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BIO 109

Prof. Edith Mathiowitz

Introduction (2 hr.) Suggested reading: 1) Young Ch. 1 2) Notes 3) Rosen I,II Topics:

Polymers as materials Distinction between synthetic polymers,

biopolymers, primary & secondary tertiary structure, (Cantor Schimmel)

Types of polymers, thermoplastics, thermosets

Basic definitions and nomenclature Bonds in polymers: bond distance

and strengths Molecular architecture and classification

of polymers Molar mass and degree of polymerization Stereoisomers: atactic, isotactic, syndiotactic

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From the preface of the first edition of Principle of Polymer Systems by Ferdinand Rodriguez.

A man was asked the question "Do you have trouble making decisions?" He thought for a while and then finally answered "Well, yes and no."

The engineer or scientist who is asked to make generalizations about polymers often finds himself in the same position.

In the interests of organizing the body of information about polymers which has accumulated since Baekeland, Staudinger, Mark, Carothers, and other pioneers started their word, there is a tendency to over generalize.

From the preface of the first edition of Principle of Polymer Systems by Ferdinand Rodriguez.

In the older literature one finds such pronouncements as: "All polymer crystals are submicroscopic," "Five-membered rings are too stable to be opened to form linear

polymers, "Maleic anhydride cannot be homopolymerized," "Stereoregular polymers can be made only with an optically active

catalyst." All of these have been disproved or qualified. In this book, any

generalizations that are encountered are subject to the following caveat:

"All generalizations are partially untrue, except this one. (from Fundamentals of Polymeric Materials by Rosen, Ch. 1)

INTRODUCTION Since World War II, polymeric materials have been the fastest growing

segment of the US chemical industry.

More than 25% of the chemical research dollar is spent on polymers.

A modern automobile contains over 200 lbs. (100 kg) of plastics, (not including paints, the rubber in tires, or the fibers in tires and upholstery).

The applications of polymers in the building construction industry (piping, resilient flooring, siding, thermal and electrical insulation, paints, decorative laminates, etc., etc.) are already impressive and will become even more so in the future.

A trip through a supermarket will quickly convince anyone of the importance of polymers in the packaging industry (bottles, films, trays, etc.).

****(your first project this year locate a topic)****

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There are eight major areas of application for polymers:

(1) plastic, (2) rubbers or elastomers, (3) fibers, (4) surface finishes and protective coatings, (5) adhesives, (6) biopolymers, (7) drug delivery and (8) gene delivery. (9) tissue engineering

What is the common need for each area?

It was only after Dr. Herman Staudinger proposed the "macromolecular hypothesis" in the 1920s explaining the common molecular makeup of these materials (for which he won the 1953 Nobel Prize in chemistry), that polymer science began to evolve from the independent technologies.

Polymers are important because of:

Economic considerations Interesting and useful properties that

cannot be explained or handled in design situations by the traditional approaches

Flexible Strong Versatile properties

A description of three simple experiments should make this obvious:

Silly putty- a silicone polymer; bounces like rubber when rolled into a

ball and dropped; if the ball is placed on a table, it will gradually spread to a puddle. The material behaves like an elastic solid under certain conditions and like a very viscous liquid under others.

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A description of three simple experiments should make this obvious:

If a weight is suspended from a rubber band and the band is then heated (taking care not to burn it),

the rubber band will contract . All materials other than polymers will undergo the expected

thermal expansion upon heating (assuming no phase transformation has occurred over the temperature range).

A description of three simple experiments should make this obvious:

When a rotating rod is immersed in a molten polymer or a fairly concentrated polymer solution,

The liquid will actually climb up the rod. This phenomenon, the Weissenberg effect, is contrary to

what is observed with non-polymer liquids. Those develop a parabolic surface profile with the lowest

point at the rod as the material is flung outward by centrifugal force.

