Polymer Classifications: Foreword.

1. Polymer Classifications: Foreword. This presentation is to be used with Chapter 2 of the Virtual Book. Students can complete their virtual book thusly: • Make simple sketches and write ideas during the class when this material is presented. • Improve that by making better sketches and editing a downloaded copy of Chapter2.

2. Linear polymers can be represented by a simple sequence such as: A-A-A-A-A . Polystyrene Styrene monomer Nylon Two monomers make one repeating unit.* Nylon 6,6 *There many different kinds of nylon.

3. # # size size size 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 Paucidisperse Monodisperse # Even in a pure sample, not all molecules will be the same. Nature often does better than people do.

4. Chain growth Step growth

5. Addition: one monomer at a time Also called chain growth. Condensation: anything goes! Also called step growth.

6. 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!

7. R’ --[P=N]-- x R There are such things as inorganic polymers. R used to be a secret. Not sure if it still is. Others: POSS, poly(phthalocyanines), many colloids (colloids are close relatives of polymers)

8. 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

9. The poly(phenylene) dendrimer at left has actually been crystallized (Mullen). The arboroldendrimer below was made by Newkome at LSU….and we still make this one at LSU.

10. Block copolymer, example: Poly(styrene)-block-poly(butadiene) Copolymers can be used to tailor functionality or generate new phases and behaviors. Random copolymer, example: Poly(styrene-ran-butadiene) Graft copolymer, example: Poly(styrene)-graft-poly(butadiene)

11. Some chemists really care about nomenclature. James Traynham—LSU, 2003 From the Chemistry at U. Missouri Rolla website

12. f = 4 What does that mean? Star polymers have the ability to act a little bit like spheres and you can get higher M’s. 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.

13. 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”

14. Combs, brushes and ladders give you ways to stiffen a polymer. Think “bottle brush”

15. Rodlike polymers are used for very high strength, liquid crystals, photonics, efficient viscosification and control of phase relations. Rodlike because of linear backbone Used in stealth bomber? Maybe. Rodlike because of helix

16. Polyelectrolytes: strange things happen when you try to separate charges by a few Angstroms. Do they still tell you about 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 Monomer: 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 some weird distortions in the molecules…and in the surrounding solution. Opposites may repel!

17. You are made of biopolymers. R group varies one unit to the next

18. 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”.

19. 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

20. Protein a-Helical secondary structure Normal synthetic polymer Subunit a Subunit b b-sheet secondary structure S-S link Structure = FunctionMore Structure = More Function http://www.sciencecollege.co.uk/SC/biochemicals/bsheet.gif Alpha helix Beta sheet http://www.search.com/reference/Alpha_helix http://www.biosci.ohio-state.edu/~prg/protein1.gif

21. There are 20 common, naturally occurring amino acids. http://www.genome.iastate.edu/edu/gene/genetic-code.html#Amino Acids

22. 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 to use nucleic acids as structural materials.

23. Biopolymers: Nucleic Acids DNA RNA

24. 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

25. Networks (Gels) combine the properties of liquids and solids. Keep on branching. The ultimate molecule: M =  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! High-Speed Jello Video CLICK IT! 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.

26. 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)

27. 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. 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.

28. 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.

29. 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.