Amorphous disordered How do the properties change when T T g When T T g

# Amorphous disordered how do the properties change

This preview shows page 25 - 29 out of 29 pages.

How do the properties change when T < Tg? When T > Tg? g
Plasticizers Small organic molecules that act as lubricants Lower Tg, make material flexible Dialkyl phthalates are commonly used as plasticizers Due to safety and health questions they have been banned in children’s toys Fibers Thin threads produced by extruding molten polymer through small holes in a die, or spinneret Fibers are cooled and drawn out orienting the crystallite regions along the axis of the fiber Contain considerable tensile strength Extend – gets stronger = more ordered Elastomers Amorphous polymers that stretch out and spring back to original shapes Entropy driving force for its return. Low T g values and small amount of cross-linking Molecular weight: M Mass of a mole chains
Not all chains in a polymer are the same length because there is a distribution of molecular weights. Degree of Polymerization : average number of repeat unit per chains M= the molecular weight of the repeating units. Number Average Molecular weight: the sum of the products of the molar mass of each fraction multiplied by its mole fraction. Where x i is the mole fraction of molecules of length i , the ratio of the number of molecules of length i , n i , to the total number of molecules, n . m is the mass of each species: M w ≥ M n Molecular weight Distribution curve: Synthetic polymers have molecules that vary in molecular weight: Natural products such as proteins and peptides have a single defined molecular weight and are called monodisperse 1 1 2 2 3 3 1 1 2 3 1 . . . . . . n i i i n n i i n M n M n M n M M n n n n = = + + + = = + + + å å
The relative viscosity rev : the ration of the viscosity of the solution , to the velocity of the pure solvent o .

#### You've reached the end of your free preview.

Want to read all 29 pages?

• Spring '17
• Polymer, Erythromycin