The molecular structure of polymers is the key to an understanding of the science and technology of polymers. The question to be considered Is: what are the key roles of molecular structure in polymer science and technology ?.

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Points to be considered

(1) How is the desired molecular structure obtained? (2) How do the polymer's processing (i.e. formability)

properties depend on its molecular structure? (3) How do material properties (mechanical, chemical,

optical, etc.) depend on molecular structure? (4) How do material properties depend on a

polymer's processing history? (5) How do its applications depend on its material

properties?

What is a polymer ?

Polymer: Molecule made by repetition of some simpler unit, the mer or monomer.

Polymer: comes from the Greek many-membered.Large molecule that is formed from a relatively large number of smaller units or "mers," held together by covalent bonding.

Macromolecules: (big molecule) Molecules built from a large number of atoms which can be found in materials of natural origin, like cellulose, proteins, and natural rubber, or those synthetically produced, like polyethylene, nylon, and silicones.

Macromolecules consist of at least one chain of atoms bonded together and running through the molecule's backbone.

Backbone consisting of carbon atoms: R ( C H2)nR' (polyethylene) Backbone consisting of carbon and oxygen atoms: R ( O C H2CH2)nR' ( p o lyoxyethylene) Backbone consisting of carbon and nitrogen atoms: R ( N H - C H R " - C O )nR' (polypeptide) Backbone containing no carbon atoms: R ( O - S i ( C H3)2)nR '(poly(dimethyl siloxane)) n = degree of polymerization (DP) = number of repeat units in a chain A simple calculation of molecular weight(MW): MW = Mr X n where Mr = weight of the repeat unit

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SIZE AND COMPLEXITY OF BIOPOLYMERS From Biophysical Chemistry - Cantor and Schimmel (Table 1-1)

Class Specific Example Typical SizeTypical MW Subunits

No. ofsubunits

Oligomers Actinomysin D 20 sphere 103-104 atoms (or residues) 100(or 10)Small proteins Chymotrypsin 40 sphere 104-105 amino acid residues(or atoms) 10

2-103(or 103-104)

Nucleic acids tRNA 100 rod 104-105 Nucleotide residues(or atoms) 102-103

(or 103-104)Large proteins Aspartate

transcarbamoylase70 sphere 105-107 Subunitsor covalent chains 10-10

2

Small assemblies Ribosome 200 sphere 105-107 Subunitsor covalent chains 10-102

Large assemblies Membranes, viruses

1000 sphere 107-1012 Regions, fragments,components 10-102

Intact DNA E. coli DNA 0.1 cm rod 107-1012 Regions, fragments,components 10-102

The whole system is called a single molecule when parts are present in a well-defined stoichiometry and when little tendency for them to dissociatespontaneously under physiological conditions.

LEVELS OF STRUCTURE IN BIOLOGICAL MACROMOLECULES

PRIMARY STRUCTURE The complete covalent structure Primary Structure (1 structure)

= sequence Typical linear polymers: Some

synthetic materials (e.g. polyamides) have no preferred chain direction, whereas other synthetics and most biopolymers are head-to-tail arrangements of monomers.

From Biophysical Chemistry - Cantor and Schimmel (Figure 1-2)

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SECONDARY STRUCTURE

(2 structure) (three-dimensional structure) - list of all three-dimensional regions that have ordered, locally symmetric backbone structures. (alpha helix, beta helix, random coil)

The geometry of a simple helix: The helix axis is coincident with the z-axis. P is the pitch, zo the vertical rise per residue.

The location of the zeroth residue is further specified by (which defines its position in the x-y plane). All identical repeating units are the same distance, r, from the helix axis; this distance is called the radius of the helix. The radius is shown more clearly in the top view. n the example illustrated, the helix is 8-fold, so the x and y coordinates of residues spaced eight residues ( 8 zo) apart are identical.

