Exam 2 Review Flashcards
What is polymer synthesis/polymerization?
The process by which monomers are linked together to generate long chains composed of repeat units.
What is initiation?
Monomer is activated by a reaction with a catalyst.
What is propagation?
Monomers continue to add to the polymer chain; increase in molecular weight, active site is transferred.
What is termination?
active sites link together (combination) or active site is destroyed and two dead chains form (disproportionation)
Will molecular weight be relatively high, medium, or low for slow initiation, rapid propagation, and slow termination?
High, fewer chains grow for a longer time
Will molecular weight be relatively high, medium, or low for rapid initiation, slow propagation, and rapid termination?
Medium, many chains are growing simultaneously.
What are the characteristics of condensation polymerization?
More than one type of monomer (usually), no radical initiator required, occurs by the elimination of one molecule, higher molecular weights require higher reaction times, variable chain length produced.
What is the purpose of polymer additives?
Added to enhance or modify chemical, mechanical, or physical properties of polymers.
What are fillers?
Inexpensive materials that replace some volume of more expensive volume of more expensive polymer
What do fillers do?
Improve tensile and compressive strength and increase thermal stability.
What do plasticizers do?
Increase flexibility and ductility, decrease stiffness. Occupy positions between large polymer chains, which increases the interchain distance and reduces secondary intermolecular bonding.
What do stabilizers do?
Increase mechanical integrity by counteracting degradation
What are phase diagrams?
Maps which incorporate T, P and composition to present the equilibrium state of materials (called phase equilibria).
True or false: A single phase material has the same composition structure at every point.
True
What is a component?
A chemically distinct, essentially indivisible substance; the species that are mixed together in a system.
What is the solubility limit?
The max concentration of solute atoms that may dissolve in solvent to form a solution.
What does phase equilibria tell you?
As you increase temperature, solubility limit increases. Thus, more solute will dissolve in solvent, until another equilibrium point is reached.
What are the characteristics of one-component heart phase diagrams?
Composition is held constant, pressure and temperature are variables. Three different phases: solid, liquid, gas. Three curves are phase boundaries. At any point on the two curves, the two phases are in equilibrium.
What is a two-component binary phase diagram?
Pressure is constant (~1 atm), relationship between temperature and composition.
What are the steps to determine the phase amount present at equilibrium as a fraction/percent?
- Tie line is constructed across the two-phase region at the temperature of the alloy.
- The overall alloy composition is located on the tie line.
- Fraction of the phase is determined (W) —> specified in terms of only one constituent
The mass fraction is proportional to what?
The opposite lever arm
What must W sub a plus W sub L equal of there are only 2 phases present?
1
