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Chapter 14: Problem 4

(a) Compute the repeat unit molecular weight of polypropylene. (b) Compute the number-average molecular weight for a polypropylene for which the degree of polymerization is 15,000

Short Answer

Expert verified
Answer: The number-average molecular weight of polypropylene with a degree of polymerization of 15,000 is 540,000 g/mol.

Step by step solution

01

(a) Identify the repeat unit of Polypropylene

Polypropylene is a polymer made up of propylene (C3H6) monomers. The repeat unit for polypropylene is -CH2-CH(CH3)-, which has one carbon and two hydrogen atoms in the first part, one carbon and one hydrogen atom in the second part, and one carbon and three hydrogen atoms in the third part.
02

(a) Calculate molecular weight of repeat unit

Now, we need to calculate the molecular weight of the repeat unit -CH2-CH(CH3)-. To do this, we will sum the molecular weights of each of the atoms within the repeat unit. Using the atomic weights from the periodic table: - Carbon has an atomic weight of 12 g/mol - Hydrogen has an atomic weight of 1 g/mol So, the molecular weight of the repeat unit is: 3 Carbon atoms * 12 g/mol + 6 Hydrogen atoms * 1 g/mol = 36 g/mol
03

(b) Find the degree of polymerization

The degree of polymerization (DP) is given as 15,000 in this exercise.
04

(b) Calculate the number-average molecular weight (Mn)

Once we know the molecular weight of the repeat unit and the degree of polymerization, we can calculate the number-average molecular weight (Mn) using the formula: Mn = (Molecular weight of repeat unit) * (Degree of polymerization) Mn = 36 g/mol * 15,000 = 540,000 g/mol Thus, the number-average molecular weight of polypropylene with a degree of polymerization of 15,000 is 540,000 g/mol.

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Most popular questions from this chapter

On the basis of the structures presented in this chapter, sketch repeat unit structures for the following polymers: (a) polychlorotrifluoroethylene, and (b) poly(vinyl alcohol).

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

Crosslinked copolymers consisting of 35 wt \(\%\) ethylene and 65 wt\% propylene may have elastic properties similar to those for natural rubber. For a copolymer of this composition, determine the fraction of both repeat unit types.

Sketch cis and trans structures for (a) butadiene, and (b) chloroprene.

The density and associated percent crystallinity for two polypropylene materials are as follows: $$\begin{array}{cc} \hline \rho\left(g / c m^{3}\right) & \text {Crystallinity (\%)} \\ \hline 0.904 & 62.8 \\ 0.895 & 54.4 \\ \hline \end{array}$$ (a) Compute the densities of totally crystalline and totally amorphous polypropylene. (b) Determine the density of a specimen having \(74.6 \%\) crystallinity.
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