P olymer science or macromolecular science is a subfield of materials science concerned with polymers, primarily synthetic polymers such as plastics and elastomers. The field of polymer science includes researchers in multiple disciplines including chemistry, physics, and engineering. Polymers which have been around, and which are in current widespread use, include polyethylene, polypropylene, PVC, polystyrene, nylons, polyesters, acrylics, polyurethanes, and polycarbonates.

Mechanical Properties: – Thermodynamics: Conservation of energy –Kinetics: Deformation: Viscoelasticity (Strain or stress controlled experiments) Failure: Observed Strength << Calculated Strength Role of Defects Failure Process: Initiation + Growth of Cracks. Mechanism of Failure: Modes of Energy Absorption Two principal tools: –Stress –Strain Behavior (tensile, shear, flexural tests, etc…) –Impact (Charpy, Izod tests)

Semicrystalline Polymers o Number of interspherulite links increases with molar mass and “purity”. More links, more ductile deformation. o Deformation Mechanism: o Stretching of amorphous chains. o Shear yielding of crystallites. o Void formation (stress whitening). o Recrystallizationwith orientation.

Stress –Strain Behavior of Polymers : Slow deformation (in/min) Five regions (at most) –Elastic region –Yield (intrinsic, extrinsic) –Strain softening –Cold drawing –Strain hardening –Failure Mechanical Properties –Young’s modulus –Yield stress and strain –Strength, Ultimate elongation –Toughness Stress-Strain Behavior sometimes does not tell you about toughening. Needs to measure fracture energy (total energy dissipated duringcrack growth) or do impact tests for toughness at high strain rates.

Elastomers Rubber is the most important of all elastomers. Natural rubber is a polymer whose repeating unit is isoprene. Much of the rubber used in the United States and whole world today is a synthetic variety called styrene-butadiene rubber (SBR). Initial attempts to produce synthetic rubber revolved around isoprene because of its presence in natural rubber. So, Natural and other synthetic rubber materials are quite important. Plastics Polymers are the raw materials (the resins) used to make what we commonly call plastics Created after one or more polymers or additives have been added to a resin during processing, which is then shaped into a final form. Plastics are generally classified as "commodity", "specialty" and "engineering" plastics. Among the most important and versatile of the hundreds of commercial plastics is polyethylene because, based on its structure, it can be produced in many different forms.

PVC inexpensive, and annual production quantities are large from artificial leather to electrical insulation and cabling, packaging and containers.The versatility of PVC is due to the wide range of plasticizers and other additives that it accepts which (additives) in polymer science refers to the chemicals and compounds added to the polymer base to modify its material properties FIBER fibers are at least 100 times longer than they are wide. Typical natural and artificial fibers can have axial ratios (ratio of length to diameter) of 3000 or more. Synthetic polymers have been developed that posess desirable characteristics, such as a high softening point to allow for ironing, high tensile strength, adequate stiffness, and desirable fabric qualities. Nylon is synthetic fiber, known for its strength, elasticity, toughness, and resistance to abrasion, has commercial applications including clothing and carpeting. very elastic however has the limit.

Polymer Structure  Terms configuration and conformation are used to describe the geometric structure of a polymer.  Configuration refers to the order that is determined by chemical bonds. The configuration of a polymer cannot be altered unless chemical bonds are broken and reformed.  Conformation refers to order that arises from the rotation of molecules about the single bonds.

Configuration  two types of polymer configurations are cis and trans.  can not be changed by physical means  cis configuration arises when substituent groups are on the same side of a carbon- carbon double bond.  Trans refers to the substituents on opposite sides of the double bond.

Stereoregularity  describe the configuration of polymer chains.  Three distinct structures can be obtained :  Isotactic is an arrangement where all substituents are on the same side of the polymer chain.  Asyndiotactic polymer chain is composed of alternating groups  Atactic is a of the groups random combination. The following diagram shows two of the three stereoisomers of polymer chain. isotatcic Syndiotactic

Conformation  The ability of an atom to rotate this way relative to the atoms which it joins is known as an adjustment of the torsional angle.  So, if the two atoms have other atoms or groups attached to them then configurations which vary in torsional angle are known as conformations.  Different conformations represent varying distances between the atoms or groups rotating about the bond t  hese distances determine the amount and type of interaction between adjacent atoms or groups, different conformation may represent different potential energies of the molecule.  There several possible generalized conformations:  Anti (Trans)  Eclipsed (Cis)  Gauche (+ or -)

# So, isotropic is body center cubic and anisotropic (calcite & amorphous) are face center cubic.