Exploring Polymerization Reactions Calculate the Mn, Mw and PDI of a polymer sample containing 5 chains with molecular weight of 5000g/mol, 2 chains with molecular weight of 50000g/mol and 1 chain with molecular weight of 500000
Mn = (5X5000) + (2X50000) + (1X500000) = 625000 = 78125 g
Mw = (5X50002) + (2X500002) + (1X5000002) =326560 g
10 X 78125
PDI = Mw =326560 = 4.178
2. Proteins are made by reaction of amino acids. Do you think this is a step growth or a chain growth polymerization? Explain your reasoning.
It is a step grown polymerization. This is because the two monomers are bi-functional and they react to form dimmers, followed by trimer and then longer oligomers. They eventually form long chain polymers.
3. Report a percentage yield on your polystyrene sample.
Suppose we have used 0.01g of AIBN.
Therefore, we can yield: (0.01 x 100) in this case we have to put into consideration the amount of styrene used.
Therefore, % yield =0.01 X mass of styrene up to 10%
4. Analyze and interpret your data, be sure to comment on whether or not it proves that you made a polystyrene
According to the empirical graph provided, 42% yield of polystyrene fall within the range. Therefore, the next step would be to analyze some of the chemical properties of styrene. Polystyrene is brittle, less viscous and leaves a dry film. These properties allow us to conclude that polystyrene is formed.
5. If a polystyrene chain has a mass of 100000g/mol, how many styrene monomers were polymerized to make the chain?
Molecular formulae of styrene is C6H5CH=CH2
Molecular mass of styrene = (12×8) + (1×8) = 104 g/mol
Number of styrene monomer = 100000 = 962 monomers
6. Nylon polymers are named according to the number of carbon atoms between nitrogen and oxygen atoms. Draw a representative segment of Nylon-4-4.
C CH2 NH
7. Draw a borate ion and show how it can cross-link two PVA chains through hydrogen bonding.
H O O H _
H O O H
Cross-link between boron ion and two PVA chains through hydrogen bonding.
8. Using your understanding of cross-linking, explain the changes observed in the physical properties of your PVA and as the borax ion concentration was increased.
The solution is a stronger fluid (fluidity), this is because the solution contains 95% water. Furthermore, there is a huge percentage of hydrogen bonding which allows the solution to be fluid-like.
The mixture becomes thicker (viscous) while the elasticity reduced as water dries up in PVA, a thick solution is left behind whose viscosity is higher than that of PVA with low concentration of borax ions. The borax ions are highly condensed leaving few spaces in between the PVA molecules.
The slime breaks. The weak hydrogen bonding links with the -OH and borate becoming separated. This disallows the solution from gelling and hence becomes brittle.
It became a dry film because a lot of water evaporates leaving behind a dry film suspended on the gel.