Polymer Chemistry Exam 1 Flashcards
What does the number average degree of polymerization represent, in words not math symbols?
The average number of monomers per polymer chain.
What does the number average molecular weight represent, in words, not math symbols?
The average molecular weight of a polymer chain
Without explaining what the two individual terms mean, what does this math as a whole represent:
(Nx) * (x)
The total number of monomers present in the sample
Without explaining what the two individual terms mean, what does this math as a whole represent:
(Mx) * (Nx)
The total mass of the sample
Without explaining what the three individual terms mean, what does this math as a whole represent:
(Mo)(x)(Nx)
The total mass of the sample
Without explaining what the three individual terms mean, what does this math as a whole represent:
(Mo)(x)
The molecular weight of a single polymer chain with a degree of polymerization x
Lower case “x” in polymer chemistry notation usually represents what?
Degree of polymerization
Lower case “n” in polymer chemistry notation usually represents what?
Number of repeat units
(Mo) in polymer chemistry notation usually represents what?
The molecular weight of an (incorporated) monomer.
(Mx) in polymer chemistry notation usually represents what?
The molecular weight of a single polymer chain whose degree of polymerization is x
(Nx) in polymer chemistry notation usually represents what?
The total number of chains whose degree of polymerization is x.
(Wx) in polymer chemistry notation usually represents what?
The total mass of ALL chains whose degree of polymerization is x
What is the mathematical relationship between number of repeat units and degree of polymerization?
Degree of polymerization = (Number of repeat units) * (Number of monomers PER repeat unit)
Conceptually, what is the difference between a number average and a weight average?
The weight average gives extra importance to longer chains by summing up quantities proportional to the SQUARE of the chain lengths instead of just summing up things that are proportional to chain length.
Describe a stepwise type of polymerization
A polymerization mechanism where chains of any length can combine with each other, as long as the function groups of the respective chains can react.
Describe an addition polymerization propagation
When a polymer chain with an active site grows by adding a single monomer to the active site. The active site is then transferred to that newly added monomer.
What is another name for a stepwise polymerization mechanism that creates a byproduct?
An elimination mechanism. Or a condensation polymerization if the byproduct is water, which it often is.
What are the three steps of an addition polymerization?
Initiation, propagation, deactivation
For an addition polymerization, what are two examples of deactivations which are terminations?
Termination by combination, Termination by disproportionation
What is the difference between a deactivation that is a termination and one that isn’t?
In a termination, the active site no longer exists anywhere. In the other types of deactivation the active site is just transferred off of the current chain to somewhere else.
In an addition polymerization, if the active site gets transferred in a deactivation step, what can it be transferred TO?
A monomer
Another polymer chain
A different region of the same chain
The solvent
A chain transfer agent
When many long branches sprout from a single monomer, what type of polymer geometry results?
A star polymer
A polymer whose branches very often quickly lead to other branches is what type of polymer geometry?
A dendrimer
A polymer with tertiary branch points spaced close together is what type of polymer geometry?
A comb polymer
A polymer with quaternary branch points spaced close together is what type of polymer geometry?
A brush polymer
A polymer where all or nearly all chains are somehow connected is what type of polymer geometry?
A network
When two polymers are chemically linked, what is that process called? Give multiple synonyms.
Crosslinking (preferred term)
Curing (also fine)
Vulcanization (Primarily used when referring to elastomers, e.g. rubber, and especially used when linking is done by adding sulfur)
What is the difference in the structure of HDPE and LDPE?
HDPE is very linear and packs well, giving it a higher density. LDPE is very branched and does not pack well.
What is LLDPE structurally?
A polyethylene polymer with regular predictable short branches that has been polymerized by a catalyst. Sometimes ethylene is not the actual monomer used.
What is the difference structurally between a thermoplastic and a thermoset?
The thermoset is crosslinked and the thermoplastic is not.
What are some differences in the properties of a thermoplastic vs a thermoset?
- The thermoplastic can be melted and reformed into a new shape and the thermoset cannot.
- The thermoplastic is easier to recycle than the thermoset.
-Thermosets have more stable dimensions (temperature resistant, fine detail is possible).
-Thermoplastics are easier to polish smooth.
-Thermoplastics resist shattering/cracking more.
What is the difference between a HHTT and a HT polymer?
In a HT polymer monomers add so that the least functionalized end of one monomer adds to the most functionalized end of the other monomer. And in HHTT they do the opposite.
What is a meso diad?
Two monomers added next to each other such that their functional groups fall on the same side of the polymer chain from a chirality standpoint.
What is a racemic diad
Two monomers added next to each other such that their functional groups fall on opposite sides of the polymer chain from a chirality standpoint
A polymer chain made up of a single type of monomer is called what?
A homopolymer
A polymer chain made up of more than one type of monomer is called what?
A copolymer
A copolymer where it is very UNLIKELY that a monomer has reacted with a monomer of the same type is called what?
An alternating copolymer
A copolymer in which the monomers types are separated spatially on a linear chain is called what?
Block copolymer
A copolymer where the branches have different monomers than the main chain is called what?
A graft polymer.
How does one calculate a polydispersity?
By dividing a weight average by a number average
Conceptually what does polydispersity represent?
How similar in length the chains are. The closer the polydispersity is to 1, the more similar the chains are.
A polymer made up of all meso diads is called what?
An isotactic polymer
A polymer made up of all racemic diads is called what?
A syndiotactic polymer
A polymer where there is no long range stereochemistry pattern is called what?
An atactic polymer
When different arms of a star polymer have different chemistry than each other, what type of polymer is that?
Variegated
A copolymer in which both types of monomers can react with each other with some predictable pattern that is not usually a block or alternating but a predictable combination of the two is called what?
A statistical copolymer
HHTT and HT are what type of isomers?
Sequence
isotactic, syndiotactic, and atactic are what sort of isomers?
Stereoisomers
If you have the same pairs of monomers, arranging them as a block copolymer vs an alternating copolymer is making what type of isomers?
Structural
Chain trainsfer to self is better known as what?
B
Backbiting
What is Fenton’s reagent
An initiator system for radical polymerizations which involves adding iron (II) ions to the radical source to better control its production
A chemical added to an addition polymerization for the express purpose of inducing chain transfer to it is called what?
A chain transfer agent
In a radical polymerization of a monomer that “should” make a linear polymer, what length branches are most common and why
1 carbon: Because the active site attacks the nearest neighbor on the chain
4 carbons: Because it forms a six membered ring intermediate when backbiting
Other numbers are unfavored either because of angle-strain or because of entropy considerations
What is it called when an addition polymerization is designed such that deactivation never or hardly ever occurs
A living polymerization