From Biophysical Chemistry - Cantor and Schimmel (Figure 1-3)

TERTIARY STRUCTURE

(3 structure) The complete three-dimensional structure of one, effectively indivisible unit. (simple covalent strand in RNA or two complementary double strands in most DNAs

Myoglobin, consisting mostly of helices, labeled A through H, and contains a heme group (dark) that binds oxygen.

From Biophysical Chemistry - Cantor and Schimmel (Figure 1-4))

QUARTERNARY STRUCTURE

(4 structure) non-covalent association of independent tertiary structure units.

Hemoglobin: There are four subunits, each with one bound heme. A twofold rotational symmetry axis exists in the center of the molecule perpendicular to the plane of the page.

From Biophysical Chemistry - Cantor and Schimmel (Figure 1-5)

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SELECTED CHRONOLOGY OF POLYMER SCIENC 1806 Gough (England) experiments with elasticity of natural rubber 1838 Regnault (France) polymerizes vinylidene chloride via sunlight 1859 Joule (England) demonstrates the thermodynamic principles of

elasticity of rubber 1884-1919 Emil Fisher (Germany) establishes formulae of many sugars

and proteins 1920 Staudinger (Germany) advances macromolecular hypothesis 1928 Meyer and Mark (Germany) measure crystallite sizes in

cellulose and rubber 1929 Carothers (U.S.) synthesizes and characterizes condensation

polymers 1930-1934 Kuhn, Guth, and Mark (Germany) derive mathematical models

for polymer configurations; theory of rubber elasticity WW II Debeye, light scattering of polymer solutions; Flory,

viscosity of polymer solutions; Harkins, theory of emulsion polymerization; Weissenberg, normal stresses in polymer flow

SELECTED CHRONOLOGY OF POLYMER SCIENC 1950's Ziegler, coordination of complex polymerization; Natta,

tacticity in polymers; Swarc, living polymers; interfacial

polymerization 1955 Williams-Landel-Ferry equation for time-temperature

superposition of mechanical properties 1957 Keller and Till, single crystals of polyethylene characterized 1960 T. Smith, the failure envelope 1960's NMR applied to polymer structure analysis Maxwell, orthogonal rheometer Moore, GPC analysis for molecular weight distribution Differential scanning calorimetry Marvel, polybenzimidazoles Gilham, torsional braid analysis 1970's Interpenetrating networks High-performance liquid chromatography

From Principles of Polymer Systems - Rodriguez (Table 1-5)

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SELECTED CHRONOLOGY OF POLYMER TECHNOLOGY 1770 Priestly givers rubber its name because it can

erase marks on paper 1839 Goodyear (U.S.) MacIntosh and Hancock

(England), vulcanization (crosslinking) of natural rubber

1860's Molding of natural plastics such as shellac and gutta-percha

1868 Hyatt (U.S.), celluloid (cellulose nitrate molded articles)

1891 Chardonnet (France), regenerated cellulose via nitrate

1893-1898 Cross, Bevan, Beadle, Stern (England), viscous rayon fibers

1907 Baekland (U.S.), phenol-formaldehyde resins 1910 First rayon plant in United States WW I Cellulose acetate solutions ("dope") for aircraft;

laminated plywood and fabric construction for aircraft fuselages

SELECTED CHRONOLOGY OF POLYMER TECHNOLOGY 1920's Cellulose Nitrate laquers for autos 1924 Cellulose acetate fibers 1926 Alkyld resins from drying oils for coatings 1927 Poly(vinyl chloride), cellulose acetate plastics 1929 Polysulfide (Thiokol) rubber, urea-formaldehyde

resins 1931 Poly(methyl methacrylate) plastics, neoprene

(Duprene) synthetic rubber 1936 Poly(vinyl acetate) and poly(vinyl butyral) for

laminated safety glass 1937 Polystyrene, styrene-butadiene (Buna S) and

acrylonitrile-butadiene (Buna N) rubbers (Germany)

1938 Nylon 66 fibers 1939 Melamine-formaldehyde resins, poly(vinylidene

chloride)

