
COOH
H2N-(CH2)6-NH2
Nylon monomer
Nylon 6,6
*There many different kinds of nylon.
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Polydispersity is the term we use to describe the
fact that not all macromolecules in a given sample
have the same “repeat number” x.
Polydisperse
#
#
size
Paucidisperse
Monodisperse
#
size
size
Even in a pure sample, not all molecules will be the same.
Nature often does better than people do.
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Addition
Condensation
Chain growth
Step growth
Example
Polystyrene
Nylon
Empirical formula
No change from
monomer.
Changes as byproduct
(often water) is given off.
How grows
One monomer at a
time
Monomer + dimer,
hexamer +
octadecamer, etc.
Polydispersity
Can be paucidisperse “Most probable”
Molecular weight
Wide range: can be
very high
Low (except
biopolymers)
Synonym
Chain growth
polymerization
Step growth
polymerization
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Addition: one monomer at a time
Also called chain growth.
Condensation: anything goes!
Also called step growth.
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The molecular weight of condensation (step
growth) polymers is limited to fairly low values.
Why?
Condensations: usually < 50,000 g/mol
Addition: can be quite high
(e.g., 46 x 106 for polystyrene)
Convert that to tons/mol
Nature makes huge polycondensates,
but they are usually made in chain growth fashion!
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There are such things as
inorganic polymers.
R’
--[P=N]-x
R
R used to be a secret. Not sure if it still is.
Others: POSS, poly(phthalocyanines), many colloids
(colloids are close relatives of polymers)
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Cascade polymers are also known as dendrimers. This
remains one of the hottest areas of macromolecular
science. Co-invented at LSU, it is still practiced here.
(McCarley, Warner, Daly, Russo)
Newkome @ LSU
Tomalia @ Dow
Future Nobelists?
Tomalia: now at MMI
Newkome: now at U. Akron
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The poly(phenylene) dendrimer at left has
actually been crystallized (Mullen).
The arborol dendrimer below was
made by Newkome at LSU….and
we still make this one at LSU.
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Copolymers can be used to tailor functionality
or generate new phases and behaviors.
Block copolymer, example:
Poly(styrene)-block-poly(butadiene)
Random copolymer, example:
Poly(styrene-ran-butadiene)
Graft copolymer,
example:
Poly(styrene)-graftpoly(butadiene)10
Some chemists really care about nomenclature.
Type
Connective Example
unspecified -co-
poly(Aco-B)
statistical
-stat-
poly(Astat-B)
random
-ran-
poly(Aran-B)
alternating
-alt-
poly(Aalt-B)
periodic
-per-
poly(Aper-Bper-C)
block
-block-
polyAblockpolyB
graft
-graft-
polyAgraftpolyB
James Traynham—LSU, 2003
From the Chemistry at U. Missouri Rolla website
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What does
that mean?
Star polymers have the
ability to act a little bit like spheres
and you can get higher M’s.
f=4
A lot of the
magic of
polymers is just
size.
Suppose each of the 4 “arms” is polydisperse. Are such molecules more
or less polydisperse than their linear counterparts?
Each “arm” of this star is a “random coil”. Star rods would be fun.
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Letter polymers are synthetically challenging
and useful for testing theories.
From the Mays website
In Hartford, Hereford and Hampshire, H’s Hardly Happen*
•In Knoxville, Tennessee (home of Jimmy Mays) they do.
•Matters in polyolefins—makes for better processing? Regular letter
polymers help manufacturers defend billion dollar patents.
*Adapted from the musical, “My Fair Lady”
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Combs, brushes and ladders give
you ways to stiffen a polymer.
Think “bottle brush”
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Rodlike polymers are used for very high
strength, liquid crystals, photonics, efficient
viscosification and control of phase relations.
Rodlike because of linear backbone
N
N
*
n
S
S
Used in
stealth
bomber?
Maybe.
Rodlike because of helix
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*
Polyelectrolytes: strange things happen when you try to
separate charges by a few Angstroms.
Strong polyelectrolytes
(e.g., salts of strong polyacids or polybases)
Do they still
tell you about
Angstroms?
