Lecture 5: Polymers Flashcards
IUPAC definition of Polymers?
A molecule of high molecular mass, the structure of which essentially comprises the multiple repetition of units derived, actually or conceptually from molecules of low relative molecular mass.
- Explain what an aromatic hydrocarbon, an aliphatic hydrocarbon, a saturated hydrocarbon, an unsaturated hydrocarbon are?
Aromatic hydrocarbons - contains a benzene ring
Aliphatic - normal hydrocarbon chaing - compared to aromatic
Saturated - no double bonds
Unsaturated - double bond(s)
- Which of the 2 nomenclatures below is the correct? Explain why.
The one with the position thats the smallest so the 2-methylbutane
- Explain how unsaturated bonds can be important for the 3D shape and reactivity of molecules.
the carbons are closer and in a double bond, it cannot rotate. single bonds can rotate.
- Explain how you could have a chiral carbon in a molecule and give an example of a molecule that has at least one chiral carbon.
-mirror image copies of the same molecule which have different properties
- What would the circle in the picture below mean?
-benzene ring all double bonded
- Explain what functional groups mean and give examples.
Functional groups are groups that determine the reactions of the molecule. E.G. benzene, alkene,alkanes, alcohol, ether, ketone.
- Why is a carboxylic acid more acidic than an alcohol functional group?
The stability of an anion determines the strength of its parent acid.
Alcohol molecules donates a proton it becomes an alkoxide ion, when an carboxylic acid donates a proton it becomes a carboxylate ion.
A carboxylate ion is more stable as it has resonance structures (a combination of two possible configurations and the electrons are spread over two atoms/delocalised), which disperses its negative charge.
- Explain why amino acids are named as such and what a peptide bond is?
Because amino acids contain an amino group (as well as a carboxyl group).
A peptide bond is
f
Are proteins crosslinked between them by peptide bonds? If not, by which region do they cross-link?
Many proteins that are secreted from cells, or find themselves on the surface of cells, are “spot welded” in places along their length by crosslinks formed between two sulfur containing amino acid R-groups. Disulfide bridges are strongly stabilizing, particularly if the protein is to be transported to the outside of the cell.
- Give examples of three composites and explain why they are considered composites.
- Collagen
- Bone
- Shells
Multicomponent material comprising multiple, different (non-gaseous) phase domains, in which at least one type of phase domain is a continuous phase.
- From these polymer chains cellulose, collagen and bone, which one would you expect to be less viscous and more crystalline?
longer chains, more IMF and less kinks in the chain = higher viscosity (more thick)
Bone = most crystalline
Collagen = semi-viscous/crystalline
Cellulose = Very viscous
- Why is there a glass transition in a polymer?
The Glass Transition is where the polymer transitions from a hard, glassy material to a soft, rubbery material.
When the temperature is warm, the polymer chains can move around easily. When the temperature is cold they wont be able to move around to relieve the stress when force is applied causing the polymer sample to break or shatter in your hands.
- What do you expect will happen to the temperature of a polymer in a glass transition? And would that change if you have a metal or ionic compound?
The plot on the left shows what happens when you heat a 100% crystalline polymer. You can look at it and see that it’s discontinuous. That break is the melting temperature. At that break, a lot of heat is added without any temperature increase at all. That’s the latent heat of melting. The slope gets steeper on the high side of the break. The slope is equal to the heat capacity.
But in the plot on the right, which shows what happens to a 100% amorphous polymer when you heat it, we don’t have a break. The only change we see at the glass transition temperature is an increase in the slope, which means, we can see a heat capacity change at the Tg, but no break, as we do in the plot for the crystalline polymer. There is no latent heat (energy required for a state change) involved with the glass transition.
This shows the difference between a first-order transition like melting and a second order transition like the glass transition.
- You decide to cross-link a polymer. How would the physical properties of that polymer change as you increase the amount of cross-link?
As you increase the number of crosslinks it becomes more stable mechanically and thermally, and once formed are difficult to break.
- Explain what collagen is and describe all the structures formed from it.
The main structural protein found in skin and other connective tissues.
Three polypeptides coil to form tropocollagen. Many tropocollagens then bind together to form a fibril, and many of these then form a fibre.
