Question

Show how to prepare polybutadiene that is terminated at both ends with primary alcohol groups.

Short answer

Answer: The process involves performing a hydroboration-oxidation reaction on polybutadiene. First, add borane (BH3-THF complex) to a solution of polybutadiene in an inert solvent. Next, perform the oxidation step by adding hydrogen peroxide (H2O2) and a hydroxide ion (OH-) source, such as sodium hydroxide (NaOH). After the reaction, isolate the product by extracting it with an organic solvent, washing it with water, and evaporating the solvent. Finally, verify the functionality using characterization techniques such as Fourier-transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR) spectroscopy.

Step-by-step solution

1. Understand the structure of polybutadiene

Polybutadiene is a polymer made up of butadiene monomers (C4H6) connected through carbon-carbon double bonds. It has two types of repeating units: cis and trans isomers. The main structure of polybutadiene is a long carbon chain with alternating single and double bonds between the carbon atoms.

2. Identify a suitable reaction to introduce primary alcohol groups

To introduce primary alcohol groups at both ends of the polybutadiene chain, we can perform a hydroboration-oxidation reaction. This reaction involves the addition of borane (BH3) to the carbon-carbon double bond, followed by oxidation with hydrogen peroxide (H2O2) and a hydroxide ion (OH-) source. The final product of this reaction is a primary alcohol group added to each end of the polymer chain.

3. Perform the hydroboration step

First, we need to carry out the hydroboration step, which requires adding borane (BH3) to the polybutadiene. This can be done using a borane-tetrahydrofuran (BH3-THF) complex, which is a commercially available and stable source of borane. Add the BH3-THF complex to a solution of polybutadiene in an inert solvent, such as toluene or THF, under an inert atmosphere (e.g., nitrogen or argon). Stir the solution for the required amount of time to allow the borane to selectively react with the carbon-carbon double bonds at the ends of the polymer chain.

4. Perform the oxidation step

After the hydroboration step is complete, the next step is to oxidize the boron-containing intermediate to form primary alcohol groups at both ends of the polybutadiene chain. To do so, add aqueous hydrogen peroxide (H2O2) and a hydroxide ion (OH-) source, such as sodium hydroxide (NaOH), to the reaction mixture. Stir the mixture for the required amount of time to allow the oxidation reaction to take place.

5. Isolate the product

Once the oxidation reaction has taken place, the resulting solution will contain the desired polybutadiene terminated with primary alcohol groups at both ends. To isolate the product, the mixture can be extracted with an organic solvent (e.g., diethyl ether), followed by washing with water to remove any inorganic byproducts and unreacted reagents. Finally, the organic layer can be dried, and the solvent can be evaporated to obtain the pure product.

6. Verify the functionality of the polybutadiene

In order to confirm that the polybutadiene has been successfully terminated with primary alcohol groups at both ends, various characterization techniques can be employed. For example, Fourier-transform infrared spectroscopy (FTIR) can be used to identify the presence of hydroxyl (OH) peaks in the spectrum, while nuclear magnetic resonance (NMR) spectroscopy can be utilized to verify the chemical structure and functionality of the modified polybutadiene.