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Chapter 14: Problem 4

(a) Compute the repeat unit molecular weight of polystyrene. (b) Compute the number-average molecular weight for a polystyrene for which the degree of polymerization is 25,000 .

Short Answer

Expert verified
(a) Calculate the repeat unit molecular weight: Molecular weight of polystyrene = (8 × 12.01 g/mol) + (8 × 1.01 g/mol) = (96.08 g/mol) + (8.08 g/mol) = 104.16 g/mol (b) Calculate the number-average molecular weight: Mn = DP × repeat unit molecular weight Mn = 25,000 × 104.16 g/mol Mn = 2,604,000 g/mol The repeat unit molecular weight of polystyrene is 104.16 g/mol, and the number-average molecular weight for a polystyrene with a degree of polymerization of 25,000 is 2,604,000 g/mol.

Step by step solution

01

(a) Compute the repeat unit molecular weight)

First, we need to find the molecular weight of the repeat unit (monomer) of polystyrene. Polystyrene has the chemical formula C8H8. Using the atomic weights of Carbon (C, 12.01 g/mol) and Hydrogen (H, 1.01 g/mol), we can calculate the molecular weight as follows: Molecular weight of polystyrene = (Number of C atoms × Atomic weight of C) + (Number of H atoms × Atomic weight of H) = (8 × 12.01 g/mol) + (8 × 1.01 g/mol) Calculate the molecular weight using the values above.
02

(b) Compute the number-average molecular weight)

To calculate the number-average molecular weight (Mn) for a polystyrene with a degree of polymerization (DP) of 25,000, we can use the following formula: Mn = DP × repeat unit molecular weight Using the value of the repeat unit molecular weight from part (a) and the given degree of polymerization (25,000), calculate the number-average molecular weight.

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Most popular questions from this chapter

The density of totally crystalline polypropylene at room temperature is \(0.946 \mathrm{~g} / \mathrm{cm}^{3}\). Also, at room temperature the unit cell for this material is monoclinic with the following lattice parameters: $$ \begin{array}{ll} a=0.666 \mathrm{~nm} & \alpha=90^{\circ} \\ b=2.078 \mathrm{~nm} & \beta=99.62^{\circ} \\ c=0.650 \mathrm{~nm} & \gamma=90^{\circ} \end{array} $$ If the volume of a monoclinic unit cell, \(V_{\text {mono }}\) is a function of these lattice parameters as $$ V_{\text {mono }}=a b c \sin \beta $$ determine the number of repeat units per unit cell.

Explain briefly why the tendency of a polymer to crystallize decreases with increasing molecular weight.

Using the definitions for total chain molecule length \(L\) (Equation 14.11) and average chain end-to-end distance \(r\) (Equation 14.12), for a linear polyethylene determine the following: (a) the number-average molecular weight for \(L=2500 \mathrm{~nm}\) (b) the number-average molecular weight for \(r=20 \mathrm{~nm}\)

Sketch the repeat structure for each of the following alternating copolymers: (a) poly (butadiene-chloroprene), (b) poly(styrene-methyl methacrylate), and (c) poly(acrylonitrilevinyl chloride).

An alternating copolymer is known to have a number-average molecular weight of \(250,000 \mathrm{~g} / \mathrm{mol}\) and a degree of polymerization of 3420 . If one of the repeat units is styrene, which of ethylene, propylene, tetrafluoroethylene, and vinyl chloride is the other repeat unit? Why?
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