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Forest Biomaterials Chemistry Introduction to Polymers

Opening Topic for Spring 2013 Class
by

Lucian Lucia

on 17 January 2013

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Transcript of Forest Biomaterials Chemistry Introduction to Polymers

WPS 723, Spring 2013
Lucian A. Lucia
lucian.lucia@gmail.com
T/R, 10:15am - 11:30am
Biltmore 2006 What are "polymers" and "biomaterials"? Refineries Take Home & Think! Petroleum crude is the lifeblood of civilization

Crude is “light, sweet” = (low , low S)

Crude must be fractionated to derive maximum value

Distillation is how crude is fractionated

The final products are plastics, solvents, elastomers, synthetic fibers, detergents, and fuels Before 1930, polymers were believed to be colloidal aggregates of many small molecules

Hermann & Staudinger showed polymers = macromolecules

Macromolecules characterized by repeat unit(s) = monomer

Homopolymer, copolymer characterized by COVALENCY and sequencing of monomeric bonding What is a "polymer"? Find three polymeric materials you use each day and determine the major component. Is it crystalline? Tacticity? If don’t know, hypothesize.
Why was this component used to manufacture each particular material?
Specify the deficiencies and advantages of each material and how you would improve upon it if you could. Vocabulary:
petroleum, distillation, colloids, bonding forces, crystallinity, tacticity The Classic refinery Biomass
Feedstock Pulping
Enzymatic Fermentation
Gas/liquid Fermentation
Acid Hydrolysis
Gasification
Combustion
Co-firing Trees
Agricultural Crops
Agricultural Residues
Animal Wastes
Municipal Solid Waste Sample Products

Fuels:
Ethanol
Renewable Diesel

Power
Electricity
Heat

Chemicals
Plastics
Solvents
Chemical Intermediates
Pharmaceuticals
Phenolics
Adhesives
Furfural
Fatty Acids
Acetic Acids
Carbon Black
Paints
Dyes, Pigments
Detergents

Paper Products

Food and Feed Conversion
Process Article of Interest:
"Spider Silk: Ancient Ideas
for New Biomaterials." Chem. Rev.
2006, 106, 3762-3774 Copied with permission from Mr. Daniel Kurtzman, About.com The Crux of the Problem: Petroleum Copied with permission from Mr. Daniel Kurtzman, About.com Biomacromolecular (polymer) understanding is key to all of our work
Very good MOEs and fracture resistance
Ease of manufacture/availability
Relatively inexpensive
RENEWABLE RESOURCE !! Animal & vegetable matter are key to our sustenance

Wood is key to our shelter

Asphalt used in pre-Biblical times (mostly bitumens, hydrocarbons)

Amber known to ancient Greeks (tree resins)
Macromolecules – what are they? Until 1920, NOT considered as such

Considered as “colloidal” state of matter

High MWs of polymers considered erroneous

Complexation of small molecules considered basis of high MW Are Polymers Macromolecules? Ionic bonding – not usual in polymers except to bridge carboxylates of adjoining chains such as in ionomers

Covalent bonding – stable octets between atoms is achieved

Coordinate bonding – the shared electrons of the “bond” come from one atom (hybrid); no commercial polymers Bonding Paradigms: Primary Forces Dipole – a molecule can have a dipole based on its atomic dipoles: can lead to attraction

Dispersion – fluctuations in valence cloud of electrons lead to perturbations in neighboring atoms: attraction as well

Induction – the influence of a polar molecule on surrounding molecules that do NOT have dipoles: related to polarizability

Hydrogen – strongest of secondary forces; essential to life, bonding effect from 2.4 – 3.2 Å and 12 – 30 kJ/mol in dissociation energy; among F, N, O, and sometimes Cl Bonding Paradigms: Secondary Forces Polyvinyl chlorides Polyesters Polyethers Structures of Polymers Quiz I Cross-linked Branched Linear Polymer Configurations Glycine Polyamides Polyethylene