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SELECTED CHRONOLOGY OF POLYMER TECHNOLOGY

1940 Butyl rubber (U.S.) 1941 Polyethylene production (England) 1942 Unsaturated polyesters for laminates WW II Silicones, fluorocarbon resins, polyurethanes

(Germany), styrene-butadiene rubber in United States, latex-based paints

1947 Epoxy resins 1948 ABS polymers 1950 Polyester fibers 1948-1950 Acrylic fibers 1954 Polyurethane foams in U.S. 1956 Linear polyethylene, acetals [poly(oxymethylene)]

SELECTED CHRONOLOGY OF POLYMER TECHNOLOGY 1957 Polypropylene, polycarbonates 1959 Chlorinated polyether, synthetic cis-polyisoprene

and cis-polybutadiene rubbers 1960 Ethylene-propylene rubber, spandex fibers 1962 Phenoxy resins, polyimide resins 1965 Poly(phenylene oxide), polysulfones, styrene-

butadiene block copolymers 1960's Cyanoacrylate adhesives, aromatic polyamides,

polyimides, silane coupling agents 1970 Isotactic polybutadiene 1971 Poly(butyl terephthalate) 1970's Thermoplastic elastomers based on copolyesters,

poly(phenylene sulfide) 1977 Polynorbornene (rubber)

POLYMER CONSUMPTION IN THE UNITED STATES (IN UNITS OF 106 kg) 1968 1978 Plastics 6,870 16,124

Thermosets 1,423 3,037Alkyd 150 215Epoxy 70 143Phenolic 408 700Polyester(unsaturated) 244 549Polyurethane foams 277 840Urea and melamine 274 590

Thermoplastics 5,477 13,087Acrylic 145 253Cellulosics 87 74Nylon 33 126Polycarbonate 12 95Polyester(saturated) --- 280Polyethylene (high density) 545 1,893Polyethylene (low density) 1,364 3,249Polypropylene 377 1,389Polystyrene and other styreneics 1,416 2,741Poly(vinyl chloride) 1,095 2,641Others 373 346

Rubber (production figures) 3,149 3,234Natural rubber (consumption) 593 779Styrene-butadiene 1,488 1,377Polybutadiene 327 379Neoprene (with "other") 160Ethylene-propylene 116 174Butyl 154 152Nitrile 82 72Other 389 141

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POLYMER CONSUMPTION IN THE UNITED STATES (IN UNITS OF 106 kg)

1968 1978 Plastics 6,870 16,124

Fibers (consumption figures) 4,400 5,677Natural and mineral 2,240 1,769Cotton 1,885 1,287Wool 172 60Glass 183 422Synthetic organic fibers 2,160 3,908Rayon 548 253Cellulose acetate 220 137Nylon 578 1,156Polyester 459 1,722Acrylic 233 328Polyolefin 122 312

CLASSIFICATION SCHEMES

1. STRUCTURE: Does the polymer exist in a mass of separable, individual molecules or as a macroscopic network?

2. PHYSICAL STATE: The polymer could be crystalline or completely disordered, molten, or glassy.

3. REACTION TO THE ENVIRONMENT THERMOPLASTIC: Materials that soften and flow upon

application of pressure and heat. THERMOSET: materials that react irreversibly once heated.

4. CHEMICAL: The elemental composition of a polymer, the chemical groups which are present.

5. FINAL USE: Adhesives, fiber, rubber, biomaterials

MOLECULAR ARCHITECTURE Thermoplastics: referred to as plastics are linear or branched

polymers which can be melted upon the application of heat. Can be molded and remolded. Make up the largest bulk of polymers used. Can be sub-divided into polymers that crystallize on cooling and those

which do not - polymer glasses. Crystallization depends on the degree of branching, and the regularity

of the molecules. Crystalline thermoplastics are only partly (semi-) crystalline and do not

crystallize completely when cooled from the melt.

