Question

What is the molecular weight of polymer such as weight average molecular weight and PDI

Answer #1

**Weight averaged molecular weight:**

It is the sum of the product of the square of the molecular weights of all the polymeric molecules in a solution with their occurences (frequency), divided by the product of the molecular weights with the occurences (frequency). In a way, the polymer's molecular weight is averaged using a distribution of the molecular weights of the individual polymeric weights themselves.

Mw = {sum (Ni * Mi2)} / {sum (Ni)}

**Poly Dispersity Index:**

It is the ratio of the weight averaged molecular weight to the number averaged molecular weight.

PDI = Mw / Mn

Calculate the Mn, Mw, and the PDI for a polymer sample that
contains equal weight of polymer having molecular weights of
30,000, 40,000, and 60,0000 .

Molecular weight data for some polymer are tabulated.
Determine:
a) The number-average molecular weight
b) The weight-average molecular weight
c) What is the number-average degree of polymerization for this
polymer?
d) What is the weight-average degree of polymerization for this
polymer?
Molecular Weight
Range (g/mol)
xi
wi
8,000-16,000
0.05
0.02
16,000-24,000
0.20
0.10
24,000-32,000
0.20
0.25
32,000-40,000
0.25
0.25
40,000-48,000
0.23
0.20
48,000-56,000
0.07
0.18

The glass transition temperature of a linear polymer with number
average molecular weight MN =2300 was measured at 120°C. This
increased to 155°C for the same linear polymer with MN =9000. A
branched version of this polymer with MN =7200 was found to have a
Tg=105°C. Calculate the average number of branches per molecule in
this branched polymer.

The tensile strength of a poly(methyl methacrylate) (PMMA)
polymer with a number-average molecular weight of 30,00 g/mol is
found to be 50 MPa, while the tensile strength of a second sample
having a number average molecular weight of 50,000 g/mol is 150
MPa.
a) Estimate the tensile strength at a number average molecular
weight of 40,000 g/mol.
b) Estimate the tensile strength at a number average molecular
weight of 1,000 g/mol.
c) Estimate the tensile strength at a number average...

What is the molecular weight of a polymer if 3.50g are dissolved
in enough water to give 252 mL of the solution and give a osmotic
pressure of 28.52 mm Hg at 25 degrees Celsius?

You made a heterogeneous batch of polyethylene (having a PDI of
3.0). Assuming that the average degree of polymerization was 1000,
determine the weight average molecular weight for the batch.

Explain why one molecular weight average is not
sufficient in describing the chain length of a polymer.

Calculate the average molecular weight for the thermoplastic
that has the following weight fractions for the molecular weight
ranges listed
Molecular Weight
Range (g/mol)
fi
Molecular Weight
range (g/mol)
fi
0-5000
0.052
20,000-25,000
0.072
5000-10,000
0.107
25,000-30,000
0.121
10,000-15,000
0.089
30,000-35,000
0.112
15,000-20,000
0.094
35,000-40,000
remainder

if there are 10^20 molecules/g of pvc, calculate a) the weight
of an individual polymer molecule. I did 1/10^20 *advogados # and
got 6022? is this right? b) the Molecular weight g/mole of polymer.
my answer was 1e^-20. is this correct? c) the degree of
polymerization of the polymer I not sure on this one. I know its
gonna be like 1e^20/ something????

The following table lists molecular weight data for a
polypropylene material. Compute (a) the number-average molecular
weight, (b) the weight-average molecular weight, and (c) the degree
of polymerization. please show equations and calculations used.
thank you
Molecular Weight Range (g/mol) xi wi
8,000–16,000 0.05 0.02
16,000–24,000 0.16 0.10
24,000–32,000 0.24 0.20
32,000–40,000 0.28 0.30
40,000–48,000 0.20 0.27 48,000–56,000 0.07 0.11

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