Sodium polystyrene sulfonate: fully charged, yet behavior depends on
added salt
Monomer:
SO3Na
CH3
Weak polyelectrolytes (e.g., weak polyacids or polybases)
Poly(acrylic acid)
Behavior depends on added salt and pH
Monomer: CH2=CH-COOH
One of the hottest areas of fundamental polymer research involves polyelectrolytes.
Concentration of charge along a backbone, with charged groups closely separated, produces 16
some weird distortions in the molecules…and in the surrounding solution. Opposites may repel!
You are made of biopolymers.
R group varies one
unit to the next
H O
N
n
H R
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Proteins can do almost anything.
Proteins are the most amazing molecules on Earth,
large or small. They have 4 levels of structure,
which can confer enormously high function. In
particular, they make excellent catalysts—you are
all “burning” fuel now…at 37oC….efficiently
compared to most human-designed combustion
devices! It’s the proteins that do this. They also
give structure and strength and resilience. They
can change their shape—the original “smart
molecule”.
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The 4 levels of structure
• Primary: the sequence of the amino acids
• Secondary: helix, coil or random sheet
(and a few others)
• Tertiary: folding of the unit, including
–S-S- bridges
• Quaternary: how the blobs assemble
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Structure = Function
More Structure = More Function
http://www.sciencecollege.co.uk/SC/biochemicals/bsheet.gif
Alpha helix
Beta sheet
http://www.search.com/reference/Alpha_helix
Protein
Normal synthetic polymer
Subunit a
Subunit b
http://www.biosci.ohio-state.edu/~prg/protein1.gif
a-Helical secondary structure
S-S link
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b-sheet secondary structure
There are 20 common, naturally occurring amino acids.
Name
ALIPHATIC Alanine
Valine
Leucine
Isoleucine
Formula
3-letter
Symbol
Ala
Val
Leu
-CH3
-CH(CH3)2
CH2CH(CH3)2
CH(CH3)Ile
C2H5
Simplified
Symbol
A
V
L
I
NONPOLAR Glycine
Proline
Cysteine
Methionine
H
XXX
-CH2SH
-C2H4-S-CH3
Gly
Pro
Cys
Met
G
P
C
M
AROMATIC Histidine
Phenylalanine
Tyrosine
Tryptophan
XXX
-CH2-
-CH2--OH
XXX
His
Phe
Tyr
Trp
H
F
Y
W
POLAR
Asparagine
Glutamine
Serine
Threonine
CH2CONH2
C2H4CONH2
CH2OH
CH(OH)CH3
Asn
Gln
Ser
Thr
N
Q
S
T
CHARGED
Lysine
Arginine
Aspartate
Glutamate
-C4H8NH3+
XXX
CH2COOC2H4COO-
Lys
Arg
Asp
Glu
K
R
B
E
http://www.genome.iastate.edu/edu/gene/genetic-code.html#Amino21
Acids
Another type of biopolymer, nucleic acids, contains the
information needed to make proteins.
Borrowed from
Natural Toxins Research Center Webpage:
http://ntri.tamuk.edu/cell/nucleic.html
An interesting sub-section of the nanotech community tries
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to use nucleic acids as structural materials.
Biopolymers: Nucleic Acids
Ribose sugar
Base
OH
3'
O
H
O ..... H N
H3 C
O P O
O
OH
O P O
OH
O
U
N
O
T N H ...... N
O
H2 C
N H
O P O
O P O
N
OH
N
O
N
OH
N
O
H2 C
G N
N
OH
O
CH2
O
G N H........ N C
N
OH
N
NH ......... O
O
NH2
O
O P O
O
N
OH
NH
N
OH
A N
N
O
H2C
N
O
A
H2C
O
O
O P O
OH
RNA
N
C
O
N
C N .....
H N G
O
O
N
O P O
O
OH
NH2
OH
N
H
N H .. O
O P O
CH2
O
N ........ H N T
O
OH
CH3
N
OH
O P O
H2 C
O
N
CH2
O
N
N
O .... H N
H
P O
O
H
N H ..... O
N
OH
O P O
P O
O
N
CH2 O
H2 C
A
H
O ... H N
OH
CH2
O
O
O
O
O
O
N
N
O
H2C
5'
O P O
O
3'
O P O
O
O
5'
DNA
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Nucleic acids code proteins, a
molecular “build sheet”
• Nucleic acids are how we get (or “code”) proteins. There are 4
bases (called A,T,G,C). Three of these in a row gives a "codon"
which tells the cellular machinery to add a particular amino acid.
