Question

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.

Answer 1

................................................(1)

Where PDI=Poly Dispersity Index

Mw=Weight average molecular weight

Mn=Number average molecular weight.

Degree of polymerisation can be defined as,Dp

...................................(2)

where Mo= Molecular weight of monomer unit. (g/mol)

For polyethyelne, molecular formula (for ethylene monomer)C2H4:

Mo=28 g/mol (for ethylene monomer)

Therefore using equation 2 we can calculate Mn,

...................................(2)

Dp=1000(given)

Mo=28 g/mol (for ethylene monomer)

Mn=Dp*Mo

Mn=1000*28

Mn=28000 g/mol..........(3)

Now using equation 1: ................................................(1)

PDI=3(GIVEN)

Mn=28000 g/mol..........(3)

So,

Mw=PDI*Mn

Mw=3*28000

Mw=84000 g/mol ------> ANSWER

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