Schematic representation of different types of polymer molecules.

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MOLECULAR ARCHITECTURE

Rubbers: materials which display elastomeric properties. They can be stretched easily to high extensions and will spring back

rapidly when the stress is released. This property is a reflection of the molecular structure of the polymer

which consists of a highly cross-linked macromolecular network. The molecules slide past each other on deformation, but the cross-

links prevent permanent flow and the molecules spring back to their original position on removal.

Schematic representation of different types of polymer molecules.

POLYMER CLASSIFICATION Polymers

Thermoplastics Rubbers Thermosets

Liquid-crystalline Crystalline Amorphous

Classification of polymers

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SINGLE POLYMER MOLECULES The single molecules may be

linear or branched (Fig. 2-1). In a polymer chain that contains

carbon atoms with two different substituents, the carbon is

asymmetric. Asymmetric atoms can exist in

two different spatial configurations which are not interchangeable without breaking covalent bonds-optical isomerism.

SINGLE POLYMER MOLECULES

Example: Consider the case of polypropylene with the repeating unit:

CH3 | [CH2CH] Every other carbon is asymmetric.

Three structures can result. These visualized by looking at the main polymer chain in an extended planar zigzag conformation. Changes in structure are caused by rotations about single bonds are termed conformations and isomers that cannot be interchanged without bond

breaking are termed configurations.

Figure 2-1: Polymer arrangements MOLECULAR STRUCTURE

Linear

Branched

Crosslinked (network)

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SINGLE POLYMER MOLECULES

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BONDING IN POLYMERS

Types of bondsVarious types of bonding hold the atoms together inpolymeric materials, as opposed to metals, for example, where onlyone type of bonding exists. These types are:(1) primary covalent,(2) hydrogen bonding,(3) dipole interaction,(4) van der Waals, and(5) ionic, examples of which are shown in Fig. 3.1.Hydrogen bonding, dipole interaction, van der Waals, and ionicbonding are known collectively as secondary forces.

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BONDING IN POLYMERS

Bond distances and strengthsThe potential energy of the interacting atoms as a function of the separation between themrepresented qualitatively by the potential function sketched in Fig. 3.2. As the interacting centers are brought together from large separation, an increasinglygreat attraction tends to draw them together (negative potential energy).Beyond the separation rm, as the atoms are brought closer together, their electronic"atmospheres" begin to interact, and a repulsion is set up. At rm the system is at a potential energy minimum, most probable equilibriumseparation, the equilibrium bond distance., is the energy required to break the bond.Primary covalent bonds are stronger than the others.As the material's temperature is raised and its thermal energy (kT) is thereby increased, theprimary covalent bonds will be the last to dissociate when the available thermal energyexceeds the dissociation energy.

EQUIVALENTS FOR SELECTED SI QUANTITIES Quantity SI unit Value in CGS units Value in British units

Mass kg 1000 g 2.2 lb. Length m 100 cm 3.281 ft Area m2 10,000 cm2 10.76 ft2 Volume m3 1,000,000 cm3 or 35.31 ft3 or 1000 liter 264.2 gal (U.S.) Force N 100,000 dyn 0.2248 lbf Energy J, N-m 10,000,000 erg or 0.7376 ft-lbf or 0.2389 cal 0.9481 x 10-3 Btu Pressure Pa, N/m2 10 dyn 1.45 x 10-4 psi Viscosity Pa-s 10 P (poise) 6.72 lbm/ft-s Power W, J/s 1 x 107 erg/s or 1.341 x 10-3 hp or 14.34 cal/min 3.413 Btu/h Specific heat J/kg-K 238.9 cal/g-C 238.9 Btu/lbm-F Heat transfer W/m2-K 0.2389 cal/m2-s-C 0.1761 Btu/ft2-h coefficient Impact strength J/m 1.873 x 10-2 ft-lbf/in