Mats Lecture 9 Flashcards
Polymers
How is the Polyethylene polymer formed?
-Starts off the ethylene molecule (stable)
-ethylene has a double covalent bond between the two C atoms
-If the double covalent bond is broken, the ethylene molecule becomes a “free radical” which will react with neighbouring molecules
-This “free radical” will combine with other “free radicals” which forms a long molecule called Polyethylene
What are most polymers composed of?
-are hydrocarbons
-Made of H and C
Describe Saturated Hydrocarbons
-Each carbon is singly bonded to four other atoms
How do double and triple bonds compare to saturated hydrocarbons?
-Double and triple bonds are somewhat unstable (can form new bonds)
Describe what polymers are simply
-are organic solids made up of long molecules containing a chain of carbon atoms (connected by covalent C-C bonds)
Are all chains in polymers the same length?
-NO
What are the four main covalent chains of configuration?
-Linear
-Branched
-Cross-linked
-Network
What are co-polymers?
-Polymers whose chains are random, alternating, blocked and grafted
What are examples of co-polymers
-Synthetic rubbers are usually co-polymers (ex. automobile tires)
Can a polymer be made crystalline?
Yes
-if it folds back upon itself easily
-if it has small side groups
-if it has no branching
What does the degree of crystallinity depend on?
-Processing conditions (such as cooling rate)
-chain configuration
What is cooling rate?
-During crystallization upon cooling through melting point, polymers become highly viscous
-Requires sufficient time for random and entangled chains to become ordered in viscous liquid
Which type of polymers are likely to crystallize?
Linear polymers
-easier since chain alignment is not prevented
For which kinds of polymers is crystallization not favoured by?
-polymers that are composed of chemically complex monomer structures
Which co-polymers are more likely to be crystallized? Alternating or random?
-Alternating co-polymers since their chains can align more easily