Polypropylene Structures of Polymers Quiz II Volatility, viscosity, surface tension, tribology, miscibility, & solubility (why important?)
Cohesive energy – required to remove atom/molecule from neighbors: for polymers, it is usually higher than decomposition energy (thus, what happens?)
PE  259 J/cc; Polyacrylonitrile (-CH2CH[CN]-)  992 J/cc
1 J = energy required (approximately) to lift a small apple one meter straight up Intermolecular Forces & Physical Properties Near field polarimetry of spherulites illustrating retardance (a,b) and topography (c,d): Appl. Phys. Lett. 2004, 85, 1338-1340. Lattice packing structure as observed in molecular aggregates does not apply
Characterized by three-dimensional ordering of units with respect to each other – may have regions of amorphous packing
Characteristic melting points as opposed to glass transition temps Crystallinity Organizational principle in nature – symmetry
Hierarchical Bonding
Strength & rigidity
Type of assembly predominant in higher order structures Why is Crystallinity Important? How is the packing affected? Z-Polyisoprene: amorphous material since packing
is prevented by interchain steric hindrance and methyl
group buttressing Influence of Stereochemistry on Crystallinity We go together like
rama lama lama
ke ding a de dinga a dong
remembered for ever like
shoo bop shoo wadda wadda yipitty boom de boom

Chang chang chang-it-ty chang
shoo-bop
That's the way it should be
Wha oooh yeah! E-Polyisoprene (gutta-percha rubber)  rigid
crystalline material due to concavities for insertion
of methyl groups Crystallinity of E-Polyisoprene H polymerization Polypropylene polymerization can produce a variety of products
The number 2 carbon is prochiral, hence it has options for stereochemistry during bonding (what are R & S forms of Br, C, F-methane Influence of Prochiral Centers on Crystallinity Atactic – the configurations for the chiral carbon along the chain of polymerization are RANDOM (“A” – without TACT)
Isotactic – the configurations for the chiral carbon along the chain of polymerization are IDENTICAL (“iso” – SAME TACT)
Syndiotactic – the configurations for the chiral carbon along the chain of polymerization are ALTERNATION (“Syndio” – PATTERN TACT)
What type of properties arise, therefore? Notice that all phenyl groups are on
same side of the hydrocarbon back-
bone. 4: 3: 2: 1: Tacticity: Introduction Tacticity: Illustration of Concept Free-radical vinyl polymerization is a very random order process!

Catalysis came along in the form of Ziegler-Natta & metallocene catalysis polymerization

Allowed for synthesis of syndiotactic polystyrene (crystalline, mp = 270°) & isotactic PP (crystalline, indoor/outdoor carpeting)
We will explore isotactic polymerizations in this lecture How to Achieve Tacticity? Need a catalyst/co-catalysts system such as TiCl3 & Al(C2H5)2Cl
The titanium complexes into an -array in which each Ti is octahedrally coordinated, but at the surface this is NOT the case
Since it is missing one dative bond, it gets it from the Al, but at the expense of losing a Cl, so it is still “impoverished”
In the event of a vinyl “visit,” an interesting development is posed! Ziegler-Natta Vinyl Polymerization Open site (deficiency) on Ti is compensated by a double bond
Blue orbital of vinyl monomer = bonding
Red = antibonding
The green orbital (Ti) lobes comprise the empty site
The pink lobes allow for backbonding to the antibonding C=C orbital lobes
In sum, a very strong complex is formed! Ziegler-Natta, Continued Process begins again! But notice that the methyl groups are all on the same side of the chain! All molecules that enter this “domain” attach the same way Another coordination
site! Migration 3: 2: 1: Ziegler-Natta, Final: Isotactic Polymerization Same principles apply as in Ziegler-Natta, except we use metallocenes as catalysts
This complexation stabilizes the zirconium
Another migration occurs in this complex as seen in the Ziegler-Natta polymerization Metallocene Catalyzed Polymerizations The zirconium now lacks a ligand, but engages in an -agostic bond with the methine H
Another propylene can enter to react as the initial one
BUT, from the other side of the complex
This ensures isotacticty Metallocene Catalyzed Polymerizations, Part II http://www.wdv.com/CellWorld/Biochemistry/Latex/ http://www.chemistrylearning.com/rubber/
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