Nucleic acids are much less prevalent than proteins, in the
same sense that auto factories are less prevalent than
automobiles. They make interesting model polymers for a
variety of studies—from better understanding of polymer
flexibility to liquid crystal behavior.
• You can get a list of the codons for the various amino acids at:
http://www.genome.iastate.edu/edu/gene/geneticcode.html#Amino Acids
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Networks (Gels) combine the
properties of liquids and solids.
Keep on branching. The ultimate
molecule: M = 
The Gentrys Sing Keep on
High-speed Jello Video
CLICK IT!
High-Speed Jello Video
CLICK IT!
Branching (or something like
that)
CLICK FOR SONG!
Pathetic Cover of Keep on
Branching by Boy Band Bay
City Rollers
CLICK FOR SONG!
High-Speed Jello Video
CLICK IT!
It only takes a little polymer (a few percent by weight) to turn the water to a
nominal solid, and the polymers in gelatin are held by noncovalent forces.
Making the network for a tire involves significantly more polymer
and covalent forces are involved.
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Thermoplastic/Thermoset is
another big distinction.
Macromolecular chemistry involves chemists,
biologists, physicists, and various engineers.
The engineers, just like average citizens,
have very little use for a molecular point of
view. They tend to divide the polymer world
into thermoplastic and thermoset “resins”.
• Thermoplastic: when you heat it, it flows
(e.g., polyethylene, polystyrene)
• Thermoset: when you heat it, it “sets up” into
a solid (e.g., epoxy glue, styrene monomer)
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Silica-Polypeptide Composite Particles
Paul S. Russo (Louisiana State University),
DMR-Award #1005707
We assist the Chemical Educational Foundation’s You Be the Chemist
Challenge program, a middle school “quiz bowl” that impacts ~16,000
students in 22 states. This year, we have focused on vetting the
thousands of questions it takes to operate Challenge. To give
Challenge a more “hands-on” and “real-world” flavor, the Louisiana
champion, Hayden Day, studied from a new Louisiana Playbook we
are designing (see sample question below and figure at left).
Louisiana YBTC Playbook, Problem #25.
The sequence of pictures at left shows the
repair of the polymeric skin of an automobile
bumper which was torn during a wreck. The
repair consists of pushing the parts together
closely, holding them with tape on the outside
(red) part, and “welding” them on the inside
(black) side using a soldering iron.
↑Grad student Javoris Hollingsworth
teaches 8th-grader Hayden Day, the 2012
Question 1: Is the bumper a thermoset or a
Louisiana state champion in the Chemical
Educational Foundation’s You Be the
thermoplastic?
Challenge, about titrations. Barely
Question 2: Suppose instead of a torn bumper Chemist
visible in the background is Hayden’s
we had a gashed tire made from vulcanized
Mom, a school teacher. Hayden’s father, a
chemical plant technician, is looking on
rubber. Would heating a vulcanized rubber
too. Dad studied every day with his son,
repair the tire?
and Hayden acquitted himself well in the
national competition in Philadelphia in
Question 3: Explain how polymer welding
June.
works at a molecular level.
Polymers can be amorphous, crystalline, or
a bit of both—corresponding to brittle,
gooey and tough (oversimplified!).
Polymers can be solid without crystalline
structures. These are called glasses.
Polymers can be crystalline (amazing).
Most useful polymers a little bit of both—
regions in the material have crystalline
inclusions and other regions are amorphous.
These materials are often tough—the
amorphous regions absorb shock.
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Transitions
We deal with this later, but even from the outset you
should know a little bit.
Glass transition is the temperature BELOW which the
amorphous regions of a sample start to act like
solids.
Melting transition is the temperature ABOVE which the
crystalline regions of a sample start to act like fluids.
Either way, these are oversimplifications—big
molecules have a number of transitions that describe
the chain mobility.
These molecular transitions, in turn, impact the physical
properties—from “feel” to “stickiness” (tack) to
elongation and breakage.
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