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13 Cards in this Set
- Front
- Back
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What are the two main mechanisms through which polymers degrade?
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1) swelling/dissolution
2) chain scission |
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Where does swelling take place in polymers?
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In the hydrophilic domains, since solvent molecules are absorbed into polymer and are small enough to occupy spaces between the macromolecular chains
This affects secondary bonding |
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What happens to polymerse if there are few covalent bonds between chains and if they are soluble enough?
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the polymer may dissolve completely in an aqueous environment
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What are some possible ways to reduce swelling?
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LOOK UP NOTES!
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What is chain scission?
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The breaking of primary bonds, where chain segments are separated at point of bond rupture which leads to overall decrease in molecular weight
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What are two ways through which chain scission occurs?
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hydrolysis or oxidation reactions
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What occurs during oxidation chain scission?
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Highly reactive species break down and attack the covalent bonds in susceptible chemical groups within macromolecule
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What does the rate of oxidation chain scission depend on?
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1) Susceptible chemical domains
2) Molecular weight- lower MW are less tightly cross linked and will degrade more rapidly because there are less primary bonds to break |
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What is metal catalyzed oxidation?
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1) fissures resulting from metal catalyzed oxidation found on the interior of a polymer coating that is in contact with a metal wire.
2) caused by corrosion of metal: releases oxidizing agents that in turn oxidize the polymer 3) results in brittle fractures |
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What is the process by which water molecules facilitate the cleavage of certain bonds in a macromolecule
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hydrolysis
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What are the factors that affect the extent of polymer hydrolysis?
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1) Reactivity of groups in polymer backbone
2) Extent of interchain bonding 3) Amount of media (water) available to the polymer |
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Why is hydrolysis a common degradation method of condensation polymers?
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LOOK IN NOTES!!!
Hydrolysis sets off initiation of polymerization |
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How do enzymes affect degradation?
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Enzymes lower the activation energy required for specific reactions, they have an affinity for certain groups
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