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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 .

Polystyrene

Styrene monomer

CH CH2

n

Nylon

Two monomers make one repeating unit.*

*There many different kinds of nylon.

H2N-(CH2)6-NH2

Nylon monomerHOOC

COOH

Nylon 6,6

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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.

size

#

size

#

size

Polydisperse Monodisperse Paucidisperse

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

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

Chain growth Step growth

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Addition: one monomer at a timeAlso 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.

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!

Why?

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There are such things as inorganic polymers.

--[P=N]--

R

R’

x

Others: POSS, poly(phthalocyanines), many colloids (colloids are close relatives of polymers)

R used to be a secret. Not sure if it still is.

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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)

Tomalia @ DowNewkome @ LSU

Tomalia: now at MMINewkome: now at U. Akron

Future Nobelists?

The poly(phenylene) dendrimer at left has actually been crystallized (Mullen).

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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)-graft-poly(butadiene)

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Some chemists really care about nomenclature.

Type Connective Example

unspecified -co- poly(A-co-B)

statistical -stat- poly(A-stat-B)

random -ran- poly(A-ran-B)

alternating -alt- poly(A-alt-B)

periodic -per- poly(A-per-B-per-C)

block -block- polyA-block-polyB

graft -graft- polyA-graft-polyB

From the Chemistry at U. Missouri Rolla website

James Traynham—LSU, 2003

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Star polymers have the ability to act a little bit like spheres and you can get higher M’s.

f = 4

Each “arm” of this star is a “random coil”. Star rods would be fun.

What does that mean?

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?

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Letter polymers are synthetically challenging and useful for testing theories.

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”

From the Mays website

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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.

S

N

S

N

* *n

Rodlike because of helix

Used in stealth bomber?Maybe.

Rodlike because of linear backbone

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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)

Sodium polystyrene sulfonate: fully charged, yet behavior depends on added salt

Weak polyelectrolytes (e.g., weak polyacids or polybases)Poly(acrylic acid)Behavior depends on added salt and pH

One of the hottest areas of fundamental polymer research involves polyelectrolytes. Concentration of charge along a backbone, with charged groups closely separated, produces some weird distortions in the molecules…and in the surrounding solution. Opposites may repel!

CH3

SO3NaMonomer:

CH2=CH-COOHMonomer:

Do they still tell you about Angstroms?

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You are made of biopolymers.

R group varies one unit to the next

N

H

R

O

n

H

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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 = FunctionMore Structure = More Function

S-S link

Subunit Subunit Normal synthetic polymer

Protein

-Helical secondary structure

-sheet secondary structure

http://www.sciencecollege.co.uk/SC/biochemicals/bsheet.gif

http://www.search.com/reference/Alpha_helix

Beta sheetAlpha helix

http://www.biosci.ohio-state.edu/~prg/protein1.gif

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There are 20 common, naturally occurring amino acids. Name Formula 3-letter

Symbol Simplified Symbol

ALIPHATIC Alanine -CH3 Ala A Valine -CH(CH3)2 Val V Leucine -

CH2CH(CH3)2 Leu L

Isoleucine CH(CH3)-C2H5

Ile I

NONPOLAR Glycine H Gly G Proline XXX Pro P Cysteine -CH2SH Cys C Methionine -C2H4-S-CH3 Met M AROMATIC Histidine XXX His H Phenylalanine -CH2- Phe F Tyrosine -CH2--OH Tyr Y Tryptophan XXX Trp W POLAR Asparagine CH2CONH2 Asn N Glutamine C2H4CONH2 Gln Q Serine CH2OH Ser S Threonine CH(OH)CH3 Thr T CHARGED Lysine -C4H8NH3+ Lys K Arginine XXX Arg R Aspartate CH2COO- Asp B Glutamate C2H4COO- Glu E

http://www.genome.iastate.edu/edu/gene/genetic-code.html#Amino Acids

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Another type of biopolymer, nucleic acids, contains the information needed to make proteins.

Borrowed fromNatural Toxins Research Center Webpage:

http://ntri.tamuk.edu/cell/nucleic.html

An interesting sub-section of the nanotech community tries to use nucleic acids as structural materials.

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Biopolymers: Nucleic Acids

RNA DNA

CH2

O

PO

OH

O

OCH2

O

OH

PO O

OH

OCH2

O

PO O

OH

O

OPO

O

O

CH2

O

PO O

OH

O

OH

OH

N N

O

O

HU

N

N

N

N

NH

N N

O

NH2

OH

N

N

N

N

O

NH2

A

C

G

Ribose sugar Base

NN

NN

O

OP

O

O

OH

CH2

O

O

OPO

OH

CH2

O

O

OPO

OH

CH2

O

O

OPO

OH

CH2

O

PO O

O

N

N

CH3 O

O

H

N

NO

NH

H

N

N

NH

H

NN

O

NH

H

CH3

N

N

N

NNH

O

H

H

NN

NNH

H

N

N

O

O

H

N

NO

NH

H

O CH2

O

P OO

OH

O

O CH2

O

P O

OH

O

O CH2

O

P O

OH

O

O

O CH2

O

P O

OH

T

G

A

C

A

C

T

G

3'

5'

5'

3'

.....

......

...

........

.........

.....

........

..

.....

....

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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/genetic-code.html#Amino Acids

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Networks (Gels) combine the properties of liquids and solids.

Keep on branching. The ultimate molecule: M =

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.

High-Speed Jello VideoCLICK IT!

High-Speed Jello VideoCLICK IT!

The Gentrys Sing Keep on Branching (or something like

that) CLICK FOR SONG! High-speed Jello Video

CLICK IT!

Pathetic Cover of Keep on Branching by Boy Band Bay

City Rollers CLICK FOR SONG!

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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)

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).

Silica-Polypeptide Composite Particles

Paul S. Russo (Louisiana State University), DMR-Award #1005707

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.

Question 1: Is the bumper a thermoset or a thermoplastic?Question 2: Suppose instead of a torn bumper we had a gashed tire made from vulcanized rubber. Would heating a vulcanized rubber repair the tire? Question 3: Explain how polymer welding works at a molecular level.

↑Grad student Javoris Hollingsworth teaches 8th-grader Hayden Day, the 2012 Louisiana state champion in the Chemical Educational Foundation’s You Be the Chemist Challenge, about titrations. Barely visible in the background is Hayden’s Mom, a school teacher. Hayden’s father, a chemical plant technician, is looking on too. Dad studied every day with his son, and Hayden acquitted himself well in the national competition in Philadelphia in June.

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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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TransitionsWe 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.